i

10001930-002_AviationDictionary_2012_BOOK.indb 1 3/27/2012 9:37:53 AM

 Jeppesen® is a registered trademark of Jeppesen Sanderson, Inc. All other trademarks,
registered trademarks, product names, and company names or logos mentioned herein are
the property of their respective owners.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or
transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or oth-
erwise, without the prior permission of the publisher.

The charts, tables, and graphs used in this publication are for illustration purposes only and
cannot be used for navigation or to determine actual aircraft performance.

ISBN-13: 978-0-88487-574-1
ISBN-10: 0-88487-574-1

Jeppesen
55 Inverness Drive East
Englewood, CO 80112-5498
Web Site: www.jeppesen.com
Email: Captain@jeppesen.com
Copyright © Jeppesen
All Rights Reserved.
10001930-002 Published 2003, 2006, 2012
ii

10001930-002_AviationDictionary_2012_BOOK.indb 2 3/27/2012 9:37:53 AM

 A • absolute pressure controller (APC)

A aborted start — In gas turbine engines, termination of the

engine starting cycle when combustion (light-off) does
A, B, C, D, E chambers — The five chambers that make up not occur within a prescribed time limit.
a diaphragm-controlled unit of a pressure type carburetor. abradable seal — A general description of knife-edge seals
Chamber A is regulated air-inlet pressure. Chamber B is which can wear away slightly and still function. Such
boost venturi pressure. Chamber C contains metered fuel seals in a gas turbine engine abrade slightly to produce
pressure. Chamber D contains unmetered fuel pressure. a close fit.
Chamber E is fuel pump pressure.
abradable shroud — Generally a honeycomb-type turbine
A chamber — One of the chambers of a pressure-type shroud ring set into the outer turbine case. Can abrade
carburetor regulator unit. A chamber regulates air-inlet without engine degradation if the turbine blades creep
pressure from the air intake. and contact the shroud.
A check — Primarily associated with large commercial abrade — To scrape or wear away a surface or a part by
aircraft, the lowest level of inspection in a Continuous mechanical or chemical action.
Airworthiness Maintenance Program. The entire program
consists of A, C, and D checks. abrasion — l. An area of roughened scratches or marks
usually caused by foreign matter between moving parts
A&B system — An emergency brake design used in some or surfaces. 2. The wearing or rubbing away of a surface
larger multiple-disc brake systems. These brakes have a by a substance used for grinding, grating, polishing, etc.
number of cylinders, with alternate cylinders connected
either to the aircraft’s “A” system or to the aircraft’s “B” abrasive — A substance used to wear away surfaces by the
system. Normal brake actuation takes over if one system use of friction. In grinding wheels, the abrasives most
fails. commonly used are silicon carbide or aluminum oxide.
A-battery — A dry cell battery with a voltage of 1.5 to 6.0 abrasive blasting — The removal of carbon and other
volts and capable of supplying a reasonable amount of deposits from machine parts using a high velocity blast
current. of air that contains fine particles of abrasive sand, glass
bead, or walnut shell.
abbreviated briefing — In meteorology, a shortened
briefing to supplement mass disseminated data. abscissa — The horizontal reference line of a graph or curve
by which a point is located with reference to a system of
abbreviated IFR flight plans — An authorization by ATC coordinates.
requiring pilots to submit only that information needed
for the purpose of ATC. It includes only a small portion of absolute altimeter — A radar altimeter used to indicate the
the usual IFR flight plan information. In certain instances, exact height of an aircraft over the terrain. See also radio
this may be only aircraft identification, location, and pilot altimeter.
request. Other information may be requested if needed by absolute altitude — The actual height above the surface of
ATC for separation/control purposes. It is frequently used the earth, either land or water.
by aircraft which are airborne and desire an instrument
approach or by aircraft which are on the ground and absolute ceiling — The maximum height above sea level at
desire a climb to VFR-on-top. which an aircraft can maintain level flight under standard
atmospheric conditions.
abeam — An aircraft is “abeam” a fix, point or object when
that fix, point, or object is approximately 90 degrees to absolute humidity — The actual water vapor present in a
the right or left of the aircraft track. Abeam indicates a given volume of air.
general position rather than a precise point. absolute instability — In meteorology, the state of an
abeam fix — A fix positioned approximately 90 degrees atmospheric layer when the actual temperature lapse rate
from a navaid along a route of flight. exceeds the dry adiabatic lapse rate. An air parcel receiving
an initial upward displacement in an absolute unstable
abnormal procedures training (APT) — The use of flight layer will accelerate away from its original position.
training devices to teach pilots how to handle procedures
such as engine failures, inflight fires, and other abnormal absolute pressure — Pressure above zero pressure as read on
situations. This training is completed on the ground and a barometer type instrument, i.e. Standard Day, 14.7 psia.
is the safest means of allowing a pilot to experience absolute pressure controller (APC) — An instrument
abnormal procedures. that regulates the maximum turbocharger compressor
abort — To terminate a preplanned aircraft maneuver; e.g., discharge pressure in a reciprocating engine turbocharger
an aborted takeoff. system. (34 + or -.5 in. Hg to critical altitude,
approximately 16,000 ft)

10001930-002_AviationDictionary_2012_BOOK.indb 1 3/27/2012 9:37:53 AM

 absolute temperature • acceleration thermostat

absolute temperature — Temperature referenced from accelerate-stop distance available — The runway plus
absolute zero. (-273.18°C or -459.6°F) There are two stopway length declared available and suitable for the
absolute scales in use, the Rankine scale using Fahrenheit acceleration and deceleration of an airplane aborting a
degrees and the Kelvin scale using Celsius degrees. takeoff.
absolute value — The value of a number without accelerating agent — A substance used to hasten a chemical
considering its sign (whether it is plus or minus). action or change.
absolute zero — The temperature (-273.18°C) at which accelerating pump — A small pump in a carburetor used
molecular motion ceases. to supply a momentarily rich mixture to the engine when
the throttle is suddenly opened. This prevents hesitation
abstraction — General rather than specific. For example, during the time of transition between operating on the
aircraft is an abstraction; airplane is less abstract; jet is idle system and the main metering system.
more specific; and jet airliner is even more specific.
accelerating system — An accelerating system used in
AC 43.13-1B — An Advisory Circular in book form issued float carburetors that supplies extra fuel during increases
by the Federal Aviation Administration (and reprinted by in engine power. This is usually accomplished by a small
others) that covers acceptable methods, techniques, and fuel pump called an accelerating pump.
practices for aircraft inspection and repair. The procedures
described in this advisory circular are considered by the accelerating well — A secondary tank built into the main
Federal Aviation Administration to be acceptable data for oil tank. The well, or hopper, retains only that portion
aircraft inspection, maintenance, and alteration. of fluid being circulated through the engine. Thus, oil
warm-up is hastened during engine warm-up. The well
AC fittings — Air Corps fittings. also makes oil dilution practical. Also referred to as
Replaced by the AN (Army/ temperature accelerating well.
Navy) standard and MS
(Military Standard) fittings. AN acceleration — The increase in velocity of an object.
fittings have a slight shoulder Acceleration is usually expressed in terms such as feet
between the cone and the first per second per second.
thread. AC fittings do not have acceleration check — A maintenance check calculating the
this shoulder. Other differences time an engine takes to spool-up from idle to rated power
include sleeve design and the without hesitation or evidence of backfire.
pitch of the threads.
acceleration due to gravity — The acceleration of a freely
AC plate resistance — The internal resistance of a vacuum falling body due to the attraction of gravity, expressed
tube to the flow of alternating current. AC plate resistance as the rate of increase of velocity per unit of time. In a
is measured in ohms. vacuum the rate is 32.2 feet per second near sea level.
accelerate — To increase the speed of an object. acceleration error — An error inherent in magnetic
accelerate stop distance available (ASDA) — The length compasses, caused by the force of acceleration acting
of the take-off run available plus the length of the on the dip compensating weight when the aircraft
stopway, if provided. accelerates or decelerates on an easterly or westerly
heading. In compasses compensated for flight in the
accelerated life test — An operational test used to predict Northern Hemisphere, when the aircraft accelerates on
the service life a system or component will have under an easterly or westerly heading, the compass gives the
normal operating conditions. indication that the aircraft is turning to the north. When
the aircraft decelerates on either of these headings, the
accelerate-go distance — In multi engine aircraft, the
compass gives the indication that the aircraft is turning
distance required to accelerate to liftoff speed or V1
to the south.
(depending on the pilot’s operating handbook (POH)),
experience an engine failure, and complete the takeoff acceleration of gravity — The rate of increase in speed
and climb to clear a 50-foot obstacle. of a freely falling body due to the attraction of gravity.
Expressed as the rate of increase of velocity per unit of
accelerate-stop distance — In multi engine aircraft, the
time (32.17 feet per second per second at sea level and
sum of the distances necessary to (1) accelerate the
45° latitude). The acceleration decreases with an increase
airplane from a standing start to VEF with all engines
in altitude until it becomes zero upon leaving the earth’s
operating; (2) accelerate the airplane from VEF to V1,
gravitational field.
assuming the critical engine fails at VEF; and (3) come
to a full stop from the point at which V1 is reached. The acceleration thermostat — A bimetallic probe positioned
light twin pilot’s operating handbook (POH) may base in the exhaust stream of an auxiliary power unit. When
the distance on an engine failure occurring at a specified overheated, it expands to dump a Pb fuel control signal
takeoff decision speed (V1) or liftoff speed. and reduce fuel flow.
2

10001930-002_AviationDictionary_2012_BOOK.indb 2 3/27/2012 9:37:53 AM

 acceleration well • acid diluent

acceleration well — An enlarged space around the discharge with a snowflake or a smaller ice particle. Such particles
nozzle of some float-type carburetors. When the throttle may become the nucleus of a hailstone.
is opened suddenly, this fuel is rapidly discharged from
accumulated error — The sum of all of the errors that
the main discharge nozzle.
occur in the operation of a system or in the manufacturing
accelerator — A substance added to a catalyzed resin to of a part.
shorten its curing time.
accumulator — A hydraulic
accelerator system — A system in an aircraft carburetor component consisting of
that supplies additional fuel to the engine when the two chambers separated
throttle is opened suddenly. by a piston, diaphragm,
or bladder. Compressed
accelerator winding — A series winding used in
air in one chamber holds
vibrating-type voltage regulators, which, when the points
pressure on hydraulic
open, decreases the magnetic field immediately, allowing
fluid in the other chamber,
the points to close more rapidly.
allowing the fluid to be
accelerometer — A sensitive instrument calibrated in stored under pressure. An
G-units that measures the amount of force exerted by accumulator is used to assist in bringing the propeller
acceleration on a body. One G-unit force is equal to the out of the feathered position by providing a burst of oil
weight of the object. pressure to the hub when the control lever is moved out
of the feather position.
acceptance test — A test performed on an airplane or piece
of equipment to ensure it is in the condition specified accumulator precharge — Compressed air stored in the air
in the purchase contract. Large and expensive aircraft chamber of a hydraulic accumulator prior to introducing
are given extensive acceptance tests before a customer hydraulic pressure into the system.
accepts them.
accuracy — The state of being exact and free from mistakes.
acceptor atom — An impurity atom in a semi­conductor Conformance to a standard without error.
material that will receive or accept electrons. Germanium
accurate — Free from error.
with an acceptor impurity is called P-type germanium
because it has a positive nature. AC/DC — Electrical components that can operate equally
well on alternating current or on direct current electricity.
access cover — See access panel.
ace — A term that originated in World War I to acknowledge
access door — A door that provides entry into or exit from
pilots who shot down five or more enemy aircraft.
an aircraft. It also provides access to servicing points and
manually operated drains. acetone — Liquid ketone (C3H60). A flammable, fast-
evaporating solvent used in many types of aircraft
access panel — A panel on an aircraft that can be removed
finishes. Also used as a cleaning fluid.
easily to facilitate inspection and maintenance.
acetylene cylinder — A seamless steel shell with welded
accessories — Components that are used with an engine,
ends, approximately 12 inches in diameter and 36 inches
but are not a part of the engine itself. Units such as
long. A fully charged acetylene cylinder of this size
magnetos, carburetors, generators, and fuel pumps are
contains approximately 225 cu. ft. of gas at pressures up
commonly installed engine accessories.
to 250 PSI.
accessory drive gearbox — Provides mounting space for
acetylene gas — A flammable, colorless non-toxic gas that
engine accessories. Also referred to as main gearbox.
has a distinctive, disagreeable odor. Calcium carbide is
accessory gear trains — Drive system containing both spur made to react with water to produce acetylene. Mixed
and bevel-type gears. Used in different types of engines with oxygen in the proper proportions and ignited,
for driving engine components and accessories. acetylene gas will produce temperatures that range from
5,700°F to 6,300°F for welding purposes.
accessory section — The part of an engine that provides
the necessary mounting pads for accessory units such as acid — A chemical substance that contains hydrogen, has
magnetos, fuel pumps, oil pumps, and generators. a characteristically sour taste, and is prone to react with
a base or an alkali to form a salt and to accept electrons
accident — An unintended event or circumstance.
from the alkali.
accommodation — The time required to focus on a distant
acid diluent — A constituent of a wash primer used to mildly
object after looking at the instrument panel.
etch the surface of the metal being primed. Provides a
accretion — The production of a precipitation particle good bond between the finishing system and the metal.
when a supercooled water droplet freezes as it collides

10001930-002_AviationDictionary_2012_BOOK.indb 3 3/27/2012 9:37:53 AM

 acid-resistant paint • additional services

acid-resistant paint — A paint that resists the etching effects at freeze calculated landing time (FCLT) or meter list
of acid. Used on battery boxes and surrounding areas. display interval (MLDI) for the adapted vertex for each
arrival aircraft based upon runway configuration, airport
acknowledge — During communications, this indicates:
acceptance rate, airport arrival delay period, and other
Let me know that you have received my message.
metered arrival aircraft. This time is either the vertex
acknowledge [ICAO] — During communications, this time of arrival (VTA) of the aircraft or the tentative
indicates: Let me know that you have received and calculated landing time (TCLT)/ACLT of the previous
understood this message. aircraft plus the arrival aircraft interval (AAI), whichever
is later. This time will not be updated in response to the
acorn nut — A dome-shaped nut with a threaded hole that
aircraft’s progress.
does not go completely through, producing a finished and
smooth appearance. Acorn nuts and cap nuts are terms actual navigation performance (ANP) — A measure of
used interchangeably. the current estimated navigational performance. Also
referred to as Estimated Position Error (EPE). See also
acrobatic category airplane — An aircraft certificated for
required navigational performance.
flight without restrictions, except those found necessary
as a result of flight tests. actuating cylinder — A cylinder and piston arrangement
used to convert hydraulic or pneumatic pressure into
acrobatic flight — An intentional maneuver involving
work by the fluid under pressure moving the piston. The
an abrupt change in an aircraft’s attitude, an abnormal
force applied is equal to the piston area times the pressure
attitude, or abnormal acceleration not necessary for
on the fluid. Actuating cylinders can be double-action or
normal flight.
single-action actuating types.
acrobatics — Flight maneuvers such as loops and rolls
actuating horns — The levers to which control cables are
that are not considered to be necessary for normal utility
attached to move the control surfaces.
category flight.
actuator — A mechanical device for moving or controlling
acrylic — A glossy, transparent thermoplastic material used
something. The action may be linear, rotary, or oscillating.
for cast or molded parts such as aircraft windshields and
Many actuators are actuated by either hydraulic or
side windows.
pneumatic pressure.
acrylic lacquer — An aircraft finish that consists of an
actuator piston — The movable part of a hydraulic or
acrylic resin base and certain volatile solvents.
pneumatic linear actuator.
acrylic nitrocellulose lacquer — A common topcoat for
acute angle — An angle of less than 90°. Also referred to
aircraft, available either as a matte or glossy finish.
as a closed angle.
acrylic resin — A clear thermoplastic produced by
adapter — A device that fits one component to another.
polymerizing acrylic acid. Used for cast and molded
aircraft windshields, windows, and parts, or as a coating Adcock radio antenna — A directional radio transmitting
and adhesive. antenna made up of two vertical conductors from which
electromagnetic energy radiates. The conductors are
acrylic vitro lacquer finish — An aircraft finish applied
connected so that they radiate signals in opposite phases.
in a specified sequence. It includes a wash primer coat,
modified zinc chromate primer coat, and an acrylic additional services — Advisory information provided by
nitrocellulose lacquer topcoat. ATC which includes but is not limited to the following:
activated charcoal — Used as a filter for liquids and as a a. Traffic advisories.
medium to absorb gases.
b. Vectors, when requested by the pilot, to assist aircraft
active current — Current in an AC circuit that is in phase receiving traffic advisories to avoid observed traffic.
with the voltage. Active current produces true power.
c. Altitude deviation information of 300 feet or more from
active detection systems — A detection system that an assigned altitude as observed on a verified (reading
transmits a signal such as radar as opposed to a passive correctly) automatic altitude readout (Mode C).
detection system that only receives a signal.
d. Advisories that traffic is no longer a factor.
active electrical component — An electrical part that
e. Weather and chaff information.
controls current or voltage for switching or amplification.
f. Weather assistance.
active runway — See runway in use, active runway, and/
or duty runway. g. Bird activity information.
actual calculated landing time (ACLT) — A flight’s frozen h. Holding pattern surveillance.
calculated landing time. An actual time determined
4

10001930-002_AviationDictionary_2012_BOOK.indb 4 3/27/2012 9:37:53 AM

 additives • advection current

Additional services are provided to the extent possible adjustable-pitch propeller — A propeller with blades
contingent only upon the controller’s capability to fit whose pitch can be adjusted on the ground with the engine
them into the performance of higher priority duties and not running, but which cannot be adjusted in flight. Also
on the basis of limitations of the radar, volume of traffic, referred to as a ground adjustable propeller.
frequency congestion, and controller workload. The
adjustable-split die — A tool used for cutting external
controller has complete discretion for determining if he/
threads on round stock. The die is split on one side and
she is able to provide or continue to provide a service in
an adjusting screw is used to spread the die to adjust the
a particular case. The controller’s reason not to provide
fit of the threads.
or continue to provide a service in a particular case is not
subject to question by the pilot and need not be made adjusting idle mixture — Adjusting carburetor idle mixture
known to him/her. tailored for the best performance of the particular engine
and installation.
additives — Materials that are mixed into a two-part resin
system to improve the properties of the system. ADM — Aeronautical decision making. A systematic
mental process used by aircraft pilots to consistently
address (computer) — A location within a computer’s
determine the best course of action in response to a given
memory where data is located.
set of circumstances.
adequate vis ref (adequate visual reference) — Runway
Administrator — The Federal Aviation Administrator
markings or runway lighting that provides the pilot
or any person to whom he/she has delegated his/her
with adequate visual reference to continuously identify
authority in the matter concerned.
the take-off surface and maintain directional control
throughout the take-off run. admittance — A measure of the ease with which alternating
current can flow in an electrical circuit. Admittance is the
adhesion — The forming of a tight bond, usually in
current divided by the voltage, and is the reciprocal of
reference to surface coatings and adhesives.
impedance. Measured in siemens.
adhesive — A substance applied to two mating surfaces to
advance — To move forward.
bond them together by surface attachment.
advanced composites — A fibrous material embedded in
adhesive film — In composites, premixed adhesives cast
a resin matrix. The term “advanced” applies to those
onto a thin plastic film. Requires refrigerated storage.
materials, which have superior strength and stiffness and
adiabatic — Air compression occurring without loss or the process in which they are manufactured. Advanced
gain of heat. composites are generally the ones used structurally on an
aircraft.
adiabatic change — A physical change in state or condition
that occurs within a material with no loss or gain of heat. advanced firing — See advanced timing.
adiabatic cooling — A process of cooling the air through advanced ground instructor — A person certificated by
expansion. For example, as air moves up a slope it the FAA who is authorized to provide: ground training
expands with the reduction of atmospheric pressure and in the aeronautical knowledge areas that are required
cools as it expands. for issuance of any certificate or rating; ground training
required for any flight review; and a recommendation
adiabatic heating — A process of heating dry air through
for a knowledge test required for the issuance of any
compression. For example, as air moves down a slope it
certificate.
is compressed, as it is compressed it warms.
advanced timing — Ignition when takes place before the
adiabatic lapse rate — The decrease in temperature that
piston reaches top dead center.
occurs with changes in altitude when no heat is added to
or taken from the air. It is nominally 5.4°F per 1,000 ft. advancing blade — The blade moving in the same direction
as the helicopter or gyroplane. In rotorcraft that have
adiabatic process — In meteorology, a closed system
counterclockwise main rotor blade rotation as viewed
where temperature, pressure, and density vary without
from above, the advancing blade is in the right half of the
any gain or loss of heat.
rotor disc area during forward movement.
adjacent — In mathematics, the two sides of a triangle that
advection — The horizontal transport of air or atmospheric
have a common angle.
properties. In meteorology, advection is sometimes
adjust — To change something in order to make it more referred to as the horizontal component of convection.
satisfactory or to make it operate better.
advection current — An air current that move horizontally
adjustable stabilizer — A stabilizer that can be adjusted in over a surface.
flight to trim the airplane, thereby allowing the airplane
to fly hands-off at any given airspeed.
5

10001930-002_AviationDictionary_2012_BOOK.indb 5 3/27/2012 9:37:53 AM

 advection fog • aerodynamic design point

advection fog — Fog that forms when moist air is moved zone, to all radio equipped aircraft, to assist in the safe
horizontally across a surface that is cold enough to cool and efficient conduct of flight.
the air to a temperature that is below its dew point.
aerodrome traffic circuit [ICAO] — The specified path
adverse yaw — A condition of flight in which the nose of to be flown by aircraft operating in the vicinity of an
an airplane starts to move in the direction opposite of the aerodrome.
intended turn. It is caused by the downward deflected
aerodrome traffic frequency (ATF) — A frequency
aileron producing induced drag. Often called aileron drag.
designated at an uncontrolled airport. An ATF is used to
advise intentions — During communications, this indicates: ensure all radio equipped aircraft operating within the
Tell me what you plan to do. area, normally within a 5 NM radius of the airport, are
listening on a common frequency. The ATF is normally
advisory — Advice and information provided to assist
the ground station frequency. Where a ground station
pilots in the safe conduct of flight and aircraft movement.
does not exist, a common frequency is designated. Radio
advisory frequency — The appropriate frequency to be call sign is that of the ground station, or where no ground
used for Airport Advisory Service. station exists, a broadcast is made with the call sign
“Traffic Advisory.” Jeppesen charts list the frequency
advisory route (ADR) — A designated route along which
and the area of use when other than the standard 5 NM.
air traffic advisory service is available. NOTE: Air traffic
control service provides a much more complete service aerodrome traffic zone (ATZ) — An airspace of detailed
than air traffic advisory service; advisory areas and routes dimensions established around an aerodrome for the
are therefore not established within controlled airspace, protection of aerodrome traffic.
but air traffic advisory service may be provided below
aerodynamic balance — The portion of a control surface
and above control areas.
on an airplane that extends ahead of the hinge line. This
advisory service — Advice and information provided by utilizes the airflow about the aircraft to aid in moving the
a facility to assist pilots in the safe conduct of flight and surface.
aircraft movement.
aerodynamic blockage thrust reverser — A configuration
aerated — 1. Mixed with air. When lubricating oil is used of thrust reverser used in turbojet engines in which thin
in an engine, it mixes with air, and it is said to be aerated. airfoils or obstructions are placed in the engine’s exhaust
2. Supplied with air or exposed to the circulation of air. stream to duct the high-velocity exhaust gases forward.
This decreases the airplane’s landing roll.
aeration — The process of mixing air into a liquid.
aerodynamic braking — The generation of aerodynamic
aerial — Of or relating to an aircraft in flight. It is used in
drag used to reduce the roll after landing or to allow the
terms such as aerial photography.
aircraft to descend at a steep angle without building up
aerial photograph — Any photograph made from an excessive airspeed. Examples would include speed brakes
aircraft in flight. and spoilers to steepen glide paths and reduce landing
roll. The reverse pitch on propellers and reverse thrust
aerial refueling — A procedure used by the military to
on turbine engines are also used in reducing landing roll.
transfer fuel from one aircraft to another during flight.
aerodynamic center — The point within the airfoil section
aerodrome — A defined area on land or water (including
located at a point approximately one-fourth of the way
any buildings, installations and equipment) intended to
back from the leading edge. It is the point at which the
be used either wholly or in part for the arrival, departure,
(pitching) moment coefficient is relatively constant for
and movement of aircraft.
all angles of attack.
aerodrome beacon [ICAO] — Aeronautical beacon used
aerodynamic center of horizontal tail — The point at
to indicate the location of an aerodrome from the air.
which the flow of air over the horizontal stabilizer creates
aerodrome control service [ICAO] — Air traffic control a force which pushes the tail up or down.
service for aerodrome traffic.
aerodynamic coefficients — Non-dimensional coefficients
aerodrome control tower [ICAO] — A unit established to for aerodynamic forces and moments.
provide air traffic control service to aerodrome traffic.
aerodynamic contrail — As an aircraft moves through
aerodrome elevation [ICAO] — The elevation of the moist air the forces created by dynamic flow over the
highest point of the landing area. lifting surfaces cause the surrounding atmosphere to
reach saturation, to form a cloud like trail. Usually this is
aerodrome flight information service (AFIS) — A
generated by high-performance aircraft.
directed traffic information and operational information
service provided within an aerodrome flight information aerodynamic design point — In turbine engines, the most
efficient compression ratio that occurs at altitude.
6

10001930-002_AviationDictionary_2012_BOOK.indb 6 3/27/2012 9:37:53 AM

 aerodynamic drag • aeronautical chart

aerodynamic drag — Drag caused by turbulent airflow on b. VFR Terminal Area Charts (1:250,000) – Depict Class
an airfoil such as a wing, propeller, or compressor blade. B airspace which provides for the control or segregation
of all the aircraft within the Class B airspace. The chart
aerodynamic factors — 1. Those factors that affect the
depicts topographic information and aeronautical
amount of lift or drag produced by an airfoil. 2. The
information which includes visual and radio aids to
forces acting on a propeller while rotating through the air
navigation, airports, controlled airspace, restricted
as it transforms the rotary power of the engine into thrust.
areas, obstructions, and related data.
aerodynamic heating — The temperature rise caused by
c. Jeppesen Class B Airspace Charts – Provide
high-speed air flowing over an aerodynamic surface.
aeronautical information for orientation purposes
aerodynamic lift — The upward force caused by high-speed by depicting airways and navaids used to assist in
air flowing over an airfoil. determining the aircraft’s position relative to the
vertical and lateral limits of the Class B airspace. Also
aerodynamic shape — The shape of an object with
include flight procedures and VFR approach control
reference to the airflow over it. Certain shapes cause
frequencies for each Class B airspace. Charts are
air pressure differentials which produce lift; others are
identified by the principal city and state using an index
designed for minimum airflow resistance.
number of 10-1A.
aerodynamic twisting force (ATF) — One of the five
d. World Aeronautical Charts (WAC) (1:1,000,000)
forces acting on a rotating propeller. The aerodynamic
– Provide a standard series of aeronautical charts
twisting force tends to twist the blade angle toward the
covering land areas of the world at a size and scale
feather position.
convenient for navigation by moderate speed aircraft.
aerodynamic twisting moment — A rotational force Topographic information includes cities and towns,
applied to an object due to aerodynamic loads on the principal roads, railroads, distinctive landmarks,
object. Usually a concern in the design of propellers, but drainage, and relief. Aeronautical information includes
also to a lesser extent for wing design. It occurs when the visual and radio aids to navigation, airports, airways,
center of lift is ahead of the center of rotation. restricted areas, obstructions and other pertinent data.
aerodynamics — The science of the action of air on e. Enroute Low Altitude Charts – Provide aeronautical
an object, and with the motion of air on other gases. information for enroute instrument navigation (IFR)
Aerodynamics deals with the production of lift by the in the low altitude stratum. Information includes the
aircraft, the relative wind, and the atmosphere. portrayal of airways, limits of controlled airspace,
position identification and frequencies of radio aids,
Aerofiche — Registered trade name for a form of microfiche
selected airports, minimum enroute and minimum
used in the aircraft industry. Two hundred eighty-eight
obstruction clearance altitudes, airway distances,
frames of information may be placed on a single 4” x 8”
reporting points, restricted areas, and related data.
card of film.
Area charts, which are a part of this series, furnish
aeronaut — A person who operates or travels in airships terminal data at a larger scale in congested areas.
or balloons.
f. Enroute High Altitude Charts – Provide aeronautical
aeronautical beacon — A visual NAVAID displaying information for enroute instrument navigation (IFR)
flashes of white and/or colored light to indicate the in the high altitude stratum. Information includes the
location of an airport, a heliport, a landmark, a certain portrayal of jet routes, identification and frequencies
point of a Federal airway in mountainous terrain, or an of radio aids, selected airports, distances, time zones,
obstruction. special use airspace, and related information.
aeronautical chart — A map used in air navigation g. Jeppesen Area Navigation Enroute Charts – Provide
containing all or part of the following: topographic aeronautical information for flight planning and flying,
features, hazards and obstructions, navigation aids, IFR or VFR, random area navigation routes in the
navigation routes, designated airspace, and airports. U.S. Depict VORTACs (and VORDMEs) with four
Common aeronautical charts include: cardinal radials marked with 10-mile ticks to establish
rho/ theta (distance and bearing) values for describing
a. Sectional Aeronautical Charts (1:500,000) – Designed
and plotting area navigation waypoints. Charts
for visual navigation of slow or medium speed aircraft.
also include VORs, station declination VORTAC
Topographic information on these charts features the
antenna elevation, FSS and ARTCC communications,
portrayal of relief, and a judicious selection of visual
controlled airspace, minimum off-route altitudes,
check points for VFR flight. Aeronautical information
airports, special use airspace, ARTCC boundaries,
includes visual and radio aids to navigation, airports,
times zones and state boundaries. Airport and Facility
controlled airspace, restricted areas, obstructions and
Listings include primary airport coordinates, elevation,
related data.

10001930-002_AviationDictionary_2012_BOOK.indb 7 3/27/2012 9:37:54 AM

 aeronautical chart [ICAO] • after-firing

identifier and bearing/distance from nearby VORTAC/ engineering solutions for aviation, airports, defense,
VORDME facilities including facility frequency, government, and transportation. In aviation, ARINC
identifier, and antenna elevation. provides standards for communications compatibility.
h. Instrument Approach Procedures (IAP) Charts – aeronautics — The science of making and flying airplanes.
Portray the aeronautical data which is required to A term that applies to anything that is in any way
execute an instrument approach to an airport. These associated with the design, construction, or operation
charts depict the procedures, including all related data, of an aircraft. Aerodynamics and aerostatics are both
and the airport diagram. Each procedure is designated branches of aeronautics.
for use with a specific type of electronic navigation
aerosol — A liquid that is broken up into tiny drops divided
system including NDB, TACAN, VOR, ILS/ MLS,
into extremely fine particles and dispersed or sprayed into
and RNAV. These charts are identified by the type
the air by the use of a propellant such as carbon dioxide,
of navigational aid(s) which provide final approach
nitrogen, or Freon.
guidance.
aerospace — Space from the Earth’s surface extending
i. Instrument Departure Procedure (DP) Charts –
outward beyond the earth into space.
Designed to expedite clearance delivery and to
facilitate transition between takeoff and enroute aerospace industry — That portion of our economy
operations. Each DP is presented as a separate chart associated with such devices as aircraft, space ships,
and may serve a single airport or more than one airport missiles, and their associated parts.
in a given geographical location.
aerospace vehicle — Any controllable device capable of
j. Standard Terminal Arrival (STAR) Charts – Designed flight in the aerospace.
to expedite air traffic control arrival procedures and
aerostat — A device such as a balloon or dirigible that is
to facilitate transition between enroute and instrument
supported in the air by displacing more than its weight.
approach operations. Each STAR procedure is
presented as a separate chart and may serve a single aerostatics — The branch of science that deals with the
airport or more than one airport in a given geographical generation of lift by the displacement of air by a body
location. lighter than the air it displaces. Balloons and dirigibles
that are filled with hot air or gas fall under the science of
k. Airport Taxi Charts – Designed to expedite the
aerostatics.
efficient and safe flow of ground traffic at an airport.
These charts are identified by the official airport name: affective domain — A grouping of learning levels
i.e. Ronald Reagan Washington National Airport. associated with a person’s attitudes, personal beliefs, and
values, which range from receiving through responding,
aeronautical chart [ICAO] — A representation of a portion
valuing, and organization to characterization.
of the earth, its culture and relief, specifically designated
to meet the requirements of air navigation. affirmative — In communications, this indicates: Yes.
aeronautical decision making (ADM) — A systematic aft — To the rear, back, dorsal, or tail of the aircraft.
approach to the mental process used by aircraft pilots
aft flap — The rear section of a triple-slotted, segmented
to consistently determine the best course of action in
wing flap.
response to a given set of circumstances.
after bottom center (ABC) — In a reciprocating engine,
Aeronautical Information Manual (AIM) — A primary
the amount of crankshaft rotation after the piston has
FAA publication whose purpose is to instruct airmen
passed the bottom of its stroke. Expressed in degrees.
about operating in the National Airspace System of the
U.S. It provides basic flight information, ATC Procedures after top center (ATC) — In a reciprocating engine, the
and general instructional information concerning health, amount of crankshaft rotation after the piston has passed
medical facts, factors affecting flight safety, accident the top of its stroke. Expressed in degrees.
and hazard reporting, and types of aeronautical charts
afterburner — A portion of a jet engine in which additional
and their use. Previously referred to as the Airman’s
fuel is sprayed into the hot, oxygen-rich exhaust, where
Information Manual.
it burns and produces additional thrust. Afterburners
aeronautical information publication (AIP) [ICAO] — A provide a great amount of additional thrust with a
publication issued by or with the authority of a State and minimum of additional weight.
containing aeronautical information of a lasting character
after-firing — A condition often resulting from either too
essential to air navigation.
rich fuel/air mixture or unburned fuel being pumped into
Aeronautical Radio, Incorporated (ARINC) — A the exhaust system of a reciprocating engine and ignited
provider of transportation communications and systems when it comes in contact with some hot component.
Sometimes referred to as afterburning or torching.
8

10001930-002_AviationDictionary_2012_BOOK.indb 8 3/27/2012 9:37:54 AM

 afterglow • air defense emergency

afterglow — The glow that remains on the phosphorescent air bleed — 1. A small hole in the fuel passage between the
screen of a cathode ray tube after the electron beam passes. float bowl and the discharge nozzle of a float carburetor.
The hole introduces air into the liquid fuel and serves
aft-fan engine — A turbofan engine that has a fan
as an aid to atomization. 2. Used in gas turbine engines
constructed as an extension of the turbine blades.
for a variety of purposes and is taken from the engine’s
age hardening — The process of increasing the hardness of compressor section.
a metal after the heat-treat process. Age hardening occurs
air brake — A plate or series of plates that can be projected
at room temperature and continues for a period of several
into the airplane’s slipstream to provide turbulence and
days until the metal reaches its fully hardened state.
drag to slow the airplane during descent, glide, or when
aggression — Because of safety concerns or social maneuvering. Air brakes differ from flaps in that they
structures, students may display the defense mechanism produce no useful lift. Also referred to as speed brakes.
of aggression. They may ask irrelevant questions, refuse
air capacitor — A capacitor that uses air as the dielectric.
to participate in class activities, or disrupt the group.
air carrier — A person who undertakes directly by lease, or
aging — See age hardening.
other arrangement, to engage in air transportation.
agitate — To stir or shake something in order to mix its
Air Carrier District Office (ACDO) — An FAA field office
ingredients.
serving an assigned geographical area, staffed with Flight
AGL altitude — The vertical elevation above ground. Standards personnel serving the aviation industry and the
Expressed in feet. general public on matters related to the certification and
operation of scheduled air carriers and other large aircraft
agonic line — An irregular imaginary line across the surface
operations.
of the earth along which the magnetic and geographic
poles are in line, and where there is no variation error. air commerce — Interstate, overseas, or foreign air
commerce or the transportation of mail by aircraft or any
agricultural aircraft — Aircraft that are specifically
operation or navigation of aircraft within the limits of any
designed and built for use in the application of chemicals
Federal airway or any operation or navigation of aircraft
to crops for insect and weed control.
which directly affects, or which may endanger safety in,
aileron — A primary control surface located near the wing interstate, overseas, or foreign air commerce.
tip that makes up part of the total wing area. Ailerons are
air commerce — Transportation by aircraft of persons or
operated by the lateral motion of the controls and cause
property for hire or compensation.
rotation of the aircraft about the longitudinal axis.
air conditioning — The process of treating air to control
aileron angle — The angle of displacement of an aileron
simultaneously its temperature, humidity, cleanliness,
from its neutral, or trailing, position.
and distribution to meet the requirements of a conditioned
aileron spar — A spar that extends only part of the span of space. In combination with pressurization, complete
the wing and provides a hinge attachment point for the environmental control is possible.
aileron. Also referred to as “false spar.”
air conditioning system — A system consisting of cabin air
aileron station — Distances measured outboard from the conditioning and pressurization that supplies conditioned
root end of an aileron, parallel to the aileron spar. air for heating and cooling the cockpit and cabin spaces.
This air also provides pressurization to maintain a safe,
air — A mixture of gases that comprises the earth’s
comfortable cabin environment.
atmosphere. Pure dry air contains approximately 78%
nitrogen and 21% oxygen. The remaining 1% consists of air cycle cooling system — One of several cooling systems
argon, carbon dioxide, hydrogen, and traces of neon and consisting of an expansion turbine, an air-to-air heat
helium. Dry air weighs 0.07651 pounds per cubic foot at exchanger, and various valves that control airflow through
sea level with a temperature of 59°F and has a barometric the system. Used to provide a comfortable atmosphere
pressure of 14.69 PSI at 40° latitude. within the aircraft cabin.
air adapters — A component in a centrifugal compressor air cycle machine — An air conditioning system That uses
gas turbine engine. Its purpose is to deliver air from the compressor bleed air to condition air and pressurize the
diffuser to the individual can-type combustion chambers cabin. Primarily used in jet turbine powered aircraft.
at the proper angle.
air data computer — A device that computes altitude,
air, ambient — The atmospheric air surrounding all sides vertical speed, airspeed, and Mach number from inputs
of the aircraft or engine. Expressed in units of lbs./sq. of pitot and static pressure and temperature.
inch or in. Hg.
air defense emergency — A military emergency condition
declared by a designated authority. This condition exists

10001930-002_AviationDictionary_2012_BOOK.indb 9 3/27/2012 9:37:54 AM

 air defense identification zone (ADIZ) • air seal

when an attack upon the continental U.S., Alaska, air inlet — A portion of a turbine engine designed to conduct
Canada, or U.S. installations in Greenland by hostile incoming air to the compressor section with a minimum
aircraft or missiles is considered probable, is imminent, energy loss resulting from drag or ram pressure loss.
or is taking place.
air lock — A pocket of trapped air that blocks the flow of
air defense identification zone (ADIZ) — The area of fluid.
airspace over land or water, extending upward from
air mass — A widespread mass of air having similar
the surface, within which the ready identification, the
characteristics (e.g., temperature) which usually helps to
location, and the control of aircraft are required in the
identify the source region of the air. Fronts are distinct
interest of national security.
boundaries between air masses.
a. Domestic Air Defense Identification Zone – An
air metering force — The force used in Bendix pressure
ADIZ within the United States along an international
carburetors and fuel injection systems in which venturi
boundary of the United States.
and ram air pressures control the amount of fuel metered.
b. Coastal Air Defense Identification Zone – An ADIZ
air navigation facility — Any facility used in, available
over the coastal waters of the United States.
for use in, or designed for use in, aid of air navigation,
c. Distant Early Warning Identification Zone (DEWIZ) including landing areas, lights, any apparatus or equipment
– An ADIZ over the coastal waters of the State of for disseminating weather information, for signaling, for
Alaska. radio-directional finding, or for radio or other electrical
communication, and any other structure or mechanism
ADIZ locations and operating and flight plan requirements
having a similar purpose for guiding or controlling flight
for civil aircraft operations are specified in FAR 99.
in the air or the landing and take-off of aircraft.
air density — The density of the air in terms of mass per
air refueling — A method of refueling aircraft while in flight
unit volume. Dense air has more molecules per unit
in order to extend the airplane’s range. The military uses
volume than less dense air. The density of air decreases
flying tankers to allow aircraft to fly extended missions.
with altitude above the surface of the earth and with
increasing temperature. air route surveillance radar (ARSR) — Air route traffic
control center (ARTCC) radar used primarily to detect
air filter — A filtering device that prevents dust and dirt
and display an aircraft’s position while enroute between
from entering the intake or induction system.
terminal areas. The ARSR enables controllers to provide
air filter system — An air filter system normally consists of radar air traffic control service when aircraft are within
a filter and a door that can either allow the air to be filtered the ARSR coverage. In some instances, ARSR may
through it or bypass the filter. When the filter system is enable an ARTCC to provide terminal radar services
operating, air is drawn through a louvered access panel similar to but usually more limited than those provided
that does not face directly into the airstream. With this by a radar approach control.
entrance location, considerable dust is removed as the air
Air Route Traffic Control Center (ARTCC) — Provides
is forced to turn and enter the duct.
enroute air traffic control guidance primarily for aircraft
air gap — The space between the reluctor and the speed operating on IFR flight plans.
sensor on some shaft rotational speed detection systems.
air route traffic control center (ARTCC) — A facility
The reluctor is a toothed gear or cam that causes variations
established to provide air traffic control service to aircraft
in the magnetic field surrounding the pickup device. This
operating on IFR flight plans within controlled airspace
varying field can be transmitted into RPM readings. The
and principally during the enroute phase of flight. When
spacing (air gap) between these parts is critical, as the
equipment capabilities and controller workload permit,
magnetic fields involved are very small.
certain advisory/assistance services may be provided to
air impingement — A fault that resembles haze in an enamel VFR aircraft.
or lacquer paint finish. It is caused by microscopic-size
air scoop — 1. A hooded opening to an engine carburetor
bubbles that form when paint is applied with too high an
or other device used to receive the ram air during flight,
atomizing air pressure.
which in turn, increases the amount of air taken into
air impingement starter — A starter used on small gas the structure. 2. A specially designed scoop or duct that
turbine engines in which a stream of high-pressure guides air to the carburetor and intake manifold of a
compressed air is directed onto the blades of the reciprocating engine induction system.
compressor or the turbine in order to rotate the engine
air seal — A seal used to keep air from passing out of a
for starting.
housing unit. Usually air seals are thin rotating or
stationary rims designed to act as air dams to reduce

10

10001930-002_AviationDictionary_2012_BOOK.indb 10 3/27/2012 9:37:54 AM

 air start • air traffic control system command center

airflow leakage between the gas path and the internal air traffic control assigned airspace (ATCAA) — Airspace
engine or over blade tips. of defined vertical/lateral limits, assigned by ATC, for the
purpose of providing air traffic segregation between the
air start — The process of starting an aircraft engine in
specified activities being conducted within the assigned
flight. In an air start, aerodynamic forces cause the
airspace and other IFR air traffic.
propeller or the compressor to turn the engine. A starter
is not generally used during an air start. air traffic control (ATC) — A service provided by the FAA
to promote the safe, orderly, and expeditious flow of air
air starter — See air-turbine starter.
traffic.
air strip — See airfield.
air traffic control clearance — An authorization by air
air taxi — Used to describe a helicopter/VTOL aircraft traffic control, for the purpose of preventing collision
movement conducted above the surface but normally not between known aircraft, for an aircraft to proceed under
above 100 feet AGL. The aircraft may proceed either via specified traffic conditions within controlled airspace.
hover taxi or flight at speeds more than 20 knots. The
air traffic control clearance [ICAO] — Authorization for
pilot is solely responsible for selecting a safe airspeed/
an aircraft to proceed under conditions specified by an air
altitude for the operation being conducted.
traffic control unit.
air temperature control — An air control door or valve,
NOTE 1: For convenience, the term air traffic control
near the entrance of the carburetor, which admits alternate
clearance is frequently abbreviated to clearance when
heated air to the carburetor to prevent carburetor ice.
used in appropriate contexts.
air temperature gauge — A gauge that indicates the
NOTE 2: The abbreviated term clearance may be prefixed
temperature of the air before it enters the carburetor. The
by the words taxi, takeoff, departure, enroute, approach
temperature reading is sensed by a bulb located in the air
or landing to indicate the particular portion of flight to
intake passage to the engine.
which the air traffic control clearance relates.
air traffic — Aircraft operating in the air or on an airport
air traffic control service — See air traffic control.
surface, exclusive of loading ramps and parking areas.
air traffic control service [ICAO] — A service provided
air traffic clearance — An authorization by air traffic
for the purpose of: a. Preventing collisions: 1) Between
control, for the purpose of preventing collision between
aircraft, and 2) On the maneuvering area between aircraft
known aircraft, for an aircraft to proceed under specified
and obstructions; and b. Expediting and maintaining an
traffic conditions within controlled airspace. The
orderly flow of air traffic.
pilot-in-command of an aircraft may not deviate from the
provisions of a visual flight rules (VFR) or instrument air traffic control specialist — A person authorized to
flight rules (IFR) air traffic clearance except in an provide air traffic control service.
emergency or unless an amended clearance has been
air traffic control system command center — An Air
obtained. Additionally, the pilot may request a different
Traffic Tactical Operations facility consisting of four
clearance from that which has been issued by air traffic
operational units.
control (ATC) if information available to the pilot makes
another course of action more practicable or if aircraft a. Central Flow Control Function (CFCF). Responsible
equipment limitations or company procedures forbid for coordination and approval of all major inter-center
compliance with the clearance issued. Pilots may also flow control restrictions on a system basis in order to
request clarification or amendment, as appropriate, any obtain maximum utilization of the airspace.
time a clearance is not fully understood, or considered
b. Central Altitude Reservation Function (CARF).
unacceptable because of safety of flight. Controllers
Responsible for coordinating, planning, and approving
should, in such instances and to the extent of operational
special user requirements under the Altitude
practicality and safety, honor the pilot’s request. FAR
Reservation (ALTRV) concept.
Part 91.3(a) states: “The pilot-in-command of an aircraft
is directly responsible for, and is the final authority as c. Airport Reservation Office (ARO). Responsible for
to, the operation of that aircraft.” The pilot is responsible approving IFR flights at designated high density traffic
to request an amended clearance if ATC issues a airports (John F. Kennedy, LaGuardia, O’Hare, and
clearance that would cause a pilot to deviate from a rule Washington National) during specified hours.
or regulation, or in the pilot’s opinion, would place the
d. ATC Contingency Command Post. A facility which
aircraft in jeopardy.
enables the FAA to manage the ATC system when
air traffic control — A service operated by an authoritative significant portions of the systems’s capabilities have
body to promote the safe, orderly, and expeditious flow been lost or are threatened.
of air traffic.

11

10001930-002_AviationDictionary_2012_BOOK.indb 11 3/27/2012 9:37:54 AM

 air traffic [ICAO] • aircraft cable

air traffic [ICAO] — All aircraft in flight or operating on air-core electrical transformer — A transformer made up
the maneuvering area of an aerodrome. of two or more coils wound on a core of non-magnetic
material. Air-core transformers are normally used for
air traffic service — A generic term meaning:
radio-frequency alternating current.
a. Flight Information Service
aircraft — Any weight-carrying device designed to be
b. Alerting Service supported by the air or intended to be used for flight in
the air.
c. Air Traffic Advisory Service
aircraft accident — Any damage or injury that occurs
d. Air Traffic Control Service
when an aircraft is moving with the intention of flight.
1. Area Control Service,
Aircraft Addressing and Reporting System (ACARS)
2. Approach Control Service, or — A digital data network using aircraft VHF and/or HF
radio to transmit and receive data to and from airline
3. Airport Control Service.
operations. The system is used by the airlines to maintain
air transportation — Interstate, overseas, or foreign air contact with their aircraft around the world and by pilots
transportation or the transportation of mail by aircraft. to obtain data such as weather.
airborne — The condition of an airplane, glider, or balloon aircraft alteration — The modification of an aircraft, its
when it is off the ground. structure, or its components that changes the physical
or flight characteristics of the aircraft. Alterations are
airborne delay — Amount of delay to be encountered in
classified as major or minor, in accordance with Federal
airborne holding.
Aviation Regulations, Part 43.
airborne intercept radar — Radar contained in fighter-type
aircraft approach category — A grouping of aircraft based
aircraft to locate and track airborne targets.
on a speed of 1.3 times the stall speed in the landing
airborne moving target indicator — A feature of airborne configuration at maximum gross landing weight. An aircraft
radar that electronically filters out targets that are either shall fit in only one category. If it is necessary to maneuver
stationary or moving at less than a preset speed. at speeds in excess of the upper limit of a speed range for
a category, the minimums for the next higher category
airborne navigation equipment — A phrase embracing
should be used. For example, an aircraft which falls in
many systems and instruments. These systems include
Category A, but is circling to land at a speed in excess of
VHF omnirange (VOR), instrument landing systems,
91 knots, should use the approach Category B minimums
distance-measuring equipment, automatic direction
when circling to land. The categories are as follows:
finders, Doppler systems, inertial navigation systems,
Global Positioning Systems (GPS), and others. a. Category A – Speed less than 91 knots.
airborne weather radar — An electronic device used to b. Category B – Speed 91 knots or more but less than
see objects in darkness, fog, or storms, as well as in clear 121 knots.
weather. The range and relative position are indicated on
c. Category C – Speed 121 knots or more but less than
the radar scope.
141 knots.
air-breathing engine — An engine that requires an intake of
d. Category D – Speed 141 knots or more but less than
air to supply the oxygen needed to operate. Reciprocating
166 knots.
and turbine engines are both air-breathing engines.
e. Category E – Speed 166 knots or more. Category
air-cool — To remove excess heat from an object by
E includes only certain Military Aircraft and is not
transferring it directly into the airstream.
included on Jeppesen Approach Charts.
air-cooled blades and vanes — Hollow airfoils in the hot
aircraft basic operating weight — The established basic
section that receive air from the cold section so they
weight of an aircraft available for flight without its fuel
can operate in a much higher temperature environment.
and payload.
Holes, sometimes referred to as gill holes, film holes, or
tip holes, direct air back to the gas path. aircraft battery — A source of electrical energy for an
aircraft that can be used for starting. The battery also
air-cooled oil cooler — A heat exchanger in the lubrication
serves as an auxiliary source of power when the engine
system of an aircraft engine that removes heat from the oil
generator is inoperable.
and transfers it into the air that flows through the cooler.
aircraft cable — Strands of wire formed into a helical or
air-cooled turbine blades — Hollow turbine wheel blades
spiral shape. Cable designations are based on the number
of certain high-powered gas turbine engines that are
of strands and the number of wires in each strand. The
cooled by passing compressor bleed air through them.
most common aircraft cables are 7x7 and 7x19.
12

10001930-002_AviationDictionary_2012_BOOK.indb 12 3/27/2012 9:37:54 AM

 aircraft checkouts • aircraft surge launch and recovery (ASLAR)

aircraft checkouts — An instructional program designed to aircraft listings — Information sheets published by the
familiarize and qualify a pilot to act as pilot in command FAA that contain essential information on particular
of a particular aircraft type. models of aircraft.
aircraft classes — For the purposes of Wake Turbulence aircraft log — A record containing the operational or
Separation Minima, ATC classifies aircraft as Heavy, maintenance history of the aircraft.
Large, and Small as follows:
aircraft operating weight — The basic weight of an
a. Heavy – Aircraft capable of takeoff weights of more aircraft plus the weight of the crewmembers, equipment,
than 255,000 pounds whether or not they are operating fuel, oil, and passengers.
at this weight during any particular phase of flight.
aircraft pitch — the movement about an aircraft’s lateral or
b. Large – Aircraft of more than 41,000 pounds, pitch axis. Movement of the cyclic forward or aft causes
maximum certificated takeoff weight, up to 255,000 the nose of the helicopter or gyroplane to pitch up or
pounds. down.
c. Small – Aircraft of 41,000 pounds or less maximum aircraft plumbing — The hoses, tubing, fittings, and
certificated takeoff weight. connections used to transfer fluids through an aircraft.
aircraft conflict — Predicted conflict, within URET aircraft quality — Indicates that aircraft equipment or
CCLD (User Request Evaluation Tool Core Capability materials are to be produced under closely controlled,
Limited Deployment), of two aircraft, or between aircraft special, and restricted methods of manufacture and
and airspace. A Red alert is used for conflicts when the inspection.
predicted minimum separation is 5 nautical miles or less.
aircraft records — Documentation of the maintenance
A Yellow alert is used when the predicted minimum
performed and the flight time on an aircraft, its engines,
separation is between 5 and approximately 12 nautical
or its components.
miles. A Blue alert is used for conflicts between an
aircraft and predefined airspace. aircraft repair — Restoration of an aircraft and/or its
components to a condition of airworthiness after a failure,
aircraft damage liability coverage — A policy that covers
damage, or wear has occurred.
any damage to the aircraft, and works much like collision
insurance on a car. aircraft rigging — The final adjustment and alignment of
the various components of an aircraft to give it the proper
aircraft dope — A colloidal solution of cellulose acetate or
aerodynamic characteristics.
nitrate, combined with sufficient plasticizers to produce a
smooth, flexible, homogeneous film. The dope increases aircraft roll — The movement of the aircraft about its
a fabric’s tensile strength, air tightness, weatherproofing, longitudinal axis. Movement of the cyclic right or left
and tautness. causes the helicopter or gyroplane to tilt in that direction.
aircraft engine — An engine that is used or intended to be aircraft steel structure — A truss-type fuselage frame
used for propelling aircraft. It includes turbosuperchargers, usually constructed of steel tubing welded together in
appurtenances, and accessories necessary for its such a manner that all members of the truss can carry
functioning, but does not include propellers. both tension and compression loads.
aircraft inspection — A systematic check of an aircraft and aircraft surge launch and recovery (ASLAR) —
its components. The purpose of an aircraft inspection is Procedures used at USAF bases to provide increased
to detect any defects or malfunctions before they become launch and recovery rates in instrument flight rules
serious. Annual inspections, 100-hour inspections, conditions. ASLAR is based on:
progressive inspections, and preflight inspections are
a. Reduced separation between aircraft which is based on
common types of aircraft inspections.
time or distance. Standard arrival separation applies
aircraft lighting system — A system that provides between participants including multiple flights until
illumination for both exterior and interior use. The system the DRAG point. The DRAG point is a published
includes lighting of instruments, cockpits, cabins and location on an ASLAR approach where an aircraft
other sections occupied by crewmembers and passengers landing second in a formation slows to a predetermined
as well as exterior lights for landing and ground taxiing. airspeed. The DRAG point is the reference point at
which MARSA applies as expanding elements effect
aircraft list (ACL) — A view available with URET CCLD
separation within a flight or between subsequent
(User Request Evaluation Tool Core Capability Limited
participating flights.
Deployment) that lists aircraft currently in or predicted
to be in a particular sector’s airspace. The view contains b. ASLAR procedures shall be covered in a Letter of
textual flight data information in line format and may be Agreement between the responsible USAF military
sorted into various orders based on the specific needs of
the sector team.
13

10001930-002_AviationDictionary_2012_BOOK.indb 13 3/27/2012 9:37:54 AM

 aircraft tires • airplane

ATC facility and the concerned FAA facility. Initial Airloc fastener — A patented form of cowling fastener
Approach Fix spacing requirements are normally in which the actual locking is done by turning a steel
addressed as a minimum. cross-pin in a spring steel receptacle.
aircraft tires — A rubber cushion filled with compressed airman — A person involved in flying, maintaining, or
air that fits around a wheel. Tires help absorb the shock operating aircraft.
and roughness of landings and takeoffs; they also support
airman certificate — A certificate issued by the FAA
the weight of the aircraft while on the ground and provide
authorizing a person to perform certain aviation-related
the necessary traction for braking and stopping aircraft
duties. Certificates are issued to pilots, technicians, and
upon landing.
parachute riggers.
aircraft welding — The process of joining metal by fusing
Airman’s Information Manual — Provides flight
the materials together while they are in a plastic or
information and air traffic control procedures for the
molten state. There are three general types of welding:
National Airspace System. Now referred to as the
gas, electric arc, and electric resistance.
Aeronautical Information Manual.
aircraft wooden structures — An aircraft structure in
airman’s meteorological information — See AIRMET.
which wood is used as the structural material.
airmass — An extensive body of air having fairly uniform
air-dry — The process of removing moisture from a
properties of temperature and moisture within a horizontal
material by exposing it to the air.
plane.
airfield — Any area in which aircraft may land, take off,
airmass thunderstorm — A “nonsevere” or “ordinary”
and park. An airfield may also be called an airstrip. The
thunderstorm produced by local airmass instability. May
term airfield includes the buildings, equipment, and
produce small hail, wind gusts less than 50 knots. See
maintenance facilities used to store or service aircraft.
also severe thunderstorm.
airflow over wing section — Air flowing over the top
airmass wind shear — Wind shear that develops near
surface of the wing must reach the trailing edge of the
the ground at night under fair weather conditions in the
wing in the same amount of time as the air flowing under
absence of strong fronts and/or strong surface pressure
the wing. The greater velocity of air traveling a larger
gradients.
distance over the top surface produces lift.
AIRMET — An advisory pertinent to aircraft with limited
airfoil — Any surface designed to obtain a desirable reaction
capabilities, containing information on:
from the air through which it moves. The airfoil converts
movement of air over its surfaces into a force useful for 1. moderate icing,
flight. Wings, control surfaces, propeller blades, and
2. moderate turbulence,
helicopter rotors are examples of airfoils.
3. sustained surface winds of 30 knots or more,
airfoil profile — The outline
of an airfoil section such 4. ceilings less than 1,000 feet and/or visibility less than
as a wing. 3 miles affecting 50 percent of the area at one time,
and
airfoil section — The cross-sectional shape of an airfoil,
viewed as if it were sliced vertically in a fore-and-aft 5. extensive mountain obscuration.
plane. Issued only to amend the area forecast concerning
airframe — The fuselage, booms, nacelles, cowlings, weather phenomena which are of operational interest to
fairings, airfoil surfaces (including rotors but excluding all aircraft and potentially hazardous to aircraft having
propellers and rotating airfoils of engines), and landing limited capability because of lack of equipment,
gear of an aircraft and their accessories and controls. instrumentation, or pilot qualifications. AIRMETs
concern weather of less severity than that covered by
airframe technician — Any person certified by the FAA to SIGMETs or Convective SIGMETs.
perform maintenance or inspections on the airframe of
certificated aircraft. air-oil separator — A device in the vent portion of the
lubrication system of a gas turbine engine that separates
airline — A company or organization that operates aircraft any oil from the air before the air is vented overboard.
for the transportation of persons or cargo.
airplane — An engine-driven, heavier-than-air, fixed-wing
airliner — A large, transport-type aircraft used in air aircraft that is supported in flight by the dynamic reaction
commerce for the transportation of passengers or cargo. of the air against its wings.

14

10001930-002_AviationDictionary_2012_BOOK.indb 14 3/27/2012 9:37:54 AM

 airplane checkouts • airport lighting

airplane checkouts — An instructional program designed 7. LDIN – Lead-in-light system: Consists of one or
to familiarize and qualify a pilot to fly an aircraft not more series of flashing lights installed at or near
previously familiar. ground level that provides positive visual guidance
along an approach path, either curving or straight,
airport — An area of land or water, including any associated
where special problems exist with hazardous terrain,
buildings and facilities, used or intended to be used for
obstructions, or noise abatement procedures.
the landing and takeoff of aircraft.
8. RAIL – Runway Alignment Indicator Lights
airport advisory area — The area within 10 statute miles
(Sequenced Flashing Lights which are installed
of an airport where a flight service station is located, but
only in combination with other light systems).
where there is no control tower in operation.
9. ODALS – Omni-directional Approach Lighting
airport arrival rate (AAR) — A dynamic input parameter
System consists of seven omni-directional flashing
specifying the number of arriving aircraft which an
lights located in the approach area of a nonprecision
airport or airspace can accept from the ARTCC per hour.
runway. Five lights are located on the runway
The AAR is used to calculate the desired interval between
centerline extended with the first light located 300
successive arrival aircraft.
feet from the threshold and extending at equal
airport departure rate (ADR) — A dynamic parameter intervals up to 1,500 feet from the threshold. The
specifying the number of aircraft which can depart an other two lights are located, one on each side of the
airport and the airspace can accept per hour. runway threshold, at a lateral distance of 40 feet from
the runway edge, or 75 feet from the runway edge
airport elevation — The highest point of an airport’s usable
when installed on a runway equipped with a VASI.
runways measured in feet from mean sea level.
b. Runway Lights/Runway Edge Lights – Lights having
airport information aid — See airport information desk.
a prescribed angle of emission used to define the
airport information desk — An airport unmanned facility lateral limits of a runway. Runway lights are uniformly
designed for pilot self-service briefing, flight planning, spaced at intervals of approximately 200 feet, and the
and filing of flight plans. intensity may be controlled or preset.
airport lighting — Various lighting aids that can be c. Touchdown Zone Lighting – Two rows of transverse
installed at an airport. Types of airport lighting include: light bars located symmetrically about the runway
centerline normally at 100 foot intervals. The basic
a. Approach Light System (ALS) – An airport lighting
system extends 3,000 feet along the runway.
facility which provides visual guidance to landing
aircraft by radiating light beams in a directional pattern d. Runway Centerline Lighting – Flush centerline lights
by which the pilot aligns the aircraft with the extended spaced at 50-foot intervals beginning 75 feet from the
centerline of the runway on his final approach for landing threshold and extending to within 75 feet of
landing. Condenser Discharge Sequential Flashing the opposite end of the runway.
Lights/Sequenced Flashing Lights may be installed in
e. Threshold Lights – Fixed green lights arranged
conjunction with the ALS at some airports.
symmetrically left and right of the runway centerline,
Types of Approach Light Systems are: identifying the runway threshold.
1. ALSF-1. – Approach Light System with Sequenced f. Runway End Identifier Lights (REIL) – Two
Flashing Lights in ILS Cat-I configuration. synchronized flashing lights, one on each side of the
runway threshold, which provide rapid and positive
2. ALSF-2. – Approach Light System with Sequenced
identification of the approach end of a particular runway.
Flashing Lights in ILS Cat-II configuration. The
ALSF-2 may operate as an SSALR when weather g. Visual Approach Slope Indicator (VASI) – An airport
conditions permit. lighting facility providing vertical visual approach
slope guidance to aircraft during approach to landing
3. SSALF – Simplified Short Approach Light System
by radiating a directional pattern of high intensity red
with Sequenced Flashing Lights.
and white focused light beams which indicate to the
4. SSALR – Simplified Short Approach Light System pilot that he is “on path” if he sees red/white, “above
with Runway Alignment Indicator Lights. path” if white/white, and “below path” if red/red.
Some airports serving large aircraft have three-bar
5. ALSF – Medium Intensity Approach Light System
VASIs which provide two visual glide paths to the
with Sequenced Flashing Lights.
same runway.
6. MALSR – Medium Intensity Approach Light
h. Boundary Lights – Lights defining the perimeter of an
System with Runway Alignment Indicator Lights.
airport or landing area.

15

10001930-002_AviationDictionary_2012_BOOK.indb 15 3/27/2012 9:37:54 AM

 airport marking aids • airstream direction detection

airport marking aids — Markings used on runway and airport traffic control tower — A terminal facility that
taxiway surfaces to identify a specific runway, a runway uses air/ground communications, visual signaling,
threshold, a centerline, a hold line, etc. A runway should and other devices to provide ATC services to aircraft
be marked in accordance with its present usage such as: operating in the vicinity of an airport or on the movement
area. Authorizes aircraft to land or takeoff at the airport
a. Visual.
controlled by the tower or to transit the Class D airspace
b. Nonprecision instrument. area regardless of flight plan or weather conditions (IFR
or VFR). A tower may also provide approach control
c. Precision instrument.
services (radar or nonradar).
airport movement area safety system (AMASS) — A
airport/facility directory — A publication designed
software enhancement to ASDE radar which provides
primarily as a pilot’s operational manual containing
logic predicting the path of aircraft landing and/or
all airports, seaplane bases, and heliports open to the
departing, and aircraft and/or vehicular movements on
public including communications data, navigational
runways. Visual and aural alarms are activated when
facilities, and certain special notices and procedures.
logic projects a potential collision. This publication is issued in seven volumes according to
airport reference point (ARP) — A point on the airport geographical area.
designated as the official airport location. Usually the airscrew — A British term for aircraft propeller.
approximate geometric center of all usable runway
surfaces. airship — An engine-driven, lighter-than-air aircraft that
can be steered.
airport reservation office — Office responsible for
monitoring the operation of the high density rule. airspace — The space lying above a certain geographical
Receives and processes requests for IFR operations at area.
high density traffic airports. airspace conflict — Predicted conflict of an aircraft and
airport rotating beacon — A visual NAVAID operated active Special Activity Airspace (SAA).
at many airports. At civil airports, alternating white airspace hierarchy — Within the airspace classes, there is
and green flashes indicate the location of the airport. a hierarchy and, in the event of an overlap of airspace:
At military airports, the beacons flash alternately white Class A preempts Class B, Class B preempts Class C,
and green, but are differentiated from civil beacons by Class C preempts Class D, Class D preempts Class E,
dual-peaked (two quick) white flashes between the green and Class E preempts Class G.
flashes.
airspeed — The speed of an aircraft relative to its
airport surface detection equipment — Radar equipment surrounding air mass. The unqualified term “airspeed”
specifically designed to detect all principal features on means one of the following: 1. Indicated Airspeed – The
the surface of an airport, including aircraft and vehicular speed shown on the aircraft airspeed indicator. This is the
traffic, and to present the entire image on a radar speed used in pilot/controller communications under the
indicator console in the control tower. Used to augment general term “airspeed.” 2. True Airspeed – The airspeed
visual observation by tower personnel of aircraft and/ or of an aircraft relative to undisturbed air. Used primarily
vehicular movements on runways and taxiways. in flight planning and enroute portion of flight. When
airport surveillance radar (ASR) — Approach control used in pilot/controller communications, it is referred to
radar used to detect and display an aircraft’s position as “true airspeed” and not shortened to “airspeed.”
in the terminal area. ASR provides range and azimuth airspeed indicator — A differential air pressure gauge
information but does not provide elevation data. Coverage that measures the difference between ram, or impact air
of the ASR can extend up to 60 miles. pressure, and the static pressure of the air to indicate the
airport taxi charts — Designed to expedite the efficient speed of the aircraft through the air.
and safe flow of ground traffic at an airport. These charts airstart — The starting of an aircraft engine while the
are identified by the official airport name: e.g., Ronald aircraft is airborne, preceded by engine shutdown during
Reagan Washington National Airport. training flights or by actual engine failure.
airport traffic area — No longer a designator of airspace. airstream direction detection — A unit of an angle-of-attack
Generally superseded by Class B, C, and D designations indicating system. The airstream direction detector
according to the type of airport. See Class B, Class C, contains the sensing element that measures local airflow
and Class D. direction relative to the angle of attack by determining
airport traffic control service — A service provided by a the angular difference between local airflow and the
control tower for aircraft operating on the movement area fuselage reference plane.
and in the vicinity of an airport.

16

10001930-002_AviationDictionary_2012_BOOK.indb 16 3/27/2012 9:37:55 AM

 air-to-air missile • alkaline

air-to-air missile — A missile launched from an aircraft wood pulp. Alcohol is used as a cleaning fluid, as a
toward an airborne target.
 solvent in many aircraft finishes, and as a fuel for certain
types of specialized engines. Isopropyl alcohol is used in
air-to-surface missile — A missile launched from an
some anti-icing systems for propellers, windshields, and
aircraft toward a target on the ground.
carburetors.
air-turbine starter — A large volume of compressed
alcohol deicing — The act of preventing or controlling ice
air from an auxiliary power unit or bleed air from an
formation by spraying alcohol onto a surface, in the case
operating engine that is directed into the air-turbine
of windshields, or into the inlet airstream of a carburetor.
starter. This air spins the turbine inside the starter, and the
starter, which is geared to the main engine compressor, ALERFA (alert phase) [ICAO] — A situation wherein
spins the engine fast enough for it to start. apprehension exists as to the safety of an aircraft and its
occupants.
airway — A Class E airspace area established in the form
of a corridor, the centerline of which is defined by radio alert — A notification to a position that there is an
navigational aids. aircraft-to-aircraft or aircraft-to airspace conflict, as
detected by Automated Problem Detection (APD).
airway beacon — A light signal used to mark airway
segments in remote mountain areas. The light flashes alert area — Special use airspace which may contain a high
Morse Code to identify the beacon site. volume of pilot training activities or an unusual type of
aerial activity.
airway [ICAO] — A control area or portion thereof
established in the form of corridor equipped with radio alert notice — A request originated by a flight service
navigational aids. station (FSS) or an air route traffic control center
(ARTCC) for an extensive communication search for
Airworthiness Certificate — A certificate issued by the
overdue, unreported, or missing aircraft.
FAA to all aircraft that have been proven to meet the
minimum standards set down by the Federal Aviation alerting service — A service provided to notify appropriate
Regulations. organizations regarding aircraft in need of search and
rescue aid and assist such organizations as required.
Airworthiness Directive — A regulatory notice sent
out by the FAA to the registered owner of an aircraft algebra — A branch of mathematics that uses letters or
informing the owner of a condition that prevents the symbols to represent numbers in formulas and equations.
aircraft from continuing to meet its conditions for
algebraic expression — A quantity made up of letters,
airworthiness. Airworthiness Directives (AD notes) must
numbers, and symbols. The parts of the expression that
be complied with within the required time limit, and
are separated by a plus or a minus sign are called the terms
the fact of compliance, the date of compliance, and the
of the expression. An algebraic expression that has only
method of compliance must be recorded in the aircraft’s
one term is called a monomial; an algebraic expression
maintenance records.
that has two or more terms is called a polynomial.
airworthy — To be airworthy, an aircraft or one of its
algorithm — A system or procedure used in solving a
component parts must meet two criteria: a. Conform
problem.
to its TC (Type Certificate). Conformity to type design
is considered attained when the aircraft configuration alignment — The arrangement or position of parts in the
and the components installed are consistent with the correct relationship to each other.
drawings, specifications, and other data that are part of
alignment pin — Installed in a helicopter rotor blade to
the TC, and would include any STC’s (Supplemental
serve as an index when aligning the blades of a semi-rigid
Type Certificates) and field approved alterations (337’s).
rotor system.
b. Must be in a condition for safe operation. This
refers to the condition of the aircraft relative to wear alignment tool — A nonmetallic adjustment tool used to
and deterioration, (been maintained, annual/100 hour align (adjust) electronic circuits that would be adversely
inspections, etc.). affected by a metallic device.
albedo — The reflectivity of the Earth and its atmosphere. alkali — A chemical substance, usually the hydroxide of a
metal. An alkali has a characteristically bitter taste and
Alclad — A clad structural aluminum alloy. Alclad is a
is prone to react with an acid to form salt, supplying
corrosion protection coating of pure aluminum that is
electrons to the acid.
rolled onto the alloy sheet in the rolling mill. It makes up
approximately 5% of the thickness on each side. alkaline — Having the property of reacting with an acid
to form a salt and of giving up electrons to the acidic
alcohol — A colorless, volatile, flammable liquid produced
material.
by the fermentation of certain types of grain, fruit, or

17

10001930-002_AviationDictionary_2012_BOOK.indb 17 3/27/2012 9:37:55 AM

 alkaline cell • altimeter setting

alkaline cell — An electrochemical cell that uses powdered alpha — The first letter of the Greek alphabet. Often used
zinc as the anode, powdered graphite and manganese to denote something that is first.
dioxide as the cathode, and potassium hydroxide as the
alpha cutoff frequency — Rated cutoff frequency of a
electrolyte. An alkaline cell has an open-circuit voltage
transistor at which gain (alpha) decreases to .707 of the
of 1.5 volts, and it has from 50% to 100% more capacity
gain measured at low-frequency.
than a carbon-zinc cell of comparable size.
alpha hinge — The hinge at the root of a helicopter rotor
alkyd resin — A synthetic resin used as the base for certain
blade that allows the tip of the blade to move back and
enamels and primers.
forth in its plane of rotation. The axis of the alpha hinge is
Allen head bolt — A bolt or screw with a hexagonal perpendicular to the plane of rotor rotation. Also referred
receptacle in its head to accommodate an Allen wrench to as a lead-lag hinge.
for turning. Also referred to as an internal hex fastener.
alpha mode — Propeller range when operating in a forward
Allen wrench — A hexagonal-shaped tool used to turn thrust condition. See also beta mode.
an Allen screw. Shaft is usually “L” shaped to provide
alpha mode of operation — The operation of a turboprop
leverage.
engine that includes all of the flight operations, from
alligator clip — A spring-loaded clip with long, narrow takeoff to landing. Alpha operation is typically 95% to
jaws and meshing teeth. It is used on the end of an 100% of the engine operating speed. See also alpha range.
electrical wire to make temporary connections in an
alpha particle — A positively charged nuclear particle that
electrical circuit.
has the same mass as the nucleus of a helium atom. Alpha
allowable — Permissible. particles consist of two protons and two neutrons.
allowance — The permissible dimensional difference alpha range — The pitch of a turbopropeller system that
between the mating parts of a machine. maintains a constant RPM of the engine in flight idle
conditions.
alloy — 1. In metallurgy, a substance of two more combined
elements, one or more which is metal. 2. In composites, a alpha transistor operation — A measure of
blend of polymers or copolymers with other polymers or emitter-to-collector current gain in a transistor that is
elastomers. Also referred to as a polymer blend. connected in a common-base amplifier circuit. The alpha
of a junction transistor is never greater than one; its
alloy steel — Steel into which certain chemical elements
output is always less than its input.
have been mixed. Alloy steel has different characteristics
from those of simple carbon steel. alpha wave detector — A device used to measure and
display alpha brain waves.
alloying agent — A chemical element used to change the
characteristics of a base metal to form an alloy. alpha waves — Waves produced by the human brain when
it is relaxed.
all-weather spark plug — A shielded spark plug for use in
an aircraft reciprocating engine. The ceramic insulator is alphanumeric — Consisting of numbers and letters.
recessed into the shell so that a resilient collar (sometimes
alphanumeric display — Letters and numerals used to
referred to as a cigarette) on the ignition harness lead can
show identification, altitude, beacon code, and other
provide a watertight seal. All-weather spark plugs are
information concerning a target on a radar display.
identified by their 3/4”, 20-thread-per-inch shielding.
alternate aerodrome [ICAO] — An aerodrome to which an
alnico — An alloy of iron, aluminum, nickel, and cobalt.
aircraft may proceed when it becomes either impossible
Alnico has an extremely high permeability and excellent
or inadvisable to proceed to or to land at the aerodrome
retentivity for use in magnets.
of intended landing.
Alodine — A registered trademark for a conversion coating
NOTE: The aerodrome from which a flight departs may
chemical that forms a hard, unbroken aluminum oxide
also be an enroute or a destination alternate aerodrome
film, chemically deposited on a piece of aluminum
for the flight.
alloy. Alodining serves the same function as anodizing,
but does not require an electrolytic bath. It conforms to alternate airport — An airport at which an aircraft may land
specification MIL-C-5541 B. if a landing at the intended airport becomes inadvisable.
along track distance (LTD) — The distance measured altimeter — An instrument that indicates flight altitude by
from a point-in-space by systems using area navigation sensing pressure changes and displaying altitude in feet
reference capabilities that are not subject to slant range or meters.
errors.
altimeter setting — The barometric pressure reading used
to adjust a pressure altimeter for variations in existing

18

10001930-002_AviationDictionary_2012_BOOK.indb 18 3/27/2012 9:37:55 AM

 altimeter setting indicator • amalgam

atmospheric pressure or to the standard altimeter setting aluminizing — 1. A form of corrosion protection for
(29.92 inches of mercury, 1013.2 hectopascals or 1013.2 steel parts. A metal coating process that bonds either a
millibars). corrosion-resistant or a wear-resistant surface to a base
metal. Older aircraft used aluminum coating for hot
altimeter setting indicator — A precision aneroid
section parts.
barometer used to determine the local current altimeter
setting. aluminum — A metallic chemical element with a symbol
of Al and an atomic number of 13. Aluminum is a bluish,
altitude — The height of a level, point, or object measured
silvery-white metal that is lightweight, malleable, and
in feet Above Ground Level (AGL) or from Mean Sea
ductile. It is the chief metal used in aircraft construction.
Level (MSL).
It is produced from the clay bauxite, which is a form of
a. MSL Altitude – Altitude expressed in feet measured aluminum oxide. In its natural form, aluminum is soft
from mean sea level. and weak, but it can be alloyed with copper, magnesium,
manganese, and zinc to give it strength. Aluminum is
b. AGL Altitude – Altitude expressed in feet measured
a good conductor of both electricity and heat and is a
above ground level.
good reflector of heat and light. Pure aluminum is highly
c. Indicated Altitude – The altitude as shown by an resistant to corrosion.
altimeter. On a pressure or barometric altimeter it is
aluminum alloy — Pure aluminum to which one or more
altitude as shown uncorrected for instrument error
alloying elements has been added to increase its hardness,
and uncompensated for variation from standard
toughness, durability, and resistance to fatigue.
atmospheric conditions.
aluminum electrolytic capacitor — An electrolytic (liquid
altitude engine — A reciprocating aircraft engine having a
dielectric) capacitor that has aluminum plates. The
rated takeoff power that is producible from sea level to an
“plates” can be windings of aluminum sheet crimped
established higher altitude.
together at the ends of the spirals in order to lessen the
altitude readout — An aircraft’s altitude, transmitted via inductance of the capacitor. Electrolytic capacitors must
the Mode C transponder feature, that is visually displayed be used on direct current only. If subjected to alternating
in 100-foot increments on a radar scope having readout current they will heat and possibly explode.
capability.
aluminum oxide — A compound of aluminum and oxygen
altitude reservation — Airspace utilization under (A12O3). It is extremely hard and is used as an abrasive.
prescribed conditions normally employed for the mass
aluminum paste — Extremely small flakes of aluminum
movement of aircraft or other special user requirements
metal suspended in a substance to make a paste.
which cannot otherwise be accomplished. ALTRVs are
Aluminum paste is mixed with clear dope to make
approved by the appropriate FAA facility.
aluminum-pigmented dope. Aluminum dope is applied
altitude restriction — An altitude or altitudes, stated in the over clear dope on aircraft fabric to prevent ultraviolet
order flown, which are to be maintained until reaching rays of the sun from damaging the clear dope and fabric
a specific point or time. Altitude restrictions may be underneath.
issued by ATC due to traffic, terrain or other airspace
aluminum welding — The welding of aluminum and
considerations.
aluminum alloys used in aircraft construction using
altitude restrictions are cancelled — Adherence to equipment and techniques acceptable to the Federal
previously imposed altitude restrictions is no longer Aviation Administration.
required during a climb or descent.
aluminum wool — Shavings of aluminum metal that
altocumulus (Ac) — Mid-level principle cloud type are formed into a pad. Aluminum wool can be used to
occurring in layers or patches, the elements of which remove corrosion products from aluminum alloy parts
appear as small fleecy, rounded clouds. Altocumulus can and also to smooth out minor scratches from the surface
contain supercooled water droplets or ice crystals. of aluminum sheets or tubing.
altocumulus castellanus — Altocumulous clouds that show aluminum-pigmented dope — Clear aircraft dope in which
vertical development resembling the turrets of a castle. extremely tiny flakes of aluminum metal are suspended.
Clouds with vertical development indicate instability at When sprayed on aircraft fabric, the flakes leaf out to
the altitude of the clouds. form an opaque covering, protecting the fabric and clear
dope from the harmful effects of the sun’s ultraviolet
alumina — An oxide of aluminum (Al2O3). Alumina occurs
rays.
in nature in the form of corundum, emery, sapphires, or
bauxite, a type of clay. amalgam — A mixture of different elements. Often used
to indicate a mixture of mercury with some other metal.
aluminium — A British term for aluminum.

19

10001930-002_AviationDictionary_2012_BOOK.indb 19 3/27/2012 9:37:55 AM

 amalgamate • AN aeronautical standard drawings

amalgamate — To combine, join, or mix ingredients. ammonia — An invisible gas made up of one atom of nitrogen
and three atoms of hydrogen (NH3). Ammonia becomes a
amber — A hard, yellowish, translucent, fossilized tree
liquid at -28°F, and it freezes at -107°F. Ammonia is used
resin. Often used in jewelry.
to case-harden steel by a process called nitriding.
ambient — The condition of the atmosphere as it exists at
amorphous — Without shape.
the time of observation.
ampere (A) — A measure of electron flow. One ampere
ambient air — See ambient.
is equal to a flow of one coulomb (6.28 billion billion
ambient pressure — The pressure of the air that surrounds electrons) past a point in one second. One ampere is the
an object. amount of current that can be forced through one ohm of
resistance by a pressure of one volt.
ambient temperature — The temperature of the air that
surrounds an object. ampere turn — A measure of magnetomotive force (mmf)
of an electromagnet. It is the force produced when one
ambiguity — Something that does not have a clear meaning.
ampere of current flows through one turn of wire in a
American Society of Testing Materials (ASTM) — A coil. One ampere turn is equal to 1.26 gilberts.
not-for-profit organization that provides a global forum
ampere-hour capacity — A measure or rating of a battery
for the development and publication of voluntary
that indicates the capacity of electrical energy the battery
consensus standards for materials, products, systems,
can supply. One ampere-hour is the product of the current
and services. Many standards in the aircraft industry are
flow in amperes, multiplied by the length of time, in
ASTM standards.
hours, that the battery can supply this current.
American Standards — Dimensional standards for
ampere-hour meter — An electrical measurement
fasteners that are issued by the American Standard
instrument that measures the rate of current flow per unit
Association.
of time.
American Wire Gauge (AWG) — The standard used for
amphibian — An aircraft designed to land on and take off
measuring the diameter of round wires and the thickness
from either land or water.
of non-ferrous metal sheets. Also referred to as the Brown
and Sharpe gauge. amphibious floats — Floats that can be attached to an
aircraft to allow it to operate from either land or water.
AMM (aircraft maintenance manual) — A manual
Retractable wheels are mounted in the floats and can be
developed by the aircraft manufacturer that includes
extended for operation on the land.
information prepared for the AMT or technician who
performs work on units, components, and systems while amplification — The increase in either voltage or current
they are installed on the airplane. It is normally supplied that takes place in a device or in an electrical circuit.
by the manufacturer and approved by the FAA as part of
amplification factor — The ratio of the output amplitude of
the original process of certification. It will contain the
an electrical or electronic circuit to its the input amplitude.
required instructions for continued airworthiness that
must accompany each aircraft when it leaves the factory. amplifier — An electronic device that increases the
An Aircraft Maintenance Manual can also be a manual amplitude of a signal relative to the amplitude of its input.
developed by a Part 125 operator as part of their specific
amplitude — The magnitude or amount a value changes
operating manual. As such the FAA does not specifically
from its at-rest condition, or its normal condition, to
approve the manual. Also referred to as an MMM or
its maximum condition. In wave motion, one half the
Manufacturers Maintenance Manual.
distance between the wave crest and the wave trough.
ammeter — An electrical measuring instrument used
amplitude modulation — A system of varying the
to measure electron flow in amperes. Ammeters that
amplitude in a radio-frequency carrier wave so that it can
measure very small rates of flow are called milliammeters
carry information.
(thousandths of an ampere) or microammeters (millionths
of an ampere). AMS specifications — Specifications for aircraft
components that conform to established engineering and
ammeter shunt — A low-resistance resistor installed in
metallurgical practices in the aircraft industries. AMS
parallel with an ammeter to allow the meter to read a flow
specifications are developed by the SAE Aeronautics
of current that exceeds the current limit of the instrument.
Committee.
The ammeter, acting as a millivoltmeter, measures the
voltage drop across the shunt, and indicates, on a scale, AN aeronautical standard drawings — Dimensional
the amount of current flowing through the circuit. standards for aircraft fasteners developed by the
Aeronautical Standards Group. AN is the part number
prefix for all fasteners that are described in these drawings.

20

10001930-002_AviationDictionary_2012_BOOK.indb 20 3/27/2012 9:37:55 AM

 AN fittings • angle of refraction

AN fittings — A series of fittings for flared tubing, using impellers or by measuring the effect of moving air on a
a 37° flare angle and having a small shoulder between hot wire.
the ends of the threads and the beginning of the flare aneroid — l. A sealed flexible container that expands or
cone. Included in the listing of parts whose design and contracts in relation to the surrounding air pressure. It
material have been approved by both the United States is used in an altimeter or a barometer to measure the
Air Force and Navy and are acceptable for use in civilian pressure of the air. 2. A thin disc-shaped box or capsule,
and military airplanes. usually metallic, which is partially evacuated of air
AN hardware — Standard hardware items such as bolts, and sealed. It expands or contracts with changes of the
nuts, washers, etc., whose design and material has been surrounding air or gas.
approved by both the United States Air Force and Navy aneroid barometer — An instrument for measuring
and are acceptable for use in civilian and military airplanes. atmospheric pressure, its key component is a partially
evacuated cell which changes dimensions in proportion
A-N radio range — An early, obsolete navigational
to the change in atmospheric pressure.
aid. Two antennas radiate signals that are heard on a
low-frequency receiver as an “N” (dah-dit) on one side of angle — A geometric figure formed by two lines or two
the desired track and an “A” (dit-dah) on the other. When plane surfaces extending from the same point.
on track, the signal received sounds as a steady tone.
angle drill — A drilling tool in which the twist drill is held
anaerobic resin — A single-component polyester resin that at an angle to the spindle of the drill motor.
hardens when all air is restricted from it.
angle of attack — 1. The acute angle formed between the
analog — A physical variable that keeps a fixed relationship relative wind striking an airfoil and the zero lift line of the
with another variable as it changes. For example, the
airfoil. The chord line of the airfoil is often substituted
position of the hands of a clock keep a fixed relationship
with time. It is because of this relationship that we can for the zero-lift line. 2. (Absolute) The angle of attack
tell the time of day by knowing the positions of the hands of an airfoil, measured from the attitude of zero lift. 3.
of the clock. The position of the clock hands is an analog (Critical) The angle of attack at which the flow about
of time. an airfoil changes abruptly as shown by corresponding
abrupt changes in the lift and drag. 4. (For infinite aspect
analog computer — An electronic computer that operates ratio) The angle of attack at which an airfoil produces
by converting different levels of voltage or current into
a given lift coefficient in a two-dimensional flow. Also
numerical values.
referred to as “effective angle of attack.” 5. (Turbine
analog data — Data represented by a continuously varying compressor) The acute angle formed between the chord
voltage or current. line of the compressor blades and the direction of the air
analog-to-digital conversion — An alteration that changes that strikes the blades.
analog information into a digital form. angle of attack indicator system — Detects the local
analyzer, engine — A portable or permanently installed angle of attack of the aircraft from a point on the side
instrument, whose function is to detect, locate, and of the fuselage and furnishes reference information to an
identify engine operating abnormalities such as those angle-of-attack indicator.
caused by a faulty ignition system, detonation, sticking
valves, poor fuel injection, etc. angle of azimuth — An angle measured radially and
horizontally clockwise from north (0º).
anchor light — A white light displayed on boats or
seaplanes indicating that they are anchored. angle of departure — In communications, the angle
between a transmitter’s signal propagation and a
anchor nut — A nut riveted or welded to a structure in horizontal plane.
such away that a screw or bolt can be screwed into it. An
anchor nut does not have to be held with a wrench to keep angle of head — In countersunk heads, the included angles
it from turning. of the conical under portion or bearing surface, usually
82° or 100°.
AND gate — A logic device whose output is high only if all
inputs are high.. angle of incidence — 1. The acute angle that the wing chord
anemometer — An instrument for measuring wind speed. makes with the longitudinal axis of the aircraft. 2. The
angle at which blades are set into the compressor disk.
anemometer — An instrument that measures the velocity A fixed angle in all cases except the variable pitch fan.
of moving air. One type of anemometer uses a series of Angles set for optimum airflow at altitude cruise and RPM.
hemispherical metal cups mounted on arms on a shaft.
The air blows the cups and rotates the shaft. A counter angle of refraction — The angle between a refracted beam as
measures and converts this into wind speed that may it passes through the refracting material (e.g., water) and a
be displayed in feet per second, meters per second, line perpendicular to the surface of the refracting material.
kilometers per hour, miles per hour, or knots. Other
anemometers convert wind speed to a reading by use of
21

10001930-002_AviationDictionary_2012_BOOK.indb 21 3/27/2012 9:37:55 AM

 angle of roll • anode

angle of roll — The angle through which an aircraft must annealing process — Heating of an alloy to a temperature
be rotated about its longitudinal axis in order to bring its called solid solution temperature. This is followed by
lateral axis into the horizontal plane. Also referred to as allowing it to cool slowly at a controlled rate through its
the angle of bank. critical range for the purpose of inducing softness. This
results in the removal of former heat-treatment strain
angle of stabilizer setting — The acute angle between
hardening and internal stresses.
the longitudinal axis of an airplane and the chord of the
stabilizer. The angle is positive when the leading edge is annual inspection — A complete inspection of an aircraft
higher than the trailing edge. and engine, required by the Federal Aviation Regulations,
to be accomplished every twelve calendar months on all
angle of wing setting — The acute angle between the
certificated aircraft. Only an A&P technician holding
plane of the wing chord and the longitudinal axis of the
an Inspection Authorization can conduct an annual
airplane. The angle is positive when the leading edge is
inspection.
higher than the trailing edge. Also referred to as angle of
incidence. annual rings — The rings that appear in the end of a tree
log. The more rings there are, and the closer they are
angle of yaw — The acute angle between the direction of
together, the stronger the wood.
the relative wind and the plane of symmetry of an aircraft.
annular, basket type — Combustion chamber. One of
angled gearbox — In helicopters, the same function as a
several basic types used in turbine engines. It consists
transfer gearbox. Receives its name because the driveshaft
of a housing and a liner. The liner is a one-piece shroud
is angled, usually 90° up toward the main rotor.
(combustion chamber) extending all the way around the
angular acceleration — The rate at which a rotating object outside of the turbine shaft housing. Fuel is sprayed from
increases its rotational speed. nozzles mounted around a full manifold into the inner
liner of the combustor. Here it is mixed with air from the
angular measurement — The measured rotational
compressor and burned.
displacement between two lines that project from the
same point. annular, can type — Combustion chamber. One of several
basic types used in turbine engines. Each of the can-type
angular momentum — The product of an object’s mass
combustion chambers consist of an outer case or
directed along a rotating axis.
housing, within which there is a perforated stainless steel
angular type piston pump — A pump with an angular combustion chamber liner or inner liner. Interconnected
housing that causes a corresponding angle to exist between tubes join each can for flame propagation that spreads
the cylinder block and the drive shaft plate to which the combustion during the initial starting operation.
pistons are attached. It is this angular configuration of the
annular combustor — l. Annular refers to ring shaped.
pump that causes the pistons to stroke as the shaft is turned.
Therefore, a ring-shaped or cylindrical one-piece
angular velocity — 1. The rate of change of an angle as combustion liner inside a combustion outer case. 2. A
a shaft rotates. Expressed in revolutions per minute or cylindrical one-piece combustion chamber, sometimes
radians per second. 2. The velocity of an object located referred to as a single basket-type combustor.
at a given distance of, and rotating about, a center point.
annulus — Opening between two concentric rings, e.g. the
Expressed in radians per second.
space between the compressor disk and outer case could
anhydrous — A material that does not contain water. be referred to as the compressor annulus.
anion — A negative ion that moves toward an anode in an annunciator panel — A set of warning lights in direct view
electrolysis process. of a pilot in a cockpit. The lights are identified by the
name of the system they represent, and they are usually
anisotropic — In composites, fibers are placed in different
covered with a colored lens to show the meaning of the
directions to respond to the stresses applied in different
condition they announce. Red lights are used to indicate
directions.
a dangerous condition, amber lights show that some
anneal — To soften by means of heat treatment. system is armed or active, and green lights represent
a safe condition. Sometimes referred to as a master
annealed wire — Wire softened by heat treatment.
warning system.
Necessary because the process of drawing the wire
through dies causes it to be work hardened. annunciator system — See annunciator panel.
annealing — A method of heat treatment in which a metal is anode — 1. The positive plate of an electrochemical
softened, losing some of its hardness. See also annealing com­bination, such as a battery or electroplating tank.
process. Electrons leaving the anode cause it to be less negative,
or positively charged. When electrons leave an anodic
material, the chemical composition of the anode changes
22

10001930-002_AviationDictionary_2012_BOOK.indb 22 3/27/2012 9:37:55 AM

 anode current • anti-icing system

from a metal to a salt caused by the reaction with the anticyclone — An area of high atmospheric pressure that
electrolyte. In the process, the anode is corroded or eaten has a closed circulation and when viewed from above,
away. 2. The electrode in a vacuum tube or a semiconductor the circulation is clockwise in the Northern Hemisphere
diode to which the electrons travel after they leave the and counterclockwise in the Southern Hemisphere.
cathode. The anode in a vacuum tube (an electron tube)
anticyclone — An area of high atmospheric pressure
is called the plate. The anode of a semiconductor diode
which has a closed circulation that is anticyclonic, i.e.,
is the end that is made of P-type material, and it is not
as viewed from above, the circulation is clockwise in the
marked (the cathode has the mark). In the diode symbol,
Northern Hemisphere, counterclockwise in the Southern
the anode is shown by the arrowhead.
Hemisphere.
anode current — The current measured at the anode of an
anticyclonic flow — In the Northern Hemisphere the
electronic device.
clockwise flow of air around an area of high pressure and
anode of a chemical cell — Within a battery (chemical a counterclockwise flow in the Southern Hemisphere.
cell), electrons flow from the anode to the cathode. This
antidetonant fluid — A fluid such as a water/alcohol mix
creates an area of less negative (more positive) charge.
that enables more power to be obtained from the engine
(Externally, the electrons flow from the cathode to the
when injected into the fuel/air stream. The fluid itself
anode.)
does not increase the engine power; it merely replaces
anodic — The positive component of an electrolytic cell. formerly excess fuel, allowing for a cooler operating
engine. The water/alcohol dissipates heat more rapidly
anodizing — The formation of a hard, unbroken film of
than fuel.
aluminum oxide on the surface of an aluminum alloy. This
film is electrolytically deposited by using the aluminum antidotes — A viable alternative to hazardous attitudes in
as the anode and chromic acid as the electrolyte. aeronautical decision-making. Each of the five hazardous
attitudes has an associated antidote, which should be
anoxia — A severe case of hypoxia (a lack of oxygen),
memorized and employed to minimize their effects.
which can cause permanent damage to the brain.
antidrag wire — A diagonal, load-carrying member of a
antenna — An electrical circuit designed to radiate and
Pratt truss wing. It runs from the rear spar inboard to the
receive electromagnetic energy. Antennas vary in shape
front spar outboard, and it opposes tensile loads tending
and design depending upon the specific purpose of the
to pull forward on the wing.
antenna and the frequency to be transmitted or received.
antifreeze — A chemical added to a liquid for the purpose
antenna coupler — A transformer used between a radio
of lowering its freezing point.
receiver or transmitter and the antenna to optimize the
amount of power passed between them. antifriction bearings — Ball or roller bearings that have a
special low drag quality.
antenna current — A measurement of radio-frequency
current in an antenna. antiglare paint — A black or dark paint that dries to a dull
or matte finish. It is applied to a surface to prevent glare
antenna duplexer — A device that allows two transmitters
from impairing the aircraft crew’s vision.
to simultaneously use a single antenna.
anti-icing — The prevention of the formation of ice on
antenna lens — A device used to focus microwaves onto a
a surface. Ice may be prevented by using heat or by
microwave antenna.
covering the surface with a chemical that prevents water
antenna matching — The process of matching the from reaching the surface. Anti-icing should not be
impedance of a radio antenna with the impedance of the confused with deicing, which is the removal of ice after it
transmission line that carries the signal from the radio has formed on the surface.
transmitter to the antenna.
anti-icing equipment — Aircraft equipment used to
antenna wire — A wire with a low electrical resistance and prevent structural icing.
a high tensile strength. Copperweld, which is a form of
anti-icing fluid — A fluid comprised of alcohol and
wire that has copper plated over a core of strong steel
glycerin, used to prevent the formation of ice on the
wire, is often used as antenna wire.
leading edge of propellers, in the throat of a carburetor,
antiblush thinner — A slow-drying thinner that is used in or on the windshield.
conditions of high humidity to prevent blushing of the
anti-icing system — 1. Any system or method used to
aircraft dope.
provide heat or supply anti-icing fluid to critical external
anticollision light — A flashing light on the exterior of the surfaces in order to prevent ice formation. 2. A system in
aircraft used to increase the visibility of the aircraft. a gas turbine engine in which some of the hot compressor

23

10001930-002_AviationDictionary_2012_BOOK.indb 23 3/27/2012 9:37:55 AM

 antiknock rating • application step

bleed air is routed through the engine air inlet system to anxiety — Mental discomfort that arises from the fear of
warm it and prevent ice from forming. anything, real or imagined. May have a potent effect on
actions and the ability to learn from perceptions.
antiknock rating — The rating of fuel that refers to the
ability of the fuel to resist detonation. A&P technician — An aircraft technician certified by
the Federal Aviation Administration as having met the
antileak check valve — A check valve used to prevent oil
experience and knowledge requirements for certification.
tank seepage to lower portions of the lube system during
An A&P technician is qualified to return licensed United
periods on engine inactivity. Anti-leak check valves hold
States airplanes to service after performing certain
the oil in the tank against the pull of gravity. When the
inspections and maintenance procedures. Increasingly
oil pump puts a low pressure on the check valve, it opens
referred to as AMTs (Aviation Maintenance Technicians).
and allows oil to flow from the tank into the engine.
aperiodic damping — Damping that prevents an object
antimissile missile — A missile used to destroy another
from over swinging, or moving past its at-rest position.
missile.
Also referred to as dead-beat damping.
antimony — A silvery, metallic element with a symbol of
aperiodic-type compass — A magnetic compass in which
Sb and an atomic number of 51. Often used as an alloying
the floating magnet assembly is fitted with damping
agent with lead for use in lead-acid batteries.
vanes to increase the period of its oscillations.
antipropeller end — The end of an engine away from the
aperture — A device used to control the bandwidth of an
propeller.
antenna.
anti-servo tab — An API scale — A scale that has been developed by the
adjust­able tab attached American Petroleum Institute to measure the specific
to the trailing edge of a gravity of a liquid.
stabilator that moves in the same direction as the primary
control. It is used to make the stabilator less sensitive. apogee — The point at which an orbiting vehicle is the
greatest distance from the center of the object it is circling.
antiskid system — A system of controls for aircraft brakes
that releases the hydraulic pressure to the brake in the apparent power — In an AC circuit, the product of RMS
event the wheel begins to lock up or skid. (Root Mean Square) current and RMS voltage, expressed
in volt-amperes.
antitear strips — Strips of aircraft fabric that are laid over
the wing rib under the reinforcing tape before the fabric apparent weight — The weight of the object plus or minus
is stitched. any outside influence. The apparent weight of an object
immersed in water would be the weight of the object
antitorque pedals — In rotorcraft, the pedals used to control minus any buoyancy. The apparent weight of an object
the pitch of the tail rotor or air diffuser in a NOTAR® in an elevator would be the weight of the object plus
system. The pilot controls the pitch of the anti-torque or minus the effects of acceleration due to the elevator
rotor or the diffuser to position the helicopter about its moving upward or downward.
vertical axis.
appliance — Any instrument, equipment, mechanism,
antitorque rotor — In rotorcraft, a rotor turning in a plane part, apparatus, or accessory, including communications
perpendicular to that of the main rotor and parallel to the equipment, used or intended to be used in operating or
longitudinal axis of the fuselage. It is used to control the controlling an aircraft in flight. An appliance is installed
torque of the main rotor and to provide movement about or attached to the aircraft, but is not part of the engine,
the yaw axis of the helicopter. airframe, or propeller.
antiwindmilling brake — A friction brake fitted as an applicability — Something that applies to and/or affects
accessory to the main gearbox of some older engines. another.
Seldom seen today. Note that the turboprops include
a brake in their propeller mechanisms, but it is not the application — A basic level of learning where the
friction brake described here. student puts something to use that has been learned and
understood.
anvil — A hard-faced block on which a material is
hammered or shaped. application step — The third step of the teaching
process, where the student performs the procedure or
anvil cloud — The top portion of a cumulonimbus (Cb) demonstrates the knowledge required in the lesson. In
consisting primarily of cirrus cloud and a spread-out area the telling-and-doing technique of flight instruction, this
that, together, resemble an anvil. step consists of the student doing the procedure while
explaining it.

24

10001930-002_AviationDictionary_2012_BOOK.indb 24 3/27/2012 9:37:55 AM

 approach • approved pilot school

approach — The flight of an airplane just preceding the segments of an approach as well as for aircraft weight
landing. and configuration.
approach clearance — Authorization by ATC for a pilot to approach with vertical guidance (APV) — An instrument
conduct an instrument approach. The type of instrument approach based on a navigation system that is not
approach for which a clearance and other pertinent required to meet the precision approach standards of
information is provided in the approach clearance when ICAO Annex 10 but provides course and glidepath
required. deviation information. Raro-VNAV, LDA with glidepath,
LNAV/VNAV and LPV are APV approaches.
approach control — A terminal air traffic control facility
providing approach control service. approach/departure control service — An air traffic
control service provided by an approach control facility
approach control facility — A terminal ATC facility that
for arriving and departing VFR/IFR aircraft and, on
provides approach control service in a terminal area.
occasion, enroute aircraft.
approach control service — Air traffic control service
appropriate ATS authority [ICAO] — The relevant
provided by an approach control facility for arriving and
authority designated by the State responsible for
departing VFR/IFR aircraft and, on occasion, enroute
providing air traffic services in the airspace concerned.
aircraft. At some airports not served by an approach
In the United States, the “appropriate ATS authority”
control facility, the ARTCC provides limited approach
is the Program Director for Air Traffic Planning and
control service.
Procedures, ATP-1.
approach end of runway (AER) — The first portion of
appropriate authority — 1. Regarding flight over the
the runway available for landing. If the runway threshold
high seas: the relevant authority is the State of Registry.
is displaced, the displaced threshold latitude/longitude is
2. Regarding flight over other than the high seas: the
the AER.
relevant authority is the State having sovereignty over
approach fix — From a database coding standpoint, an the territory being overflown.
approach fix is considered to be an identifiable point in
appropriate obstacle clearance minimum altitude —
space from the intermediate fix (IF) inbound. A fix located
Any of the following: Minimum IFR Altitudes MIA,
from the initial approach fix (IAF) to the intermediate fix
Minimum Enroute IFR Altitude MEA, Minimum
is considered to be associated with the approach transition
Obstruction Clearance Altitude MOCA, Minimum
or feeder route.
Vectoring Altitude MVA.
approach gate — An imaginary point used within ATC as
appropriate terrain clearance minimum altitude — Any
a basis for vectoring aircraft to the final approach course.
of the following: Minimum IFR Altitudes MIA, Minimum
The gate will be established along the final approach
Enroute IFR Altitude MEA, Minimum Obstruction
course 1 mile from the final approach fix on the side away
Clearance Altitude MOCA, Minimum Vectoring Altitude
from the airport and will be no closer than 5 miles from
MVA.
the landing threshold.
approved — Unless used with reference to another person,
approach light system (ALS) — An airport lighting facility
means approved by the Administrator.
which provides visual guidance to landing aircraft by
radiating light beams in a directional pattern by which the approved data — Data which may be used as an
pilot aligns the aircraft with the extended centerline of authorization for the techniques or procedures for making
the runway on his final approach for landing. Condenser a repair or an alteration to a certificated aircraft. Approved
Discharge Sequential Flashing Lights/Sequenced data may consist of such documents as Advisory Circular
Flashing Lights may be installed in conjunction with the 43.13-lB and -2A, Manufacturer’s Service Bulletins,
ALS at some airports. a manufacturer’s kit, instructions, Airworthiness
Directives, or specific details of a repair issued by the
approach lights — High intensity lights along the approach
engineering department of the manufacturer.
end of an instrument runway that aid the pilot in the
transition from instruments to visual flight at the end of approved inspection system — A maintenance program
an instrument approach. consisting of the inspection and maintenance necessary to
maintain an aircraft in airworthy condition in accordance
approach sequence — The order in which aircraft are
with approved Federal Aviation Administration practices.
positioned while on approach or awaiting approach
clearance. approved parachute — A parachute manufactured under a
type certificate or a technical standard order.
approach speed — The recommended speed contained
in aircraft manuals used by pilots when making an approved pilot school — Pilot schools that: are approved
approach to landing. This speed will vary for different by the FAA, must conduct flight and ground training

25

10001930-002_AviationDictionary_2012_BOOK.indb 25 3/27/2012 9:37:56 AM

 approved repair station • area navigation (RNAV)

under specific guidelines in FAR Part 141, and meet rigid arc tangent — Inverse tangent function , that is, the angle
operational requirements. Graduates of these schools are for which the tangent is calculated. Also written as arc
permitted certification with less total flight experience tan or tan-1.
than that specified in Part 61.
arc welding — Welding in which the heat required to melt
approved repair station — A facility approved by the the metal is produced by an electric arc.
Federal Aviation Administration for certain types of
arch — A normally curved structure that spans an opening.
repair to certificated aircraft.
In architecture, it is self supporting with lower members
approved type certificate — An approval issued by the supporting higher members.
Federal Aviation Administration for the design of an
Archimedes’ principle — The principle of buoyancy,
airplane, engine, or propeller. This certifies that the
which states that a body immersed in a fluid is buoyed up
product has met at least the minimum design standards.
with a force equal to the weight of the fluid it displaces.
approximate — Close to, but not exactly correct. Located
arctic air — Air with its origins in an arctic region. Normally
close together.
much colder than the region it subsequently passes over.
apron — A defined area on an airport or heliport intended
arctic airmass — An airmass with characteristics developed
to accommodate aircraft for purposes of loading or
mostly in winter over Arctic surfaces of ice and snow.
unloading passengers or cargo, refueling, parking, or
Surface temperatures are basically, but not always, lower
maintenance. With regard to seaplanes, a ramp is used
than those of polar air.
for access to the apron from the water.
area — The number of square units in a surface.
Aqua-dag — A non-petroleum lubricant used for
components in an oxygen system. Oil or other petroleum area control center [ICAO] — An air traffic control
products cannot be used with oxygen system components facility primarily responsible for ATC services being
because of petroleum’s propensity to ignite when in provided IFR aircraft during the enroute phase of flight.
contact with high concentrations of oxygen. The U.S. equivalent facility is an air route traffic control
center (ARTCC).
Arabic numerals — The numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 0,
and any combination thereof. area navigation high route — An area navigation route
within the airspace extending upward from, and
aramid — A fiber that is Aromatic Polyamide. Kevlar is ®
including, 18,000 feet MSL to flight level 450.
the brand name which is manufactured by Dupont. There
are other companies which also weave aramid fabrics for area navigation [ICAO] — A method of navigation which
aircraft use. permits aircraft operation on any desired flight path
within the coverage of station-referenced navigation aids
arbor for balancing a prop — A low-friction spindle or
or within the limits of the capability of self-contained
axle used to support the center of a propeller during
aids, or a combination of these.
maintenance procedures to ensure the blades of a
propeller all weigh the same. area navigation low route — An area navigation route
within the airspace extending upward from 1,200 feet
arbor press — A press with either a mechanically or
above the surface of the earth to, but not including,
hydraulically operated ram. Often used to press bearings
18,000 feet MSL.
into their race.
area navigation (RNAV) — A system that provides
arc — 1. A portion of the circumference of a circle. 2. A
enhanced navigational capability to the pilot. RNAV
sustained luminous discharge of electricity across a gap.
equipment can compute the airplane position, actual
3. The track over the ground of an aircraft flying at a
track and ground speed and then provide meaningful
constant distance from a navigational aid by reference to
information relative to a route of flight selected by the
distance measuring equipment (DME).
pilot. Typical equipment will provide the pilot with
arc cosine — Inverse cosine function, that is, the angle for distance, time, bearing and crosstrack error relative to
which the cosine is calculated. Also written as arc cos or the selected “TO” or “active” waypoint and the selected
cos-1 route. Several distinctly different navigational systems
with different navigational performance characteristics
arc lamp — A source of light produced by an electric arc.
are capable of providing area navigational functions.
The arc is produced when electrons flow through ionized
Present day RNAV includes INS, LORAN, VOR/DME,
gases between two electrodes.
and GPS systems. Modern multi-sensor systems can
arc sine — Inverse sine function, that is, the angle for which integrate one or more of the above systems to provide
the sine is calculated. Also written as arc sin or sin-1. a more accurate and reliable navigational system. Due
to the different levels of performance, area navigational
capabilities can satisfy different levels of required
26

10001930-002_AviationDictionary_2012_BOOK.indb 26 3/27/2012 9:37:56 AM

 area navigation (RNAV) approach configuration • argon

navigational performance (RNP). The major types of d. Terminal Arrival Area (TAA) – The TAA is controlled
equipment are: airspace established in conjunction with the Standard or
Modified T and I RNAV approach configurations. In the
a. VORTAC referenced or Course Line Computer (CLC)
standard TAA, there are three areas: straight-in, left base,
systems, which account for the greatest number of
and right base. The arc boundaries of the three areas of
RNAV units in use. To function, the CLC must be
the TAA are published portions of the approach and allow
within the service range of a VORTAC.
aircraft to transition from the en route structure direct
b. OMEGA/VLF, although two separate systems, can to the nearest IAF. TAAs will also eliminate or reduce
be considered as one operationally. A long-range feeder routes, departure extensions, and procedure turns
navigation system based upon Very Low Frequency or course reversal.
radio signals transmitted from a total of 17 stations
1). Straight-In Area – A 30NM arc centered on the IF
worldwide.
bounded by a straight line extending through the IF
c. Inertial (INS) systems, which are totally self-contained perpendicular to the intermediate course.
and require no information from external references.
2). Left Base Area – A 30NM arc centered on the
They provide aircraft position and navigation
right corner IAF. The area shares a boundary with the
information in response to signals resulting from
straight-in area except that it extends out for 30NM
inertial effects on components within the system.
from the IAF and is bounded on the other side by a line
d. MLS Area Navigation (MLS/RNAV), which provides extending from the IF through the FAF to the arc.
area navigation with reference to an MLS ground facility.
3). Right Base Area – A 30NM arc centered on the
e. LORAN-C is a long-range radio navigation system left corner IAF. The area shares a boundary with the
that uses ground waves transmitted at low frequency straight-in area except that it extends out for 30NM
to provide user position information at ranges of from the IAF and is bounded on the other side by a line
up to 600 to 1,200 nautical miles at both enroute extending from the IF through the FAF to the arc.
and approach altitudes. The usable signal coverage
area navigation/RNAV — A method of navigation that
areas are determined by the signal-to-noise ratio,
permits aircraft operations on any desired course within
the envelope-to-cycle difference, and the geometric
the coverage of station referenced navigation signals or
relationship between the positions of the user and the
within the limits of self contained system capability.
transmitting stations.
area of decision — The most critical time for an engine
f. GPS is a space-based radio positioning, navigation,
failure to occur in a multi-engine airplane, which is
and time-transfer system. The system provides highly
just after liftoff while the airplane is accelerating and
accurate position and velocity information, and precise
climbing over immediate obstacles. The area of decision
time, on a continuous global basis, to an unlimited
exists between the point where obstacle clearance speed
number of properly equipped users. The system is
is reached and landing gear retracted, and the point
unaffected by weather, and provides a worldwide
where the single-engine best angle-of-climb speed
common grid reference system.
(Vxse) is reached. An engine failure in this area requires
area navigation (RNAV) approach configuration — an immediate decision to abort takeoff or to continue
a. Standard T – An RNAV approach whose design allows climbing. To make an intelligent decision in case of a
direct flight to any one of three initial approach fixes failure within this area of decision, one must consider
(IAF) and eliminates the need for procedure turns. The aircraft performance with the following conditions:
standard design is to align the procedure on the extended runway length, obstruction height, field elevation, density
centerline with the missed approach point (MAP) at the altitude, air temperature, headwind, takeoff weight, and
runway threshold, the final approach fix (FAF), and the pilot proficiency.
initial approach/ intermediate fix (IAF/IF). The other two
area weight — In composites, the weight of fiber
IAFs will be established perpendicular to the IF.
reinforcement per unit area (width × length) of tape or
b. Modified T – An RNAV approach design for single or fabric.
multiple runways where terrain or operational constraints
areas of operation — Phases of the practical test arranged in
do not allow for the standard T. The “T” may be modified
a logical sequence within the PTS. Each area of operation
by increasing or decreasing the angle from the corner
has several task listings to be evaluated during the flight.
IAF(s) to the IF or by eliminating one or both corner IAF’s.
Areas of operation are based on the corresponding flight
c. Standard I – An RNAV approach design for a single proficiency requirements in the FARs.
runway with both corner IAFs eliminated. Course reversal
argon — A gaseous element with a symbol of Ar and an
or radar vectoring may be required at busy terminals with
atomic number of 18. It is an inert gas often used in
multiple runways.
welding, to shield the molten metal from oxidation.

27

10001930-002_AviationDictionary_2012_BOOK.indb 27 3/27/2012 9:37:56 AM

 ARINC • artificial aging

ARINC — An acronym for Aeronautical Radio, Inc., used to prevent aircraft from overrunning runways when
a corporation largely owned by a group of airlines. the aircraft cannot be stopped after landing or during
ARINC is licensed by the FCC as an aeronautical station aborted takeoff. Arresting systems have various names;
and contracted by the FAA to provide communications e.g., arresting gear, hook device, wire barrier cable.
support for air traffic control and meteorological services
arrival aircraft interval — An internally generated
in portions of international airspace.
program in hundredths of minutes based upon the AAR.
arithmetic — A mathematical system dealing with real AAI is the desired optimum interval between successive
numbers. Consists of addition, subtraction, multiplication, arrival aircraft over the vertex.
and division.
arrival center — The ARTCC having jurisdiction for the
arithmetic sum — The result of adding the absolute values impacted airport.
(without regard to sign) of real numbers.
arrival delay — A parameter which specifies a period of
arm — The horizontal distance in inches between the time in which no aircraft will be metered for arrival at the
reference datum line and the center of gravity of an object. specified airport.
If the object is behind the datum, the arm is positive, and
arrival routes (ICAO) — Routes on an instrument
if in front, the arm is negative.
approach procedure by which aircraft may proceed from
armature — The rotating or moving component of a the enroute phase of flight to the initial approach fix.
magnetic circuit. Motors, generators, and alternators
arrival sector — An operational control sector containing
have armatures.
one or more meter fixes.
armature core — In an electrical apparatus (motor,
arrival sector advisory list — An ordered list of data on
generator, servo, etc.), a laminated soft iron about which
arrivals displayed at the PVD/MDM of the sector which
the armature coils are wound.
controls the meter fix.
armature gap — In a motor or generator, the space between
arrival sequencing program — The automated program
the armature and the field poles.
designed to assist in sequencing aircraft destined for the
armature reaction — The distortion of the generator field same airport.
flux by the current flowing in the windings of the armature.
arrival stream filter (ASF) — An on/off filter that allows
Armature reaction causes the brushes to pick up current
the conflict notification function to be inhibited for
from the armature at a point on the commutator where
arrival streams into single or multiple airports to prevent
there is a potential difference. This causes the brushes
nuisance alerts.
to spark.
arrival time — The time an aircraft touches down on
armed — A condition in which a device is made ready for
arrival.
actuation.
arsenic — A chemical element with the symbol of As and
Armed Forces — The Army, Navy, Air Force, Marine
an atomic number of 33. An extremely small amount of
Corps, and Coast Guard, including their regular and
arsenic is alloyed with silicon or germanium to make
reserve components and members serving without
N-type semiconductor material.
component status.
articulated connecting rod — A link rod that connects the
Army Aviation Flight Information Bulletin — A bulletin
pistons in a radial engine to the master rod. There is one
that provides air operation data covering Army, National
less articulated rod than there are cylinders in each row
Guard, and Army Reserve aviation activities.
of cylinders in a radial engine since one piston is attached
aromatic gasoline — Gasoline that has had its to the master rod.
anti-detonation characteristics improved by blending in
articulated rod assembly — See articulated connecting rod.
aromatic additives such as benzene, toluene, or xylene.
articulated rotor — In rotorcraft, a rotor system in which
aromatics — Chemical compounds such as toluene,
each of the blades is connected to the rotor hub in such a
xylene, and benzene. These aromatics may be blended
way that it is free to change its pitch angle, and move up
with gasoline to improve its anti-detonation qualities.
and down and fore and aft in its plane of rotation.
Aromatics are also known to soften rubber hoses,
diaphragms, and seals used in fuel metering system artificial aging — A process of increasing the strength of a
components. heat-treated aluminum alloy by holding it at an elevated
temperature after it has been solution heat treated.
arresting system — A safety device consisting of two major
Artificial aging is Also referred to as precipitation heat
components, namely, engaging or catching devices, and
treatment. See also precipitation heat treatment.
energy absorption devices for the purpose of arresting
both tail hook and/or nontail hook-equipped aircraft. It is
28

10001930-002_AviationDictionary_2012_BOOK.indb 28 3/27/2012 9:37:56 AM

 artificial feel • astronomical twilight

artificial feel — A force feedback or cushioning effect assembly drawing — An aircraft drawing that shows a
that is used in the automatic flight control systems of group of parts laid out in the relationship they will have
some aircraft. Artificial feel produces an opposition when they are assembled.
to the movement of the controls proportional to the
assembly line — An arrangement of work stations in
aerodynamic load that is acting on the control surfaces.
an aircraft factory that allows certain functions to be
artificial horizon — A flight instru­ment in which a bar or a performed on the aircraft being manufactured.
display is held in a constant relationship with the earth’s
assigned radio frequency — The frequency of a carrier
horizon. An artificial horizon provides the pilot with a
signal produced by a radio transmitter. The frequency is
visual reference when the natural horizon is not visible.
assigned by the Federal Communications Commission for
artificial radio antenna — A device attached to the output a particular transmitter or particular type of transmission.
of a radio transmitter when adjusting the transmitter. The
associated conditions — The conditions found on
artificial antenna has the same impedance as the antenna,
performance charts in the pilot’s operating handbook
but the radio signal put into the artificial antenna is not
(POH). The information on the chart is based on the
radiated.
given associated conditions and any other conditions do
asbestos — A fiber of magnesium silicate that has a high not provide the same performance.
resistance to fire. It has good insulating qualities.
astable — Not stable. An astable electronic device has two
A-scan — A display on which the indications appear similar conditions of temporary stability, but no condition of
to the capital letter “A” along a horizontal time line. permanent stability.
Found in the displays of ultrasonic test equipment and
astable multivibrator — A free-running multivibrator.
sometimes radar.
They contain two devices such as transistors to control
ASCII (American Standard Code for Information the flow of electrons. When one transistor is conducting,
Interchange) — A format of data used as a standard to the other is not conducting. The two transistors alternate
transmit information between computers. Consists of 128 between a condition of conducting and not conducting.
characters that are each made up of seven binary bits.
A-stage — In composites, the intermediate stage in the
Pronounced “as-kee.”
reaction of the two parts of the resin system after being
ash — The solid residue remaining after a substance has mixed. The resin system reacts to heat by softening. The
burned. resin in a prepreg material is usually in the B-stage before
the curing process.
ashless dispersant oil (AD) — A popular mineral oil used
as a lubricant for aircraft reciprocating engines. Ashless A-stage — In composites, the initial stage of mixing the
dispersant oil does not contain any metallic ash-forming two parts of a thermosetting resin system together. The
ingredients. It has additives in it that keep the contaminants material is soluble in some liquids and fusible.
that form in the oil dispersed throughout the oil so they
astern — A location or direction to the rear or rear part of
will not join together and clog the oil filters.
an aircraft.
aspect ratio — 1. The ratio of the span of the wing to its
ASTM specifications — Standards developed by the
chord. The aspect ratio of a tapered wing is found by
American Society for Testing Materials. See also
dividing the square of the wing span by its area. 2. In
American Society of Testing Materials (ASTM).
composites, the ratio of length to diameter of a reinforcing
fiber. astrocompass — An optical device used to determine
direction by reference to the stars (celestial
asphalt — A heavy, brownish-black mineral that is found in
navigation).
astrodome 
— A hemispherical window,
crude oil. Asphalt is used as a base for some acid-resistant
usually in the ceiling of an aircraft whereby a navigator
paints.
can use an astrocompass to determine heading or a
aspheric — In optics, an element such as a lens that is not sextant to determine position.
perfectly spherical.
astronaut — A person who travels beyond the earth’s
aspirator — A device for producing suction or for moving atmosphere.
or collecting materials by suction.
astronautics — The field of science that deals with space
assembly — The fitting together of parts to form a complete flight and includes the design, construction, and operation
structure or unit. of space vehicles and their related support activities.
assembly break — A joint in the structure of an aircraft that astronomical twilight — The period of time before sunrise
is formed when two sub-assemblies are removed from or after sunset when the sun is not more than 18º below
their jigs and joined together to form a single unit. the horizon.

29

10001930-002_AviationDictionary_2012_BOOK.indb 29 3/27/2012 9:37:56 AM

 astronomical unit • atmospheric pressure

astronomical unit — One astronomical unit is the average not fully understood, or considered unacceptable because
distance between the earth and the sun. Approximately of safety of flight. Controllers should, in such instances
93 million miles. and to the extent of operational practicality and safety,
honor the pilot’s request. FAR Part 91.3(a) states: “The
astrophysics — The field of science that deals with
pilot-in-command of an aircraft is directly responsible
the physical characteristics of heavenly bodies.
for, and is the final authority as to, the operation of that
Characteristics include their mass, density, temperature,
aircraft.” The pilot is responsible to request an amended
size, luminosity, and origin.
clearance if ATC issues a clearance that would cause a
asymmetrical — A condition in which the shape of a body pilot to deviate from a rule or regulation, or in the pilot’s
is NOT the same on both sides of its center line. opinion, would place the aircraft in jeopardy.
asymmetrical airfoil — An airfoil that has a different curve ATC clears — Used to prefix an ATC clearance when it is
above the chord line than it has on the underside. relayed to an aircraft by other than an air traffic controller.
asymmetrical lift — A condition of unequal lift produced ATC instructions — Directives issued by air traffic control
by the rotor disc of a helicopter in motion. The advancing for the purpose of requiring a pilot to take specific actions
blade travels at its peripheral speed plus the forward such as “Turn left heading two five zero,” “Go-around,”
speed while the airspeed of the retreating blade is the or “Clear the runway.”
peripheral speed minus the forward speed. ATC preferred route notification — URET CCLD
asymmetrical thrust — In single-engine airplanes, left (User Request Evaluation Tool Core Capability Limited
turning tendencies are caused by both asymmetrical Deployment) notification to the appropriate controller of
propeller loading (P-factor) and torque. Multi-engine the need to determine if an ATC preferred route needs to
airplanes have an even greater tendency to turn during be applied, based on destination airport.
climbs or other high angle-of-attack maneuvers due to ATC preferred routes — Preferred routes that are not
the additional engine and propeller. The position of these automatically applied by Host.
engines in relation to the airplane’s centerline causes
asymmetrical propeller loading to exert a more forceful ATC requests — Used to prefix an ATC request when it is
turning moment. relayed to an aircraft by other than an air traffic controller.

asynchronous — In electronics, signals generated as ATCSCC delay factor — The amount of delay calculated
required by the equipment instead of by a timing device. to be assigned prior to departure.

ATA system — Airline Transport Association’s standardized athodyd — Aero-thermodynamic duct. An open tube
format for maintenance manuals. shaped to produce thrust when fuel is ignited inside. Fuel
is added to incoming air as the athodyd moves through
ATC advises — Used to prefix a message of noncontrol the air at a high speed. This burning causes air expansion
information when it is relayed to an aircraft by other than that speeds up the air and produces thrust.
an air traffic controller.
athwartships — At right angles to the longitudinal axis of
ATC assigned airspace — Airspace of defined vertical/ an aircraft.
lateral limits, assigned by ATC, for the purpose of
providing air traffic segregation between the specified atmosphere — The envelope of gases that surrounds the
activities being conducted within the assigned airspace Earth.
and other IFR air traffic. atmospheric electricity — Any electrical phenomena in the
ATC clearance — An authorization by air traffic control, Earth’s atmosphere, usually occurring between clouds or
for the purpose of preventing collision between known between clouds and ground.
aircraft, for an aircraft to proceed under specified atmospheric moisture — The presence of H2O in any one
traffic conditions within controlled airspace. The or all of the states: water vapor, water, or ice.
pilot-in-command of an aircraft may not deviate from the
provisions of a visual flight rules (VFR) or instrument flight atmospheric noise — A noise (commonly referred to
rules (IFR) air traffic clearance except in an emergency as “static”) on the radio. It is caused by the discharge
or unless an amended clearance has been obtained. of atmospheric electricity between clouds or between
Additionally, the pilot may request a different clearance clouds and the ground.
from that which has been issued by air traffic control atmospheric pressure — The pressure that is exerted on
(ATC) if information available to the pilot makes another the surface of the earth by the air that surrounds the earth.
course of action more practicable or if aircraft equipment Within standard conditions, at sea level, the atmospheric
limitations or company procedures forbid compliance with
pressure is 14.69 PSI.
the clearance issued. Pilots may also request clarification
or amendment, as appropriate, any time a clearance is

30

10001930-002_AviationDictionary_2012_BOOK.indb 30 3/27/2012 9:37:56 AM

 atmospheric sounding • augmenter tube

atmospheric sounding — A measure of atmospheric to respond to persons, situations, or events in a given

variables aloft, usually pressure, temperature, humidity manner that can, nevertheless, be changed or modified
and wind. through training as a sort of mental shortcut to decision
making.
atmospheric stability — Describes a state in which an air
parcel will resist vertical displacement, or once displaced attitude gyro — A gyro-actuated flight instrument that
(for instance by flow over a hill) will tend to return to its displays the attitude of the aircraft relative to the earth’s
original level. horizon.
atom — The smallest particle of an element, consisting attitude indicator — An
of a positively charged nucleus orbited by one or more instrument that gives a pilot
negatively charged electrons. an artificial reference of the
airplane’s attitude in pitch
atomic fission — The splitting of the nucleus of a heavy
and roll with respect to the
atom such as uranium. This creates nuclei of two or more
earth’s surface.
lighter atoms releasing a tremendous amount of energy in
the form of heat and light. attitude management — The ability to recognize one’s own
hazardous attitudes and the willingness to modify them
atomic fusion — The combining of two nuclei of light
as necessary through the application of an appropriate
atoms to create a single nucleus of a heavy atom. This
antidote thought.
releases a tremendous amount of energy in the form of
heat and light. attraction — A force acting mutually between particles of
matter, tending to draw them together.
atomic number — The number of protons in the nucleus of
an atom. The atomic number of an element determines the audio frequency (af) — Frequency in a range that can
position of the element in the periodic table of elements. normally be heard by the human ear, ranging from about
16 Hz to 16,000 Hz.
atomic weight — The average weight of a single atom in a
chemical element. audio sweeps — Tones in the audio band that increase and
decrease in frequency (sweep). A siren is an audio sweep
atomize — To reduce a liquid to a fine spray.
as is the signal transmitted by an Emergency Locator
atomizing nozzle — A device that converts a liquid to a Transmitter (ELT).
fine spray.
audio-frequency amplifier — An electronic amplifier
ATR racking system — A widely accepted size and that is capable of amplifying alternating current with a
mounting standard for airborne electronic equipment. frequency in the range of human hearing.
ATS route — A specified route designated for channeling audio-frequency oscillator — An electronic device used to
the flow of traffic as necessary for the provision of air create an alternating current in the audio range, generally
traffic services. NOTE: The term “ATS Route” is used from 16-16,000 Hz.
to mean variously, airway, advisory route, controlled or
audio-frequency vibrations — Vibrations in a range heard
uncontrolled route, arrival or departure route, etc.
by the human ear, generally from 16-16,000 Hz.
attention — An element that helps your students gain
audiovisual system — A communication system utilizing
interest in the lesson.
both sound and pictures. Film and television are examples
attenuate — To diminish the intensity or strength of a of audiovisual systems.
signal, for instance of a radar beam. In electronics, the
auditory learners — Students who acquire knowledge best
volume control changes (attenuates) the sound level
by listening.
without changing any other characteristics of the sound.
augmentation — Any designed method of increasing the
attenuation — 1. A reduction in the strength of a signal,
basic thrust of an engine for a short period such as for
the flow of current, flux, or other energy in an electronic
takeoff or combat; usually accomplished by coolant
system. 2. In radar meteorology, any process which
injection or afterburning.
reduces intensity of radar signals.
augmenter — A device used to draw cooling air through an
attenuator — A device in electronics that changes the
engine cowling by the use of a low pressure created by
level of a signal’s intensity without changing any other
the rapid moving exhaust gases as they leave the exhaust
characteristics of the signal.
pipes.
attitude — 1. The position of an aircraft as determined by
augmenter tube — A specially shaped tube mounted around
the relationship of its axes and a reference, usually the
the exhaust tail pipe of an aircraft reciprocating engine.
earth’s horizon. 2. A personal motivational predisposition
When exhaust gases flow through the augmenter tube,

31

10001930-002_AviationDictionary_2012_BOOK.indb 31 3/27/2012 9:37:56 AM

 aural radio range • automated radar terminal systems

they produce a low pressure in the engine compartment autofeather — A portion of a propeller control system that
that draws cooling air into the compartment. causes the propeller to feather automatically if the engine
on which it is mounted is shut down during flight.
aural radio range — A navigational system in which the
pilot positions the airplane in accordance with audio autogyro — Gyroplane. Autogiro. A heavier-than-air
signals over a radio receiver. The A-N range is an rotorcraft whose rotor is spun by aerodynamic forces that
example of an aural radio range. As a note, such a range act on the blades. No engine power is used to drive the
is now obsolete. rotor in flight.
aural warning system — A bell or horn type warning autoland approach — An autoland approach is a precision
sounding system that alerts the pilot during an abnormal instrument approach to touchdown and, in some cases,
takeoff condition, landing condition, pressurization through the landing rollout. An autoland approach is
condition, mach-speed condition, an engine or wheel performed by the aircraft autopilot which is receiving
well fire, calls from the crew call system, and calls from position information and/or steering commands from
the SELCAL system. onboard navigation equipment.
aurora — An eerie nighttime illumination that consists NOTE: Autoland and coupled approaches are flown in
of streamers or arches of light appearing in the upper VFR and IFR. It is common for carriers to require their
atmosphere of a planet’s magnetic polar regions. Auroras crews to fly coupled approaches and autoland approaches
are caused by the emission of light from atoms excited by (if certified) when the weather conditions are less than
electrons as they accelerate along the planet’s magnetic approximately 4,000 RVR.
field lines. Two such auroras are the aurora borealis,
automated information transfer — A precoordinated
which occurs in the Northern Hemisphere, and the aurora
process, specifically defined in facility directives,
australis, which occurs in the Southern Hemisphere.
during which a transfer of altitude control and/or radar
austenite — A supersaturated solution of carbon that exists identification is accomplished without verbal coordination
in iron at high temperatures. between controllers using information communicated in
a full data block.
authorized — Approved by the Federal Aviation
Administration to act or perform certain functions. automated mutual-assistance vessel rescue system —
A facility which can deliver, in a matter of minutes, a
authorized instructor — According to FAR Part 61.3, a
surface picture (SURPIC) of vessels in the area of a
person who holds a valid ground instructor certificate
potential or actual search and rescue incident, including
issued under Part 61 or Part 143 when conducting ground
their predicted positions and their characteristics.
training in accordance with the privileges and limitations
of his or her ground instructor certificate; or a person who automated problem detection (APD) — An Automation
holds a current flight instructor certificate issued under Processing capability that compares trajectories in order
Part 1 when conducting ground training or flight training to predict conflicts.
in accordance with the privileges and limitations of his
automated problem detection boundary (APB) — The
or her flight instructor certificate; or a person authorized
adapted distance beyond a facilities boundary defining
by the Administrator to provide ground training or flight
the airspace within which URET CCLD (User Request
training under SFAR No. 58, or Part 61, 121,135, or 142
Evaluation Tool Core Capability Limited Deployment)
when conducting ground training or flight training in
performs conflict detection.
accordance with that authority.
automated problem detection inhibited area (APDIA) —
auto lean — A lean fuel-air mixture whose ratio is kept
Airspace surrounding a terminal area within which APD
constant by an automatic mixture control in the carburetor.
is inhibited for all flights within that airspace.
auto rich — A rich fuel-air mixture whose ratio is kept
automated radar terminal systems — The generic term
constant by an automatic mixture control in the carburetor.
for the ultimate in functional capability afforded by
autoclave — A pressure vessel in which the air inside can several automation systems. Each differs in functional
be heated to a high temperature and the pressure raised capabilities and equipment. ARTS plus a suffix Roman
to a high value in order to decrease the amount of time numeral denotes a specific system. A following letter
needed to cure plastic resins. Improves the quality of the indicates a major modification to that system. In general,
curing process. an ARTS displays for the terminal controller aircraft
identification, flight plan data, other flight associated
autoclave molding — In composites, a manufacturing
information; e.g., altitude, speed, and aircraft position
method that uses an autoclave. The composite assembly
symbols in conjunction with his radar presentation.
is placed into an autoclave at 50 to 100 psi to consolidate
Normal radar co-exists with the alphanumeric display.
the laminate by removing entrapped air and excess resin.
In addition to enhancing visualization of the air traffic

32

10001930-002_AviationDictionary_2012_BOOK.indb 32 3/27/2012 9:37:56 AM

 automated surface observation system (ASOS) • automatic adjusters

situation, ARTS facilitate intra/inter-facility transfer and designed to support aviation operations and weather
coordination of flight information. These capabilities are forecast activities. The ASOS provides continuous
enabled by specially designed computers and subsystems minute-by-minute observations and performs the basic
tailored to the radar and communications equipment and observing functions necessary to generate an aviation
operational requirements of each automated facility. routine weather report (METAR) and other aviation
Modular design permits adoption of improvements in weather information. ASOS information may be
computer software and electronic technologies as they transmitted over a discrete VHF radio frequency or the
become available while retaining the characteristics voice portion of a local NAVAID.
unique to each system.
automated terminal tracking system (ATTS) — ATTS is
a. ARTS II – A programmable nontracking, computer used to identify the numerous tracking systems including
aided display subsystem capable of modular ARTS IIA, ARTS IIE, ARTS IIIA, ARTS IIIE, STARS,
expansion. ARTS II systems provide a level of and M-EARTS.
automated air traffic control capability at terminals
automated unicom — Provides completely automated
having low to medium activity. Flight identification
weather, radio check capability and airport advisory
and altitude may be associated with the display of
information on an Automated UNICOM system. These
secondary radar targets. The system has the capability
systems offer a variety of features, typically selectable
of communicating with ARTCCs and other ARTS II,
by microphone clicks, on the UNICOM frequency.
IIA, III, and IIIA facilities.
Availability will be published in the Airport/Facility
b. ARTS IIA – A programmable radar-tracking computer Directory and approach charts.
subsystem capable of modular expansion. The
automated weather observing system (AWOS) — An
ARTS IIA detects, tracks, and predicts secondary
automated weather reporting system which transmits
radar targets. The targets are displayed by means of
local real-time weather data directly to the pilot.
computer-generated symbols, ground speed, and
flight plan data. Although it does not track primary a. AWOS-A only reports altimeter setting.
radar targets, they are displayed coincident with
b. AWOS-1 Usually reports altimeter setting, wind data,
the secondary radar as well as the symbols and
temperature, dewpoint and density altitude.
alphanumerics. The system has the capability of
communicating with ARTCCs and other ARTS II, IIA, c. AWOS-2 Reports same as AWOS-1 plus visibility.
III, and IIIA facilities.
d. AWOS-3 Reports the same as AWOS-2 plus cloud/
c. ARTS III – The Beacon Tracking Level (BTL) of ceiling data.
the modular programmable automated radar terminal
automated weather sensor system (AWSS) — The AWSS
system in use at medium to high activity terminals.
is part of the Aviation Surface Weather Observation
ARTS III detects, tracks and predicts secondary
Network suite of programs and provides pilots and other
radar-derived aircraft targets. These are displayed
users with weather information through the Automated
by means of computer-generated symbols and
Surface Observing System. The AWSS sensor suite
alphanumeric characters depicting flight identification,
automatically collects, measures, processes, and
aircraft altitude, ground speed and flight plan data.
broadcasts surface weather data.
Although it does not track primary targets, they are
displayed coincident with the secondary radar as well automated weather system — Any of the automated
as the symbols and alphanumerics. The system has the weather sensor platforms that collect weather data at
capability of communicating with ARTCC’s and other airports and disseminate the weather information via
ARTS III facilities. radio and/or landline. The systems currently consist
of the Automated Surface Observing System (ASOS),
d. ARTS IIIA – The Radar Tracking and Beacon Tracking
Automated Weather Sensor System (AWSS) and
Level (RT&BTL) of the modular, programmable
Automated Weather Observation System (AWOS).
automated radar terminal system. ARTS IIIA detects,
tracks and predicts primary as well as secondary automatic — An operation that occurs by itself. An
radar-derived aircraft targets. This more sophisticated automatic operation has all the necessary signals built
computer-driven system upgrades the existing ARTS into it so that it will perform its function without any
III system by providing improved tracking, continuous external decision or manipulation.
data recording and fail-soft capabilities.
automatic adjusters — A portion of the return spring
automated surface observation system (ASOS) — A system of disk brakes that maintain a constant clearance
surface weather observing system implemented by between the disk and the brake linings as the lining wears.
the National Weather Service, the Federal Aviation The automatic adjusters allow the brake piston to move
Administration and the Department of Defense. It is back a specific amount each time the brake is released.

33

10001930-002_AviationDictionary_2012_BOOK.indb 33 3/27/2012 9:37:56 AM

 automatic altitude report • auxiliary

automatic altitude report — An aircraft’s altitude, Left approach in use, Runway Two Five Right closed,
transmitted via the Mode C transponder feature, that advise you have Alfa.”
is visually displayed in 100-foot increments on a radar
automatic volume control (AVC) — A circuit that regulates
scope having readout capability.
a volume relative to the strength of the input signal.
automatic altitude reporting — That function of a
automatic-reset circuit breaker — An electrical circuit
transponder which responds to Mode C interrogations by
protection device that opens a circuit during a current
transmitting the aircraft’s altitude in 100-foot increments.
overload and then automatically resets itself and restores
automatic carrier landing system — U.S. Navy final the circuit when the overload is no longer present.
approach equipment consisting of precision tracking radar Automatic reset circuit breakers are installed in some
coupled to a computer data link to provide continuous electric motors, but they are not approved for use in
information to the aircraft, monitoring capability to the aircraft.
pilot, and a backup approach system.
automaton — A machine that operates in a preset and
automatic direction finder (ADF) — An aircraft radio relatively unsupervised manner. A robot is an example
navigation system which senses and indicates the of an automaton.
direction to a L/MF nondirectional radio beacon (NDB)
autopilot — Those units and components that furnish a
ground transmitter. Direction is indicated to the pilot
means of automatically controlling the aircraft.
as a magnetic bearing or as a relative bearing to the
longitudinal axis of the aircraft depending on the type of Autopilot Flight Director System (AFDS) — An integrated
indicator installed in the aircraft. In certain applications, system of autopilot, flight instrumentation, and feedback
such as military, ADF operations may be based on to flight controls. Individual components of the system
airborne and ground transmitters in the VHF/UHF are controlled from the autopilot system.
frequency spectrum.
autorotation — A rotorcraft flight condition in which the
automatic flight control system (AFCS) — A complete lifting rotor is driven entirely by action of the air when
instrument system including an automatic pilot that is the rotorcraft is in motion.
coupled with radio navigation and approach equipment.
a. Autorotative Landing/Touchdown Autorotation –
An aircraft with an AFCS can be flown in a completely
Used by a pilot to indicate that the landing will be
automatic mode.
made without applying power to the rotor.
automatic frequency control (AFC) — A circuit in a
b. Low Level Autorotation – Commences at an altitude
radio receiver that keeps the receiver tuned to a desired
well below the traffic pattern, usually below 100
frequency within specific limits.
feet AGL and is used primarily for tactical military
automatic gain control (AGC) — An electronic circuit training.
within a radio receiver that keeps the output volume
c. 180 degrees Autorotation – Initiated from a downwind
relatively constant.
heading and is commenced well inside the normal
automatic mixture control (AMC) — A device in a fuel traffic pattern. “Go-around” may not be possible
metering system (carburetor or a fuel injection system) during the latter part of this maneuver.
that keeps the fuel-air mixture ratio constant as the
autorotation region — The portion of the rotor disk of a
density of the air changes with altitude.
helicopter that produces an autorotative force.
automatic pilot — An automatic flight control system that
autorotative force — An aerodynamic force that causes
keeps an aircraft in level flight or on a set course. Automatic
an autogyro or helicopter rotor to turn when no power is
pilots can be given course guidance by the human pilot, or
supplied to it.
they may be coupled to a radio navigation signal.
Autosyn — A remote-indicating instrument or system based
Automatic Terminal Information Service (ATIS) —
upon the synchronous-motor principle, in which the
The continuous broadcast of recorded noncontrol
angular position of the rotor of one motor at the measuring
information in selected terminal areas. Its purpose is to
source is duplicated by the rotor of the indicator motor.
improve controller effectiveness and to relieve frequency
Used in fuel-quantity or fuel-flow measuring systems,
congestion by automating the repetitive transmission
position-indicating systems, etc.
of essential but routine information, e.g., “Los Angeles
information Alfa. One three zero zero Coordinated autotransformer — A single winding transformer having a
Universal Time. Weather, measured ceiling two thousand carbon brush that can tap off any number of turns for the
overcast, visibility three, haze, smoke, temperature seven secondary. It produces variable voltage AC output.
one, dew point five seven, wind two five zero at five,
auxiliary — A supplement, or an addition, to a main unit.
altimeter two niner niner six. I-L-S Runway Two Five

34

10001930-002_AviationDictionary_2012_BOOK.indb 34 3/27/2012 9:37:57 AM

 auxiliary flight surfaces • Avogadro’s principle

auxiliary flight surfaces — Lift-modifying devices on an aviation — The branch of science, business, or technology
airfoil, such as flaps, slots, or slats. that deals with any part of the operation of machines that
fly through the air.
auxiliary fuel pump — An electrically operated fuel pump
used to supply fuel to the engine for starting, takeoff, or aviation maintenance technician (AMT) — An aviation
in the case of engine-driven fuel pump failure. Auxiliary maintenance technician is a person certificated by the FAA
fuel pumps are also used to pressurize the fuel in the line to work on aircraft structures and engines. Also referred
to the engine-driven fuel pump in order to prevent vapor to as an A&P (airframe and powerplant) mechanic.
lock at altitude when the fuel is warm.
aviation medical examiner (AME) — A person to whom
auxiliary hydraulic pump — A hydraulic pump that is the FAA delegates authority to examine applicants for, and
used as an alternate source of hydraulic pressure for holders of, airman medical certificates to determine whether
emergencies, or to produce hydraulic pressure when the or not they meet the medical standards for its issuance.
aircraft engines are not in operation. AMEs also issue or deny airman medical certificates based
upon whether or not they meet the applicable medical
auxiliary ignition units — An auxiliary ignition system
standards. The medical standards are found in Title 14 of
that facilitates engine starting. The auxiliary device is
the Code of Federal Regulations Part 67.
incorporated in the ignition system to provide a high
ignition voltage. Reciprocating engine starting systems aviation medicine — A special field of medicine that
normally include one of the following types of auxiliary establishes standards of physical fitness for pilots.
starting systems: booster coil, induction vibrator,
aviation physiology — The study of the biological processes
impulse coupling, or other specialized retard-breaker and
and functions of life and living matter, and the physical
vibrator-starting systems.
and chemical aspects involved in those processes as it
auxiliary power unit (APU) — A gas turbine, usually located relates to aviation.
in the aircraft fuselage, whose purpose is to provide either
aviation safety counselors — Volunteers within the
electrical power, air pressure for starting main engines, or
aviation community who share their technical expertise
both. Similar in design to ground power units.
and professional knowledge as a part of the FAA Aviation
auxiliary pump — Any pump used as an alternate source Safety Program.
or in an emergency situation. An auxiliary pump provides
aviation safety reporting system (ASRS) — The ASRS
assistance or support to the main pump.
investigates the causes underlying a reported event, and
auxiliary rotor — A rotor that serves either to counteract incorporates each report into a database, which provides
the effect of the main rotor torque on a rotorcraft or to information for research regarding aviation safety and
maneuver the rotorcraft about one or more of its three human factors. Each report is held in strict confidence and
principal axes. the FAA cannot use ASRS information in enforcement
actions against those who submit reports.
auxiliary view — A view used in an aircraft drawing that
is made at some angle to one of the three views of an aviation shears — Compound-action hand shears used for
orthographic drawing. It is used to show details that cutting sheet metal. They normally come in sets of three:
would not otherwise be visible. one that cuts to the left, one that cuts to the right, and one
that cuts straight. Also referred to as aviation snips.
available landing distance (ALD) — The amount of
runway remaining when operating at a controlled airport aviation turbulence — Bumpiness in flight.
where land and hold short operations (LAHSO) are in
aviation weather — Specific characteristics of weather that
effect. Pilots may accept such a clearance provided that
pertain to flight or to the operation of aircraft.
the pilot-in-command determines that the aircraft can
safely land and stop within the ALD. Aviation Weather Service — A service provided by
the National Weather Service (NWS) and FAA which
avalanche diode — Zener diode. Semiconductor diode
collects and disseminates pertinent weather information
in which reverse breakdown voltage current causes the
for pilots, aircraft operators, and ATC. Available aviation
diode to develop a constant voltage. Used for voltage
weather reports and forecasts are displayed at each NWS
regulation.
office and FAA FSS.
avalanche voltage — The reverse voltage required to cause
avionics — AVIation electrONICS. Airborne electronic
a zener diode to break down.
equipment.
average value — Sine wave alternating current. 0.637 times
Avogadro’s principle — A principle of physics, that states
the peak value of alternating current or voltage, measured
that under equal pressure and temperature, equal volumes
from the zero reference line.
of all gases will contain equal numbers of molecules.

35

10001930-002_AviationDictionary_2012_BOOK.indb 35 3/27/2012 9:37:57 AM

 avoirdupois weight • azimuth

avoirdupois weight — The system of weight for measuring axial-lead resistor — A disparate electronic component that
the weight of most substances. In avoirdupois weight, provides a given amount of resistance to a circuit. The
one pound is equal to 453.6 grams. wire leads of an axial-lead resistor extend from the ends
in a direction that is parallel to the axis of the resistor.
awl — A sharp-pointed tool that is used to make holes in
soft materials such as leather, plastic, or wood. axis — A straight line about which a body can rotate.
axes of an aircraft — Three mutually perpendicular axis of symmetry — An imaginary center line about which
imaginary lines about which an aircraft is free to rotate. a body or object is symmetrical in either weight or area.
The longitudinal axis passes through the aircraft’s center
axis-of-rotation — In rotorcraft, the imaginary line about
of gravity from front to rear. The lateral axis passes
which the rotor rotates. It is represented by a line drawn
through the aircraft’s center of gravity from wingtip to
through the center of, and perpendicular to, the tip-path
wingtip, and the vertical axis passes through the aircraft’s
plane.
center of gravity from top to bottom.
axle — The shaft on which one or more wheels are mounted
axial — Motion along a real or imaginary straight line on
and about which the wheels are free to rotate.
which an object supposedly or actually rotates. Turbine
engine centerline. axonometric projection — A projection used in mechanical
drawing that shows a solid rectangular object inclined
axial flow — The straight-through flow of a fluid. In
in a way that three of its faces are visible. An isometric
an axial-flow compressor, the air flows through the
projection is a form of axonometric projection.
compressor parallel to the engine and the stages of
compression do not essentially change the direction of azimuth — The angular measurement in a horizontal plane
the flow. and in a clockwise direction.
axial flow compressor — In gas turbine engines, a
compressor with the airflow parallel to the axis of the
engine. The numerous compressor stages raise pressure
of air but essentially make no change in direction of
airflow.
axial flow turbine engine — A turbine engine in which
the air is compressed by a series of rotating airfoils. The
airflow through the engine is essentially in a straight line.
axial load — A load on a bearing that acts parallel to the
shaft supported in the bearings. The thrust load produced
by a propeller is an axial load. Axial loads are usually
carried by ball bearings or by tapered roller bearings and
are carried into the engine crankcase through the thrust
bearing.
axial loading — An aerodynamic force that tries to move
the compressor forward. Axial loading is supported in a
gas turbine engine by ball bearings.
axial velocity — The speed of a gas traveling in a circular
path. Usually applied to the speed combustion gases as
they rotate through the combustor section of a turbine
engine.
axial winding — In composites, a manufacturing method
using filament-winding equipment. In axial winding the
filaments are parallel to the axis.
axial-centrifugal compressor — A combination axial
and centrifugal compressor usually fitted together with
the axial portion as the front stages and the centrifugal
portion as the rear stage. This is a popular design for
smaller turbine engines.

36

10001930-002_AviationDictionary_2012_BOOK.indb 36 3/27/2012 9:37:57 AM

 B • bag molding

B of backlash. However, too much movement due to

backlash can be undesirable.
babbitt metal — An alloy of tin, lead, copper, and antimony backlash check — Measuring of the amount of movement
used for lining engine bearings. It is used because of its of one gear when the gear meshed with it is held rigid. It
exceptional low-friction qualities. is an indication of the amount of space between meshed
back — The curved portion of a propeller blade that gears.
corresponds to the curved upper surface of an airfoil. backsaw — A fine-toothed wood cutting saw that has a stiff
back current — The current that flows in a semiconductor lip along its upper edge. Backsaws are used to make cuts
(such as a transistor or diode) when the device is reverse across a board.
biased. backscatter — The signal, reflected back to the transmitter/
back plate — A floating plate on which the wheel cylinder receiver, when a radar beam hits an object. Also referred
and brake shoes attach on an energizing-type brake. to as an echo.
back pressure — 1. In a reciprocating engine, the pressure back-taxi — A term used by air traffic controllers to taxi
caused by the exhaust system that opposes the evacuation an aircraft on the runway opposite to the traffic flow. The
of the burned gases from the cylinders. 2. Pressure in an aircraft may be instructed to back-taxi to the beginning of
aft direction when applied to the control wheel or stick the runway or at some point before reaching the runway
of an airplane. end for the purpose of departure or to exit the runway.
back voltage — Counter-electromotive force generated in a backup ring — An anti-extrusion ring used on the side of
conductor by the action of changing lines of flux cutting an O-ring packing away from the pressure. This stiff ring,
across the conductor. As the magnetic field produced by usually made of some material such as Teflon®, prevents
the changing current builds up and decays, it cuts across the resilient O-ring from being extruded by hydraulic
the conductor and induces a voltage in it. The polarity of pressure into the space between the cylinder wall and the
this induced voltage is opposite to that of the voltage that piston.
caused the original current to flow. bacteria — Microscopic plant life that lives in the water
backfire — 1. In welding, a momentary backward flow of the entrapped in fuel tanks. The growth of bacteria in jet
gases at the torch tip that causes the momentary burning aircraft fuel tanks causes a film, which holds water against
back of a flame into the tip, followed by a snap or pop, the aluminum alloy surface. This can result in corrosion.
then either a relight or the flame extinguishing. A backfire bactericide — An agent that is used to destroy bacteria.
may be caused by touching the tip against the work, by
overheating the tip, or by operating the torch at other than baffle — 1. A series of partitions inside an aircraft fuel
recommended pressures. 2. A burning or explosion within tank. These baffles have holes in them that allow the fuel
a reciprocating engine when the fuel-air mixture in the to feed to the tank outlet, but they keep the fuel from
induction system is ignited by gases that are still burning surging enough to uncover the fuel outlet. 2. A partition
inside the cylinder when the intake valve opens. separating the upper portion of the tank that prevents oil
pump cavitation as the oil tends to rush to the top of the
backfiring — See backfire. tank during periods of deceleration. The baffle is fitted
background noise — An unwanted signal found in an with a weighted swivel outlet control valve, which is free
electronic device. to swing below the baffle. The valve is normally open,
but closes when the oil in the bottom of the tank rushes
backhand welding — The technique of pointing the torch to the top of the tank during deceleration. 3. Sheet metal
flame toward the finished weld and moving away in the shields used to direct the flow of air between and around
direction of the unwelded area, welding the edges of the cylinders of an air-cooled reciprocating engine. Also
the joint as it is moved. The welding rod is added to the referred to as cylinder deflectors. 4. A structure used to
puddle between the flame and the finished weld. impede, regulate, or alter the flow direction of a gas,
backing — In meteorology, change of wind direction in a fluid, or sound.
counterclockwise sense in the northern hemisphere (for bag molding — A method of applying pressure to a piece of
example, northwest to west) with respect to either space laminated plastic material so that all of the layers are held
or time; opposite of veering. in tight contact with each other. The reinforcing material
backing plate — A reinforcing plate used when making a is injected with plastic resin, which is laid up over a rigid
sheet metal repair. It is often a doubler. mold in as many layers as are needed. A sheet of flexible,
air-tight plastic material is placed over the mold and the
backlash — The clearance measured between the meshing edges are sealed to form a bag over the part. The entire
teeth of two gears. Usually units such as selector valves, assembly is then placed in an autoclave for curing. In the
pumps, etc. are required to have a predetermined amount

37

10001930-002_AviationDictionary_2012_BOOK.indb 37 3/27/2012 9:37:57 AM

 bag side • ballast

absence of an autoclave, a vacuum pump can be attached Fluid power into the actuator produces the same amount
to the bag, and the air pumped out. The atmospheric of force in either direction of piston movement.
pressure pressing on the outside of the bag supplies the
balanced amplifier — An electronic amplifier that has two
needed force.
output circuits that are equal, but opposite in phase. Also
bag side — In composites, the side of a part that is cured referred to as a push-pull amplifier.
against the vacuum bag.
balanced control surface — A primary control surface
bagging — In composites, applying an impermeable layer with an overhang ahead of the hinge line that provides an
of film over an uncured part and sealing the edges so that aerodynamic assist to reduce control pressures.
a vacuum can be drawn.
balanced design — In filament-winding of composites,
bailout bottle — Small oxygen cylinder connected to the a winding pattern so designed that the stresses in all
oxygen mask supplying several minutes of oxygen. It can filaments are equal.
be used in case of primary oxygen system failure or if an
balanced laminate — In composites, each layer except
emergency bailout at high altitude became necessary.
the 0/90° is placed in plus and minus pairs around the
Bakelite — A phenol resin, often used as electrical centerline. These plies do not have to be adjacent to each
insulation, made by the Bakelite Corporation. other.
baking soda — The common term for bicarbonate of soda balanced transmission line — A radio frequency
(NaHC03). transmission line matched in impedance between each
conductor and ground, and between conductors and
balance — A state of equilibrium.
the electronic equipment to which the conductors are
balance bridge — A method of measuring resistance. It connected. Neither conductor is grounded.
consists of three known resistances and an unknown
balancing — The act of performing a balance procedure
resistance. When the known resistances are adjusted so
using prescribed methods.
the bridge is balanced, the output is zero. The unknown
resistance can then be calculated using the relationship ball bearing — An anti-friction bearing consisting of
R1:R2=R3:R4. See also Wheatstone bridge. grooved inner and outer races and one or more sets of
steel balls held in a sheet metal retainer. Ball bearings can
balance chamber — An internal air chamber in a turbine
be designed to support thrust loads as well as radial loads.
engine used to absorb some of the compressor axial
loading “thrust.” ball bearing assembly — Consists of grooved inner and
outer races, one or more sets of balls, and, in bearings
balance checks — A check or series of inspections
designed for disassembly, a bearing retainer. They are
performed on rotating components after overhaul to
used for supercharger impeller shaft bearings and rocker
statically and dynamically check for correct balancing.
arm bearings in some engines. Special deep-groove ball
balance point — 1. A point within an object at which the bearings are used in aircraft engines to transmit propeller
sum of all its components have zero rotation. 2. The point thrust to the engine nose section.
about which an object will balance.
ball check valve — A
balance pressure torch — A welding torch where the check valve in a fluid
oxygen and acetylene are both fed to the torch at the power system that uses a
same pressure. The openings to the mixing chamber for spring-loaded steel ball and
each gas are equal in size, and the delivery of each gas is a seat to allow flow in one
independently controlled. direction only. The ball is forced tightly against its seat by
fluid flowing into the valve from the end that contains the
balance, static — 1. A condition of balance which does not
spring, thereby stopping the fluid flow through the valve.
involve any dynamic forces. 2. When a body will stand
Fluid flowing into the valve from the ball end forces the
in any position as the result of counterbalancing and/or
ball off its seat, allowing flow through the valve.
reducing the heavy portions, it is said to be in standing
or static balance. ball joint — A flexible expansion joint used in an aircraft
engine exhaust system to allow relative movement of the
balance tab — An auxiliary control mounted on a primary
parts as a result of their expansion and contraction.
control surface, which automatically moves in the
direction opposite the primary control to provide an ball peen hammer — A hammer with one side of its head
aerodynamic assist in the movement of the control. shaped like a ball.
Sometimes referred to as a servo tab.
ballast — 1. Permanently installed weight in an aircraft used
balanced actuator — A hydraulic or pneumatic actuator to bring the center of gravity into the allowable range.
having the same area on each side of the actuator piston. 2. An electrical circuit component designed to stabilize

38

10001930-002_AviationDictionary_2012_BOOK.indb 38 3/27/2012 9:37:57 AM

 ballast lamp • barometric altimeter

current flow. 3. In gliding, used to describe any system that bank — To incline or tilt an airplane about its longitudinal
adds weight to the glider. Performance ballast employed axis.
in some gliders increases wing loading using releasable
bank indicator — A flight instrument consisting of a curved
water in the wings (via integral tanks or water bags).
glass tube filled with a liquid similar to kerosene and
This allows faster average cross-country speeds. Trim
enclosing a round ball. When the aircraft is horizontal,
ballast is used to adjust the flying CG, often necessary for
the ball is located in the lowest part of the tube; as the
light-weight pilots. Some gliders also have a small water
aircraft banks, gravity holds the ball at the lowest point
ballast tank in the tail for optimizing flying CG.
as the tube rotates from side to side. The tube can be
ballast lamp — A resistance-type lamp connected into a calibrated to show the angle of banking. It can also
circuit in a series in order to maintain a constant current. indicate the relationship between the force of gravity and
As current increases, the filament gets hotter and creates centrifugal force in a turn. If the bank angle is correct for
a higher resistance, lowering the current until a balance the rate of turn, the ball will stay in the center of the tube.
(and constant current) is achieved. However, if the angle of bank is too steep for the rate of
turn, the ball will roll to the inside of the turn. If the angle
ballistic missile — A self-propelled long-range missile,
of bank is not steep enough for the rate of turn, the ball
which is guided by preset mechanisms as it goes upward,
will roll to the outside of the turn. A bank indicator is
but is free falling as it comes down.
built into the face of a turn and slip indicator.
balloon — A lighter-than-air, non-steerable aircraft that is
bar — A metric unit of pressure equal to 1,000,000 dynes
not engine-driven. Its rising capability comes from gases
per square centimeter. Pressure is often measured in
or hot air that fill the gas envelope.
meteorological services in millibars, which is 1/1,000 of
balsa wood — The light, strong wood of the balsa, a tropical a bar. The standard absolute pressure of the atmosphere
tree. It is sliced across its grain and sandwiched between at sea level is 1013.2 millibars.
two face sheets of thin metal or fiberglass to make rigid,
bar folder — A forming machine used for making bends
lightweight panels.
or folds along edges of metal sheets. It is best suited for
balun — A transformer used to match a balanced antenna to folding small hems, flanges, seams, and edges. Most bar
an unbalanced transmission line. folders have a capacity for metal up to 22 gauge thickness.
bamboo — A species of tree consisting of light weight, bar graph — A graph used to show relationships between
strong, tubular sections. Used in some early aircraft different values. Each value in a bar graph is represented
construction. by a bar of an appropriate length.
banana plug — A mechanism used to make a temporary bare conductor — An electrical conductor that is not
connection to an electrical circuit. The contacts of a protected with any type of insulating material.
banana plug are springs that have the general shape of a
barnstormers — Early aviation pioneers who traveled
banana. These springs press out against the walls of the
from town to town piloting their planes in sight-seeing
banana jack in order to make a low-resistance contact.
flights with passengers or in exhibition stunts. Some
band — A range of electro-magnetic frequencies. were clowns and characters, but others were more
serious and showed the promises for the future of aircraft
band saw — A controllable-speed power saw used to cut
transportation. Barnstorming included acrobatics and
wood, plastics, or metal. The band saw blade is in the
stunts such as picking up handkerchiefs off the ground
form of a narrow strip of steel with teeth along one
with hooks attached to the wing tips etc.
edge. The ends of the blade are welded together to form
a continuous loop, and the loop passes over two large barograph — An instrument used to measure absolute
wheels, one above the saw table and the other below the pressure. Barographs are often sealed and carried in
table. an aircraft in order to make a permanent record of the
altitude reached by the aircraft.
band-pass filter — An electronic filter that passes a band
of frequencies while rejecting all frequencies above or barometer — An instrument used to measure atmospheric
below the band. pressure. Used in forecasting weather or measuring
the height above sea level. The two principle types are
band-reject filter — An electronic filter that rejects a
mercury and aneroid.
specific band of frequencies while passing those above
and below the band. barometric altimeter — An instrument that measures
altitude above mean sea level using an internal aneroid
bandwidth — The difference between the maximum and
barometer to compare pressure of the ambient air in
minimum frequencies in a band.
relation to known lapse rates of pressure as altitude varies
with height. Also referred to as a pressure altimeter.

39

10001930-002_AviationDictionary_2012_BOOK.indb 39 3/27/2012 9:37:57 AM

 barometric pressure • bastard file

barometric pressure — Pressure existing above zero basic fuel system — The tanks, booster pumps, lines,
pressure. Measured in millibars or inches of mercury. selector valves, strainers, engine-driven pumps, and
pressure gauges that make up an aircraft’s basic fuel
barometric tendency — The change in barometric pressure
system.
over a set period of time. For example, “The barometric
tendency in the past three hours has been a 1 mb rise” basic ground instructor — A person authorized by the
Also referred to as pressure tendency. FAA to provide: ground training in the aeronautical
knowledge areas required for issuance of a recreational
barrel — The part of a reciprocating engine cylinder made
pilot certificate, private pilot certificate, or associated
of a steel alloy forging. The inner surface of the barrel is
ratings under Part 61; ground training required for a
hardened to resist wear of the piston and the piston rings
recreational pilot and private pilot flight review; and
which bear against it during operation. In some instances
recommendation for a knowledge test required for
the barrel will have threads on the outside surface at one
issuance of a recreational pilot certificate or private pilot
end so that it can be screwed into the cylinder head.
certificate under Part 61.
barrel roll — An airplane flight maneuver in which the
basic load — The load on a structural member or part in
airplane rolls around a distant visual point with a constant
any condition of static equilibrium of an airplane. When
angular displacement from the point throughout the roll.
a specific basic load is expressed, the particular condition
barriers to effective communication — Things which of equilibrium must be indicated in the context.
impede communication, such as lack of common
basic magneto — A high-voltage generating device in a
experience, or confusion between the symbol and the
reciprocating engine. It is adjusted to give maximum
symbolized object. Other examples include overuse of
voltage at the time the points break and ignition occurs.
abstractions and interference.
It must also be synchronized accurately to the firing
base — 1. The center electrode of a transistor. The signal is position of the engine.
normally applied to the base. 2. The electrode between
basic maneuvers — Straight-and-level flight, climbs,
the emitter and the collector in a bipolar transistor. 3. A
descents, and turns. These four maneuvers form the
bipolar transistor electrode that normally receives the
foundation of the development of all piloting skills.
signal.
Each flight maneuver, regardless of its complexity, is
base leg — A flight path at right angles to the landing composed of combinations of the basic maneuvers.
runway off its approach end. The base leg normally
basic need — A perception factor that describes a person’s
extends from the downwind leg to the intersection of the
ability to maintain and enhance the organized self.
extended runway centerline.
basic radar service — A radar service for VFR aircraft that
base line — A line used as a basis for measuring.
includes safety alerts, traffic advisories and limited radar
base metal — The metal to which alloying agents are added. vectoring, as well as aircraft sequencing at some terminal
locations.
baseball stitch — A hand stitch similar to that used to sew
the cover on a baseball. It is used for hand sewing of basic size — The size from which the limits of size are
aircraft fabric. derived by the application of allowances and tolerances.
BASIC (computer) — A programming language used by basic weight — The weight of an aircraft, its power plant,
digital computers. BASIC is an acronym for Beginners and all of the fixed equipment. It includes unusable fuel
All-purpose Symbolic Instruction Code. and undrainable oil for aircraft not certified under FAR
Part 23 (aircraft certified under FAR Part 23 include full
basic empty weight — The weight of the standard aircraft,
oil as part of empty weight).
operational equipment, unusable fuel, and full operating
fluids, including full engine oil. basket weave — In composites, a woven reinforcement
where two or more warp threads go over and under two
basic empty weight (GAMA) — Standard empty weight
or more filling threads in a repeat pattern. The basket
(airframe, engines, and all items of operating equipment
weave is less stable than the plain weave but produces a
that have fixed locations and are permanently installed,
flatter and stronger fabric. It is also a more pliable fabric
including fixed ballast, hydraulic fluid, unusable fuel,
than the plain weave and maintains a certain degree of
and full engine oil, in addition to optional and special
porosity.
equipment that has been installed. (Except aircraft
certified under CAR Part 3, the standard empty weight bastard file — A double-cut, metal-working file that has
does not include oil.) coarse cutting teeth. There are five grades of cuts from
the coarsest to the finest: coarse cut, bastard cut, second
cut, smooth cut, and dead-smooth cut.

40

10001930-002_AviationDictionary_2012_BOOK.indb 40 3/27/2012 9:37:57 AM

 batch • beads

batch — In composites, material that was made with bayonet gauge — A dipstick-type gauge used to measure
the same process at the same time having identical the quantity of a liquid such as oil or hydraulic fluid.
characteristics throughout. Also referred to as a lot.
bayonet thermocouple — A thermocouple used to indicate
bathtub capacitor — A bathtub-shaped capacitor that is engine temperature. The bayonet probe fits into an
sealed in a metal container. adapter that is screwed into the cylinder.
battery — A device made up of a number of individual cells bayonet thermocouple probe — A pickup for cylinder head
used to store electricity by converting it into chemical temperature that presses into an adapter screwed into the
energy. Electrons are caused to flow from one pole, the side of a cylinder head. Used for measuring cylinder head
anode, to another pole, the cathode, by a chemically temperature on an air-cooled aircraft engine.
produced potential difference.
B‑battery or B‑power supply — In electronic vacuum
battery analyzer — A transformer rectifier unit used to tubes, positive plate voltage is called B+ voltage.
charge nickel-cadmium batteries. The analyzer has a The source of voltage for these plates is referred to as
built-in load bank as well as timers, indicators, and B-battery or B-power supply.
controls for deep-cycling and recharging these batteries.
beacon — See radar, nondirectional beacon, marker
battery bus — The electrical tie point in an airplane where beacon, airport rotating beacon, aeronautical beacon,
power from the battery is distributed to the various loads. and/or airway beacon.
battery charger — A power supply that converts alternating bead — 1. A trough-like impression formed in a sheet metal
current into direct current for charging batteries. member for the purpose of stiffening the member. 2. A
raised rounded ridge formed near the end of a piece of
battery charger/analyzer — A power supply that converts
rigid tubing. A hose is slipped over the end of the tube,
alternating current into direct current for charging
then the hose clamp is installed between the end of the
batteries. The charger/analyzer is a special device with a
hose and the bead. The bead keeps the tube from being
timer, load bank, and monitoring equipment for complete
pulled from the hose.
servicing of aircraft batteries.
bead heel — On tires, the outer bead edge that fits against
battery ignition system — An ignition system that uses
the wheel flange.
a battery as its source of energy, rather than a magneto.
This system is similar to that used in an automobile. A bead seat area — The highly stressed portion of a wheel
cam driven by the engine opens a set of points to interrupt where the bead of the tire seats against the wheel.
current in a primary circuit. The resulting collapsed
bead thermistor — A component in a fire detection system
magnetic field induces a high voltage in the secondary
that signals the presence of a fire or an overheat condition.
circuit, which is directed by a distributor to the proper
The beads in the detector are wetted with a eutectic salt,
cylinder.
which possesses the characteristic of suddenly lowering
baud — In computers, a measure of data transmission rate. its electrical resistance as the sensing element reaches
One baud is equal to one bit per second. its alarm temperature. The lowered resistance starts the
fire-warning procedure by turning on the fire-warning
bauxite — A clay-like substance that is the source of
light and sounding the fire-warning bell.
aluminum. To extract the aluminum, the bauxite is changed
into alumina (aluminum oxide). Then the alumina is bead toe — On tires, the inner bead edge closest to the
reduced to metallic aluminum by an electrolytic process. aircraft tire center line.
bay — Any specific compartment in the body of an aircraft. bead welds — The part of a weld that joins edges of metal
It may also refer to a portion of a truss, or fuselage, parts that have been heated and melted together to form
the area between adjacent bulkheads, struts, or frame one solid piece when solidified. The bead sticks up
positions. above the surface of metal that has been welded. Usually
some additional metal is added to the weld, in the form
bayonet — Something that is detachable and can be easily
of a wire or rod, to build up the weld seam to a greater
put on or removed.
thickness than the base metal. The characteristics of a
bayonet exhaust pipe — The elongated and flattened end of bead on a good weld are: height uniformity, a smooth and
the exhaust pipe of a reciprocating engine. It is designed uniform ripple on its surface, and an even blend into the
to minimize exhaust noise prevent exhaust valve warpage base metal.
by maintaining a relatively constant temperature at the
beads — On tires, steel wires embedded in rubber and
exhaust ports of the cylinders.
wrapped in fabric. The beads anchor the carcass plies and
bayonet exhaust stack — See bayonet exhaust pipe. provide firm mounting surfaces on the wheel.

41

10001930-002_AviationDictionary_2012_BOOK.indb 41 3/27/2012 9:37:57 AM

 beam • beat-frequency oscillator (BFO)

beam — 1. A supporting structural member in any race on the axle and a hardened steel race, the cup, inside
construction designed to withstand loads in both shear the wheel.
and bending. 2. A radio signal sent continuously in one
bearing scratch detector — A hand-held ball bearing
direction.
tipped tool, which is passed over bearing surfaces. If the
beam power tube — An electron tube that utilizes directed ball finds a depression, the bearing is usually rejected.
electron beams to add to its power-handling capability.
bearing seal — A device used in turbine engines to seal the
Beam power tubes are power amplifier tubes, rather than
lubricating oil in the bearing cavity. Usually located at
a voltage amplifier.
main bearings.
beam radio antenna — A directional radio transmitting
bearing stack — A group of thrust-type bearings placed
antenna that radiates its energy in a narrow beam.
one on top of the other to form a stack. Primarily used
bearing — 1. An angular measurement of direction from to allow propeller blades to rotate in the hub under high
an airplane in flight and a known point. 2. A surface that centrifugal loads.
supports and reduces friction between moving parts.
bearing strain — In composites, the ratio of the deformation
bearing area — The cross-section area of the bearing load of the bearing hole, in the direction of the applied force,
member on a sample. to the pin diameter.
bearing burnishing — An aircraft engine run-in process bearing strength — The force required to pull a rivet
that creates a highly polished surface on new bearings through the edge of the sheet or to elongate the hole.
and bushings installed during overhaul. The burnishing The bearing strength of a material is affected by both its
is usually accomplished during the first periods of the thickness and by the size of the rivet.
engine run-in at comparatively slow engine speeds.
bearing stress — In composites, the applied load in pounds
bearing cage — A thin sheet-metal separator that holds the divided by the bearing area.
bearing rollers equally spaced around the race. The cage
bearing sump — The compartment housing the engine
should not contact either of the races.
main bearings, formed by bearing seals on either side
bearing cone — The assembly, which consists of a tapered, of the bearing on the shaft. Seals are used to control the
hardened steel, cone-shaped bearing race that fits over inward leakage of gas path air.
the axle, the rollers, and the cage that holds the rollers in
bearing support — The inner hub of a major engine case,
position.
which is supported by struts and houses a main bearing.
bearing cup — The steel race of a roller bearing that is
bearing surface — A surface that supports and reduces
shrink-fitted into the bearing cavity of the wheel.
friction between moving parts or a moving load. Bearing
bearing degausser — A device that removes magnetism surfaces are ordinarily treated in several ways to decrease
from bearings and other engine components. the friction between the surface and the moving load.
bearing failure — The failure of a riveted joint caused by bearing wheel — An airplane wheel that has tapered,
the sheets tearing at the rivet holes rather than the rivets roller-type bearings that consist of a bearing cone, rollers
shearing. with a retaining cage, and a bearing cup, or outer race.
Each wheel has the bearing cup, or race, pressed into
bearing field detector — A device that detects magnetism
place and is often supplied with a hubcap to keep dirt
in rotating engine components.
out of the outside bearing. Retainers and felt seals are
bearing friction — Friction caused by a bearing. supplied inboard of the inner bearing to prevent grease
from reaching the brake lining.
bearing heater tank — An oil bath heater used to expand a
bearing so that it can be hand fitted over its shaft journal. beat — A low frequency vibration produced when two
sources of vibration act on the same object at the same
bearing navigation — The horizontal direction of one
time. In a multi-engine airplane, if two engines have
object in relation to another object.
slightly different RPMs, the airframe vibrations caused
bearing pressurizing — The process of increasing air by these engines will produce a very noticeable beat. This
pressure in the bearing pockets by admitting compressor beat is caused by the difference in the frequency of the
air. two vibrations.
bearing race — The hardened steel surface upon which beat-frequency oscillator (BFO) — A variable frequency
anti-friction bearings ride. electronic oscillator designed to produce a signal
frequency that is mixed with another frequency in
bearing rollers — Hardened steel rollers that support the
order to develop an intermediate frequency or an audio
wheel. They roll between a hardened steel, cone-shaped
frequency that can be heard.

42

10001930-002_AviationDictionary_2012_BOOK.indb 42 3/27/2012 9:37:58 AM

 Beaufort scale • benzene

Beaufort scale — In meteorology, a scale used to describe action involved; e.g., landing minimums, takeoff
wind force, ranging from 0 to 12, 0 (zero) represents less minimums.
than 1 MPH, and 12 represents speeds of more than 72
belt frame — A circumferential fuselage frame usually
MPH, or hurricane force.
having a channel or hat section.
beef up — To strengthen or reinforce.
bench check — A functional check performed on a part
beehive spring — A hard that has been removed from an aircraft to determine its
steel retaining spring condition of serviceability. The equipment is set up on
used to hold a rivet set a test bench and operated to find out whether or not it is
in a pneumatic rivet gun. functioning as it should.
Prevents the set from being
bench plate — A flat, cast iron plate built into a bench used
driven out of the gun. It derives its name, beehive, from
for working sheet metal. Holes in the bench plate support
its shape.
stakes that are used to form the sheet metal.
beep button — A switch on the collective control used
bench timing — A functional procedure to time a magneto
to trim a helicopter turbine engine by increasing or
by setting the breaker points, and for checking the rotor
decreasing the steady state RPM. Also referred to as a
for the E-gap position. This process is done in the shop
beeper button.
before installation in the engine.
beeswax — A substance secreted by bees. It is used to coat
bend allowance — The
rib lacing cord to protect it from moisture and prevent
amount of material actually
slippage.
used in the bend of sheet
before bottom center (BBC) — The degrees of crankshaft metal. This amount of
travel before the piston stops at the bottom of its stroke. metal must be added to the
overall length of the layout
before top center (BTC) — The degrees of crankshaft
pattern to assure adequate
travel before the piston reaches the top of its stroke.
metal for the bend. Bend
behaviorism — Theory of learning that learning is allowance depends on four factors: the degree of the
dependent on particular behaviors being positively bend, the radius of the bend, the thickness of the metal,
reinforced by someone other than the student. and the type of metal used. The amount of material in the
bend is usually found by using a bend allowance chart.
bel — A unit used to express the ratio of two values of
power. The number of bels is the logarithm to the base 10 bend allowance chart — A chart used to save time in
of the power ratio. calculating the bend allowance of sheet metal. Formulas
and charts for various angles, radii of bends, material
bell gear — The large stationary gear used in a spur
thicknesses, and other factors have been established to
gear-type planetary reduction gearing system.
make up the chart.
bellcrank — A double lever in an aircraft control system
bend radius — The radius of the bend as measured on the
used to change the direction of motion. Bellcranks are
inside of the curve.
commonly used in an aileron system to change spanwise
movement into chordwise movement to move the control bend tangent line (BL) — A line made on a sheet metal
surface. layout to indicate the beginning of the bend, and the line
at which the metal stops curving. All the space between
bellmouth — A turbine engine air inlet duct having a
the bend tangent lines is the bend allowance.
flared or convergent shape used to direct air into a gas
turbine engine. The shape of the bellmouth increases the bending — The stresses in an object caused by a load being
efficiency of the incoming air to the engine. applied to one end while the other is restrained. This
results in a tensile load on one side of the material and a
bellows — Circular, pleated, or corrugated capsules or
compressive load on the other.
compartments used to measure pressure. They may
be either evacuated or filled with a specific pressure of bending strength — The resistance of a material to curving
inert gas and exposed to the pressure to be measured. under load and bending stresses.
Their dimensional change is measured as the pressure
Bendix fuel injection system — A continuous-flow fuel
surrounding them varies.
metering system that measures engine air consumption
Bellville washer — A lock washer made in the form of a and uses airflow forces to control fuel flow to the engine.
cupped steel washer.
benzene — A colorless, volatile, flammable, aromatic
below minimums — Weather conditions below the hydrocarbon liquid (C6H6). Used as a solvent in aircraft
minimums prescribed by regulation for the particular finishing materials.

43

10001930-002_AviationDictionary_2012_BOOK.indb 43 3/27/2012 9:37:58 AM

 Bernoulli’s principle • bi-directional cloth

Bernoulli’s principle — In physics, the interrelation beta particle — A particle emitted from the nucleus of an
between pressure, velocity, and gravitational effects atom during radioactive decay.
in moving fluids. It states that for the steady flow of a
beta range — The pitch range of a turbopropeller system
frictionless and incompressible fluid, the total energy
for ground handling and reversing whereby the propeller
(consisting of the sum of the kinetic energy due to
can be operated to provide either zero or negative thrust.
the velocity, the potential energy due to elevation in a
gravitational field, and the pressure energy given by the beta tube — An oil passage and control valve that connects
pressure divided by the density) is a constant along the crankcase oil to the propeller hub. Enables variable
flow path. An increase in velocity at constant elevation propeller pitch including beta mode.
must therefore be matched by a decrease in pressure. This
bevel — An angle other than a right angle.
principle is used to explain the lift of an airfoil, the theory
of carburetors, etc. bevel gears — A pair of toothed wheels having angled
surfaces and whose shafts are not parallel. Bevel gears
Bernoulli’s theorem — The principle that states static
permit a shaft to drive another shaft that is not parallel
pressure and velocity (RAM) pressure of a gas or fluid
to it.
passing through a duct (at constant subsonic flow rate)
are inversely proportional, i.e. total pressure does not bezel — The rim that holds the glass in an instrument case.
change.
B-H curve — A curve that shows the association between
beryllium — A hard metallic chemical element with the flux density (B) in a piece of magnetized material and
a symbol of Be and an atomic number of 4. Found in the magnetizing force (H), which is needed to produce
combination with other alloys. the flux density.
beryllium bronze — An alloy of copper which is combined biannual — Occurring twice each year.
with approximately 3% beryllium.
bias — 1. A cut, fold, or seam made diagonally to the warp
best angle‑of‑climb airspeed — The best angle‑of‑climb or fill threads of a fabric. 2. An electrical reference used
airspeed (VX) will produce the greatest gain in altitude to establish the operating condition of a semiconductor
for horizontal distance traveled. device or an electron tube. 3. In composites, a 45° angle
to the warp threads. Fabric can be formed into contoured
best economy mixture — The fuel-air mixture used in
shapes by using the bias.
reciprocating engines to achieve the greatest range of
flight. It can only be used with reduced power, as it does bias current — The current that flows in the emitter-base
not have the additional fuel needed for cooling. circuit of a transistor.
best glide speed (best L/D speed) — The airspeed that bias, forward — The polarity relationship between a power
results in the least amount of altitude loss over a given supply and a semiconductor that allows conduction.
distance. This speed is determined from the performance
bias, reverse — The polarity relationship between a
polar. The manufacturer publishes the best glide (L/D)
power supply and a semiconductor that does not allow
airspeed for specified weights and the resulting glide
conduction.
ratio. For example, a glide ratio of 36:1 means that the
glider will lose one (1) foot of altitude for every 36 feet bias voltage — The DC voltage placed on the grid of an
of forward movement in still air at this airspeed. electron tube.
best power mixture — The fuel-air mixture ratio used to bias-cut surface tape — Aircraft covering surface tape that
allow the engine to produce its maximum power. The is cut at a 45° angle to the length of the tape from selvage
best power fuel-air mixture ratio is richer than the ratio edge to selvage edge.
that is used for the best economy. It uses an excess of fuel
bicarbonate of soda — Common baking soda (NaHC03).
to provide for cooling.
It is used as a neutralizing agent for spilled battery acid.
best rate-of-climb airspeed — The best rate‑of‑climb
bicycle gear — A landing gear that supports the main
airspeed (VY) produces the maximum gain in altitude
weight of the aircraft on wheels in line with each other
per unit of time.
along the length of the fuselage. The wings are supported
beta — The current gain of a transistor when it is connected by smaller outriggers near the wing tips.
as a grounded emitter amplifier. Beta is the ratio of the
bidirectional antenna — A radio antenna that produces
change in collector current to the change in base current
maximum signal strength in two directions, 180º apart.
when the collector voltage is held constant.
bi-directional cloth — In composites, a cloth in which the
beta mode — The reverse pitch area of propeller. Used for
fibers run in various directions. Usually woven together
slowing the aircraft and maneuvering on the ground. See
in two directions.
also alpha mode.

44

10001930-002_AviationDictionary_2012_BOOK.indb 44 3/27/2012 9:37:58 AM

 bi-directional laminate • bistable multivibrator

bi-directional laminate — In composites, a laminate with binomial — An algebraic expression that contains two
the fibers oriented in more than one direction. terms connected by a plus or minus sign.
bifilar — A system developed by Sikorsky for dampening bioastronautics — The science that deals with the medical
rotor vibration. and biological aspects of astronautics.
bifilar resistor — A resistor wound of wire, which is biochemistry — Chemistry that deals with the chemical
doubled back on itself in order to decrease the amount of compounds and processes involved with living organisms.
inductance in the resistor.
biocidal action — The function of certain fuel additives
bifilar transformer — An electrical transformer in which that kill microbes and bacteria living in water in aircraft
the primary and the secondary are wound side by side to fuel tanks. This prevents scum that would promote
increase the coefficient of coupling between the windings. corrosion in these tanks. Biocidal additives are also put
in aircraft dope that is used on cotton or linen fabric to
bifurcated duct — A split exhaust duct used on turbofan or
kill the bacteria that can destroy organic fabrics.
lift fan engines.
biocidal agent — A chemical combination destructive to
bilge — The lowest part of an aircraft structure where water,
certain types of living organisms.
dirt, and other debris accumulate.
biodegradable — A condition of a material that allows it
bill of material — A list of the materials and parts necessary
to be broken down into simple products by the action of
for the fabrication or assembly of a component or a
certain types of microorganisms.
system.
biophysics — The interdisciplinary study of biological
billet — A bar of semi-finished iron or steel nearly square
phenomena and problems using the principles and
in section.
techniques of physics.
billow cloud — A cloud layer having a “herring bone”
biplane — An airplane having two wings, one placed above
appearance, these nearly parallel lines of clouds are
the other.
oriented at right angles to the wind shear.
bipolar transistor — The term used to describe either an
bimetallic circuit breaker — An electrical circuit
NPN or a PNP transistor.
protective device that consists of a sandwich of two
metals having dissimilar expansion characteristics. When birch — One of several high-grade woods used in the
current exceeds the breaker rating, one of the metals manufacturing of fixed-pitch wooden propellers.
expands more than the other causing the sandwich to
bisector of a line — A position on a line that divides it into
warp and break the circuit. Upon cooling, the circuit can
two segments of equal length.
be reconnected, sometimes automatically.
bisector of an angle — A line that divides an angle into two
bimetallic element — A device using two different metals
equal angles.
joined together to produce either a mechanical bending
or an electrical voltage as the temperature varies. bismaleimide (BMI) — In composites, a polyimide resin
that cures at a very high temperature, and has a very
bimetallic strip — Two dissimilar metals, such as chromel
high operating temperature range in the 550 – 600° F
and constantan that are in close proximity to each other,
range, and some around the 700ºF range. These are more
used in fire detection systems.
difficult to cure because of the moisture emissions during
binary coded decimal — In computing, a system of the cure may cause voids or delaminations.
encoding numbers in which each number is represented
bismuth — A hard, brittle, grayish-white, trivalent, metallic
by a series of four binary digits.
chemical element that has the symbol Bi and atomic
binary number — A number in the binary number system number 83. Used as an alloying agent for changing the
that consists of only two digits: zero and one. characteristic of certain metals. It is also used to dope
silicon or germanium to make a P-type semiconductor
binding post — A subassembly used for clamping or
material.
holding electrical conductors in a rigid position. It
commonly consists of a screw having a collar head or bistable — A condition that exists in a circuit in which
body with one or more clamping screws. either of two conditions may exist as a steady state.
binoculars — A form of hand-held optical instrument used bistable circuit — A circuit that has two stable conditions.
to look at objects that are far away. Binoculars have a set The circuit will operate in the condition selected until it
of magnifying lenses for each eye. Prisms are used to get is intentionally changed.
a high degree of magnification in a short physical length.
bistable multivibrator — An oscillator circuit that uses
Also referred to as field glasses.
two transistors of which only one transistor conducts at

45

10001930-002_AviationDictionary_2012_BOOK.indb 45 3/27/2012 9:37:58 AM

 bistatic radar • blade flapping

a time. When the first transistor stops conducting, the blade beam — A paddle-shaped lever having a slot shaped
second transistor automatically starts to conduct. to fit the cross section of a propeller blade. Used for
manually turning propeller blades. Blade beams are also
bistatic radar — A radar system that uses separate
referred to as blade wrenches.
transmitter and receiver antennas.
blade blending — A process used to remove small shallow
bit — One unit of a binary number.
scratches or dents of turbine blades using mild abrasive
bitumen — An asphaltic residue that remains after the materials and sanding techniques. Blending requires
fractional distillation of crude oil. Asphalt and tar are two maintaining the original contour and shape of the blade
commonly used bitumens. within prescribed limits.
bituminous paint — A heavy, thick, tar-based paint used as blade butt — The root end of a propeller blade that fits into
an acid-resistant paint to reduce the corrosive action of the hub of a propeller assembly.
fumes and spilled electrolytes in battery compartments.
blade chamber — The top or convex side of a rotating
black box — A piece of electronic equipment that may be airfoil such as a compressor blade.
removed and replaced as a single unit.
blade chord line — An imaginary line drawn through the
black ice — Transparent ice that forms on black pavement, blade from the leading edge to the trailing edge.
making it difficult to see. It may be caused by the
blade climbing — In rotorcraft, a condition when one
refreezing of melted water or from freezing rain. Also a
or more blades are not operating in the same plane of
thin sheet of transparent ice that forms on the surface of
rotation during flight. Might not exist during ground
water.
operation.
black light — Ultraviolet light with rays that are in the
blade coning — In rotorcraft, an upward sweep of rotor
lower end of the visible spectrum. While more or less
blades as a result of lift and centrifugal force.
invisible to the human eye, black lights excite, or make
visible, certain materials such as fluorescent dyes. blade cross over — See blade climbing.
bladder-type fuel cell — A neoprene impregnated fabric blade cuff — A metal, wood, or plastic fairing installed around
bag installed in a portion of the aircraft structure to form the shank of a propeller blade to carry the airfoil shape of
a cell and used to hold fuel. the blade all of the way to the propeller hub. The airfoil
shape of the cuff pulls cooling air into the engine nacelle.
blade — In gas turbine engines, a rotating airfoil utilized
in a compressor as a means of compressing air or in a blade dampener — A shock absorbing mechanism installed
turbine for extracting energy from the flowing gases. between a helicopter rotor blade and the hub to diminish
or dampen blade movement on the lead-lag axis.
blade alignment — In rotorcraft, an adjustment procedure,
used on semi-rigid rotor systems, to place the blades in blade droop — The angle of the spanwise axis of the
proper positions on the lead-lag axis of the rotor system. helicopter rotor at rest with only the forces of gravity
Blade alignment is sometimes referred to as chordwise acting on it.
balance.
blade face — The flat portion of a propeller blade,
blade angle — The angle between the plane of propeller resembling the bottom portion of an airfoil.
rotation and the face of the propeller blade.
blade feather/feathering — In rotorcraft, the rotation of
blade angle check and adjusting — A method used to the blade around the spanwise (pitch change) axis.
check the blade-angle setting at a predetermined blade
blade fillet — The portion of the blade closest to the base
station. The blade angle is checked using a device called
or platform. Usually an area where the least damage is
a Universal Protractor.
allowed.
blade antenna — A wide-band, quarter-wavelength antenna
blade flap — In rotorcraft, the ability of the rotor blade
used on aircraft for communications or navigation in the
to move in a vertical direction. Blades may flap
ultra-high or very-high frequency bands.
independently or in unison.
blade back — The cambered side of a propeller blade that
blade flapping — The movement of helicopter rotor blades,
corresponds to the curved upper surface of an airfoil,
about a horizontal hinge, in which the blades tend to
similar to that of an aircraft wing. The opposite side of
rise and descend as they rotate. Blade flapping tends to
the blade face.
minimize asymmetrical lift by increasing the angle of
blade base — The portion of the blade where the contoured attack of the retreating blade while decreasing the angle
section meets the root area. Also referred to as the blade of attack of the advancing blade.
platform.

46

10001930-002_AviationDictionary_2012_BOOK.indb 46 3/27/2012 9:37:58 AM

 blade grips • bleed valve

blade grips — The part of a helicopter rotor hub into which other under dynamic conditions so that all blades rotate
the blades are attached by a lead-lag hinge pin. Blade in a common plane.
grips are sometimes referred to as blade forks.
blade twist — The variation in the angle of incidence of a
blade inspection method (BIM) — A system using an blade between the root and the tip. The amount of thrust
indicator and inert gas to detect rotor blade cracking. that is produced by a propeller blade is determined by the
Used by Sikorsky Helicopter. pitch angle of the blade at each blade station, and by the
speed at which the blade is moving through the air. In
blade inspection system (BIS) — A method used by Bell
order to maintain a constant amount of thrust along the
Helicopter to determine if rotor blades have cracked.
blade, the blade angle must be twisted; however, some
blade lead or lag — In rotorcraft, the fore and aft movement degree of twist can also be caused by aerodynamic forces.
of the blade in the plane of rotation. It is sometimes called
blade wrench — A paddle-shaped lever having a slot
hunting or dragging.
shaped to fit the cross section of a propeller blade. Used
blade loading — In rotorcraft, the load imposed on rotor for manually turning propeller blades. Blade beams are
blades, determined by dividing the total weight of the also referred to as blade wrenches.
helicopter by the combined area of all the rotor blades.
blade-disk — A forged, one-piece compressor or turbine
blade root — The portion of a propeller blade that fits into blade and disk as opposed to separate blades fitted into
the propeller hub. The blade root is also called the blade a disk.
butt.
blank — To cut out the surplus material from a part, prior
blade section — A cross section of a propeller blade made to finishing.
at any point by a plane parallel to the axis of rotation of
blank blade — The identification of one blade of a
the propeller and tangent at the center of the section to an
helicopter during electronic balancing. It is the blade
arc drawn with the axis of rotation as its center.
with the single interrupter. The target blade will have the
blade shank — The thick, rounded portion of a propeller double interrupter.
blade near the hub.
blanket — 1. A sheet of insulation material in the cabin and
blade span — In rotorcraft, the length of a blade from its passenger compartments used to aid in suppressing noise.
tip to its root. 2. A shroud covering for airplane heat ducts.
blade stall — A condition of the rotor blade in flight when blanket method of recovering — The method of applying
it is operating at an angle of attack greater than the fabric to an aircraft structure so that the fabric is wrapped
maximum angle of lift. This occurs at high forward speed around the structure and attached by sewing or cementing
to the retreating blade and to all blades during “settling it in place to either the trailing edge of a wing or to the
with power.” longerons of a fuselage.
blade station — Reference points on the blade measured in blanking — The process of forcing stock material through
inches from the center of the propeller hub. Blade station a cutout in a die plate with a die that is slightly smaller,
measurements are used to identify locations along the and the same shape, as the cutout in the die plate. Creates
blade of a propeller. a shaped piece (blank) of the same shape as the punch.
blade sweeping — An adjustment of the dynamic chordwise blast fence — A sturdy structure used to prevent jet blast
balance in which one or both blades are moved aft of the damage to equipment and personnel located behind
alignment point. operating aircraft.
blade tabs — Fixed tabs mounted on the trailing edge of bleed — In composites, an escape passage at the parting
helicopter rotor blades for track adjustment. line of a mold (like a vent, but deeper), which allows
material to escape, or bleed out.
blade tip — In rotorcraft, the part of the blade the furthest
from the hub of the rotor. bleed air — Compressed air tapped from the compressor
stages of a turbine engine by use of ducts and tubing. Bleed
blade track — In rotorcraft, the relationship of the blade
air can be used for deice, anti-ice, cabin pressurization,
tips in the plane of rotation. Blades that are in track will
heating, and cooling systems.
move through the same plane of rotation.
bleed orifice — A calibrated orifice used to bleed down or
blade tracking — 1. The process of determining the
adjust the pressure in a system.
position of the tips of the propeller blades relative to each
other. 2. The mechanical procedure used to bring the bleed valve — In a turbine engine, a flapper valve, a popoff
blades of the rotor in satisfactory relationship with each valve, or a bleed band designed to bleed off a portion of
the compressor air to the atmosphere. Used to maintain

47

10001930-002_AviationDictionary_2012_BOOK.indb 47 3/27/2012 9:37:58 AM

 bleeder • blocked

blade angle of attack and provide stall-free engine blind spot — 1. An area from which radio transmissions
acceleration and deceleration. and/or radar echoes cannot be received. 2. Portion of the
airport not visible from the control tower.
bleeder — In composites, a layer of material used during
the manufacture or repair of a part to allow entrapped blind spot — An area that is not visible.
air and resin to escape. It is removed after curing. It also
blind transmission — A transmission from one station
serves as a vacuum valve contact with the part.
to other stations in circumstances where two-way
bleeder current — A current drawn from a source through communication cannot be established, but where it is
a bleeder resistor to ground. Used to stabilize the output believed that the called stations may be able to receive
voltage. the transmission.
bleeder resistance — A permanently connected resistor blind velocity [ICAO] — The radial velocity of a moving
connected across the output of a power supply and target such that the target is not seen on primary radars
designed to “bleed off” a small portion of the current. fitted with certain forms of fixed echo suppression.
bleeder resistor — The resistor of a voltage divider through blind zone — See blind spot.
which the smallest amount of current flows. This resistor
blink Zyglo — A method of Zyglo inspection wherein a
is generally selected so that the current through it is
part is cleaned and soaked with a fluorescent penetrant
about 10% of the total circuit current. Also used in power
for an appropriate length of time. The part is rinsed and
supplies to stabilize the output voltage or to bleed the
all of the penetrant is cleaned from its surface. The part is
voltage from capacitors after a component is turned off.
vibrated while it is being examined under a black light. If
bleeding — 1. The act of removing air from a system. 2. A the vibration opens up a crack that has accepted some of
maintenance procedure for purging the fuel system of air the penetrant, the crack will show up as a blinking light.
locks and to aid in flushing any traces of preservative oil
blinker — Oxygen-flow indicator acting as a moveable
from a pressure carburetor. 3. A maintenance procedure
shutter, opening and closing with each breath.
in which air is removed from the hydraulic fluid in the
brake system of an aircraft. If there is any air in the blister — 1. An enclosed raised spot on the surface of a finish
fluid in hydraulic brakes, the air will compress when the on a metal. It may be filled with vapor or with products
brakes are applied, the brakes will feel “spongy,” and of corrosion. 2. In composites, an undesirable rounded
their effectiveness will be reduced. elevation of the surface of a plastic, and somewhat
resembling in shape a blister on the human skin.
bleedout — In composites, excess resin that flows out
during the curing process, usually into a bleeder cloth. blizzard — A severe weather condition characterized by low
Sometimes appears during the filament winding process temperatures and strong winds bearing a great amount of
if the fiber has been through a resin bath. snow, either falling or picked up from the ground.
blemish — A defect or injury mark that damages an object block — To secure from, or release an airplane for flight. It
or diminishes its value. includes actions by ground crew personnel who aid the
pilot in parking, mooring, or releasing by handling the
blending — A metal filing and stoning procedure used to
wheel chocks, gear pins, etc.
recontour damaged compressor and turbine blades to an
aerodynamic shape. A fine stone is used to blend (smooth) block diagram — A functional diagram of a system in
the reworked area into the original surface of the blade. which the units are represented by squares that describe
the functions of the unit and show its relationship to the
blimp — A non-rigid airship.
other units of the system. Arrows between the blocks
blind flight — An early aviation term for instrument flying. show the direction of the flow of energy or information
within the system. Block diagrams do not show any of
blind rivet — A rivet designed
the actual components.
to be used in sheet metal
structure where it is not block heater — An electrical heater embedded in die that is
possible to use a bucking used for hot dimpling sheet metal.
bar for riveting.
block plane — A small, hand-held carpenter’s tool used for
blind speed — The rate of smoothing the surface of wood.
departure or closing of a
block test — An operational test of an aircraft engine when the
target relative to the radar
engine is installed in a test cell to determine its condition.
antenna at which cancellation of the primary radar target
by moving target indicator (MTI) circuits in the radar blocked — Phraseology used to indicate that a radio
equipment causes a reduction or complete loss of signal. transmission has been distorted or interrupted due to
See also blind velocity. multiple simultaneous radio transmissions.

48

10001930-002_AviationDictionary_2012_BOOK.indb 48 3/27/2012 9:37:58 AM

 blocking capacitor • bob weight

blocking capacitor — A capacitor that has high impedance to boundary layer control uses high-velocity air blown
DC and low frequency AC. However, it has low impedance through ducts or jets to energize the boundary layer.
to the AC signal being passed through the circuit.
blow-out plug — A safety plug or disc on the outside skin of
block-to-block time — The lapsed time between an an aircraft fuselage near the installation of high pressure
airplane leaving the ramp for the purpose of flight and its oxygen and C02, or other fire extinguisher agents. It is
returning after landing. designed to rupture and discharge its contents overboard
if, for any reason, the pressure of the gas in the cylinders
bloom — A bar of iron or steel hammered or rolled from
rises to a dangerous value. Colored disks in the blow-out
an ingot.
plugs identify the system that has been relieved in this
blow molding — A plastic molding process in which a manner.
hollow tube of thermoplastic material is heated inside a
blowtorch — A small burner having a device to intensify
mold. Air pressure is applied to the inside of the tube, and
combustion by means of a blast of air or oxygen. Usually
the soft plastic material is forced out against the walls of
includes a fuel tank pressurized by a hand pump. Used
the mold. The outside of the part takes the form of the
for soldering, welding, and glass blowing.
inside of the mold.
blue arc — An instrument marking that indicates an
blowback — In rotorcraft, the tendency of the rotor disc to
operating range. For example, the blue arc might indicate
tilt aft in forward flight as a result of flapping.
the manifold pressure gauge range in which an engine can
blowdown turbine — A power recovery device used on be operated with the carburetor control set at automatic
the Wright R-3350 engine that is driven by the exhaust lean.
gases from the engine, and coupled through a clutch to
blueprint — An engineering drawing used to convey the
the engine crankshaft. Also referred to as Power-recovery
construction or assembly of objects with the help of
turbine (PRT).
lines, notes, abbreviations, and symbols. Blueprints are
blower — 1. A mechanical device such as a fan that is made by placing a tracing of the drawing over a sheet
used to move a column of air. 2. An internal gear-driven of chemically treated paper and exposing it to a strong
supercharger in an aircraft reciprocating engine. Blowers light for a short period of time. When the exposed paper
are used to increase the pressure of the fuel/air mixture after is developed, it turns blue. The inked lines of the tracing
it has passed through the carburetor, and to improve the now show as white lines on a blue background, thus its
distribution of the fuel-air mixture to all of the cylinders. name blueprint. Blueprints have been replaced in many
engineering departments by prints.
blower clutch — A unit in a two-speed supercharger
system of a reciprocating engine that can be driven at blush — The white or grayish cast that forms on a lacquer
two different speeds by means of a clutch. or dope film, which has been applied under conditions of
too high humidity. It is actually nitrocellulose, which has
blower section — The blower section of an aircraft
precipitated from the finish.
reciprocating engine crankcase that houses the internal,
gear-driven supercharger. BMEP Indicator — An engine instrument that measures
output shaft torque and converts it to brake mean effective
blow-in doors — In gas turbine engines, spring-loaded
pressure (BMEP).
doors located ahead of the first stage of the compressor.
These doors are spring-loaded to hold them closed, but B-nut — A nut used to connect a piece of flared tubing to
under conditions of low airspeed and high engine power, a threaded fitting. B-nuts are used with a sleeve that is
they open automatically to allow more air to enter the slipped over the tubing before the tubing is flared. The
compressor. Blow-in doors help prevent compressor B-nut forces the sleeve tight against the flare, sealing
stall. Also referred to as auxiliary air-intake doors. against the flare cone of the male fitting. The B-nut
derives its nickname from its predecessor (no longer in
blowing dust — Dust particles picked up locally from the
use), which was called an A-nut.
surface and blown about in clouds or sheets.
board-foot — A commercial unit of measurement used to
blowing sand — Sand picked up locally from the surface
measure lumber. One board-foot is the amount of lumber
and blown about in clouds or sheets.
in a piece of 1-inch thick wood that measures l’ x l.’
blowing snow — Snow picked up from the surface by the
bob weight — A mechanical weight in the elevator control
wind and carried to a height of 6 feet or more.
system of some airplanes. In some aircraft it is used to
blowing spray — Water particles picked up by the wind apply a nose-down force on the elevator control system.
from the surface of a large body of water. This force is counteracted by an aerodynamic force that
is caused by the elevator trim tab. If the aircraft slows
blown boundary layer control — A system used to decrease
down enough that the aerodynamic force on the trim
aerodynamic drag on the surface of a wing. Blown

49

10001930-002_AviationDictionary_2012_BOOK.indb 49 3/27/2012 9:37:58 AM

 bogie landing gear • boosted brake

tab is lost, the bob weight forces the nose down, and voltage that is high enough to allow it to jump to another
the airplane picks up speed. In some other aircraft, a part causing radio interference.
bob weight is used to counteract rapid control inputs to
bonding agent — An adhesive used to bond structure parts
prevent overstressing the aircraft.
together.
bogie landing gear — The landing gear of an aircraft that
bonding braid — A soft annealed, tinned copper flat braid
uses tandem wheels connected by a central strut. Aircraft
used for battery grounding or bonding strap for electrical
having bogie landing gear are sometimes supported by
equipment.
outrigger wheels mounted far out on the wing when the
aircraft is parked. bonding jumper — A low-resistance wire or electrical
connection used to electrically ground a component or
bogus parts — Parts that are not approved for use in aircraft.
structure to an airframe. Bonding jumpers carry the return
Bogus parts are often illegally marked so as to appear to
current from an electrical component back to the battery.
be authorized parts. The use of bogus parts compromises
the safety of an aircraft and makes it unairworthy. bonnet assembly — The operating head of a fire
extinguisher, which contains an electrically ignited
boiling — The process whereby water changes state to
powder charge used to rupture a disc and release the
vapor throughout a fluid. Occurs when saturation vapor
extinguishing agent.
pressure equals the total air pressure.
bookmark — A means of saving addresses on the World
boiling point — Temperature at which a liquid changes
Wide Web for easy future access. Usually done by
to vapor. The boiling point of water, under standard
selecting a button on the web browser screen, it saves the
conditions, is 212°F, or 100°C.
current web address so it does not have to be input again
bolt — An externally threaded fastener with an enlarged into the computer (web addresses are often a lengthy
head on one end and threads on the other end. series of characters).
bolt bosses — The enlarged portion of a casting or forging boom — A spar or outrigger connecting the tail surfaces or
where the bolts pass through. auxiliary equipment to the main supporting structure of
an aircraft.
bomb tester — A spark plug tester in which the plug is
exposed to approximately 200 PSI of air pressure. High boost — 1. To assist. 2. An older term synonymous with
voltage is applied to the center electrode cavity of the manifold pressure.
spark plug, and the electrodes are observed to see the
boost charge — A constant-voltage charge applied to a
type and amount of spark being produced. Plugs that can
discharged battery installed in an airplane to restore a
spark in this atmosphere are considered to be acceptable
charge sufficient to start the engine.
for use in the aircraft engine.
boost pump — An electrically driven fuel pump, usually
bond — An attachment of one material to another or of a
of the centrifugal type, located in one of the fuel tanks.
finish to the metal or fabric.
It is used to provide fuel to the engine for starting and
bond ply — In composites, the ply or fabric patch which providing fuel pressure in the event of failure of the
comes in contact with the honeycomb core. engine driven pump. It also pressurizes the fuel lines to
prevent vapor lock.
bond strength — In composites, the stress required to pull
apart two plies or from the ply to the core. The amount of boost system — A hydraulically actuated system that aids
strength of the adhesion. the pilot in operation of the flight controls.
bonded structure — A structure whose parts are joined boost venturi — A small
together by chemical methods rather than mechanical venturi whose discharge
fasteners. Honeycomb material, laminated fiberglass, end is at the throat of
and composite materials are examples of aircraft bonded the main venturi, and
structure. which surrounds the main
discharge nozzle of a
Bonderizing — The registered trade name for a patented
float-type carburetor. It increases the pressure drop for a
process of covering steel parts with a phosphate coating
given airflow.
to protect the parts from corrosion.
boosted brake — A form of brake power source using a
bonding — 1. A procedure used in joining parts by using
master cylinder in which the hydraulic pressure from the
adhesives rather than any form of mechanical fastener. 2.
aircraft hydraulic power system is used to aid the pilot
A method of electrically connecting all the components
in applying force to the master cylinder. This boost, or
of an aircraft structure together so that static electricity
assistance, is automatically applied when the pressure
cannot build up on one part of the structure to create a

50

10001930-002_AviationDictionary_2012_BOOK.indb 50 3/27/2012 9:37:59 AM

 boosted control system • bow or camber

required at the brake is greater than the pilot can produce bottle bar — A special bucking bar recessed to hold a rivet
with foot pressure alone. set. It is used in reverse riveting.
boosted control system — A hydraulically actuated system bottled gas — Any of the gases kept under pressure
that aids the pilot in operation of the flight controls. (acetylene, propane, oxygen, and nitrogen) in heavy steel
containers.
booster coil — A transformer coil used with a vibrator to
produce a high voltage at the spark plugs during starting. bottom dead center (BDC) — The crankshaft position
when the piston is at the bottom extreme of its stroke,
booster magneto — A small, high-voltage magneto used
and the crank pin is below and directly in line with the
to produce a hot spark for starting reciprocating engines.
wrist pin and the center of the crankshaft.
The output for the booster magneto is fed into a trailing
finger on the distributor. This spark follows the normal bottoming reamer — A reamer used to smooth and enlarge
ignition spark. holes to exact size, but having no starting taper. A
bottoming reamer completes the reaming of blind holes by
boot — A telescoping rubber seal. Sometimes placed over
finishing the hole to size nearly to the bottom of the hole.
a cable that passes through a bulkhead separating a
pressurized and non-pressurized section, or around the bottoming tap — A tap used
portion of a strut where it telescopes into another section. to cut full threads at the
bottom of a blind hole.
bootstrapping — 1. Technique with which something is
The bottoming tap is not
brought into the desired state through its own action.
tapered. It is used after the hole has been partially tapped
Derived from the term “picking oneself up by the
with a tapered tap.
bootstraps.” 2. A condition in a turbocharged engine when
a turbocharger system senses small changes in temperature bounce — A condition where the breaker points of a
or RPM and continually changes the turbocharger output magneto tend to bounce after they close. This is caused
in an attempt to establish equilibrium. Typically occurs by a weak breaker spring.
during part-throttle operation and is characterized by a
boundary layer — 1. The layer of air between the surface
continual drift or transient increase in manifold pressure.
of an object, such as an airfoil, and the freestream air.
bore — 1. Diameter of an engine cylinder. 2. The internal At the surface of an object air particles are slowed to a
diameter of a pipe, cylinder, or hole. relative velocity of near zero due to the viscosity of the
air. Surrounding this area, the air gradually increases in
borescope — An optical tool with which a visual inspection
speed until it reaches the velocity of the freestream air
can be made inside an area that is otherwise impossible to
at a given distance from the surface. 2. The layer of the
see. It consists of a light, mirrors, and lenses.
earth’s atmosphere from surface to approximately 2,000
boric acid — A white crystal that can be dissolved in feet AGL, where surface friction influences are large.
water to make a weak acid solution. Boric acid is used
boundary layer control — A method of removing random
to neutralize spilled electrolyte from nickel-cadmium
flowing air from the immediate surface of an airfoil
batteries.
caused by the turbulent flow of the boundary layer.
boring — A process of increasing the size of a hole in a Boundary layer control is obtained by either adding
piece of material by cutting it with a rotary cutting tool. energy to it through vortex generators (added energy
delays the airflow from separating from the airfoil) or
boron — A non-metallic chemical element with a symbol
by sucking or vacuuming it off through tiny holes on the
of B and an atomic number of 5. When it is used to dope
surface of the airfoil.
silicon or germanium, it produces a P-type material.
Boron fibers are also used to add stiffness and strength to boundary lights — Lights defining the perimeter of an
some of the composite structural materials use in modern airport or landing area.
aircraft.
Bourdon tube — The mechanism in a pressure gauge
boron filament — In composites, a strong, lightweight consisting of a flat or elliptical cross-sectioned tube bent
fiber used as a reinforcement. A tungsten-filament core into a curve or spiral. When pressure is applied, the tube
with boron gas deposited on it. Has a high strength to attempts to straighten. The amount the tube straightens
weight ratio. is proportional to the amount of pressure inside the
tube, and as it straightens, it moves a pointer across the
boss — An enlarged or thickened part of a forging or casting to
instrument dial.
provide additional material for strength at its attaching point.
bow or camber — The amount that a side of a surface
deviates from being straight.

51

10001930-002_AviationDictionary_2012_BOOK.indb 51 3/27/2012 9:37:59 AM

 bow wave • braking action

bow wave — 1. The v-shaped disturbance through a fluid braid — The rubber-coated, woven metal fabric reinforcing
such as water or air as the result of being displaced by the cord used to encase hydraulic flex hoses.
foremost point of an object moving through it. 2. A shock
braided shield — A covering of braided metal over one
wave that forms immediately ahead of an aircraft that is
or more insulated conductors to form shielded cable.
flying at a speed faster than the speed of sound.
This braid intercepts the magnetic field produced by the
Bowden cable — A control system that uses a spring steel alternating current and keeps the field from causing radio
wire, enclosed inside a helically wound wire casing, used interference.
to transmit both pushing and pulling motion to the device
braiding — Weaving of fibers into a tubular shape instead
being actuated. Often used as throttle cables or mixture
of a flat fabric
control cables.
brake — 1. A device inside an aircraft wheel used to apply
bowline knot — A knot used to tie down an aircraft and to
friction to the wheel to slow or stop its rotation. Wheel
start the rib-stitching when attaching fabric to an aircraft
brakes slow the aircraft down during taxiing and landing.
structure. A properly tied bowline knot will not slip yet
Types of brakes used on aircraft are in four general
is easy to untie.
categories: shoe, expander tube, single disc, and multiple
box brake — A metal-forming machine similar to a leaf disc. 2. A metal-working shop tool that is used to make
(cornice) brake. It is used to form all four sides of a straight bends across sheets of metal. Brakes can be
box by allowing the sides that have been bent up to fit adjusted to make bends with the proper bend radius and
between the fingers of the clamp while the last bends are correct number of degrees.
being made. A box brake is also called a finger brake.
brake back plate — A retainer plate to which the wheel
box spar — A design for wood spars in the shape of a box cylinder and the brake shoes attach.
or a square. The top and bottom of the box are called the
brake caliper — The clamp in a disc brake system that
caps of the spar, and the sides of the box are called the
grips the brake disc. When pressure is applied to the
webs of the spar.
brake, the calipers apply pressure to the disc to produce
box wrench — A wrench with an enclosed end that has six, the braking action.
eight, or twelve points. It can be used to tighten or loosen
brake horsepower — The actual horsepower delivered
nuts and bolts, and can easily fit into close spaces and can
to the propeller shaft (main drive or main output) of
be used to apply a greater amount of force than can be
an aircraft engine. Prior to electronic bench testing,
applied with an open-end wrench.
horsepower was calculated by measuring the amount of
boxbeam wing — A wing construction made in the form of resistance against a flywheel brake. This method is no
a box, which uses two main longitudinal members with longer used but the term remains an industry standard.
connecting bulkheads to furnish additional contour and
brake line — The mark on a flat sheet of metal that is set
strength.
even with the nose of the radius bar of a cornice brake
boxing of paint — A mixing procedure in which the paint is and serves as a guide in bending. The brake line can
poured back-and-forth between two containers until the be located by measuring out one radius from the bend
pigment and the base paint are completely mixed. tangent line closest to the end that is to be inserted under
the nose of the brake. Also called a sight line.
Boyle’s law — A gas law, which states that at a constant
temperature the volume of the gas will vary inversely as brake lining — A material with a high coefficient of friction
its pressure changes. and the ability to withstand large amounts of heat. It acts
as the wearing surface in aircraft brakes.
brace — A device that holds parts together, or in place.
Something that gives support. brake mean-effective pressure (BMEP) — A computed
value of the average pressure that exists in the cylinder
braced wing — A wing that requires external bracing and
of an engine during the power stroke. BMEP is measured
is not self-supporting. See cantilever for contrasting
in pounds per square inch and is used to compute the
definition.
amount of power the engine is developing.
bracketing — A technique for navigating by VOR in a
brake specific fuel consumption (BSFC) — The number
crosswind, where the course is maintained by a series
of pounds of fuel burned per hour to produce one
of turns into the crosswind to regain and maintain the
horsepower in a reciprocating engine.
desired course.
braking action — A report of conditions on the airport
brad — A thin wire nail or spike that has a small-diameter
movement area providing a pilot with a degree/quality
and a small barrel-shaped head.
of braking that might be expected. Braking action is
reported in terms of good, fair, poor, or nil.

52

10001930-002_AviationDictionary_2012_BOOK.indb 52 3/27/2012 9:37:59 AM

 braking action advisories • breech chamber

braking action advisories — An air traffic control advisory breaker contact — A pair of electrical contacts that are
issued to arriving and departing aircraft to inform them opened and closed by a cam in the magneto for the
about degraded braking action. purpose of timing the ignition of a reciprocating engine.
branching — A programming technique, which allows breaker point bounce — A condition caused by a weak
users of interactive video, multimedia courseware, or breaker point spring. It is a fault in which the breaker
online training to choose from several courses of action points in an aircraft magneto bounce open rather than
in moving from one sequence to another. remaining closed when the cam follower moves off the
cam lobe.
brass — A metal alloy consisting of copper and zinc.
breaker points — Interrupter contacts in the primary
Brayton cycle — The name given to the thermodynamic
circuit of a magneto or battery ignition system. They are
cycle of a gas turbine engine to produce thrust. This is a
opened by a cam the instant the highest current flows in
varying volume, constant pressure, cycle of events and
the primary circuit, thus producing the maximum rate of
is commonly called the constant-pressure cycle. A more
collapse of the primary field.
recent term is continuous combustion cycle because
of the four continuous and constant events: intake, breakers — On tires, extra layers of reinforcing nylon chord
compression, expansion (including power), and exhaust. fabric are placed under the tread rubber to protect casing
plies and strengthen tread area. Breakers are considered
brazier-head rivet — A form of aircraft rivet with a large
an integral part of the carcass construction.
thin head. Its specification is AN 455. These rivets have
been superseded in use by AN 470 (MS 20470) universal breakout — 1. In composites, when drilling or cutting the
head rivets. edges of a composite part, the fibers may separate or
break. 2. A technique to direct aircraft out of the approach
brazing — Refers to a group of metal-joining processes in
stream. In the context of close parallel operations, a
which the bonding material is a nonferrous metal or alloy
breakout is used to direct threatened aircraft away from a
with a melting point higher than 800°F. It is a method of
deviating aircraft.
joining two pieces of metal by wetting their surface with
a molten alloy of copper, zinc, and tin. The brazed joint breast drill — A drill designed to hold a larger size twist
has more strength than a soldered joint but less than a drill than the hand drill, and is used to drill relatively
welded joint. large holes in wood. A breast plate affixed at the upper
end of the drill permits the use of body weight to increase
breadboard (electronics) — A structure that allows
the pressure on the drill.
electronic circuits to be constructed with components
that are not permanently connected. Allows circuits to be breather — 1. A vent in an engine oil system that keeps
tested and modified before being put into a permanent pressure within the tank the same as the atmospheric
configuration. pressure. 2. In composites, a loosely woven fabric that
does not come in contact with the resin and used to
break line — A line used in drawings to indicate that a
provide venting and pressure uniformly under a vacuum
portion of the object is not shown.
cure. Breather material is used under the vacuum valve to
break-away point — Refers to an intentionally weakened allow the air to be evacuated inside the vacuum bagged
point on a shaft such as in a dual element fuel pump. part. Removed after curing.
The shear point is designed to break away if one
breather pressure system — The breather pressurizing
element becomes jammed, leaving the other element still
system ensures a proper oil spray pattern from the main
functioning.
bearing oil jets and furnishes a pressure head to the
break-before-make switch — A double-throw switch that scavenge system.
breaks one circuit before it makes contact with the other
breather pressurizing valve — An aneroid-operated valve
circuit.
and a spring loaded blowoff valve. Pressurization is
breakdown voltage — The voltage at which the dielectric provided by compressor air that leaks by the seals and
is ruptured, or the voltage level in a gas tube at which the enters the oil system. At sea level pressure the breather
gas becomes ionized and starts to conduct. pressurizing valve is open. It closes gradually with
increasing altitude and maintains an oil system pressure
breaker assembly — A mechanism used in high-tension
sufficient to assure oil flows similar to those at sea level.
magneto ignition systems to automatically open and
close the primary circuit at the proper time in relation breech chamber — The component of a self-contained
to piston position in the cylinder to which an ignition cartridge/pneumatic starter for gas turbine engines. A
spark is being furnished. The interruption of the primary solid propellant cartridge is placed in the breech chamber.
current flow is accomplished through a pair of breaker When electrically ignited, it produces a low pressure,
contact points.

53

10001930-002_AviationDictionary_2012_BOOK.indb 53 3/27/2012 9:37:59 AM

 bridge circuit • bubble memory (computer)

high-volume pneumatic source to turn the turbine blades broken-line — A graph using sharp, abrupt changes in the
fast enough to enable starting the engine. information line.
bridge circuit — An electrical circuit that contains four broken-line graph — A graph that represents the way in
impedances connected in such a way that their schematic which values change. The horizontal axis of the graph
diagram forms a square. One pair of diagonally opposite represents one value, and the vertical axis represents
corners is connected to an input device, and the other two another value. Straight lines are used to connect points
corners are connected to the output device. that show true values at each plotted point.
bridge rectifier — An electrical rectifier circuit using four bromochlorodifluoromethane (Halon 1211) — Chemical
diodes arranged in a bridge circuit to change AC to DC. formula (CBrClF2). A liquefied gas with a UL toxicity
rating of 5, used as a fire extinguishing agent. It is
bridging — In composites, this term can refer to plies of colorless, non-corrosive and evaporates rapidly without
fabric over a curved edge that don’t come in full contact leaving residue. It does not freeze or cause cold burns
with the core material. It is also used to describe excess and will not harm fabrics, metals, or other materials it
resin that has formed on edges during the curing process. contacts. Halon 1211 acts rapidly on fires by producing
briefing — An oral presentation where the speaker presents a heavy blanketing mist that eliminates air from the fire
a concise array of facts without inclusion of extensive and interferes chemically with the combustion process.
supporting material. bromotrifluoromethane (Halon 1301) — Chemical
brine — A solution of salt (sodium chloride) and water formula (CF3Br). A liquefied gas with a UL toxicity
used as a quenching agent in the heat treatment of metal. rating of 6, used as a fire extinguishing agent. It has
Greater hardness is obtained from quenching in salt all the characteristics of Halon 1211. The significant
brine, and less in oil, than is obtained by the use of water. difference between the two is that Halon 1211 throws a
spray similar to C02 while Halon 1301 has a vapor spray
Brinell hardness test — A test used to determine the that is more difficult to direct.
hardness of a metal by forcing a hardened steel sphere
into the surface with a given force. The diameter of the bronze — An alloy of copper and tin. Used for bearing
indention, measured with a special microscope, is directly surfaces.
related to the hardness of the material.
brush — 1. A component device in an electric generator or
brinelling — Indentations in bearing races usually caused motor designed to provide an electrical contact between a
by high static loads or application of force during stationary conductor and a rotating element. Brushes are
installation or removal. They are usually rounded or made of a carbon compound that contacts each segment
spherical due to the impressions left by contacting balls of a rotating commutator. The brush conducts voltage
or the rollers of the bearing. between the rotating armature and an external circuit. 2.
A device composed of bristles or hairs fastened to a wood
bristle brush — A brush with non-metallic bristles
or plastic handle. Brushes are used to apply paint or other
constructed of short, stiff, coarse hair or filament. Bristle
substances to a surface.
brushes are used to clean metal parts to prevent metal
particles from becoming embedded in the structural brush guard — A protective device used to guard the tail
metal, which could cause dissimilar metal corrosion. rotor blades of a helicopter from damage during ground
operations.
British Thermal Unit (BTU) — A unit of heat. One BTU
equals the heat energy required to raise one pound of brush run-in — The procedure of running a motor or
water one degree Fahrenheit (e.g. one pound of jet fuel generator for a time after installing new brushes to allow
contains approximately 18,600 BTU). the brushes to shape themselves to the commutator. Also
brittleness — The propensity of a material to break when referred to as brush break-in.
bent, deformed, or hammered. Brittleness is the resistance brushing — A motion that barely touches an object in
to change in the relative position of the molecules within passing.
the material.
BTU — See British thermal unit.
broaching — The process of removing metal by pushing or
pulling a cutting tool, called a broach, along the surface. bubble — A small space filled with a volume of air or gas
entrapped in a liquid.
broad-band antenna — An antenna constructed in such a
way as to receive or transmit a wide range of frequencies. bubble memory (computer) — Non-volatile memory.
Consists of a thin layer of material normally magnetized
broadcast — The transmission of radio waves without in one direction. When an oppositely polarized magnetic
intent of receiving information. One way communication. field is applied to a circular area of this substance, the
area is reduced to a smaller circle, or bubble. The bit of

54

10001930-002_AviationDictionary_2012_BOOK.indb 54 3/27/2012 9:37:59 AM

 bubble octant • bungee cord

information is thus stored until changed by application of buffeting — Erratic movement of aircraft controls caused
a new magnetic field. by the turbulent flow of air over the surfaces.
bubble octant — A celestial navigation instrument, like the bug — An unexpected malfunction.
sextant, that uses a bubble level in the octant to provide an
bug light — A tool made up of an electrical wire, flashlight
artificial horizon that allows a navigator to find the angle
battery, and bulb used to check the continuity of an
between a line tangent to the earth’s surface (the horizon)
electrical circuit.
and a line to the stars that are used for navigation.
building block concept — Concept of learning that new
bucker — The person holding the bucking bar used to upset
skills and knowledge are best based on a solid foundation
a rivet.
of previous experience or knowledge. As knowledge
bucket — Accepted jargon for turbine blade. and skill increase, the base expands, supporting further
learning. Also referred to as blocks of learning.
bucket root — A method of turbine disk blade retention in
which the blade root has a stop made on one end of the build-up and vent valve — A manually operated valve on a
root so that the blade can be inserted and removed in one liquid oxygen converter. In the build-up position, pressure
direction only, while on the opposite end is a tang. This is allowed to reach a preset value and excess pressure is
tang is bent to secure the blade in the disk. vented into the atmosphere. In the vent position, gas is
vented into the atmosphere without pressure buildup.
bucket wheel — Slang for turbine wheel in turbine engines.
bulb angle — An extruded angle of metal with a rounded
bucking — The coordinated process between the bucking
edge resembling a bulb on one of the legs.
bar holder and the pneumatic rivet gun operator, whereby
a shop head is formed on a solid rivet. A special hardened bulb root — A means by which turbine engine rotor blades
steel bar is held against the rivet shank, which has been are attached to the rotor hub. The base of the blade is
inserted into a hole drilled in metal to be joined, while cylindrical and larger than the rest of the blade. This fits
the pneumatic hammer is held at the rivet head during into a mated hole in the rotor hub.
the hammering.
bulb temperature — A unit of a carburetor induction
bucking bar — A tool made of alloy steel stock that is held system that monitors the air inlet temperature to be sure
against the shank end of a rivet while the shop head is the inlet temperature does not exceed the maximum value
being formed. specified by the engine manufacturer.
buckle — A bend or kink in or on a surface of a metal bulbed Cherrylock® rivet — A special form of blind rivet
structure. Caused by the failure of the part under a manufactured by the Cherry division of Textron Inc.,
compressive load or excessive localized heating. in which the stem is locked into the hollow shank by a
special locking collar that swages into a groove in the
buckle line — In composites, on a honeycomb core, it is
stem.
a line of collapsed cells with undistorted cells on either
side. It usually is found on the inside of the radius on a bulb-fit — A design of compressor blade attachment to the
formed core. disk shaped in a bulb fashion.
buckled areas — Localized areas in a turbine engine bulkhead — A structural partition in a fuselage or wing.
combustion chamber liner in which small areas have Bulkheads usually divide the fuselage or wing into bays
been heated to an extent to cause the area to buckle. and provide additional strength to the structure.
buckling — In composites, a failure of the fabric in which bumping — The shaping or forming of sheet metal by
it deflects up or down rather than breaking. hammering or pounding. During this process, the metal
is supported by a dolly, sandbag, or die.
buffer — 1. Any device used to absorb shock. 2. Used
to isolate an input or to strengthen a signal in a digital bundled cable — Any number of individually insulated
electronic circuit to match inputs and outputs having electrical wires tied together with lacing cord or with
differing values. special plastic wire-wrapping straps.
buffer amplifier — An amplifier in a transmitter circuit bungee — A shock-absorber cord made from natural rubber
designed to isolate the oscillator section from the power strands encased in a braided cover of woven cotton cords
section thus preventing a frequency shift or otherwise and then treated to resist oxidation and wear.
operate improperly.
bungee cord — An elastic cord encased in a braided cloth
buffet — A series of waves or blows caused by imbalance cover that holds and protects the rubber, yet allows the
such as those that can occur with flight controls. The rubber to stretch. Bungee cords are used in some of the
aircraft feels as though it were being hit with a series of simpler aircraft landing gears to assist in retracting the
blows, shocks, or waves. landing gear and to absorb shock.

55

10001930-002_AviationDictionary_2012_BOOK.indb 55 3/27/2012 9:37:59 AM

 buntover • butyrate dope

buntover — The tendency of a gyroplane to pitch forward A lubricant is usually required. Small scratches can be
when rotor force is removed. smoothed by burnishing.
buoyancy — The property of an object that allows it to burnishing — The process of polishing a surface by sliding
float on the surface of a liquid, or ascend through and contact with a smooth, harder surface. Displacement
remain freely suspended in a compressible fluid such as or removal of metal does usually not occur during
the atmosphere. burnishing.
burble — A breakdown of the laminar airflow over an burr — A sharp or roughened projection of metal usually
airfoil caused by too high an angle of attack. The result is resulting from machine processing.
an increase in drag and a loss of lift.
burring — The forming of a sharp or roughened projection
burble point — The angle of attack at which burbling first usually as a result of a machining operation.
occurs on an airfoil.
burst RPM — The RPM at which the blades of a turbine
burn down coat — A coat of dope with some of its thinner motor will separate from the rotor due to excessive
replaced with retarder. The coat is sprayed on a blushed centrifugal loads.
area to soften and reflow the surface in order to remove
bus — A main electrical power circuit to which a number of
the blush.
component circuits connect.
burned areas — Localized areas of a turbine engine
bus bar — An electrical power distribution point to which
combustion chamber liner that have been heated to an
several circuits may be connected. It is often a solid metal
extent to cause visible damage.
strip having a number of terminals installed on it.
burned surface — A condition resulting from high
bushing — A removable cylindrical lining for an opening
surface temperatures with relatively low pressures and
used to minimize resistance and serve as a guide.
accompanied by heat discoloration. This condition may or
may not mark the surface. The cause is usually improper butt fusion — A method of joining two pieces of
clearance or insufficient lubrication. Areas affected are thermoplastic material. Butt fusion is done by heating the
bearings or journals. ends of the two pieces until they are in a molten state and
forcing them together before they cool and harden.
burner — The section of a turbine engine into which fuel
is injected and burned. The point within the engine where butt joint — A welded joint made by placing two pieces of
combustion occurs. material edge to edge, so that there is no overlapping, and
then welding them to form one piece. The types of butt
burner cans — Any number of individual combustion
joints are: flanged, plain, single bevel, and double bevel.
chambers in the combustion section of a gas turbine
engine. butt rib — The last rib at the inboard end of an airfoil. The
rib on a wing which is closest to the wing attachment
burner compartment — A section of the cowling behind
fittings.
which the burner section of a turbine engine is located.
butterfly tail — A design that
burner pressure (Pb) — Static pressure signal used as a
combines the vertical and
measure of mass airflow through the engine and sent to
horizontal surfaces of the
the fuel control unit for fuel scheduling purposes.
empennage. The shape is
burning — 1. Surface damage due to excessive heat. It is that of a “V.”
usually caused by improper fit, defective lubrication, or
butterfly valve — A damper or valve consisting of a disk
over temperature operation. 2. The combustion process
turning about one of its diameters to control the flow of
that occurs when fuel is mixed with air and ignited.
fluid in a round tube.
burning in — An electronic components manufacturing
buttock line — A measurement of width, left or right of,
process in which the equipment is operated for a
and parallel to, the longitudinal axis. Also referred to as
specified period of time in order to stabilize the operating
BL or butt line.
characteristics of the components.
butyl — The trade name of a synthetic rubber product made
burning point — The lowest temperature at which a
by the polymerization of isobutylene. It withstands such
petroleum product in an open container will ignite and
potent chemicals as Skydrol hydraulic fluid.
continue to burn when an open flame is held near its
surface. butyrate dope — A finish for aircraft fabric consisting of
a film base of cellulose fibers dissolved in acetic and
burnish — To polish a metal surface by rubbing it with
butyric acids, with the necessary plasticizers, solvents,
a smooth, extremely hard tool, called a burnishing tool.
and thinners.

56

10001930-002_AviationDictionary_2012_BOOK.indb 56 3/27/2012 9:37:59 AM

 Buys-Ballot’s law • byte

Buys-Ballot’s law — A law of meteorology which states

that if a person stands in the Northern Hemisphere
with the wind striking at their back, the center of the
low-pressure area, around which the wind is blowing, is
ahead and to the left.
buzz — In turbine engines, an airflow instability that
occurs when a shock wave is alternately swallowed and
regurgitated by the inlet. At its worst, the condition can
cause violent fluctuations in pressure through the inlet,
which may result in damage to the inlet structure or,
possibly, to the engine itself.
bypass capacitor — A capacitor that provides a
low-impedance path for alternating current to bypass a
circuit component, when the component is being used to
produce a DC voltage drop.
bypass duct — A cold airstream duct. Also referred to as a
fan exhaust duct on a turbofan engine.
bypass jacket — An annular bypass around an oil cooler
through which oil flows when it does not need cooling.
bypass jet — A form of turbojet engine in which a portion
of the compressor air is bypassed around the combustion
chamber and into the tailpipe.
bypass ratio — 1. The ratio of the mass airflow in pounds
per second through the fan section of a turbofan engine
to the mass airflow that passes through the gas generator
portion of the engine. 2. Ratio between fan mass airflow
(lb/sec.) and core engine mass airflow (lb/sec.).
bypass turbojet engine — Forerunner of the bypass fan
engine, whereby the low pressure compressor discharge
is divided in two; one portion of air to enter a bypass
duct and the other portion of air to enter the high pressure
compressor inlet.
bypass valve — A valve whose function is to maintain a
constant system pressure. When the system pressure is
exceeded by a predetermined amount, the valve will
allow excess pressures to bypass the system, thereby, not
allowing the system to rupture from excess pressure.
byte — A computer term used to describe a group of binary
digits consisting of eight bits.

57

10001930-002_AviationDictionary_2012_BOOK.indb 57 3/27/2012 9:37:59 AM

 C • calibration curve, instrument

C cadmium cell — A basic unit of the nickel-cadmium battery.

It consists of positive and negative plates, separators,
C battery — A small, low-voltage battery. Also referred to electrolyte, a cell vent, and a cell container. The
as a C-cell battery or C-cell. positive plates are made from porous plaque on which
nickel-hydroxide is deposited. The negative plates are
C check — The intermediate level of inspection in a made from similar plaques on which cadmium-hydroxide
Continuous Airworthiness Maintenance Program. The is deposited. The voltage that is produced by a cadmium
entire program consists of A, C, and D checks. cell at 20°C is 1.0186 volts.
cabane — An arrangement of struts used to support a wing cadmium plating — A thin coating of cadmium metal
above the fuselage of an airplane. Such an airplane wing electroplated on a steel part to protect the steel from
attachment is called a parasol. corrosion. This is accomplished by the cadmium serving
cabin — That portion of an aircraft used for cargo and/or as the anode in a corrosive action.
passengers. caging device — A mechanism used in a gyroscopic
cabin altitude — Cabin pressure in terms of equivalent instrument to erect the rotor of a gyro to its normal
altitude above sea level. operating position prior to flight or after tumbling.
cabin differential pressure — The difference between the caging system — See caging device.
pressure inside a cabin and the outside air pressure. The calcium — A hard metallic element with a symbol of Ca
maximum cabin differential pressure is determined by and an atomic number of 20. Used as an alloying element
the aircraft structural strength. with other metals.
cabin pressure regulator — A means of controlling cabin calcium carbide — A combination of calcium and carbon.
pressure by regulating the outflow of air from the cabin. Reacts chemically with water to produce acetylene gas.
cabin pressurization safety valve — A combination calculated landing time — A term that can be used in place
pressure and vacuum relief and dump valve used to of tentative or actual calculated landing time, whichever
prevent cabin pressurization exceeding safe limits. applies.
cabin supercharger — Mechanical air pumps used to calendar month — The measure of time used by the Federal
provide the air pressure for cabin pressurization. Aviation Administration for inspections and certification
cabinet file — A coarse file that is flat on one face, and purposes. A calendar month ends at midnight of the last
rounded on the other face, used for metalworking and day of the month, regardless of the day it began.
woodworking. Sometimes referred to as a half-round file. calendering — The process of dipping cotton yarn or fabric
cable — 1. In common usage, any heavy conductor. 2. into a hot solution of caustic soda to shrink the material
In electronics, two or more conductive paths bound and give it greater strength and luster.
into a single package. 3. A group of insulated electric calibrate — A procedure in which the indication of an
conductors usually covered with rubber or plastic to form instrument is compared with a standard value in order
a flexible transmission line. 4. A stranded wire generally to inspect and correct the graduations of a measuring
composed of a number of wires enclosed in a single device.
bundle or group.
calibrated airspeed (CAS) — The indicated airspeed of
cable control — The system of operating aircraft controls an aircraft, corrected for position and instrument error.
by the use of high-strength flexible steel cables. Calibrated airspeed is equal to true airspeed in standard
cable drum — A cylindrically shaped spool around which atmosphere at sea level.
a control cable is wound to increase the amount of cable calibrated orifice — A hole with a specific internal diameter
moved each time the handle is turned. used to measure or control the amount of flow through it.
cable guard — A pin installed in the flange of a control calibration — Testing the accuracy of a measuring
cable pulley bracket to prevent the cable from jumping instrument or scale by comparing it with a known
out of the pulley grooves. standard.
cable rigging tension chart — Charts showing the calibration card — A card mounted on an instrument panel
relationship between control cable tension and near an instrument to show the errors in an instrument
temperature. in order for the pilot to apply an appropriate correction.
cadmium — A bluish-white, malleable, ductile, toxic, calibration curve, instrument — A curve on a graph
metallic chemical element with a symbol of Cd and an plotted to show the instrument errors at different points
atomic number of 48. on the scale of the instrument. The pilot uses the curve

58

10001930-002_AviationDictionary_2012_BOOK.indb 58 3/27/2012 9:37:59 AM

 californium • cannibalize

to interpolate the error at points between those that have the wheels of an aircraft are from the vertical. If the top
been plotted. of the wheel tilts outward, the camber is positive; if it tilts
inward, the camber is negative.
californium — A radioactive, synthetically pro­duced
element with a symbol of Cf and an atomic number of 98. cambric — A finely woven cotton or linen material.
call for release — Wherein the overlying ARTCC requires cam-ground piston — An aircraft engine piston ground
a terminal facility to initiate verbal coordination to secure in such a way that its diameter parallel to the wrist pin
ARTCC approval for release of a departure into the boss is less than its diameter perpendicular to the boss.
enroute environment. When the piston reaches its operating temperature, the
difference in mass has caused the piston to expand to a
callouts — Numbers or names used to identify components
perfect circular form.
or parts in an aircraft drawing. Callouts are placed near
the part being identified and are connected by a thin Camlock fastener — A patented
leader line. cowling fastener in which a hard
steel pin is turned in a special
call-up — Initial voice contact between a facility and an
cam-shaped receptacle.
aircraft, using the identification of the unit being called
and the unit initiating the call. camshaft — A long shaft running
parallel to the crankshaft of an
calm — The absence of wind or of apparent motion of the
inline or horizontally opposed
air.
reciprocating engine. Lobes are
calorie — The amount of heat required to raise the ground at intervals along its length to operate the valves
temperature of one gram of water 1°C. through push rods and rocker arms.
calorimeter — An apparatus for measuring specific heat. can tap valve — A valve fastened onto a small can of Freon
refrigerant. It punctures the can seal and controls the flow
cam — An eccentric plate or shaft used to impart motion to
of refrigerant.
a follower riding on its surface or edge.
Canadian Minimum Navigation Performance
cam dwell — The cam dwell is the number of degrees the
Specification Airspace — That portion of Canadian
cam rotates between the time the breaker points close and
domestic airspace within which MNPS (Minimum
the time they open.
Navigation Performance Specification) separation may
cam lobe — An eccentric used to change rotary motion be applied.
into linear motion. For example, the cam followers that
can-annular combustor — Can annular combustion
operate valves ride on the cam lobes and as the cam shaft
chambers arranged radially around the axis of a gas
rotates, the cam lobes move the cam followers up and
turbine engine. The combustion chambers are enclosed
down in a direction that is perpendicular to the axis of
in a movable steel shroud, which covers the entire burner
the cam shaft.
section, and is designed for more complete cooling and
cam nose — The peak, or highest point on a cam, that mixing of fuel and air. The burners are interconnected by
pushes up on the cam follower. projecting flame tubes that facilitate the engine-starting
process.
cam pawl — A special device that allows a wheel or gear to
turn in one direction but prevents its from turning in the canard — 1. The forward wing of a canard config­uration
opposite direction. and may be a fixed, movable, or variable geometry
surface, with or without control surfaces. 2. An aircraft
cam plate — In radial-engines, a disc or plate with lobes
with its horizontal stabilizing and control surfaces in front
machined onto its circumference. Cam followers ride on
of the wings. Also used to describe the forward-mounted
the lobes and open the engine valves through a system of
control surface.
push rods and rocker arms.
canard configuration — A configuration in which the span
cam ring — An open cam plate driven by teeth around its
of the forward wing is substantially less than that of the
circumference.
main wing.
camber — 1. The curvature of
candela — A unit of incandescent intensity.
an air­foil above and below
the chord line surface. An candlepower — The luminous intensity of light expressed
airfoil is often described as having an upper and lower in candelas.
camber. 2. The mean camber of an airfoil section is a line
cannibalize — To remove serviceable parts from a
drawn through a series of points located midway between
non-flying aircraft for use on another machine.
the upper and the lower camber. 3. The amount of angle

59

10001930-002_AviationDictionary_2012_BOOK.indb 59 3/27/2012 9:38:00 AM

 cannon connector • capacitor-start induction motor

cannon connector — A connector used to attach the battery (amount) of charge in coulombs, and E is the electrical
to the aircraft electrical system. It is a high-current pressure in volts.
connector in which the cables are held onto the battery
capacitance box — An electronic device used to select a
by pressure applied by a hand screw.
capacitance to insert into a circuit for testing purposes.
canopy — 1. A transparent cover for the airplane’s cockpit.
capacitance bridge — A null-type precision measuring
It provides streamlining and protection for the pilot
instrument used to measure capacitance.
against the elements. Sometimes referred to as a cockpit
canopy. 2. The large, umbrella-shaped material of a capacitance-type fuel gauging system — A fuel quantity
parachute. indicating system using the fuel as the dielectric of a
capacitor. It measures the weight of the fuel instead of
canted bulkhead — A bulkhead or wall that is slanted
its volume.
(canted) vertically.
capacitive coupling — The use of a capacitor or capacitors
cantilever — A beam or other member that is supported at
to connect electronic circuits. This type coupling allows
or near only one end, without external bracing.
AC to pass through and blocks DC.
cantilever wing — A cantilever wing uses no external wing
capacitive electrical load — An electrical load that
struts. All of its support is obtained inside the wing itself.
produces more capacitive reactance than inductive
can-type combustor — A combustor, or burner section of reactance in the circuit.
a gas turbine engine, made up of eight to ten individual
capacitive feedback — A process of feeding a portion of
burner cans. These cans are long cylinders that consist of
the output of a circuit through a capacitor back into the
an outer case or housing within which there is a perforated
input section of the circuit. Can allow the circuit to be
stainless steel combustion chamber liner or inner liner.
somewhat self-regulating.
The can-type combustors are arranged radially around the
axis of the engine. Compressed air from the compressor capacitive reactance (XC) — The opposition to the flow of
flows through the cans and fuel is sprayed into them and alternating current electricity caused by the capacitance in
burned to add energy to the air. Cooling air flows through a circuit, and is measured in ohms. Capacitive reactance
holes in the inner liners to keep the temperature of the is calculated using the capacitance of the circuit and the
liners low enough so that they will not be damaged. frequency of the AC.
canvas — A heavy, woven coarse cloth generally made of capacitive time constant — The amount of time, determined
cotton. by the resistance of the circuit and by the capacitance
of the capacitor, measured in seconds, needed for the
cap —The longitudinal members at the top and bottom of
voltage across a capacitor to rise to 63% of the source
a beam that resist most of the bending loads because of
voltage.
their strength in compression and tension.
capacitor — A device used to store electrical energy in the
cap cloud — A standing or stationary cap‑like cloud
form of electrostatic fields. A capacitor is essentially two
forming on mountain or ridge tops due to cooling of
conductors separated by an insulator.
moist air rising on the upwind side followed by warming
and drying of downdrafts on the lee side. Also referred to capacitor-discharge ignition system — An ignition system
as a Foehn cloud. consisting of two identical independent ignition units
operating from a common low-voltage DC electrical
cap screw — A threaded fastener. The head of the cap screw
power source, the aircraft battery. A high voltage,
that, when turned with a wrench, clamps two pieces of
supplied by the ignition exciter unit, charges a storage
material together.
capacitor with a charge, up to four joules, that generates
cap strip — Cap strips are extrusions, formed angles, or an arc across a wide igniter spark gap to ignite the fuel.
milled sections to which the web is attached. These
capacitor-input filter — An electronic filter used to smooth
members carry the loads caused by wing bending and
out the pulsations in the output of an electrical power
also provide a foundation for attaching the skin.
supply. A capacitor-input filter is installed in parallel with
capacitance — The ability of an insulator to store electrical the rectifier output, and an inductor is installed in series
energy in the form of electrostatic fields, expressed in with the rectifier output.
farads. The amount of electricity a capacitor can store
capacitor-start induction motor — An AC motor whose
depends on several factors, including the type of material
rotor is excited by voltage induced from the field
of the dielectric. It is directly proportional to the plate
windings. A second winding whose phase is shifted by a
area and inversely proportional to the distance between
capacitor is used to provide a rotating field for starting.
the plates. The formula for capacitance is C=Q/E, in
When the motor gets up to speed, a centrifugal switch
which C is the capacitance in farads, Q is the quantity
opens the circuit in which the capacitor is situated.

60

10001930-002_AviationDictionary_2012_BOOK.indb 60 3/27/2012 9:38:00 AM

 capacitor-type ignition system • carbon monoxide detector

capacitor-type ignition system — An ignition system carbon arc — An electric arc, produced by a welding
consisting of two identical independent ignition units machine, that jumps between two carbon electrodes or
operating from a common low-voltage DC electrical from a carbon electrode to a metal electrode. A carbon arc
power source, the aircraft battery. A high voltage, supplied makes an intensely bright light and produces enough heat
by the ignition exciter unit, charges a storage capacitor (approximately 10,000°F) to melt metals for welding or
with a charge, up to four joules, which generates an arc cutting.
across a wide igniter spark gap to ignite the fuel.
carbon arc lamp — An electrical lamp in which an electric
cape chisel — A cold chisel used when cutting square arc between carbon electrodes produces a high-intensity
comers or slots. light.
capillary action — An action causing a liquid to be drawn carbon black — A soft and fluffy carbon deposit. Carbon
up into extremely tiny tubes or between close-fitting black is produced by the incomplete burning of acetylene
parts. gas when the flame does not have enough oxygen for
complete combustion.
capillary tube — A tube with a very small bore used to
meter a fluid or transmit pressure of fluid or gas to an carbon brake — An aircraft brake required for extremely
indicating gauge. high energy dissipation. Both the rotating and stationary
discs are made of pure carbon.
capping stable layer — The elevated stable layer found
on top of a convective boundary layer. Usually marks a carbon composition resistor — A resistor formed by
sharp transition between smooth air above and turbulent embedding wire leads in a cylindrical slug of carbon and
air below. filler material. Usually covered with an epoxy or other
plastic insulating jacket.
capstan — A spool-shaped device in the control system
of an aircraft similar to a grooved drum-like wheel. A carbon deposits — Residue from overheated oil or
control cable is wound around the capstan, and the ends incompletely burned gasoline. It forms as a hard, black
of the guide are attached to the aileron, the elevator, or crust inside the engine.
the rudder control cable.
carbon dioxide (CO2) — A colorless, odorless,
capstan screw — A special purpose machine screw with nonflammable gas often used as a fire extinguishing
holes across the head to accommodate a bar that can be agent in aircraft.
passed through these holes to turn the screw.
carbon fiber — Produced by placing carbon (an element) in
captive balloon — An aerial platform anchored to the an inert atmosphere at temperatures above 1,800°F. Used
ground. as a reinforcing material. Carbon fiber is a lightweight,
high strength and high stiffness fiber. The material can be
captive screw — A fastener that has the ability to turn in the
graphitized by heat-treating at a very high temperature.
body in which it is mounted, but which will not drop out
when it is unscrewed from the part it is holding. carbon fouling — A carbon deposit that forms as a result of
overly rich, idle fuel/air mixtures. The carbon forms on
capture — The process by which small droplets are swept up
the inside of combustion chambers and spark plugs.
by faster-falling large droplets. Also called coalescence.
carbon knock — The pre-ignition of the fuel/air charge
carbide drill — A specially manufactured cutting drill
inside the cylinder of a reciprocating engine before the
that has a cutting edges surfaced with tungsten carbide,
engine is ready for ignition to occur. Caused by the
tantalum carbide, or titanium carbide.
glowing of carbon deposits.
carbide tool — A metal-cutting machine tool that has
carbon microphone — A microphone used in telephones
cutting faces surfaced with either tungsten carbide,
and some types of radio transmitters. It consists of a
tantalum carbide, or titanium carbide.
flexible diaphragm of carbon granules. Sound waves
carbo-blast — A grit blast. Field cleaning agent, a pressing against the microphone change its resistance,
lignocellulose material consisting of ground up walnut thus modulating the voltage and creating the electronic
shells and apricot pits. signal that is transmitted to a receiver.
Carboloy — A brand name of certain cutting tools and dies carbon monoxide (CO) — A colorless, odorless, highly
having tungsten carbide bonded to their cutting surface. toxic gas that forms from incomplete combustion of a
hydrocarbon fuel.
carbon — Nonmetallic element with a symbol of C and
an atomic weight of 6. Carbon is a part of all organic carbon monoxide detector — A device used to detect the
compounds. It ranges in appearance from black, fluffy presence and concentration of carbon monoxide gas.
soot, to hard, transparent diamond.

61

10001930-002_AviationDictionary_2012_BOOK.indb 61 3/27/2012 9:38:00 AM

 carbon oil seal • carburetor ice

carbon oil seal — An oil seal used in gas turbine engines. carbon/graphite fiber or fabric — A fiber used in advanced
These seals are usually spring loaded and are similar composites comprised of carbon filaments which may be
in material and application to the carbon brushes used woven together. The terms carbon and graphite have been
in electrical motors. Carbon seals rest against a surface used interchangeably for years. The Americans prefer
to prevent oil from leaking out along the shaft into the the term graphite, while the Europeans prefer carbon.
compressor airflow or the turbine sections. Depending on the manufacturer of the aircraft, different
terms may be used. The term Carbon/Graphite is used
carbon pile resistor — A variable resistor used in some
throughout this book to include both terms.
electrical equipment. A carbon pile is made of a stack
of thin, pure carbon disks. Its resistance is changed by carbon-zinc cell — A portable primary cell such as a
varying the amount of pressure applied to the stack. flashlight battery consisting of a carbon rod placed in a
can made of zinc and filled with a paste of ammonium
carbon pile voltage regulator — A voltage regulator that
chloride. The chemical reaction between the paste and
depends on the resistance of a number of carbon disks
zinc causes electrons to leave the zinc can and travel
arranged in a pile or stack. The resistance of the carbon
through an external circuit to the carbon rod.
stack varies inversely with the pressure applied. When
the stack is compressed under appreciable pressure, the carborundum — A manufactured aluminum oxide abrasive
resistance in the stack is less. Pressure on the carbon similar to natural emery. It is used for grinding wheels
pile depends upon two opposing forces: a spring and and abrasive papers.
an electromagnet. The spring compresses the carbon
carburetor — 1. Pressure: A hydromechanical device
pile, and the electromagnet exerts a pull that decreases
employing a closed feed system from the fuel pump to
the pressure. When the generator voltage varies, the
the discharge nozzle. It meters fuel through fixed jets
pull of the electromagnet varies, thereby increasing or
according to the mass airflow through the throttle body
decreasing the pressure on the disks. This change allows
and discharges it under a positive pressure. Pressure
a change in the generator output voltage.
carburetors are distinctly different from float-type
carbon resistor — An electrical component used to put a carburetors, as they do not incorporate a vented float
controlled amount of resistance in an electrical circuit. chamber or suction pickup from a discharge nozzle located
Carbon resistors are composed of a rod of compressed in the venturi tube. 2. Float-type: Consists essentially of
graphite and binding material with wire leads, called a main air passage through which the engine draws its
“pigtail” leads, attached to each end of the resistor. supply of air, a mechanism to control the quantity of fuel
Colored bands marked on the resistor indicate its discharged in relation to the flow of air, and a means of
resistance value. regulating the quantity of fuel/air mixture delivered to
the engine cylinders.
carbon seal — A heat-resistant device used in turbine
engines to seal the lubricating oil in the bearing cavity. A carburetor air temperature — The temperature of
ring of carbon material rides on a highly polished metal the induction air before it enters the carburetor. The
surface to prevent lubricating oil from seeping into the temperature of the air as it enters the carburetor must be
gas path. Usually located at main bearings. controlled to keep the fuel/air mixture temperature high
enough to prevent water from condensing out of the air
carbon steel — A group of iron alloys having carbon as the
and freezing and low enough to prevent detonation.
principal alloying agent. Low-carbon steel contains less
than 0.20% carbon and is not as strong as high-carbon carburetor float — A component between the fuel supply
steel that contains up to 0.95% carbon. and the metering system of a carburetor. The float
carbon tetrachloride (Halon 104) — Once used as a fire chamber provides a nearly constant level of fuel to the
extinguishing agent. A chemical formula CCl4, a liquid main discharge nozzle. The float is connected to a needle
with a UL toxicity rating of 3. When used as a fire valve and seat that meters the correct amount of fuel to
extinguishing agent it becomes very toxic and harmful to the induction system according to the demand.
humans and other animals. carburetor heater — A heater muff or jacket installed
carbon tracking — A fine track of carbon deposited inside around the exhaust manifold through which induction air
the magneto, distributor, or terminal cavity of a spark is drawn to warm it before it enters the carburetor. This
plug as a result of a flashover. It acts as an electrical heat prevents the formation of carburetor ice.
conductor to ground or to another electrical lead. carburetor ice — Ice that forms inside the carburetor due
carbonaceous — Containing carbon. to the temperature drop caused by the vaporization of
the fuel. Induction system icing is an operational hazard
carbon-film resistor — An electrical resistor composed because it can cut off the flow of the fuel/air charge or
of a thin film of carbon on a ceramic cylinder. Wires vary the fuel/air ratio.
connected to each end of the carbon film allow the
resistor to be connected to an electrical circuit.
62

10001930-002_AviationDictionary_2012_BOOK.indb 62 3/27/2012 9:38:00 AM

 carburetor icing • castle nut

carburetor icing — Occurs when moist air is drawn into cascade electrical circuits — A system of connecting
the carburetor and is cooled to a dewpoint temperature multiple levels of electrical circuits so that the output of
less than 0º C. one level feeds the input of the next level.
carburetor maintenance — Maintenance that may include cascade thrust reverser — A configuration of thrust
idle speed adjustment, removal and installation, adjusting reverser used in turbojet engines in which thin airfoils
idle mixtures, rigging, and inspection of carburetors. or obstructions are placed in the engine’s exhaust stream
to duct the high-velocity exhaust gases forward. This
carburizing — A form of case hardening of steel in which
decreases the airplane’s landing roll. Also referred to as
carbon is infused into the surface of the steel to increase
an aerodynamic thrust reverser.
its hardness.
cascade transformer — A device used in an electrical
carburizing flame — A
circuit to generate a high voltage. A system of connecting
flame used in oxy­acetylene
multiple levels of electrical step-up transformers
welding in which there is
where the output of one level feeds into the next level
an excess of acetylene gas. Also called a reducing flame.
transformer, cascading until the required high-output
This type of flame introduces carbon into the steel. It can
voltage is obtained.
be recognized by the greenish-white, brush-like second
cone at the tip of the first cone. The outer flame is slightly cascade vane — An air turning vane. One common use is
luminous and has about the same appearance as an in thrust reversers.
acetylene flame burning freely in air alone.
case hardening — A form of heat treatment of a metal in
cardinal altitudes — Full thousands of feet of altitude or flight which the surface is made extremely hard and brittle
level. (3,000 feet/4,000 feet/etc. or FL 330/FL 340/etc.) while the core of the metal retains its toughness.
cardinal flight levels — See cardinal altitudes. case pressure — A low pressure maintained inside the case
of a hydraulic pump. In the event of a damaged seal, fluid
cardinal headings — Headings along the four main points
will be forced out of the pump rather than allowing air to
of a compass: North, South, East, and West.
be drawn in.
cardioid microphone — A microphone with the ability to
casein glue — A form of powdered glue made from milk.
pick up sounds ahead of it, rejecting sounds behind it.
Casein glues are widely used in wood aircraft repair
cargo — Freight transported in an airplane. work. For aircraft use, casein glues should contain
suitable preservatives such as the chlorinated phenols
cargo aircraft — An airplane whose main function is to
and their sodium salts, to increase resistance to organic
carry freight.
deterioration under high humidity.
carrier frequency — The high frequency alternating
casing — The rubber and fabric body of a pneumatic tire.
current that produces the electromagnetic waves that
The casing is the same as the carcass of the tire. It is
radiate from a radio transmitting antenna.
composed of diagonal layers of rubber-coated fabric cord
carrier wave — The high frequency alternating current that (running at right angles to one another), providing the
can be modulated to carry intelligence by propagation as strength of a tire.
a radio wave.
casing plies, aircraft tires — Diagonal, strength-providing
cartridge fuse — A fuse used to protect an electrical circuit layers of rubber-coated nylon cord fabric (running at
from an excess of current. It consists of a fusible link held right angles to one another).
between metal rings, or caps, that screw onto each end of
cast iron — Iron that contains 6% to 8% carbon and silicon.
an insulating tube.
Cast iron is a hard unmalleable pig iron made by casting.
cartridge starter — An engine starting device that uses
cast-aluminum alloy — Aluminum alloy that has been
electrically ignited solid fuel pellets. The pressure is used
heated to its molten state and poured into a mold to give
to move a piston to start a reciprocating engine or to turn
it a desired shape.
a turbine wheel to start a turbine engine.
castle nut — A general
cartridge-pneumatic starter — A combination air-turbine
purpose hexagonal nut for
starter and cartridge starter. It can be operated by bleed air
aircraft or engine use Their
or by an explosive charge, both of which exhaust through
shape resembles a castle
a turbine wheel connected to a reduction gearbox. Its
with the slots between the
purpose is to start main engines.
“turrets” used for locking
cartridge-type filter — A disposable filter element. Used the nut to the bolt with cotter pins.
for both fuel and oil systems.

63

10001930-002_AviationDictionary_2012_BOOK.indb 63 3/27/2012 9:38:00 AM

 catalyst • catwalk

catalyst — A material used to bring about a change, or category IIIA operations — An ILS approach and landing
speeds up the rate of change of a chemical action, but with no decision height (DH), or a DH below 100 feet
does not actually enter into the change itself. (30 meters), and controlling runway visual range not less
than 700 feet (200 meters).
catalytic cracking — A method of refining petroleum
products in which a catalyst is used to change category IIIB operations — An ILS approach and landing
high-boiling-point hydrocarbons into low-boiling-point with no DH, or with a DH below 50 feet (15 meters), and
hydrocarbons. controlling runway visual range less than 700 feet (200
meters), but not less than 150 feet (50 meters).
catalyzed material — A material whose cure is initiated by
the addition of a catalyst. category IIIC operations — An ILS approach and landing
with no DH and no runway visual range limitation. Also
catalyzed resin — A term used to describe the resin mixture
known as zero-zero landing.
after it has been mixed with the catalyst or hardener. It
may still be in the workable state. catenary curve — A curve formed by a flexible cord or
rope suspended between two points at the same level.
catapult — A mechanism used to launch an object into the
air. Catapults are used to launch heavily loaded aircraft catenary thermal shield — A curved sheet metal section
from the decks of aircraft carriers at a high rate of speed. between turbine wheels of a particular set. It serves as a
heat barrier between the gas path and the inner portion of
category — 1. As used with respect to the certification,
a drum- type turbine wheel.
ratings, privileges, and limitations of airmen, means
a broad classification of aircraft. Examples include: cathedral — The downslope of the wings from the
airplane; rotorcraft; glider; and lighter-than-air. 2. As fuselage. It is the opposite of dihedral. Airplanes that
used with respect to the certification of aircraft, means a employ cathedral have an increase in maneuverability
grouping of aircraft based upon intended use or operating but a decrease in stability.
limitations. Examples include: transport, normal, utility,
cathode — 1. The negative terminal of a semiconductor
acrobatic, limited, restricted, and provisional.
diode or the element in an electron tube from which
category A — With respect to transport category rotorcraft, the electrons are emitted. 2. An active element in an
means multiengine rotorcraft designed with engine and electrochemical cell that loses oxygen in the chemical
system isolation features specified in Part 29 and utilizing action that causes electrons to flow.
scheduled takeoff and landing operations under a critical
cathode of a semiconductor diode — The end of a
engine failure concept which assures adequate designated
semiconductor diode made of N-type material.
surface area and adequate performance capability for
continued safe flight in the event of engine failure. cathode protection — A material more anodic than the
material being protected is attached to or plated on the
category B — With respect to transport category rotorcraft,
material, which then becomes the cathode and is not
means single-engine or multiengine rotorcraft which
corroded. Also referred to as sacrificial corrosion
do not fully meet all Category A standards. Category B
rotorcraft have no guaranteed stay-up ability in the event Cathode-ray oscilloscope — An electrical measuring
of engine failure and unscheduled landing is assumed. instrument in which the readout is on the surface of a
tube similar to that in a television set. Electrons are
category II operation — With respect to the operation
made to strike the inside of the tube where they cause the
of aircraft, this is a straight-in ILS approach to the
coating of the tube to glow. Recurring voltage changes
runway of an airport, under a category II ILS instrument
are displayed on the tube in the form of a green line.
approach procedure issued by the Administrator or other
appropriate authority. cathode-ray tube (CRT) — An electron tube in which a
stream of electrons (cathode rays) from an electron gun
category II operations — With respect to the operation
impinges upon a fluorescent screen, thus producing a
of aircraft, means a straight-in ILS approach to the
bright spot on the screen. The electron beam is deflected
runway of an airport under a Category II ILS instrument
electrically or magnetically to produce patterns on the
approach procedure issued by the Administrator or other
screen. Also referred to as a display tube.
appropriate authority.
cation — A positive charged ion that moves toward the
category III operations — With respect to the operation of
cathode in the process of electrolysis.
aircraft, means an ILS approach to, and landing on, the
runway of an airport using a Category III ILS instrument catwalk — A narrow walkway (as along a bridge or elevated
approach procedure issued by the Administrator or other on the side of a building).
appropriate authority.

64

10001930-002_AviationDictionary_2012_BOOK.indb 64 3/27/2012 9:38:00 AM

 caul plates • center head

caul plates — In composites, smooth plates used during the from the compressor flows through the cans and fuel is
cure process to apply pressure in a uniform manner. sprayed into them and burned to add energy to the air.
Cooling air flows through holes in the inner liners to keep
caustic material — Any substance having the ability
the temperature of the liners low enough so that they will
of burning, corroding, or eroding other substances by
not be damaged.
chemical action.
Celluloid — The registered trade name of a thermoplastic
caustic soda — A common name for sodium hydroxide.
material consisting essentially of cellulose nitrate and
cavitation — A partial vacuum of an area of low pressure camphor.
behind an object that is moving in a fluid.
cellulose — A material that comes from the cell walls of
cavity — A hole or hollow within a body or structure. plants and is the raw material of many manufactured
goods.
C-clamp — A metal clamp
in the general shape of the cellulose acetate butyrate — A compound formed by the
letter C. It is used to exert action of acetic and butyric acid on cellulose.
pressure and to temporarily
cellulose acetate butyrate dope — An aircraft dope
hold objects together.
having a cellulose acetate butyrate film base and suitable
C-D inlet or exhaust — 1. plasticizers, along with the necessary solvents and
Inlet. The forward section diluents. Butyrate dope has a better tautening effect on
is convergent to increase fabric and is less flammable than nitrate dope.
air pressure and reduce air
cellulose nitrate — A compound formed by treating
velocity to subsonic speed. The aft section is divergent
cellulose with a mixture of nitric and sulfuric acids.
to increase air pressure still further and slow airflow to
approximately Mach 0.5 before entering the engine. 2. cellulose nitrate dope — Aircraft dope consisting of a
Exhaust. The forward section is convergent to increase nitrocellulose film base with the appropriate plasticizers,
gas pressure. The aft section is divergent to increase gas thinners, and solvents. It has excellent encapsulating
velocity to supersonic speed. This arrangement is necessary properties, but its high flammability has caused its
in order for the aircraft to attain supersonic speed. decrease in popularity as a finish for fabric covered
aircraft.
Ceconite — A fabric woven from polyester fibers.
Celsius (C) — A temperature scale with zero degrees as the
ceiling — In meteorology in the U.S., (1) the height above
melting point of pure ice and 100 degrees as the boiling
the surface of the base of the lowest layer of clouds or
point of pure water at standard sea level atmospheric
obscuring phenomena aloft that hides more than half of
pressure.
the sky, or (2) the vertical visibility into an obscuration.
CENRAP — See center radar ARTS presentation/
ceiling balloon — A small balloon used to determine the
processing.
height of a cloud base or the extent of vertical visibility.
CENRAP-plus — See center radar ARTS presen­tation/
ceiling light — A light used by weather observers to measure
processing-plus.
the height of the bottom of a layer of clouds at night.
center — 1. A point that is equally distant from the sides or
ceilometer — A device used to measure the height of the
outer boundaries of something. The middle. 2. Air Route
bottom layer of clouds above a weather station. Consists
Traffic Control Center.
of a light transmitter and receiver separated by a known
horizontal distance. A beam of light shines on the cloud center console — The space between the pilot and copilot
layer and height is calculated using trigonometry. where the power lever control system is positioned on
most multi-engine airplanes.
celestial dome — The hemisphere of the sky as observed
from a point on the ground. center drill — A combination of a twist drill and a 60°
countersink. Used to center a hole and a countersink in
celestial navigation — Navigating by use of the stars and sun.
a piece of metal.
cellular combustor — A combustor, or burner section
of a gas turbine engine, that is made up of eight to ten center head — A tool, in a
individual burner cans. These cans are long cylinders that combination measuring set,
consist of an outer case or housing within which there used for finding the center
is a perforated stainless steel combustion chamber liner of circular objects such as a
or inner liner. The can-type combustors are arranged piece of round bar stock.
radially around the axis of the engine. Compressed air

65

10001930-002_AviationDictionary_2012_BOOK.indb 65 3/27/2012 9:38:00 AM

 center line • Central Processing Unit (CPU)

center line — In aircraft drawings, the alter­nate long and Center Weather Advisory (CWA) — Unscheduled
short dashes indicating the center of an object or part of in-flight, flow control, air traffic, and air crew advisory.
an object. These can be a supplement to an existing SIGMET/
AIRMET, or when conditions are observed or expected
center of airfoil moments — The point about which the
to adversely affect air traffic.
basic airfoil moment coefficients are given, usually the
aerodynamic center. centering — In gliders, adjusting circles while thermalling
to provide the greatest average climb.
center of gravity (CG) — The theoretical point where
the entire weight of the airplane is considered to be centerline thrust — An aircraft design for multi-engine
concentrated. airplanes that eliminates engine-out asymmetrical thrust
and asymmetrical drag. Mounting the engines along
center of gravity envelope —
the fuselage centerline eliminates directional control
A graphic depiction of the
problems of the conventional twin following an engine
fore-and-aft range of center
failure. However, the loss of an engine can still reduce
of gravity limits, showing
climb performance significantly. Airplanes incorporating
the way these limits vary
centerline thrust do not have a published Vmc speed.
with the gross weight of the
Pilots who receive a multi-engine rating in an airplane of
aircraft.
this type have the restriction “Limited to Center Thrust”
center of gravity limits — placed on their pilot certificates. This restriction can
The extreme forward and rearward positions at which the be removed when they subsequently demonstrate the
center of gravity of an aircraft may be located. maneuver during a practical test in a conventional twin.
center of gravity range — The distance between the center-of-rotation line — The line on a drawing about
forward and rearward center of gravity limits, as specified which an object will rotate.
on the Type Certificate Data Sheet for the aircraft.
center’s area — The specified airspace within which an air
center of lift — The resultant of all of the centers of route traffic control center (ARTCC) provides air traffic
pressures of an airfoil. control and advisory service.
center of mass — The location within an aircraft at which center-tapped winding — A winding on an electrical
its entire mass can be considered to be in equilibrium. transformer that has a connection (tap) located in its
electrical center. It is used to divide the winding in half.
center of pressure — The point along the wing chord line
where lift is considered to be concentrated. centervent system — Use of the main rotorshaft as an
air-oil separator in place of a driven centrifugal device.
center of pressure coefficient — The ratio of the distance
After separation, oil is scavenged back to the oil reservoir
of the center of pressure from the leading edge to the
and air, which was entrained in the oil, is vented through
chord length.
the rotorshaft into the gas path in the area of the turbine
center of thrust — The resultant of all of the thrust forces wheel.
of the propellers or the exhaust jet stream.
centigrade — Formerly used for Celsius temper­ature.
center punch — A punch having a somewhat blunt point,
centigrade temperature scale — Same as Celsius
used to form an indentation in sheet metal that can be
temperature scale.
used to start the twist drill.
centimeter‑gram‑second (cgs) system — Metric system
center radar arts presentation/processing (CENRAP)
of measurement using the centimeter as the basic unit
— A computer program developed to provide a back-up
of measurement of length, the gram as the basic unit for
system for airport surveillance radar in the event of a
weight, and the second as the basic unit for time.
failure or malfunction. The program uses air route traffic
control center radar for the processing and presentation centistoke — A unit of viscosity measurement of both fuels
of data on the ARTS IIA or IIIA displays. and oils. 1/100 of a “stoke.”
center radar arts presentation/processing-plus Central East Pacific — An organized route system between
(CENRAP-plus) — A computer program developed to the U.S. West Coast and Hawaii.
provide a back-up system for airport surveillance radar
Central Processing Unit (CPU) — The main processing
in the event of a terminal secondary radar system failure.
portion of a computer. The CPU stores and operates on
The program uses a combination of Air Route Traffic
data, provides time signals, and performs arithmetic/
Control Center Radar and terminal airport surveillance
logic functions.
radar primary targets displayed simultaneously for the
processing and presentation of data on the ARTS IIA or
IIIA displays.
66

10001930-002_AviationDictionary_2012_BOOK.indb 66 3/27/2012 9:38:01 AM

 central refueling system • certified tower radar display (CTRD)

central refueling system — An aircraft fuel system in centrifugal twisting force — The centrifugal forces acting
which all tanks may be filled from one fueling point. on a propeller blade. The twisting force is present in all
Also referred to as a single-point refueling system or a rotating propellers and always acts to send the blades
pressure refueling system. toward a lower pitch position.
centrifugal — An apparent force that opposes centripetal centrifugal twisting moment — The tendency of a
force, resulting from the effect of inertia during a turn. propeller blade to twist on its axis due to the centrifugal
forces acting on the blade. The twisting moment is
centrifugal brake — A friction brake used to apply friction
present in all rotating propellers and always acts to send
if the unit rotating turns at a speed that is faster than is
the blades toward a lower pitch position.
permitted.
centrifugal-type pump — A pump that uses a high-speed
centrifugal breather — A centrifugal device through
impeller to throw the fluid outward at a high velocity.
which oil laden air from the vent subsystem passes.
Oil is returned to the reservoir and air exits back to the centrifuge — A device used to separate a liquid mixture
atmosphere. or a suspension into its various components that have
different specific gravities.
centrifugal clutch — A friction clutch that engages when
a drive wheel reaches a predetermined speed. The clutch centrifuge action — A force that tends to separate particles
is engaged by centrifugal force that acts on a flyweight according to their density, or to pull an object apart by
mechanism. rotating it rapidly about its center.
centrifugal filter — A filtering element that separates centrifuging — A method of separating particles of varying
contaminants from a fluid by centrifugal action. It throws density by spinning them in a centrifuge.
contaminants by rotary motion into traps that hold them
centripetal force — The force within a body that opposes
until they can be removed.
the centrifugal force as the body rotates or spins.
centrifugal flow compressor — An impeller-shaped device
centroid — The center of mass of a body or a point about
that receives air at its center and slings air outward at
which all of its mass is concentrated.
high velocity into a diffuser for increased pressure. Also
referred to as a radial outflow compressor. ceramic — A clay-like material composed primarily of
magnesium and aluminum oxide, which may be molded
centrifugal force — The apparent force that an object
and fired to produce an excellent insulating material.
moving along a circular path exerts on the body
constraining the object and that acts outwardly away ceramic magnet — A permanent magnet made by
from the center of rotation. compressing a mixture of ceramic material and sintered
magnetic particles.
centrifugal force — The outward pull on a body as it
rotates or spins. CERAP — See combined center-RAPCON.
centrifugal moment — A force that tries to produce a certificate — An official Federal Aviation Administration
rotation caused by the amount of centrifugal force acting document authorizing a privilege, fact, or legal concept.
on an object.
certificated — An object or person that has been granted
centrifugal oil filter — A rotary filtering element used to a certificate of approval, usually by the Federal Aviation
throw contaminants outward into sediment traps. Administration.
centrifugal pump — Any pump that uses a high-speed certificated aircraft — An aircraft designed to meet
impeller to throw the fluid outward by centrifugal action. minimum specifications and requirements specified
by the Federal Aviation Admin­istration. When these
centrifugal switch — An electrical switch mounted inside
conditions are met, an Approved Type Certificate is
of a rotating induction motor of a capacitor-starter.
issued for the aircraft. In order for the aircraft to maintain
The switch, actuated by centrifugal force, disconnects
the certificate (to be considered legally airworthy) it must
the starter winding when the rotor is turning at a
be maintained in such a way that it continues to meet
predetermined speed.
these specifications.
centrifugal tachometer — A mechanical tachometer that
certificated technician — A person who holds a valid
measures the speed of a rotating shaft. Flyweights are
technician’s certificate issued by the Federal Aviation
mounted on a collar around the rotating shaft in such
Administration with either an Airframe or Powerplant
away that centrifugal force pulls the flyweights away
rating, or both ratings.
from the shaft. As the flyweights move away from the
shaft, the collar moves up the shaft causing a pointer to certified tower radar display (CTRD) — A radar display
move over a dial registering the shaft speed. that provides a presentation of primary, beacon radar

67

10001930-002_AviationDictionary_2012_BOOK.indb 67 3/27/2012 9:38:01 AM

 cesium • channel iron

videos, and alphanumeric data from an Air Traffic chafing strip — See chafing tape.
Control radar system, which is certified by the FAA to
chafing tape — Cloth or paper tape placed over a metal
provide radar services. Examples include Digital Bright
seam or protruding screw head that is to be covered with
Radar Indicator Tower Equipment (DBRITE), Tower
fabric. It is used to protect the fabric from wear.
Display Workstation (TDW) and BRITE.
chain gear — A gear or sprocket used to transmit motion
cesium — A soft, ductile, bluish-gray metallic chemical
from one shaft to another shaft connected by a roller
element with a symbol of Cs and an atomic weight of 55.
chain similar to that used in a bicycle.
Used in the manufacture of photoelectric cells.
chain hoist — A mechanism used in a shop to lift heavy
cesium-barium 137 — A radioactive substance used to coat
weights. A chain hoist uses an endless loop of chain to
ignition system air-gap points to synchronize discharge
drive a geared wheel that also supports and lifts the load
of current to the igniter plug.
as it is pulled up by the geared wheel.
CFI renewal — A process that allows CFIs to renew their
chain reaction — A self-sustaining action in which one
certificates since flight instructor certificates are only
event causes other events to happen.
valid for 24 months. CFI renewal is not automatic by any
means since it requires a specific certificate action by the chaining — Combines behaviors students already know to
FAA. Certificate renewal should be in accordance with assemble more complex behaviors.
FAR Part 61.197 by any of the following methods. A CFI
chamfer — A bevel cut on the edge of a piece of material.
can present the FAA with a record of training that shows
endorsement of at least 5 students for a practical test for chamfered point of a threaded fastener — The point of a
a certificate or rating, and at least 80% of the students bolt or a screw formed in the shape of a cone with its top
passed on their first attempt. A CFI can also show the cut off. The chamfered point allows easy entry into the
FAA a satisfactory record as a Part 121 or 135 check pilot, hole for starting.
chief flight instructor, check airman or flight instructor,
chamfered tooth — The tooth of the gear on the rotating
or that he or she is in a position involving the regular
magnet or the distributor gear which is beveled to identify
evaluation of pilots. Graduation from an approved flight
it for use when timing the magneto.
instructor refresher course (FIRC), consisting of at least
16 hours of ground and/or flight training, also may be the chamois — A piece of soft leather used to filter gasoline.
basis of renewing certificates at the discretion of the FAA. Gasoline will pass through a chamois, but water will not.
Gasoline that has been filtered through a chamois can be
CFR engine — An engine used by Cooperative Fuel
considered to be free from water.
Research to determine the octane rating of a hydrocarbon
fuel. A CFR engine has a variable compression ratio, chandelle — A maximum performance 180º climbing turn.
and it can cause any of the fuels that are being tested to It involves continual changes in pitch, bank, airspeed,
detonate. When the correct percentages of iso-octane are and control pressures. During the maneuver, the airspeed
obtained, an octane number is given to the fuel. gradually decreases from the entry speed to a few knots
above stall speed at the completion of the 180º turn.
Chadwick balancer — The electronic balancing or tracking of
rotor blades. It is manufactured by Chadwick-Helmuth, Inc. change of state — The transformation of a substance from
one form (state) to another such as a solid changing to a
chafe — To wear away by a rubbing action.
liquid. In meteorology, a change of state usually refers to
chafed surface — A surface resulting from a slight relative the change of water from one form to another.
movement between two surfaces under high contact
Examples include: condensation – vapor to liquid;
pressure. The surface of each part reveals metal removed
evaporation – liquid to vapor; sublimation – solid (ice) to
and metal added.
vapor; freezing – liquid to solid; melting – solid to liquid.
chafers — In tires, layers of fabric and rubber that protect
changeover point (COP) — The point at which a pilot
the tire carcass from damage during mounting and
changes frequencies between navigation aids when other
demounting. They insulate the carcass from brake
than the midpoint on an airway.
heat and provide a good seal against movement during
dynamic operations. channel — A metal structural member either extruded or
bent into a U-shape
chaff — Thin, narrow metallic reflectors of various lengths
and frequency responses, used to reflect radar energy. These channel iron — Extruded steel
reflectors, when dropped from aircraft and allowed to drift either extruded or bent into a
downward, result in large targets on the radar display. U-shape.
chafing — Rubbing action between adjacent or contacting
parts under light pressure which results in wear.

68

10001930-002_AviationDictionary_2012_BOOK.indb 68 3/27/2012 9:38:01 AM

 channel section • check list

channel section — A form of structural material that has permanent change appears on revised charts. Enroute
the cross sectional shape of a channel or the letter U. chart numbers / panel numbers / letters and area chart
identifiers are included for each entry in the enroute
characteristic curves — 1. A series of graphically
portion of the chart NOTAMs. To avoid duplication
presented curves that describe in mathematical terms
of information in combined Enroute and Terminal
the characteristics of lift and drag produced by an airfoil
Chart NOTAMs, navaid conditions, except for ILS
section. 2. A graph that shows the performance of an
components, are listed only in the Enroute portion of
electron tube or a transistor under various operating
the Chart NOTAMs. All times are local unless otherwise
conditions.
indicated. Arrows indicate new or revised information.
characteristic potential difference — The theoretical Chart NOTAMs are only an abbreviated service. Always
potential difference produced by a chemical cell using ask for pertinent NOTAMs prior to flight.
specific pole materials.
charted VFR flyways — Charted VFR Flyways are flight
characteristics of learning — Effective learning shares paths recommended for use to bypass areas heavily
several common characteristics. Learning is dynamic and traversed by large turbine-powered aircraft. Pilot
should be purposeful, based on experience, multifaceted, compliance with recommended flyways and associated
and involve an active process. altitudes is strictly voluntary. VFR Flyway Planning
charts are published on the back of existing VFR Terminal
charcoal — Black porous carbon.
Area charts.
charge — 1. A quantity of electricity. If the charged material
charted visual flight procedure (CVFP) approach — An
holds a greater number of electrons than normal, it is said
approach conducted while operating on an instrument
to be negatively charged. If the material has a deficiency
flight rules (IFR) flight plan which authorizes the pilot
of electrons, it is positively charged. 2. The physical
of an aircraft to proceed visually and clear of clouds to
condition that gives rise to an electric field.
the airport via visual landmarks and other information
charging a battery — The preparation of battery for service depicted on a charted visual flight procedure. This
by passing low-voltage DC through the battery in the approach must be authorized and under the control of the
opposite direction of normal battery output. A lead acid appropriate air traffic control facility. Weather minimums
battery should be recharged when a cell has a hydrometer required are depicted on the chart.
reading of 1.240 or below. A fully charged battery reads
chase — An aircraft flown in proximity to another aircraft
about 1.300 on the hydrometer.
normally to observe its performance during training or
charging current — A current passed through a secondary testing.
cell that restores the active material on the plates to a
chase aircraft — See Chase.
condition that allows them to change chemical energy
into electrical energy. chasing threads — The process of cutting screw threads
by moving a tool along the surface of the work to be
charging stand — A handy and compact arrangement of
threaded.
air conditioning service equipment containing a vacuum
pump, manifold set, and a method of measuring and chassis — An aluminum, copper, or plated steel body around
dispensing the refrigerant. which an electronic unit is built. It serves as the support
for the electronic components, power supply, etc., and is
Charles’ law — A law of physics which states that if a gas
often used as a voltage reference point.
is held at a constant pressure, it will expand in direct
relationship to the increase in its absolute temperature. chassis ground — In electricity, a ground connected to the
case or chassis of electronic equipment. See also earth
chart — 1. A pictorial presentation of data. 2. A graph.
ground.
3. A graphic representation of the operation of engine
performance, fuel consumption, horsepower, or limitation chattering brakes — A heavy vibration in the brakes
of some specific unit. 4. A map. produced by the brake friction as the disks rotate.
Chattering can be caused by glazed discs.
chart, navigation — A special map used for aerial
navigation that gives the location and the necessary check flight — A test flight to check the aircraft performance
information about all of the navigation aids. A chart after major re-work or repairs.
shows the grids of latitude and longitude and provides a
check list — A sequential systematic list of specific
surface for plotting courses and locating fixes.
procedures to be followed when performing any
chart NOTAMS — Jeppesen Chart NOTAMs include complex operation. For example, check lists are used
significant information changes affecting Enroute, in the performance of preflight inspections, 100-hour
Area, and Terminal charts. Entries are published until inspections, and annual inspections of aircraft to ensure
the temporary condition no longer exists, or until the all required operations are completed.

69

10001930-002_AviationDictionary_2012_BOOK.indb 69 3/27/2012 9:38:01 AM

 check nut • chlorate candle

check nut — A thin nut jammed against another nut to Cherry® rivet — A form of
prevent it from loosening. blind rivet patented and
manufactured by the Cherry
check valve — A valve that allows free flow of fluid in one
division of Textron, Inc.
direction but prevents or restricts fluid from flowing in
An upset head is formed by
the opposite direction.
pulling the tapered stem through its hollow shank.
checklist — A systematic list of items and equipment on
chevron seal — A single-direction seal in a hydraulic or
board an aircraft intended for reference, verification,
pneumatic actuator. It derives its name from its V-shaped
or identification. An essential tool for safely flying the
(chevron) cross section.
airplane.
chilled iron — Cast iron that has been cast in a steel mold.
checkpoint — A navigation location identified either
The casting is quickly cooled by the steel mold so that
visually or electronically.
it retains most of the carbon as well as a high degree of
cheesecloth — A lightweight cotton gauze that has no hardness.
sizing in it. It is used as a polishing cloth or as a straining
chin — An aircraft structure that sticks out from the bottom
element to remove lumps and contaminants from liquids.
of the forward part of the fuselage.
chemical bond — An adhesive agent that is applied to two
chine — The longitudinal member on the side of a float or
or more parts or pieces. Joins them together by molecular
seaplane hull where the bottom and the side meet.
attraction
chine tire — A nose wheel tire that has a deflector molded
chemical compound — The substance formed by the
into its sidewall. Chine tires are mounted on the nose
chemical reaction between two or more chemical
wheel of jet aircraft and prevent water, ice, snow, and
elements.
slush from getting into the intake of the engines by
chemical element — A fundamental substance that consists throwing the water and slush outward and away from the
of atoms of only one kind. Examples of chemical elements engines.
include oxygen, carbon, gold, silver, and hydrogen.
chinook — A warm, dry wind that blows down the eastern
chemical energy — The energy stored in chemicals due to slopes of the Rocky Mountains into the United States
their attraction to or reaction with other chemicals. from Canada. The moisture in the air of a chinook is
almost completely lost as it blows up the western slopes
chemical etching — 1. A process in which small cracks in
of the mountains, and it is dry and warm as it blows down
aluminum are detected by application of a caustic soda
the eastern slopes.
solution. 2. A chemical process used to etch (roughen) the
surface of metal in preparation for priming or painting. chip — 1. A small fragment of metal removed from a
surface by cutting with a tool. 2. An electronic component
chemical fire extinguisher — A fire extinguisher
containing an integrated circuit.
that extinguishes fire by expelling a chemical fire
extinguishing agent. chip detector — An electrical metal detection warning
system. A magnetic sump or drain plug with an electrode
chemical milling — A chemical etching process used
at its center and with ground potential at its casing.
to machine large sheets of metal. Chemical milling
When ferrous particles bridge the gap, the current path is
economically reduces the weight of the aircraft and
completed and a warning light illuminates in the cockpit.
produces a lightweight skin that has all of the needed
strength and rigidity than can be done with conventional chipping — The breaking away of pieces of material by
machining or by using riveted-on stiffeners. excessive stress or by careless handling.
chemical reaction — A chemical alteration in a substance to chisel — A hard steel cutting tool used to shear metal when
form a chemical compound. This is always accompanied it is hammered.
by an energy change.
chlorate candle — A chemical oxygen
chemical salt — The result of the combination of an alkali supply used as an emergency
with an acid. Salts are generally porous and powdery in oxygen supply in large aircraft and
appearance and are the visible evidence of corrosion in in some smaller aircraft. When the
a metal. candle is heated, it emits oxygen
that is then routed to a mask for
cherry picker — A hydraulically operated boom with a large
breathing by the passenger. Also
basket on its end. A person can be lifted into the basket in
referred to as an oxygen candle.
order to work at high locations on large airplanes.

70

10001930-002_AviationDictionary_2012_BOOK.indb 70 3/27/2012 9:38:01 AM

 chlorine • chrome-alumel

chlorine — A gaseous chemical element with a symbol of chord — 1. An imaginary line drawn through an airfoil
Cl and an atomic number of 17. from its leading edge to its trailing edge. The chord, or
chord line, is used as a reference (a datum line) for laying
chlorobromomethane (Halon 1011) — A chemical formula
out the curve of the airfoil. 2. A straight line that passes
– CH2ClBr. A liquefied gas with a UL toxicity rating of
through a circle and touches the circumference at two
3. Commonly referred to as CB, chlorobromomethane
points. Also referred to as the diameter of the circle.
is more toxic than C02. It is corrosive to aluminum,
magnesium, steel, and brass. It is not recommended for chord line — An imaginary line drawn through an airfoil
aircraft use. from its leading edge to its trailing edge. The chord, or
chord line, is used as a reference (a datum line) for laying
chock — A block of material wedged under the tires of an
out the curve of the airfoil.
aircraft to prevent it from rolling on the ground.
chordwise — Passing from the leading edge to the trailing
choke — An electrical inductor used to oppose the flow of
edge of an airfoil.
pulsating DC electricity. Chokes are used with capacitors
to make filter circuits that smooth out the voltage changes chordwise axis — In rotorcraft, a term used in reference to
and make pulsating direct current into smooth flowing DC. semirigid rotors describing the flapping or teetering axis
of the rotor.
choke bore — A method of boring the cylinder of an aircraft
engine in which the top, that portion affected by the mass chrome molybdenum steel — A strong, tough and
of the cylinder head, has a diameter slightly less than that highly weldable alloy steel containing chromium and
of the main bore of the barrel. When the cylinder reaches molybdenum. The most commonly used steel for aircraft
operating temperature, the increased expansion due to the structure is the SAE 4100 series.
larger mass of the head has caused the bore to be straight
chrome nickel molybdenum steel — Steel that has been
throughout its length.
alloyed with chromium, nickel, and molybdenum.
choke coil — An inductance coil designed to provide a high
chrome pickling — A method used to convert the surface
reactance to certain frequencies and generally used to
of magnesium to a hard oxide film in order to protect
block or reduce currents at these frequencies.
it from corrosion. This is accomplished by soaking the
choked — A condition of a turbojet engine where airflow magnesium in a solution of potassium dichromate.
from a convergent nozzle is at Mn = 1.0 (speed of sound)
chrome plated cylinder — Hard chrome plating applied
and cannot be further accelerated regardless of the
to the inside walls of an aircraft cylinder to form a hard,
pressure applied. Choke normally occurs at the turbine
wear-resistant surface.
nozzle and exhaust nozzle, although it is a cause of stall
conditions in the compressor. chrome plating — 1. An electroplating process transferring
chromium to the surface of the steel. Either hard chrome
choked airflow — In gas turbine engines, an airflow
or decorative chrome can be applied. 2. A treatment for
condition from a convergent shaped nozzle, where the
cylinder walls of reciprocating engines. It hardens the
gas is traveling at the speed of sound and cannot be
walls and helps lubricate them. Worn cylinder barrels
further accelerated. Any increase in internal pressure will
may be ground so that their bore is straight and round.
pass out the nozzle in the form of pressure.
Then hard chromium is electroplated on the cylinder
choked cylinder bore — The cylinder of a reciprocating walls to a depth that brings the diameter of the cylinder
engine whose bore is slightly smaller in the part of the bore back to its original dimensions. The surface of the
cylinder that is screwed into the cast aluminum head chrome plating on the cylinder walls resembles a maze of
than it is in the center of the cylinder barrel. The cylinder spider webs. There are thousands of tiny, interconnected
head expands at normal operating temperature enough so cracks in its surface. The electroplating current is then
that the bore straightens out and has the same diameter reversed, and these tiny cracks open up enough so that
throughout. they can hold oil. Porous chrome plating provides a hard,
wear-resistant surface for the piston rings to ride on.
choked nozzle — A jet engine nozzle whose flow rate has
The oil that is trapped in the tiny grooves helps seal the
reached the speed of sound.

rings and lubricate the wall to minimize piston ring and
choke-input filter — A form of filter used with an electronic cylinder wall wear.
power supply to change pulsating direct current into
chrome vanadium steel — A steel alloyed with chromium
smooth DC.
and vanadium. It is the SAE 6100 series and is used
choo-choo — A mild compressor surge condition caused extensively in the manufacturing of technicians’ hand
by insufficient compression ratio across the compressor. tools.
chopper — Slang for helicopter. chrome-alumel — Bimetallic strip of metal used in the
exhaust temperature indicating system. Alumel contains

71

10001930-002_AviationDictionary_2012_BOOK.indb 71 3/27/2012 9:38:01 AM

 chromel • circular saw

an excess of free electrons which, when heated, move the circling maneuver in relation to the airport/runway
into the chromel lead. This current flow is read as an is required, the controller will state the direction (eight
indication of temperature. cardinal compass points) and specify a left or right
downwind or base leg as appropriate; e.g., “Cleared
chromel — An alloy of nickel and chromium that is highly
VOR Runway Three Six Approach circle to Runway
resistant to oxidation and has a high electrical resistance.
Two Two,” or “Circle northwest of the airport for a right
chromel‑alumel thermocouple — A thermocouple is a downwind to Runway Two Two.”
device that generates a small current when heated. A
circle-to-land maneuver — A maneuver initiated by the
chromel-alumel thermocouple consists of a positive
pilot to align the aircraft with a runway for landing when
lead of chromel and a negative lead of alumel. This
a straight-in landing from an instrument approach is not
device is used primarily to measure high temperatures in
possible or is not desirable. At tower controlled airports,
reciprocating and jet turbine engines.
this maneuver is made only after ATC authorization has
chromic acid — An acid similar to sulfuric acid except for been obtained and the pilot has established required
the substitution of chromium for sulfur. It is used as an visual reference to the airport.
etchant to prepare aluminum alloys for finishing and as a
circling — A maneuver to align the aircraft with a runway
corrosion inhibitor.
for landing when a straight-in landing from an instrument
chromic acid etch — A solution of sodium dichromate, approach is not possible or desirable. This maneuver is
nitric acid, and water used to etch or roughen a surface. made only after ATC authorization and the pilot has
established the required visual reference to the airport.
chromium — A hard, brittle, white metallic chemical
element with a symbol of Cr and an atomic number of circling approach — See circle-to-land maneuver.
24. Chromium is highly resistant to corrosion and is used
circling maneuver — See circle-to-land maneuver.
for plating metal to harden its surface or to protect it from
rust or corrosion. circling minima — A statement of MDA and visibility
required for the circle-to-land maneuver.
chronometric tachometer — An instrument used
to measure the speed in revolutions per minute of NOTE: Descent below the established MDA or DH is not
a reciprocating aircraft’s engine crankshaft. The authorized during an approach unless the aircraft is in a
chronometric tachometer repeatedly counts the number position from which a normal approach to the runway of
of revolutions in a given period of time and displays the intended landing can be made and adequate visual
average speed on its dial. reference to required visual cues is maintained.
chuck — A special clamp-like device on a lathe used to hold circuit — The complete path in which electrical current flows.
the material being worked or a drill to hold the drill bit. It must contain a source of electrical energy, a load to absorb
Chucks have three or more jaws that are used to clamp this energy, and conductors to carry the electron flow.
and hold the material or the tool.
circuit breaker — A circuit-protecting device that opens
chugging — Low frequency airflow oscillations within the circuit in case of excess current flow. A circuit breaker
a turbine engine. Chugging is a mild, audible stall differs from a fuse in that it can be reset without having
condition that can usually be controlled by proper throttle to be replaced.
movement.
circuit diagram — An electrical drawing that uses
chute — An inclined trough or channel used to allow objects conventional symbols to show how the components in an
or materials to be sent from one level or place to another. electrical system are interconnected.
cigarette — A ceramic or synthetic rubber insulator used at circuit protector — A device that opens an electrical circuit
the end of an ignition lead to insulate it from the shielded in the event of an excessive current flow.
barrel of a spark plug.
circular inch — The area of a circle whose diameter is 1.”
circle — A closed-plane curve in which all points along the
circular mil (CM) — A
curve are equidistant from a point within the center of
measurement of area equal to
curve.
that of a circle having a diameter
circle graph — A graph using a circle divided into pieces of 1/1,000,” 1 mil., or 0.001.”
like a pie to convey data. Also referred to as a pie chart.
circular motion — The motion of an object along a curved
circle to runway (runway number) — Used by ATC to path in which the object stays a constant distance from
inform the pilot that he must circle to land because the the center of the motion.
runway in use is other than the runway aligned with the
circular saw — A power saw driven by an electric motor
instrument approach procedure. When the direction of
that uses a circular blade.

72

10001930-002_AviationDictionary_2012_BOOK.indb 72 3/27/2012 9:38:01 AM

 circular slide rule • class of thread

circular slide rule — A slide rule having scales arranged clamshell thrust reverser — A thrust reverser, clamshell
in circles on the surface of a disk. Transparent runners door system that fits in the exhaust system of a turbojet
attached at the center of the disk can be moved over the engine. When the reverser is deployed for thrust reversing,
scale to perform various mathematical operations. the doors move into position to block the normal tailpipe
and duct the exhaust gases around so that they flow
circulation — In meteorology, the organized movement of
forward to oppose the forward movement of the aircraft.
air. Also called an eddy.
class — 1. As used with respect to the certification,
circumference of a circle — The linear distance around
ratings, privileges, and limitations of airmen, means a
a circle. The circumference of a circle is always 3.1416
classification of aircraft within a category having similar
times the length of the diameter of the circle.
operating characteristics. Examples include: single
circumferential frame — A circular or oval frame. It gives engine; multiengine; land; water; gyroplane; helicopter;
shape to a fuselage or nacelle. Also referred to as a belt airship; and free balloon. 2. As used with respect to
or transverse frame. the certification of aircraft, means a broad grouping of
aircraft having similar characteristics of propulsion,
circumscribed circle — A circle drawn around the outside
flight, or landing. Examples include airplane, rotorcraft,
of another figure in such a way that all of the points touch
glider, balloon, landplane, and seaplane.
the circumference of the circle.
class A airspace — Controlled airspace covering the 48
cirriform — High altitude clouds made up mostly of small
contiguous United States and Alaska, within 12 nautical
ice crystals.
miles of the coasts, from 18,000 feet MSL up to and
cirrocumulus (Cc) — Cirroform clouds, elements of which including FL600, but not including airspace less than
appear as small puffy clouds sometimes aligned in rows. 1,500 feet AGL.
cirrostratus (Cs) — Layer of cirroform clouds that appear class B airspace — Controlled airspace designated around
as thin white or light-gray sheets. certain major airports, extending from the surface or
higher to specified altitudes. For operations in Class B
cirrus (Ci) — Detached cirroform clouds that appear as
airspace, all aircraft must receive an ATC clearance to
white feathers or filaments.
enter, and are subject to the rules and pilot/equipment
cistern — A container used to store a liquid. requirements listed in FAR Part 91.
CIT sensor — A device that sends an inlet duct temperature class C airspace — Controlled airspace surrounding
signal to the fuel control as a scheduling parameter. designated airports where ATC provides radar vectoring
and sequencing on a full-time basis for all IFR and VFR
civil aircraft — Aircraft other than public aircraft.
aircraft. Participation is mandatory, and all aircraft must
civil twilight — The period of time before sunrise or establish and maintain radio contact with ATC , and are
after sunset when the sun is not more than 6° below the subject to the rules and pilot/equipment requirements
horizon. listed in FAR Part 91.
clad aluminum — An aluminum alloy with a coating of class D airspace — Controlled airspace around at least one
pure aluminum rolled onto both sides for corrosion primary airport which has an operating control tower.
protection. Aircraft operators are subject to the rules and equipment
requirements specified in FAR Part 91.
cladding — A method of protecting aluminum alloys from
corrosion by rolling a coating of pure aluminum onto the class E airspace — Controlled airspace which covers
surface of the alloy. Although cladding protects the alloy, the 48 contiguous United States and Alaska, within 12
it also reduces its strength. nautical miles of the coasts, from 14,500 feet MSL up
to but not including 18,000 feet MSL. Exceptions are
clamp — Any device used to exert pressure to temporarily
restricted and prohibited areas, and airspace less than
hold objects together.
1,500 feet AGL. Class E airspace also includes Federal
clamp-on ammeter — A hand-held ammeter that clamps airways, with a floor of 1,200 feet AGL or higher, as well
around a current-carrying wire that is to be measured. as the airspace from 700 feet or more above the surface
The changing magnetic field around the wire induces a designated in conjunction with an airport which has an
voltage in the jaws of the ammeter proportional to the approved instrument approach procedure.
amount of current flowing in the line.
class G airspace — Airspace that has not been designated
clamshell doors — Two doors that open on the opposite as Class A, B, C, D, or E, and within which air traffic
sides of the center line similar to the way the shell of a control is not exercised.
clam opens.
class of thread — In threaded fasteners, classes of threads
are distinguished from each other by the amount of

73

10001930-002_AviationDictionary_2012_BOOK.indb 73 3/27/2012 9:38:02 AM

 class‑A amplifier • cleared approach

tolerance and/or allowance specified. Classes 1A, 2A, position marking. 3. Pilots and controllers shall exercise
and 3A apply to external threads, whereas classes 1B, 2B, good judgement to ensure that adequate separation exists
and 3B apply to internal threads. Classes 2 and 3 apply to between all aircraft on runways and taxiways at airports
both external and internal threads. with inadequate runway edge lines or holding position
markings.
class‑A amplifier — An electronic amplifier that produces
current during 100% of the input cycle. clearance — 1. The clear space or distance between two
mechanical objects or moving parts. 2. An authorization
class‑B amplifier — An electronic amplifier whose two
by air traffic control, for the purpose of preventing
output devices (vacuum tubes or solid-state) conduct
collision between known aircraft, for an aircraft to
one at a time to produce a composite output signal. One
proceed under specified traffic conditions within
device conducts for the positive portion of an input signal
controlled airspace. The pilot-in-command of an aircraft
and the other device conducts during the negative portion.
may not deviate from the provisions of a visual flight
class‑C amplifier — An electronic amplifier that produces rules (VFR) or instrument flight rules (IFR) air traffic
current during a small part (less than half) of the input clearance except in an emergency or unless an amended
cycle. clearance has been obtained. Additionally, the pilot
may request a different clearance from that which has
claw hammer — A hammer used primarily for carpentry. Has
been issued by air traffic control (ATC) if information
a claw-like device opposite the face for removing nails.
available to the pilot makes another course of action
clean and true — A term used in valve seat grinding more practicable or if aircraft equipment limitations
whereby the rough stone is used until the seat is true or or company procedures forbid compliance with the
exactly matches the valve guide and until all pits, scores, clearance issued. Pilots may also request clarification or
and burned areas are removed. amendment, as appropriate, any time a clearance is not
fully understood, or considered unacceptable because
clean room — A room used to house manufacturing and
of safety of flight. Controllers should, in such instances
servicing of high-precision products. Usually has air
and to the extent of operational practicality and safety,
filtration to prevent contaminating particles from entering
honor the pilot’s request. FAR Part 91.3(a) states: “The
the products.
pilot-in-command of an aircraft is directly responsible
cleanout — The process of cleaning out or cutting away a for, and is the final authority as to, the operation of that
damaged area to prepare it for a repair. aircraft.” The pilot is responsible to request an amended
clearance if ATC issues a clearance that would cause a
clear air turbulence — Turbulence that occurs in clear
pilot to deviate from a rule or regulation, or in the pilot’s
air, and is commonly applied to high‑level turbulence
opinion, would place the aircraft in jeopardy.
associated with wind shear. It is often encountered
near the jet stream, and it is not the same as turbulence clearance fit — An assembly that leaves a clearance between
associated with cumuliform clouds or thunderstorms. mating parts. The shaft will be smaller than the hole.
clear air turbulence (CAT) — Usually, high level (or jet clearance limit — The fix, point, or location to which an
stream) turbulence encountered in air where no clouds aircraft is cleared when issued an air traffic clearance.
are present, may occur in nonconvective clouds.
clearance void if not off by (time) — Used by ATC to advise
clear icing (or clear ice) — Generally, the formation of an aircraft that the departure clearance is automatically
a layer or mass of ice which is relatively transparent cancelled if takeoff is not made prior to a specified time.
because of its homogeneous structure and small number The pilot must obtain a new clearance or cancel his IFR
and size of air spaces; used commonly as synonymous flight plan if not off by the specified time.
with glaze, particularly with respect to aircraft icing.
clearance void time — A time specified by an air traffic
Compare with rime icing. Factors that favor clear icing
control unit at which a clearance ceases to be valid unless
are large drop size, such as those found in cumuliform
the aircraft concerned has already taken action to comply
clouds, rapid accretion of supercooled water, and slow
therewith.
dissipation of latent heat of fusion.
clearance volume — The volume of the cylinder of a
clear of the runway — 1. A taxiing aircraft, which is
reciprocating aircraft engine with the piston at the top of
approaching a runway, is clear of the runway when
its stroke.
all parts of the aircraft are held short of the applicable
holding position marking. 2. A pilot or controller may cleared approach — An ATC authorization for an aircraft
consider an aircraft, which is exiting or crossing a runway, to execute any standard or special instrument approach
to be clear of the runway when all parts of the aircraft are procedure for that airport. Normally, an aircraft will be
beyond the runway edge and there is no ATC restriction cleared for a specific instrument approach procedure.
to its continued movement beyond the applicable holding

74

10001930-002_AviationDictionary_2012_BOOK.indb 74 3/27/2012 9:38:02 AM

 cleared as filed • climbout speed

cleared as filed — A statement that refers to an aircraft runway, at an elevation no higher than the elevation of
being cleared to proceed in accordance with the route the end of the runway, clear of all fixed obstacles, and
of flight filed in the flight plan. This clearance does not under the control of the airport authorities.
include the altitude, DP, or DP Transition.
Cleco fastener — A spring-type fastener used to hold metal
cleared for takeoff — An ATC authorization for an aircraft sheets together until drilling or riveting procedures are
to depart. It is predicated on known traffic and known accomplished.
physical airport conditions.
clevis — The forked end of a push-pull tube usually fastened
cleared for the option — An ATC authorization for an to a bell crank in a control assembly.
aircraft to make a touch-and-go, low approach, missed
clevis bolt — A special-purpose bolt whose round head is
approach, stop and go, or full stop landing at the
slotted or recessed to accept a screwdriver. Used only
discretion of the pilot. It is normally used in training so
for shear loads, the threaded portion of the shank is very
that an instructor can evaluate a student’s performance
short and used only to secure the bolt in the clevis.
under changing situations.
clevis pin — A high‑strength steel pin with a flat head on one
cleared through — An ATC authorization for an aircraft
end and a hole for a cotter pin on the other end. A clevis
to make intermediate stops at specified airports without
pin is used as a hinge for control surfaces or for attaching
refiling a flight plan while enroute to the clearance limit.
a clevis to a control horn. Clevis pins are designed to take
cleared to land — An ATC authorization for an aircraft to shear loads only. Also referred to as a flathead pin.
land. It is predicated on known traffic and known physical
climate — Weather conditions such as temperature, wind,
airport conditions.
cloud cover, precipitation, etc. that typically exist in a
cleared (type of) approach — An ATC authorization for specified area when averaged over a long time, usually
an aircraft to execute a specific instrument approach decades.
procedure to an airport, i.e. “Cleared ILS Runway Three
climatological forecasts — A forecast based on the average
Six Approach.”
weather (climatology) of a particular region.
clearing engine — Purging the combustion chambers of
climatology — The study of the average conditions of the
unburned fuel by rotating the engine with the starter.
atmosphere.
The air flow through the engine carries off dangerous
accumulations of fuel vapors and vaporizes any liquid climb gradient — A minimum climb rate expressed in feet
fuel present. per nautical mile. For example, a climb gradient of 400 feet
per nautical mile requires a minimum climb performance
clearing turns — Turns consisting of at least a 180°change
of 400 feet in a horizontal distance of one n.m. Climb
in direction, allowing the pilot to see areas blocked by
gradient can be converted mathematically (or by use of a
blind spots. A visual check of the airspace around the
table) to feet per minute if groundspeed is known.
airplane to avoid conflicts while maneuvering.
climb indicator — A rate of pressure change indicator used
clearway — 1. An area beyond the takeoff runway under
to furnish the pilot with information regarding the rate of
the control of airport authorities within which terrain or
vertical ascent or descent.
fixed obstacles may not extend above specified limits.
These areas may be required for certain turbine-powered climb propellers — A fixed-pitch propeller that provides the
operations and the size and upward slope of the clearway aircraft with the best performance during takeoff and climb.
will differ depending on when the aircraft was certificated.
climb to VFR — An ATC authorization for an aircraft
2. For turbine engine powered air­planes certificated after
to climb to VFR conditions within Class B, C, D, and
August 29, 1959, an area beyond the runway, not less
E surface areas when the only weather limitation is
than 500 feet wide, centrally located about the extended
restricted visibility. The aircraft must remain clear of
centerline of the runway, and under the control of the
clouds while climbing to VFR.
airport authorities. The clearway is expressed in terms of
a clearway plane, extending from the end of the runway climbing blade — A condition when one or more blades are
with an upward slope not exceeding 1.25 percent, above not operating in the same plane of rotation during flight.
which no object nor any terrain protrudes. However, This might occur only in flight and not occur during
threshold lights may protrude above the plane if their ground operations.
height above the end of the runway is 26 inches or less
climbout — That portion of flight operation between
and if they are located to each side of the runway. 3.
takeoff and the initial cruising altitude.
For turbine engine powered airplanes certificated after
September 30, 1958, but before August 30, 1959, an climbout speed — With respect to rotorcraft, means a
area beyond the takeoff runway extending no less than referenced airspeed which results in a flight path clear
300 feet on either side of the extended centerline of the of the height-velocity envelope during initial climbout.

75

10001930-002_AviationDictionary_2012_BOOK.indb 75 3/27/2012 9:38:02 AM

 clinometer • CMM

clinometer — A closed-end, cloud detection radar — Radar used to determine bases

curved glass tube filled with and tops of clouds (rather than precipitation) above a
a liquid similar to kerosene reporting station.
and enclosing a round glass cloud height — The height of the base of the cloud layer
ball. It may be used as a above ground level (AGL).
leveling device or in a turn
and slip indicator to indicate the relationship between the cloud layer — Clouds with bases at approximately the
force of gravity and centrifugal force in a turn. same level.
clip — A small attachment device used to join parts in cloud point — The temperature of an oil at which its wax
aircraft construction. content, normally held in solution, begins to solidify
and separate into tiny crystals, causing the oil to appear
clock — In electronic equipment, a pulse generator that cloudy or hazy.
allows all components to be synchronized.
cloud streets — Parallel rows of cumulus clouds. Each row
clockwise rotation — The direction in which the hands of can be as short as 10 miles or as long as a hundred miles
a clock rotate. or more.
close parallel runways — Two parallel runways whose cloudburst — A sudden and heavy rain shower.
extended centerlines are separated by less than 4,300 feet,
having a Precision Runway Monitoring (PRM) system clouds with great vertical development — Cumulus and
that permits simultaneous independent ILS approaches. cumulonimbus clouds.
closed angle — The angle formed in sheet metal after it has cloudy convection — The upward movement of saturated
been bent more than 90°. For example, if a piece is bent air that is warmer than its surroundings.
through 135°, it forms a 45° closed angle. clove hitch — A knot used for making individual spot ties
closed loop — An electronic circuit that allows some of the for securing electrical wire bundles. In this use, the clove
output signal to be fed back into the input section in order hitch is locked with a square knot.
to allow the circuit to be self regulating. club propeller — A short, stubby propeller used for ground
closed low — A low-pressure area enclosed in at least one testing of reciprocating engines.
closed isobar or (aloft) one closed contour. clubhead — A formed rivet head tipped to one side.
closed runway — A runway that is unusable for aircraft Tipping can be corrected by rapidly moving the bucking
operations. Only the airport management/military bar across the rivet head in a direction opposite that of
operations office can close a runway. the malformed travel. This corrective action can only be
accomplished during the forming of the rivet head.
closed traffic — Successive operations involving takeoffs
and landings or low approaches where the aircraft does cluster — Part of an airframe
not exit the traffic pattern. structure made up of two
or more tubes meeting at
close‑grain wood — Wood that has grown with the annual one point. They are welded
rings very close together. Close-grain wood is very together in a cluster weld.
consistent in its cross-sectional strength.
cluster weld — A welded joint made at the intersection of a
close-tolerance bolt — A hex-head aircraft bolt with a shank number of tubes that meet at a common point.
that has been ground to a tolerance of + 0.000 —0.0005”.
It is identified by a triangle on its head enclosing the clutch — A device used to connect and disconnect a
material identification mark. driving and driven part of a system such as between the
transmission and main rotor of a helicopter.
cloud — A visible accumulation of minute water droplets
and/or ice particles in the atmosphere above the Earth’s clutter — Undesirable signals that show up on a radar
surface. Cloud differs from ground fog, fog, or ice fog screen and mask the desired signal return. Topographical
only in that the latter are, by definition, in contact with and meteorological phenomena are some of the causes
the Earth’s surface. of clutter.
cloud amount — The amount of sky covered by each layer CMM — Component Maintenance Manual. A manual
of clouds. developed by the component manufacturer and frequently
adopted by an airframe manufacturer. A CMM is most
cloud bank — A mass of cloud seen from a distance, frequently not approved by the FAA. Blanket approval
spreading across an appreciable section of horizon, but comes through the AMM (Aircraft Maintenance Manual)
not extending directly over the observation location. or SRM Structural Repair Manual).

76

10001930-002_AviationDictionary_2012_BOOK.indb 76 3/27/2012 9:38:02 AM

 coalesce • coherent light

coalesce — To unite into a single entity. To come together. cock — A valve (British).
coalescent bag — A bag in the water separator of an cockpit — The pilot’s compartment of an aircraft.
air-cycle air conditioning system on which the moisture
cockpit resource management (CRM) — Effective use
that condenses from the air may coalesce.
of all resources by a flight crew. Emphasis on good
coastal fix — A navigation aid or intersection where an communication and interpersonal skills.
aircraft transitions between the domestic route structure
code markings — Aircraft fluid lines are often identified by
and the oceanic route structure.
markers of color codes, words, and geometric symbols.
coast-down check — The amount of time a turbine engine These identify each line’s function, content, direction of
takes to motor down to a complete stop from idle speed fluid flow, and primary hazard.
after the fuel is shut off. A maintenance test cell check of
codes, transponder — The number assigned to a particular
engine performance.
multiple pulse reply signal transmitted by a transponder.
coated cathode — In a vacuum tube, the cathode emits
coefficient — A dimensionless number expressing degree
electrons. Coated cathodes are covered with a substance
of magnitude.
that enhances the emission of electrons.
coefficient of expansion — A dimensionless number
coating — The application of material such as a metal or
relating dimensional changes in a material with changes
organic compound to a surface.
in temperature.
coaxial — Having a common axis or shaft.
coefficient of friction — The coefficient of friction is the
coaxial cable — A transmission line in which the center value obtained by dividing the force necessary to move
conductor is surrounded by an insulator and a braided one substance over another at a constant speed by the
outer conductor. All of this is enclosed in a weatherproof weight of the substance.
outer insulator.
coefficient of linear expansion — A value obtained by
coaxial propellers — Propellers with concentric shafts that measuring the length (inches or centimeters) a material
allow them to rotate in opposite directions, canceling expands per degree Celsius change in temperature, i.e.
torque and p-factors inherent in single propellers. Coaxial the thermal expansion properties.
propellers can be geared for power by a single engine or
coefficient of thermal expansion — The change in unit of
by multiple engines.
length of volume accompanying a change of temperature.
coaxial rotors — Rotors with concentric shafts that allow
coercive force — The amount of force (in the form of
them to rotate in opposite directions, canceling torque
magnetism with opposite polarity) required to remove
factors inherent in single rotors. Coaxial rotors can
magnetism from an object.
be geared for power by a single engine or by multiple
engines. cog belt — A drive belt that incorporates teeth on the drive
surface in order to prevent slippage. Cog belts are often
coaxial shafts — Shafts that are mounted concentrically
used in systems where timing is critical.
(having a common center) in order to drive two or more
propellers, rotors, compressors, etc. cognitive domain — A grouping of levels of learning
associated with mental activity which range from
cobalt — A metallic chemical element with a symbol of Co
knowledge through comprehension, application, analysis,
and an atomic number of 27.
and synthesis to evaluation.
cobalt chloride — An additive to silica gel dehydrator plugs
cognitive information processing — The method in which
that serves as an indicator of the amount of moisture
information is gathered, processed, and stored by the
absorbed by the plug. A dry dehydrator with this additive
brain in much the same way as a computer.
will be bright blue, but if it has been exposed to excessive
moisture, it will turn pink. cognitive theory — Learning is not just a change in
outward behavior but involves changes in thinking,
cobalt chromium steel — A steel alloy containing cobalt
feeling, or understanding. It involves mental processes,
and chromium. Used in exhaust valves.
such as decision making and problem solving, which are
cobalt-based alloy — A cobalt, tungsten, molyb­denum difficult, if not impossible, to observe or measure.
alloy of extreme high temperature strength. Very
coherent light — Light such as that produced by a laser,
expensive and used almost exclusively in the hot section
made up of waves of the same wavelength and in phase.
of turbine engines.
Ordinary light consists of light of different wavelengths
COBOL — A high-level computer language designed for and phase relations.
business applications. Stands for COmmon Business
Oriented Language.
77

10001930-002_AviationDictionary_2012_BOOK.indb 77 3/27/2012 9:38:02 AM

 cohesion • cold soaked

cohesion — The tendency of a single substance to adhere cold cylinder test — A method of determining an inoperative
to itself. The force holding a single substance together. cylinder on a reciprocating engine by measuring the
relative lack of heat on the bad cylinder compared with
coil — A conductor consisting of turns of wire in which
the normal cylinders.
the magnetic field around one turn cuts across the other
turns, increasing the inductive effect of the wire. cold dimpling — Accomplished while the material is at
room temperature by either the coin ram or coin dimpling
coil assembly — The magneto coil assembly consists of a
method.
soft iron core around which is wound the primary and
secondary coil with the secondary coil wound on top of cold downslope winds — A bora type wind.
the primary coil.
cold drawing — The process of pulling rod or tubing
coil booster — A transformer coil used with a vibrator to through progressively smaller dies in order to reduce the
produce a high voltage at the spark plugs during starting. diameter of the material. The material is not heated for
this process.
coil spring — A spiral of hardened steel wire. When loosely
wound, it is used in compression applications to provide cold flow — The deep and permanent impressions or cracks
cushioning, while tightly wound coils are used in tension in a hose caused by hose clamp pressure.
applications.
cold front — The boundary between two airmasses where
coin dimpling — Performed by a special machine that cold air is replacing warm air.
has, in addition to the usual dies, a “coining ram.” This
cold front occlusion — An occlusion where very cold
ram applies an opposing pressure to the edges of the
air behind a cold front lifts the warm front and the cool
hole so that the metal is made to flow into all the sharp
airmass preceding it.
contours of the die giving the dimple greater accuracy
and improving the fit. cold heading — The process of cold forming wire or bar
stock into intricate shapes by reducing the diameter of
coin pressing — A dimpling process using a countersunk
the stock in some areas, while expanding the diameter
rivet as the male dimpling die, placing the female die in
in others. Cold heading is performed by upsetting or
the usual position, and backing it with a bucking bar. The
heading the metal into larger diameters or extruding it
rivet is then struck with a pneumatic hammer to form the
into smaller diameters.
dimple.
cold junction — In electricity, the reference junction
coin tap — In composites, the use of a coin to tap a laminate
in a thermocouple. A thermocouple produces current
in different spots to detect a change in sound, which
in relation to the difference in temperature between
would indicate the presence of a defect.
a reference junction, known as the cold junction, and
coke — A solid, carbon-like residue left by mineral oil after the junction where temperature measurement is taken,
the removal of the volatile material by heat. known as the hot junction.
coking — The carbon buildup from decomposition of oil in cold light — Light that produces very little heat. Used
vent lines. This buildup can, over a period of time, cause for applications requiring low intensity lights such as
a restriction of flow. formation lights and obstruction lighting.
cold — The absence of heat. cold rolling — The process of rolling sheets of metal in
order to produce a specific thickness of material. The
cold air funnel — A weak vortex that occasionally develops
material is not heated for this process.
behind a cold front with rainshowers and nonsevere
thunderstorms. cold section — The air compression sections of a turbine
engine.
cold airmass — An airmass that is colder than the ground
it is passing over. cold soaked — 1. The condition of a unit of equipment being
extremely cold after prolonged exposure to very cold
cold bending — The bending of sheet metal without the
temperatures. Often makes operation extremely difficult.
use of heat. Thin sheets of metal and some soft metals
This is caused by the waxes and tars in paraffin-based
are bent in this manner. Thick sheets of metal and some
and asphalt-based engine oils precipitating out after a
harder materials must be heated to allow bending without
week or so of very cold temperatures. When they seep
causing the material to break.
out, the viscosity of the engine oil rises much more
cold chisel — A hardened steel cutting tool. Used to cut metal than that caused by the cold-induced rise in viscosity.
materials without the need for softening by use of heat. 2. In gliding, the condition of a self-launch or sustainer
engine making it difficult or impossible to start in flight
cold circuit — An electrical circuit without power. As
due to long-time exposure to cold temperatures. Usually
opposed to a “hot circuit” that has electrical power applied.
occurs after a long soaring flight at altitudes with cold
temperatures, e.g., a wave flight.
78

10001930-002_AviationDictionary_2012_BOOK.indb 78 3/27/2012 9:38:02 AM

 cold spark plug • combination wrench

cold spark plug — A spark collective pitch control — The control in a helicopter in
plug in which the nose which the pitch of all the rotor blades are changed at the
insulator provides a short same time.
path for heat to travel from collector — 1. The electrode in a transistor through which
the center electrode to the conventional current leaves the transistor. 2. The exhaust
shell. Cold spark plugs are cone collector in a turbine engine that collects the exhaust
used in high-compression gases discharged from the engine turbine buckets and
engines to minimize the gradually converts them into a solid jet. In performing
danger of preignition. this, the velocity of the gases is decreased slightly and the
cold swaging process — A method of reducing or forming pressure increased. It also helps to direct the flow of hot
steel or other material while it is cold by drawing it to a gases rearward and prevents turbulence and, at the same
point or reducing its diameter. time, imparts a high final exit velocity to the gases.
cold tank system — A lubrication system wherein the oil collector ring — A corrosion-resistant steel assembly that
cooler is located in the scavenge oil subsystem. The oil collects the exhaust gases from the cylinders of a radial
passes through the cooler and returns to the tank cooled. engine and routes them overboard.
cold weld — The process where two pieces of metal are collimated light — An optical device that causes all light
joined by pressing them together until the materials are beams passing through to be parallel.
fused. No external heat is applied during this process. color code — A means of identifying an object by the use of
cold working — Any mechanical process that will increase various combinations of colors.
the hardness of a metal. This may be done by repeatedly color temperature — The approximate temperature of an
hammering the material, passing it through rollers, or object, based on the peak intensity-emitting wavelength
pulling it through dies. (its color). Specified in degrees Kelvin.
cold‑cathode vacuum tube — A vacuum tube that assists a color tempering — A method of removing brittleness
cathode in emitting electrons without the use of a heater. from a part during heat treatment. The part is heated to a
cold‑cranking amps — The capacity of a battery under specified color, then quenched (cooled by dipping into a
extreme usage conditions. This gives a rough estimate specified liquid).
of the ability of a battery to operate under extreme color wheel — A circular diagram or tool that helps the
conditions, and allows for comparison between batteries. user visualize colors that result when colors are mixed
Also referred to as a high-rate discharge. together.
cold-rolled steel — Steel that has been cold worked by combination compressor — In turbine engines, a
passing through a series of compression rollers or dies. compressor design that utilizes an axial compressor and
cold‑solder joint — An improperly soldered joint. Usually a centrifugal compressor (usually attached together) to
caused by movement of the components before the solder compress incoming air prior to combustion.
sets. Has a grainy appearance. It is not satisfactory, and combination inertia starter — An inertia starter for
must be reheated and allowed to set without movement reciprocating aircraft engines that can be energized by
of the components. either an electric motor or a hand crank.
cold-starting oil relief valve — A bypass relief valve in a combination set — A set of
main oil system that acts as an emergency pop-off valve measuring tools that often
when cold oil causes excessive system pressure. Used in includes a tri-square, a
systems having no oil pressure regulating relief valve. 45˚ miter, a depth gauge, a
collapsed surface — A dimensional change with neither marking or scribing gauge,
removal of material nor an abrupt change of surface and and a level.
usually affecting large sections of the object. Causes are combination square — A
excessive pressure or forces and improper abusive engine device used in laying out
operation. Parts affected usually include valves, piston material. It consists of a
rings, and springs. steel scale attached to a squaring device that is machined
collar — A collar is a raised ring or flange of material on the with precise 90º and 45º angles.
head or shank of a fastener. combination wrench — A tool that has a box-end wrench
collective pitch control — In rotorcraft, the control for on one end and an open-end wrench on the other.
changing the pitch of all the rotor blades in the main rotor
system equally and simultaneously and, consequently,
the amount of lift or thrust being generated.
79

10001930-002_AviationDictionary_2012_BOOK.indb 79 3/27/2012 9:38:02 AM

 combined center-RAPCON (CERAP) • community aerodrome radio station (CARS)

combined center-RAPCON (CERAP) — An air traffic generally recognized by manufacturers and users as
facility which combines the functions of an ARTCC and commercial quality.
a radar approach control facility.
commercial maneuvers — Consists of maximum
combustibles — Materials capable of burning. performance takeoffs and landings, steep turns,
combustion — A chemical process in which a material is chandelles, lazy eights, and eights-on-pylons
united with oxygen at such a rapid rate that light and heat commercial operator — A person who, for compensation or
are released. hire, engages in the carriage by aircraft in air commerce of
combustion chamber — The section of the engine into persons or property, other than as an air carrier or foreign
which fuel is injected and burned. See also combustor. air carrier or under the authority of Part 375. Where it is
doubtful that an operation is for “compensation or hire”,
combustion liner — In a turbine engine, the perforated and the test applied is whether the carriage by air is merely
louvered inner section of the combustor in which fuel incidental to the person’s other business or is, in itself, a
burning is controlled. major enterprise for profit.
combustion liner louvers — In a turbine engine, small commercial pilot — An FAA pilot certificate that allows
slots in the liner that direct cooling airflow and provide the pilot to operate an aircraft for hire.
the inner walls with a cooling air blanket.
common point — A significant point over which two or more
combustion section — The section located directly between aircraft will report passing or have reported passing before
the compressor and the turbine sections. It contains a proceeding on the same or diverging tracks. To establish/
casing, a perforated inner liner, a fuel injection system, maintain longitudinal separation, a controller may
some means for initial ignition, and a fuel drainage determine a common point not originally in the aircraft’s
system to drain off unburned fuel after engine shutdown. flight plan and then clear the aircraft to fly over the point.
The combustion section houses the combustion process,
common portion — See common route.
which raises the temperature of the air passing though the
engine. This process releases energy contained in the air/ common route — That segment of a North American Route
fuel mixture. between the inland navigation facility and the coastal fix.
combustion starter — A fuel engine starting accessory that common traffic advisory frequency (CTAF) — A
utilizes a combustion section similar to a turbine engine frequency designed for the purpose of carrying out
combustor. Combustion products are exhausted through airport advisory practices while operating to or from an
a turbine connected to a reduction gearbox to create uncontrolled airport. The CTAF may be a UNICOM,
starting torque. MULTICOM, FSS, or tower frequency and it is identified
in appropriate aeronautical publications.
combustor — In gas turbine engines, the section of the
engine into which fuel is injected and burned to create communication process — Consists of three basic
expansion of the gases. elements: the source, the symbols used to communicate
the message, and the receiver. In addition, feedback is
combustor drain valve — A spring-loaded valve in a essential for effective communication to take place.
turbine engine that drains excess fuel from the combustion
section when the engine is not running. It is normally communication skills — The skills an instructor must
open and is held closed by the pressures of combustion develop to communicate effectively with students. The
when the engine is operating. ability to communicate effectively as an instructor begins
with an understanding of the communication process and
combustor efficiency — A measure of the percentage is enhanced by experience and training.
of fuel burned completely or Btus of heat attained as
opposed to the Btu potential of fuel introduced. Typical communications — In electronics, changing information
figures are in the 99% range. (audible or digital) into a form that can be transmitted
and then changed back into information at the receiver.
coming-in speed — The speed of a magneto that is just
sufficient to produce the voltage required to fire all of the communications receiver — A device that receives
spark plugs consistently. electronic data and converts it into information
appropriate for use.
comma cloud — A cloud mass shaped like a comma as seen
in satellite imagery. communications satellite — A satellite placed in
geo-stationary orbit used for the relay of communications
commercial fastener — A fastener manufactured to transmissions from Earth.
published standards and stocked by manufacturers
community aerodrome radio station (CARS) — An
or distributors. The material, dimensions, and finish aerodrome radio that provides weather, field conditions,
of commercial fasteners conform to the quality level accepts flight plans and position reports.

80

10001930-002_AviationDictionary_2012_BOOK.indb 80 3/27/2012 9:38:02 AM

 commutator • complement of an angle

commutator — The copper bars on the end of a generator compass rose — A circle marked out on a flat part of an
armature to which the rotating coils are attached. AC is airport away from magnetic interference. It is marked
generated in the armature and the brushes riding on the every thirty degrees of magnetic direction. The airplane
commutator act as a mechanical rectifier to convert it into is taxied onto this rose, and the magnetic compass is
DC. adjusted to agree with the heading of each of the marks.
compact disk (CD) — A small plastic optical disk that compass saw — A small, thin-bladed saw used to cut
contains recorded music or computer data. Also, a popular intricate designs into a material.
format for storing information digitally. The major
advantage of a CD is its capability to store enormous compass swinging — The process of aligning the aircraft
amounts of information. on a series of known magnetic headings and adjusting the
compensating magnets to bring the compass heading as
comparator — A device for inspecting parts by comparing near the magnetic heading as possible.
them with a greatly enlarged standard chart.
compass turns — Maintaining heading and making turns
compartment — A separate and enclosed space in an with reference to the magnetic compass only.
aircraft structure.
compensated cam — The magneto cam used on
compass — 1. A device for determining direction measured high-performance radial engines. One lobe is provided
from magnetic north. 2. A drafting instrument used to for each cylinder, and the lobes are ground in such a way
create circles or arcs. that the magneto points will open when the piston is a
compass card — In navigation, a card affixed to a magnet given linear distance from the top of the cylinder rather
and allowed to rotate freely so as to show the direction than a given angular distance. This compensates for the
of travel. Divided into degrees and cardinal compass relationship of the master rod pistons and those connected
headings. to the crankshaft through the link rods.

compass compensation — The procedure of adjusting the compensated relief valve — An oil pressure relief valve
magnetic compass in an aircraft for deviation caused by with a thermostatic valve that decreases the regulated oil
magnetic forces within the aircraft. pressure when the oil warms up. High pressure is allowed
to force the cold oil through the engine, but the pressure
compass correction card — A card mounted near a is automatically decreased when the oil temperature
compass and in full sight of the pilot that indicates the increases.
difference between the compass reading and the actual
magnetic heading. compensating cam — A cam used in conjunction with
the collective pitch control to add the correct amount of
compass heading — A compass reading that will make engine power for the pitch of the rotor. Used on turbine
good the desired course. It is the desired course (true powered helicopters.
course) corrected for variation, deviation, and wind.
compensating port — A port inside a brake master cylinder
compass locator — A low power, low or medium frequency that vents the wheel cylinder to the reservoir when the
(L/MF) radio beacon installed at the site of the outer or brake is not applied. It prevents fluid expansion from
middle marker of an instrument landing system (ILS). It causing the brakes to drag when temperatures increase.
can be used for navigation at distances of approximately
15 miles or as authorized in the approach procedure. compensating winding — A series winding in a
high-output generator wound between the main pole
a. Outer Compass Locator (LOM) – A compass locator and the interpoles to aid in brushless commutation and
installed at the site of the outer marker of an instrument overcoming armature reaction.
landing system.
compensation — A defense mechanism that attempts to
b. Middle Compass Locator (LMM) – A compass disguise a weak or undesirable quality by emphasizing a
locator installed at the site of the middle marker of an more positive one. Students may lower the scope of their
instrument landing system. goals to avoid possible failure in achieving goals that are
compass locator — A low-frequency, non-directional more difficult.
beacon (NDB) co-located with the marker beacons on an compiler — A special computer program that converts a
ILS approach. Used to help establish the pilot’s position high-level computer language used by a programmer into
on the localizer. machine language that can be used by the computer.
compass north — The north to which a compass actually complement of an angle — The angle that, when added to
points. Its field is produced by the combination of the the original angle, makes a 90º angle.
Earth’s magnetic field and the local magnetic fields
within the aircraft.

81

10001930-002_AviationDictionary_2012_BOOK.indb 81 3/27/2012 9:38:03 AM

 complex airplane • compression rib

complex airplane — An airplane that has a retractable comprehensiveness — A characteristic of a measuring

landing gear, flaps, and either a controllable pitch instrument when it is based on a liberal sampling of the
propeller or a full authority digital engine control. knowledge or skill to be measured. It must be broad
enough to ensure that conclusions are representative of
complex circuit — A circuit consisting of a number of
the whole.
components, where some are arranged in series and
others in parallel. compressed air — Air compressed until its pressure is
above ambient.
complex number — The sum of a real number and an
imaginary number. compressibility — The capability of a material to be
compressed to a smaller volume. Gases are compressible;
compliance — Being in accordance with a regulation or
liquids are not.
directive.
compressibility burble — A region of disturbed flow
component — Any one of several parts in a combination of
produced by a shock wave. The region is produced aft of
parts that make up a unit or whole.
the shock wave.
composite — Two or more substances which are combined
compressibility error — An error introduced to the
to produce material properties not present when either
pitot system due to the compressibility of air. The air
substance is used alone.
entering the pitot tube is compressed slightly as a result
composite fan blades — An advanced technology blade of impacting air that has stopped within the system. At
design not yet in current use. Its composition is an altitudes below 10,000 feet and airspeeds below 200
epoxy-resin material and graphite fiber. It is stronger knots the amount of error is negligible, but it becomes
than fiberglass and 20% to 30% lighter than metals of the significant at higher altitudes and airspeeds.
same strength.
compressible flow — In aerodynamics, airflow that is
composite flight plan — A flight plan which specifies VFR inconsistent in the degree of compressibility, that is,
operation for one portion of flight and IFR for another it experiences a fractional volume change per unit of
portion. It is used primarily in military operations. pressure change.
composite route system — An organized oceanic route compression — The resultant of two forces that act along
structure, incorporating reduced lateral spacing between the same line and also act toward each other.
routes, in which composite separation is authorized.
compression failure — The failure of a material due to
composite separation — A method of separating aircraft compression. Usually causes material to buckle or bulge.
in a composite route system where, by management of
compression fastener — A fastener with the primary
route and altitude assignments, a combination of half the
function of resisting forces that tend to compress it.
lateral minimum specified for the area concerned and half
the vertical minimum is applied. compression ignition — An ignition used in diesel engines.
Rather than an electrical discharge causing ignition, the
composite structure — A structure made up of two or more
fuel ignites when compression causes the temperature of
substances that, when combined, produce a structure with
the fuel-air mixture to rise to the ignition point.
properties not present when the individual substances are
used alone. compression member or strut — A heavy member, usually
of tubular steel, that separates the spars in a Pratt truss
composition resistor — An electrical device made up of
wing and is used to carry only compression loads.
carbon and some insulator. The amount of resistance to
current flow depends on the relative amounts of carbon compression molding — The creation of parts by
and the insulator. compressing a material into a mold. This ensures the
complete filling of all parts of the mold.
compound — A new entity formed by a union of elements
or parts. The constituents lose their original identity and compression ratio — 1. The ratio of the volume of an
assume the characteristics of the compound. engine cylinder with the piston at the bottom center to
the volume when the piston is at top center. 2. Sometimes
compound curve — A metal surface curved in more than
used to refer to compressor pressure ratio; however, this
one plane.
is not entirely correct because compression ratio infers a
compound lever — A series of two or more levers connected ratio of volumes as in a piston engine.
to achieve a result. Usually used to multiply force.
compression rib — A heavy-duty rib made with heavy
compound-wound generator — A generator with both a cap strips and extra strength webs. A compression rib is
series and a shunt field. designed to withstand compression loads between the
wing spars.

82

10001930-002_AviationDictionary_2012_BOOK.indb 82 3/27/2012 9:38:03 AM

 compression rings • computer assisted instruction (CAI)

compression rings — In reciprocating engines, the top compressor efficiency — A measure of aerodynamic
piston rings. Used to provide a seal for the gases in the efficiency, one important factor of which is the ability
cylinder and to transfer heat from the piston into the to compress air to the maximum pressure ratio with the
cylinder walls. minimum temperature rise.
compression spring — A spring used to withstand compressor front frame — The compressor inlet case.
compression. The coils are loosely wound in order to
compressor hub — The front and rear portion of the
leave room for compression.
compressor to which the compressor shafts attach.
compression stress — Stress applied to a material by a
compressor pressure ratio — The ratio of compressor
squeezing force.
discharge pressure to compressor inlet pressure.
compression strut — A brace that fits between two structural
compressor stage — 1. Each section of a compressor in
members. The members tend to move toward each other
which the air pressure is progressively increased. A
in compression. One example is the compression struts
stage of compression consists of one row of blades and
used between upper and lower spar sections in Pratt truss
one row of stator vanes in an axial flow compressor.
construction.
2. A rotor blade set followed by a stator vane set. The
compression test — A test used to determine the condition rotating airfoils create air velocity, which then changes
of the cylinders on a reciprocating engine. The test to pressure in the numerous diverging ducts formed by
pressurizes the cylinder and then measures excessive loss the stator vanes.
of pressure, which indicates bad rings or bad exhaust or
compressor stall — In gas turbine engines, a condition in
intake valves.
an axial-flow compressor in which one or more stages of
compressive load — A load or a force that tends to compress rotor blades fail to pass air smoothly to the succeeding
or squeeze an object together. stages. A stall condition is caused by a pressure ratio that
is incompatible with the engine rpm. Compressor stall
compressive strength — The will be indicated by a rise in exhaust temperature or rpm
ability of a body to resist a force fluctuation, and if allowed to continue, may result in
that tends to shorten, compress, flameout and physical damage to the engine.
or squeeze it.
compressor stall-margin curve — A curve showing a
compressive stress — The basic relationship between the compression ratio and mass air
stress that tends to shorten an flow that must be maintained for a particular engine. If either
object by pressing its ends of the factors goes out of limits, a compressor stall results.
together.
compressor surge — 1. A severe compressor stall across
compressor — In gas turbine the entire compressor that can result in severe damage
engines, an impeller or a multi-bladed rotor assembly. if not quickly corrected. This condition occurs with a
A component which is driven by a turbine rotor for the complete stoppage of airflow or a reversal of airflow. 2.
purpose of compressing incoming air. An operating region of violent pulsating air flow usually
compressor blade — A rotating airfoil in a turbine engine. outside of the operating limits of the engine flow control
Compresses and accelerates the air before arrival at the settings. A primary cause is compressor blade stall. Surge
combustion chamber. can result in flameout and, in severe cases, structural
damage.
compressor bleed air — Air taken out of the compressor
section of a turbine engine to prevent stall and to operate compulsory reporting points — Reporting points which
certain components. must be reported to ATC. They are designated on
aeronautical charts by solid triangles or filed in a flight
compressor case — The outer compressor housing, usually plan as fixes selected to define direct routes. These
split front to rear or top to bottom. This case provides points are geographical locations which are defined by
support for the stator vanes. navigation aids/ fixes. Pilots should discontinue position
compressor discharge pressure (Pt4) — A measurement reporting over compulsory reporting points when
taken at the compressor exit and sent to the fuel control informed by ATC that their aircraft is in “radar contact.”
unit for fuel scheduling purposes. computer — A device (usually electronic) that receives
compressor disk — The inner section of the compressor to information, performs some sort of operation on the data,
which the blades are attached. A disk assembly is made and then produces an output.
up of one segment per stage and bolted together to form computer assisted instruction (CAI) — Similar to
one large rotating piece. computer-based training, except emphasizes the point

83

10001930-002_AviationDictionary_2012_BOOK.indb 83 3/27/2012 9:38:03 AM

 computer-based instruction (CBI) • conformance region

that the instructor is responsible for the class and uses the conductance — The ability of a substance to conduct
computer to assist in the instruction. electricity.
computer-based instruction (CBI) — Synonymous with conduction — The transfer of heat through a substance or
computer-based training. The use of the computer as a from one substance in contact with another; transfer is
training device. always from warmer to colder temperature.
computer-based training (CBT) — The use of the conductive coating — A coating applied to the surface of a
computer as a training device. CBT is sometimes called material in order to allow it conduct electricity or to make
computer-based instruction (CBI); the terms and acronyms it able to conduct electricity more efficiently.
are synonymous and may be used interchangeably.
conductivity — The characteristic of a material that makes
concave surface — An inwardly curved surface. it possible for it to transmit heat or electrical energy by
conduction.
concentration cell corrosion — A corrosion in which the
electrode potential difference is caused by a difference in conductor — A material whose outer ring electrons are
ion concentration of the electroyte instead of a difference loosely bonded. Therefore, a relatively low voltage will
in galvanic composition within the metal. cause a flow of these electrons.
concentric — Having a common center. conduit — A duct or tube enclosing electrical wires or
cable.
concentric circles — Circles having the same center point.
cone — A three-dimensional geometric surface formed by
concentric shafts — Two shafts having a common axis,
the rotation of a line around a fixed axis such that the line
one inside the other.
always passes through a fixed point on the axis (called the
concurrent lines — Lines that pass through a common vertex) and always makes the same angle with the axis.
point.
cone clutch — A drive clutch consisting of nesting cones as
condensation — The process of changing state from a the contact surface.
vapor into a liquid.
cone of confusion — The cone shaped area above a VOR
condensation level — The height at which a rising parcel or station in which there is no signal and the TO/FROM flag
layer of air would become saturated if lifted adiabatically. momentarily flickers to OFF.
condensation nuclei — Small particles in the air on which cones — The cells concentrated in the center of the retina
water vapor condenses. which provide color vision and fine detail.
condensation trail (or contrail) — A cloud‑like streamer conflict alert — A function of certain air traffic control
frequently observed to form behind aircraft flying in automated systems designed to alert radar controllers to
clear, cold, humid air. existing or pending situations between tracked targets
(known IFR or VFR aircraft) that require his immediate
condenser — 1. Another name for capacitor. 2. The
attention/action.
component in a vapor cycle air conditioning system
where heat energy is given up to the air and the refrigerant conflict resolution — The resolution of potential
vapor is changed into a liquid. conflictions between aircraft that are radar identified and
in communication with ATC by ensuring that radar targets
condition lever — A turboprop cockpit lever. On some
do not touch. Pertinent traffic advisories shall be issued
aircraft, it serves as prop control lever for flight (alpha
when this procedure is applied. NOTE: This procedure
range). On other engines, it serves only as a fuel shut-off
shall not be provided utilizing mosaic radar systems.
lever.
conformance — The condition established when an
conditional routes (CDR) — (Europe) — Category
aircraft’s actual position is within the conformance
1,2,3. Category 1: Permanently plannable CDR during
region constructed around that aircraft at its position,
designated times. Category 2: Plannable only during
according to the trajectory associated with the aircraft’s
times designated in the Conditional Route Availability
Current Plan.
Message (CRAM) published at 1500Z for the 24 hour
period starting at 0600Z the next day. Category 3: Not conformance region — A volume, bounded laterally,
plannable. Useable only when directed by ATC. vertically, and longitudinally, within which an aircraft
must be at a given time in order to be in conformance
conditionally unstable air — Unsaturated air that will
with the Current Plan Trajectory for that aircraft. At a
become unstable on the condition it becomes saturated.
given time, the conformance region is determined by
conditions — The second part of a performance-based the simultaneous application of the lateral, vertical, and
objective, which describes the framework under which longitudinal conformance bounds for the aircraft at the
the skill or behavior will be demonstrated. position defined by time and aircraft’s trajectory.
84

10001930-002_AviationDictionary_2012_BOOK.indb 84 3/27/2012 9:38:03 AM

 conformity • contact

conformity — Meeting all of the requirements of its original constant pressure chart — A weather chart that represents
conditions as specified in the Type Certificate Data (TCD) conditions on a constant pressure surface; may contain
Sheets and the manufacturer’s specifications, or properly analyses of height, wind, temperature, humidity, and/or
altered per Supplemental Type Certificates (STC). other elements.
conformity inspection — An inspection of an aircraft constant pressure cycle — The thermodynamic cycle of
or component to verify that all components installed a gas turbine engine to produce thrust. This is a varying
on the aircraft are approved either in the original Type volume, constant pressure, cycle of events. A more recent
Certificate Data and manufacturer’s specifications or term is continuous combustion cycle because of the four
as modified by Supplemental Type Certificates or Field continuous and constant events, including the intake,
Approvals (337’s). compression, expansion (including power), and exhaust.
Also referred to as the Brayton cycle.
confusion between the symbol and the symbolized object
— Results when a word is confused with what it is meant constant section — That part of an aircraft’s fuselage
to represent. Words and symbols create confusion when having a uniform cross-sectional shape.
they mean different things to different people.
constant voltage charge — A method of charging a battery
congeal — Changing from a fluid to a solid state, or from in which the voltage across the battery remains constant.
a free flowing liquid state to one that is less free flowing. The current is high at the start of the charge but tapers off
to a low value as the charge progresses.
congealed oil — Oil that has solidified because of cold or
contaminants. constantan — A copper-nickel alloy used as a negative
lead in thermocouples used for measuring temperatures
conical — Cone-shaped.
in reciprocating engines.
conifer — A softwood cone-bearing tree.
constant‑force spring — A spring that exerts a constant
coning — In rotorcraft, an upward sweep of rotor blades as pressure regardless of how much the spring is compressed
a result of lift and centrifugal force. or extended.
coning angle — The angle formed by the rotor blades and constant-speed drive (CSD) — A hydraulic transmission
the axis of rotation of a helicopter rotor system. The that can be controlled either electrically or mechanically.
magnitude of the angle is determined by the relationship It is used for alternators and enables the alternator to
between the centrifugal force and the lift produced by the produce the same frequency regardless of the engine’s
blades. variation of speed from idle to maximum RPM.
connecting rod — The component in an internal combustion constant-speed propeller — A controllable-pitch propeller
engine that connects the piston to the crankshaft. whose pitch is automatically varied in flight by a governor
to maintain a constant RPM in spite of varying air loads.
connector — A device used to join two pieces of wire,
tubing, or hose to a component. constant‑voltage power supply — A voltage supply that
is regulated so that voltage remains constant through a
CONSOLAN — A low frequency, long-distance NAVAID
range of loads.
used principally for transoceanic navigations.
constrained-gap igniter — A turbine igniter plug that has
console — The pedestal or panel in an aircraft cockpit
the center electrode recessed in the insulator in order to
where the operating controls are located.
cause the spark to arc well past the tip of the igniter. This
constant — A value used in a mathematical computation allows it to operate at cooler temperatures than other
that is the same every time. For instance, the relationship igniter plugs.
between the circumference of a circle and its diameter is
constructivism — Provides a unique way of thinking about
a constant, 3.1416 (pi, П).
how students learn. Constructivism is based upon the idea
constant current charge — A method of charging a battery that learners construct knowledge through the process of
in which the voltage is adjusted as the charge progresses discovery as they experience events and actively seek to
in order to keep the current constant. understand their environment.
constant displacement pump contact — 1. Establish communication with (followed by
— A pump that displaces the name of the facility and, if appropriate, the frequency
a constant amount of fluid to be used). 2. A flight condition wherein the pilot
each time it turns. The faster ascertains the attitude of his aircraft and navigates by
it turns, the greater the visual reference to the surface.
output.

85

10001930-002_AviationDictionary_2012_BOOK.indb 85 3/27/2012 9:38:03 AM

 contact approach • continuous-element-type detector

contact approach — An approach where an aircraft on an necessary to maintain an aircraft or a fleet of aircraft in
IFR flight plan, having an air traffic control authorization, airworthy condition. Large or turbine powered aircraft
operating clear of clouds with at least one mile flight typically go through a continuous airworthiness program.
visibility, and a reasonable expectation of continuing to 2. A program of Federal Aviation Administration-approved
the destination airport in those conditions, may deviate inspection schedules that allows aircraft to be continually
from the instrument approach procedure and proceed to maintained in a condition of airworthiness without being
the destination airport by visual reference to the surface. taken out of service for long periods of time. Usually
This approach will only be authorized when requested consists of a system of “letter checks.”
by the pilot and the reported ground visibility at the
continuous casting — A manufacturing method that injects
destination airport is at least one statute mile.
a molten substance into a mold, but is then continuously
contact cement — A syrupy adhesive that bonds on contact. pulled from the mold as it cools; similar to extrusion.
contact cooling — The process by which heat is conducted continuous curved-line graphs — A graph utilizing a
away from the warmer air to the colder earth. smooth and even line to convey data.
contactor — A heavy-duty electrical switch. Used to continuous filament — An individual reinforcement that is
connect high current loads to the power supply. flexible and indefinite in length. The fibers used to weave
fabric are considered continuous filaments.
contaminant — An impurity or foreign substance present
in a material or environment that affects one or more continuous gusset — A brace used to strengthen corners in
properties of the material. a structure. It runs the full width of the structure.
contaminated runway — A runway is considered continuous ignition system — A secondary, lower power,
contaminated whenever standing water, ice, snow, slush, ignition system installed along with the main system. It
frost in any form, heavy rubber or other substances are is used to fire one igniter plug during takeoff, landing,
present. A runway is contaminated with respect to rubber and in bad weather, or for relight purposes in case of
deposits or other friction-degrading substances when the flameout.
average friction value for any 500-foot segment of the
continuous load — In electrical equipment, a
runway within the ALD (Available Landing Distance) falls
non-intermittent draw of electrical current. Many
below the recommended minimum friction level and the
electrical devices have a continuous-duty rating that
average friction value in the adjacent 500-foot segments
specifies the maximum continuous load the device can
fails below the maintenance planning friction level.
withstand.
contamination — The entry of foreign materials into the
continuous wave (cw) — An RF carrier wave whose
fuel, oil, hydraulic, or other system.
successive oscillations are identical in magnitude and
conterminous U.S. — The 48 adjoining States and the frequency. Often used to indicate Morse code.
District of Columbia.
continuous‑duty ignition system — An ignition system
continental control area — Obsolete term. Formerly used on turbine engines where an igniter plug continues
a control area consisting of the airspace covering the firing even after the engine is operating. Used in situations
continental United States above 14,500 feet, not including where there is danger of flameout. One area of use would
airspace below 1,500 feet AGL, and most prohibited and be in icing conditions where airflow to the turbine could
restricted areas. be interrupted.
Continental United States — The 49 states located on the continuous‑duty rating — Many electrical devices are
continent of North America and the District of Columbia. limited to operation only for a specified percentage
of time without being turned off for cooling. A device
continue — When used as a control instruction should be
that can run continuously will specify the amount of
followed by another word or words clarifying what is
continuous load.
expected of the pilot. Example: “continue taxi”, “continue
descent”, “continue inbound” etc. continuous-element-type detector — A fire detection
system consisting of a stainless steel tube containing a
continuity — The condition of being unbroken or
discrete element that has been processed to absorb gas in
uninterrupted.
proportion to the operating temperature set point. When
continuity light — A simple test device in which a light the temperature rises due to fire, overheating, etc., the gas
indicates continuity in an electrical circuit while an open is released from the element, causing a pressure increase
circuit prevents the light from illuminating. in the tube. This mechanically actuates a diaphragm
switch, activating the warning lights and an alarm bell.
continuous airworthiness program — 1. A maintenance
program consisting of the inspection and maintenance

86

10001930-002_AviationDictionary_2012_BOOK.indb 86 3/27/2012 9:38:03 AM

 continuous-flow oxygen system • controlled airport

continuous-flow oxygen system — Any oxygen system control column — A vertical column in the cockpit on
that provides a continuous flow of oxygen at a rate which a yoke is mounted. The ailerons are controlled by
constant for any given altitude. rotation of the yoke and the elevators are controlled by its
fore-and-aft movement.
continuous-loop fire detector system — A fire detection
system utilizing a continuous loop consisting of two control grid — The electrode in a vacuum tube to which the
conductors separated by a thermistor material. At normal signal is applied.
temperatures, the thermistor is an insulator, but in the
control locking devices — Devices used to secure control
presence of a fire or overheat condition, the thermistor
surfaces in their neutral positions when the aircraft is
becomes conductive and signals the presence of a fire.
parked. Prevents damage from strong winds that could
contour — 1. The outline of a figure. 2. In meteorology, force the controls violently against the stops.
a line of equal height on a constant pressure chart;
control rod — A rigid, tubular rod used to actuate control
analogous to contours on a relief map.
surfaces. Also referred to as a push-pull rod or torque
contour map — A map with lines of equal elevation drawn tube.
on it. Closely-spaced lines indicate steeper terrain.
control sector — An airspace area of defined horizontal
contour template — A tool used to measure or duplicate and vertical dimensions for which a controller, or group
the contour of a surface. of controllers, has air traffic control responsibility,
normally within an air route traffic control center or
contouring circuit — An electronic circuit that adjusts
an approach control facility. Sectors are established
output devices to match the following input stage. Often
based on predominant traffic flows, altitude strata, and
used to match amplifier characteristics to speakers.
controller workload. Pilot-communications during
contract — To become reduced in size by squeezing or operations within a sector are normally maintained on
drawing together. discrete frequencies assigned to the sector.
contrail — Condensation trail. Cloud-like streamer that control slash — A radar beacon slash representing the actual
frequently forms behind an aircraft. There are two types position of the associated aircraft. Normally, the control
of contrails. Aerodynamic contrails are caused by sudden slash is the one closest to the interrogating radar beacon site.
lowering of pressure over wings and propellers. Exhaust When ARTCC radar is operating in narrow-band (digitized)
contrails are caused by the hot, moist air from turbine mode, the control slash is converted to a target symbol.
engines mixing with the cold air at high altitudes.
control snubber — A method of protecting control surfaces
contrarotating propellers — Two propellers mounted on equipped with a hydraulic booster unit.
concentric shafts that turn in opposite directions. This
control stick — A vertical stick in the cockpit of an airplane
type of rotation cancels the torque forces caused by the
used to move the elevators by fore-and-aft movement or
rotation of propellers.
the ailerons by side-to-side movement.
control — The act of regulating, directing, or coordinating
control surface — Any of the major flight controls such as
any device or activity.
the ailerons, elevator, and rudder.
control and performance concept — A method of teaching
control wheel — The hand-operated wheel in the cockpit
attitude instrument flying, which focuses on controlling
of an airplane used to actuate the elevators by in-and-out
attitude and power as necessary to produce the desired
movement and the ailerons by rotation of the wheel. Also
performance. This method divides the instruments into
referred to as the yoke.
three categories: control, performance, and navigation.
It is used predominantly with high-performance turbine control zone — Obsolete term. Formerly controlled
aircraft. airspace extending upward from the surface of the Earth
to a specified upper limit.
control area — A controlled airspace extending upwards
from a specified limit above the Earth. control zone (ICAO) — A controlled airspace extending
upwards from the surface of the earth to a specified upper
control cable — Specially designed steel cable connected
limit.
to linkages used in flight control systems and engine
controls. controllability — A measure of the response of an aircraft
relative to the pilot’s flight control inputs.
control circuit — Any one of a variety of circuits designed
to exercise control of an operating device, to perform controllable-pitch propeller — A propeller with a pitch
counting, timing, switching, and other operations. that can be changed in flight.
controlled airport — An airport which has a control tower,
sometimes called a tower airport.

87

10001930-002_AviationDictionary_2012_BOOK.indb 87 3/27/2012 9:38:03 AM

 controlled airspace • controlled flight into terrain (CFIT)

controlled airspace — An airspace of defined dimensions 4. CLASS D: Generally, that airspace from the surface to
within which air traffic control service is provided to IFR 2,500 feet MSL above the airport elevation surrounding
flights and to VFR flights in accordance with the airspace those airports that have an operational control tower.
classification. The configuration of each Class D airspace area is
individually tailored and, when instrument procedures
a. Controlled airspace is a generic term that covers Class
are published, the airspace will normally be designed
A, Class B, Class C, Class D, and Class E airspace.
to contain the procedures. Arrival extensions for
b. Controlled airspace is also that airspace within instrument approach procedures may be Class D or
which all aircraft operators are subject to certain Class E airspace. Unless otherwise authorized, each
pilot qualifications, operating rules, and equipment person must establish two-way radio communications
requirements in FAR Part 91. For IFR operations in with the ATC facility providing air traffic services prior
any class of controlled airspace, a pilot must file an IFR to entering the airspace and thereafter maintain those
flight plan and receive an appropriate ATC clearance. communications while in the airspace. No separation
Each Class B, Class C, and Class D airspace area services are provided to VFR aircraft.
designated for an airport contains at least one primary
5. CLASS E: Generally, if the airspace is not Class
airport around which the airspace is designated.
A, Class B, Class C, or Class D, and it is controlled
Controlled airspace in the United States is designated as airspace, it is Class E airspace. Class E airspace extends
follows: upward from either the surface or a designated altitude
to the overlying or adjacent controlled airspace. When
1. CLASS A: Generally, that airspace from 18,000
designated as a surface area, the airspace will be
feet MSL up to and including FL600, including the
configured to contain all instrument procedures. Also
airspace overlying the waters within 12 nautical miles
in this class are Federal airways, airspace beginning
of the coast of the 48 contiguous States and Alaska.
at either 700 or 1,200 feet AGL used to transition to/
Unless otherwise authorized, all persons must operate
from the terminal or enroute environment, enroute
their aircraft under IFR.
domestic, and offshore airspace areas designated
2. CLASS B: Generally, that airspace from the surface below 18,000 feet MSL. Unless designated at a lower
to 10,000 feet MSL surrounding the nation’s busiest altitude, Class E airspace begins at 14,500 MSL over
airports in terms of airport operations or passenger the United States, including that airspace overlying the
enplanements. The configuration of each Class B waters within 12 nautical miles of the coast of the 48
airspace area is individually tailored and consists of contiguous States and Alaska, up to, but not including
a surface area and two or more layers (some Class B 18,000 feet MSL, and the airspace above FL 600.
airspaces areas resemble upside down wedding cakes),
controlled airspace [ICAO] — An airspace of defined
and is designed to contain all published instrument
dimensions within which air traffic control service is
procedures once an aircraft enters the airspace. An
provided to IFR flights and to VFR flights in accordance
ATC clearance is required for all aircraft to operate
with the airspace classification. NOTE: Controlled
in the area, and all aircraft that are so cleared receive
airspace is a generic term which covers ATS (Air Traffic
separation services within the airspace. The cloud
Services) airspace Classes A, B, C, D, and E.
clearance requirement for VFR operations is “clear of
clouds”. controlled departure time programs — These programs
are the flow control process whereby aircraft are held
3. CLASS C: Generally, that airspace from the surface
on the ground at the departure airport when delays are
to 4,000 feet MSL above the airport elevation
projected to occur in either the enroute system or the
surrounding those airports that have an operational
terminal of intended landing. The purpose of these
control tower, are serviced by a radar approach control,
programs is to reduce congestion in the air traffic system
and that have a certain number of IFR operations or
or to limit the duration of airborne holding in the arrival
passenger enplanements. Although the configuration
center or terminal area. A CDT is a specific departure
of each Class C airspace area is individually tailored,
slot shown on the flight plan as an expected departure
the airspace usually consists of a surface area with a
clearance time (EDCT).
5 nautical mile (NM) radius, an outer circle with a 10
nm radius that extends from 1,200 feet to 4,000 feet controlled firing area — A controlled firing area is
above the airport elevation and an outer area. Each established to contain activities, which if not conducted
person must establish two-way radio communications in a controlled environment, would be hazardous to
with the ATC facility providing air traffic services nonparticipating aircraft.
prior to entering the airspace and thereafter maintain
controlled flight into terrain (CFIT) — An accident
those communications while within the airspace. VFR
where an aircraft is flown into terrain or water with no
aircraft are only separated from IFR aircraft within the
prior awareness by the crew that the crash is imminent.
airspace.

88

10001930-002_AviationDictionary_2012_BOOK.indb 88 3/27/2012 9:38:03 AM

 controlled time of arrival • cooperative or group learning

controlled time of arrival — The original estimated time conventional tail — An aircraft design with the horizontal
of arrival adjusted by the ATCSCC ground delay factor. stabilizer mounted at the bottom of the vertical stabilizer.
controller — A person authorized to provide air traffic converge — The process of two objects moving closer
control services. to each other. Two lines forming an angle are said to
converge at that angle.
convection — 1. In general, mass motions within a fluid
resulting in transport and mixing of the properties of that convergence — In meteorology, the condition that exists
fluid. 2. In meteorology, the circular motion of air that when the distribution of winds within a given area is such
results when warm air rises and is replaced by cooler air. that there is a net horizontal inflow of air into the area.
These motions are predominantly vertical, resulting in
convergence zone — In meteorology, an area of
vertical transport and mixing of atmospheric properties.
convergence, sometimes several miles wide, at other
On a global scale, convection causes warm air to move
times very narrow. In soaring these zones often provide
from the warmer latitudes to the cooler latitudes.
organized lift for many miles along the convergence, for
convection cooling — The internal cooling air that escapes instance, a sea-breeze front.
through small holes and slots, as opposed to transpiration
convergent duct — In gas turbine engines, a cone-shaped
cooling through porous walls.
passage or channel in which a gas may be made to flow
convection current — Transport and mixing of a fluid from its largest area to its smallest area, resulting in an
caused by mass movement in the fluid. For example, as a increase in velocity and a decrease in pressure. Referred
fluid is heated, warmer portions of the fluid tend to rise in to as nozzle shaped. With this relationship present, the
a current while cooler portions descend. weight of airflow will remain constant.
convective cloud — A cloud of vertical develop­ment convergent-divergent exhaust — An afterburner design,
that forms in an unstable environment (stratocumulus, a supersonic exhaust duct. The forward section is
cumulus, cumulonimbus, altocumulus, cirrocumulus). convergent to increase gas pressure. The aft section is
divergent to increase gas velocity to supersonic speed.
convective condensation level (CCL) — The lowest level
at which condensation will occur as a result of convection convergent-divergent inlet — A supersonic engine inlet
due to surface heating. When condensation occurs at this duct. The forward section is convergent to increase
level, the layer between the surface and the CCL will air pressure and reduce air velocity to subsonic speed.
be thoroughly mixed, temperature lapse rate will be dry The aft section is divergent to increase air pressure still
adiabatic, and mixing ratio will be constant. further and slow airflow to approximately Mach 0.5
before entering the engine.
convective lifting — In unstable atmospheric conditions, a
parcel of air warmer than its surroundings rises. conversion coating — A chemical solution used to form a
dense, nonporous oxide or phosphate film on the surface
convective sigmet — A weather advisory concerning
of aluminum or magnesium alloys.
convective weather significant to the safety of all aircraft.
Convective SIGMET’s are issued for tornadoes, lines of converter — A circuit in the control box of an anti-skid
thunderstorms, embedded thunderstorms of any intensity system using AC wheel speed sensors. It converts
level, areas of thunderstorms greater than or equal to VIP changes in AC frequency into changes in DC voltage.
(video integrator and processor thunderstorm intensity
convex — Having a surface that curves outward.
standard) level 4 with an area coverage of 4/10 (40%) or
more, and hail 3/4 inch or greater. convey — To communicate or transmit.
convective significant meteorological information — See convoluted — Involved, intricate. Often used to describe
Convective SIGMET. routing of tubing or conduit that winds circuitously
around and through other components.
conventional — Conforming to formal or accepted
standards in drawings or rules. coolant — A fluid used to remove heat from a system or
component. Anti-freeze is used to remove heat from a
conventional current — Current flowing in an electrical
reciprocating engine and a coolant oil is used to remove
circuit from positive to negative, outside the power
heat from cutting tools.
source. This current flow theory is not in common use
today. cooling fins — Ribs projecting from the surface of a
component to increase its area so that heat may be more
conventional landing gear — A landing gear with wheels
easily transferred into the airstream flowing over the fins.
attached to a strut assembly located forward of the center
of gravity and either a skid or wheel assembly at the tail. cooperative or group learning — An instructional strategy
which organizes students into small groups so that they

89

10001930-002_AviationDictionary_2012_BOOK.indb 89 3/27/2012 9:38:04 AM

 coordinated universal time • corrosion

can work together to maximize their own and each lightweight, high strength component when laminated
other’s learning. with face sheets.
coordinated universal time — Greenwich Mean Time. core crush — In composites, compression damage of the
Referred to as coordinated universal time because the core.
time is the average of the times from a network of atomic
core depression — In composites, a gouge or indentation
clocks around the world. Abbreviated UTC. (Formerly
in the core material.
abbreviated Z.)
core engine — The basic portion of a turbine engine
coordinates — The intersection of lines of reference,
consisting of the compressor that supplies air for
usually expressed in degrees/minutes/ seconds of latitude
combustion, the combustor section, and the turbine
and longitude, used to determine position or location.
section.
coordination fix — The fix in relation to which facilities
core orientation — In composites, the placement of the
will handoff, transfer control of an aircraft, or coordinate
honeycomb core to line up the ribbon direction, thickness
flight progress data. For terminal facilities, it may also
of the cell depth, cell size, and transverse direction.
serve as a clearance for arriving aircraft.
core separation — In composites, a breaking of the
copal resins — A natural resin that is used in some aircraft
honeycomb core cells.
finishes.
core speed sensor — Same as tachometer generator speed
copilot — A pilot on a flight crew who assists in flying the
(N2 speed on a dual spool engine).
aircraft, but who is not the pilot-in-command.
core splicing — In composites, joining two core segments
coping saw — A small handsaw with a U-shaped frame and
by bonding them together, usually with a foaming
a thin blade. Used for making curved cuts.
adhesive.
copper — A metallic element with a symbol of Cu and an
coriolis effect — In rotorcraft, the tendency of a rotor blade
atomic number of 29.
to increase or decrease its velocity in its plane of rotation
copper brazing — A method of joining metals where when the center of mass moves closer or further from the
molten copper is used to stick to and flow between two axis of rotation.
or more metallic objects. Differs from welding in that the
Coriolis force — The apparent force that is produced when
object metals are not melted and fused together.
an object moves in relation to a surface that is rotating
copper crush gasket — A copper gasket with a fiber core beneath it. Used to explain why the wind moves in a
that crushes when tightened between mating surfaces. counter-clockwise direction around a low-pressure area
Takes the shape of the mating surfaces for the purpose of (in the Northern Hemisphere).
creating a leakage-free seal.
cork — A lightweight wood used for gaskets and sometimes
copper steel — When any minimum copper content is as an insulator.
specified, the steel is classed as copper steel. The copper
cornice brake — A large sheet metal forming tool used to
is added to enhance corrosion resistance of the steel.
make straight bends. Also referred to as a leaf brake.
copper‑constantan thermocouple — A low-temperature
corona — The discharge of electricity from a wire when it
thermocouple that has a copper positive element and a
has a high potential.
constantan reference element.
corrected altitude — Altitude corrected for temperature.
copper‑oxide rectifier — A rectifier that utilizes a
Approximately the same as true altitude.
copper-oxide coating to restrict the flow of electrons to
one direction and not the other. Such a device is used to correction — An error has been made in the transmission
convert alternating current to direct current. and the correct version follows.
copperweld — An electrical conductor that uses a steel core correlation — A basic level of learning where the student
for strength and copper coating for good conductance of can associate what has been learned, understood, and
electricity. applied with previous or subsequent learning.
copter — Slang expression for helicopter corrolation box — Correlator. A device to automatically
add power to a helicopter engine as the collective pitch
cord body — The diagonal layers of rubber-coated nylon
control is raised.
cord fabric (running at right angles to one another),
which provide the strength to a tire. corrosion — An electrochemical process in which a metal is
transformed into chemical compounds that are powdery
core — In composites, the central member of a sandwich
and have little mechanical strength.
part (usually foam or honeycomb). Produces a

90

10001930-002_AviationDictionary_2012_BOOK.indb 90 3/27/2012 9:38:04 AM

 corrosion inhibiting primer • covalent bond

corrosion inhibiting primer — A primer formulated to As a result, the propeller rotates in a counterclockwise
stop, slow down, or prevent corrosion on the surface of fashion from the pilot’s perspective.
the material to which the primer is applied..
countersink — A cutting tool used to cut a recess into
corrosion inhibitor — A substance added to a coating that material so the rivet or screw head is flush with the
slows down, stops, or prevents corrosion on the surface surface of the material.
of the material to which the coating is applied.
countersunk‑head rivet — A rivet designed with a cone
corrosion prevention compound — An oil that has shaped head that allows the rivet to fit flush with the skin
special corrosion prevention properties that is added to of the material being riveted.
a reciprocating engine to prevent corrosion while the
counterweight (control surface) — A weight attached to
engine is in storage.
a control surface in order to reduce the effort required to
corrosion resistant steel — Stainless steel. A steel that has move the surface and to eliminate flutter in flight.
resistance to corrosion.
counterweight (crankshaft) — A weight attached to the
corrugated fastener — A fastener made up of wrinkles or crankshaft of a reciprocating engine to balance the piston/
folds that is used to hold two pieces of wood together in connecting rod/crankshaft assembly.
a butt joint.
coupled approach — A coupled approach is an instrument
corrugated sheet metal — Metal sheets that have been approach performed by the aircraft autopilot which is
formed into wrinkles or folds in order to increase rigidity. receiving position information and/or steering commands
from onboard navigation equipment. In general, coupled
corrugation — Parallel wrinkles or folds in a material that
nonprecision approaches must be discontinued and
increase the material’s rigidity.
flown manually at altitudes lower than 50 feet below
cosecant — In trigonometry, the ratio of the hypotenuse of the minimum descent altitude, and coupled precision
a right triangle of which the angle is considered part and approaches must be flown manually below 50 feet AGL
the leg opposite the angle. (See Autoland Approach). NOTE: Coupled and autoland
approaches are flown in VFR and IFR. It is common for
cosine — In trigonometry, the ratio between the leg adjacent
carriers to require their crews to fly coupled approaches
to the angle when it is considered part of a right triangle
and autoland approaches (if certified) when the weather
and the hypotenuse.
conditions are less than approximately 4,000 RVR.
cotter pin — A metal fastener with a shank that splits into
course — 1. The intended direction of flight in the horizontal
two halves. It is used to lock castellated nuts onto drilled
plane measured in degrees from north. 2. The ILS
bolts by passing the cotter pin through the hole and then
localizer signal pattern usually specified as front course
spreading the ends of the cotter pin.
or back course. 3. The intended track along a straight,
cotton braid — A loosely woven fabric used to encase curved, or segmented MLS path.
rubber hoses and shock cords to protect them from wear
course deviation indicator (CDI) — The instrument used
and ultraviolet radiation.
for flying along a VOR-defined course. Also referred to
coulomb — A measure of electrical charge. Equal to 6.28 X as a left-right indicator.
1018 electrons. One ampere of electricity is equal to the
course of training — A complete series of studies leading
flow of one coulomb per second.
to attainment of a specific goal, such as a certificate of
counter bore — A tool used to cut a counterbore. A completion, graduation, or an academic degree.
counterbore is cut into the surface of a material at the top
course reversal — A method of reversing course, which
of a smaller hole to allow the head of the bolt or the nut
is depicted on an instrument approach procedure. Some
to be recessed below the surface.
procedures do not provide for straight-in approaches
counterboring — The act of cutting a counterbore into a unless the airplane is being radar vectored. In these
material. situations, the pilot is required to complete a course
reversal, generally within 10 nautical miles of the
counterelectromotive force — When alternating current is
primary navaid or fix designated on the approach chart,
conducted through a winding, a small current is generated
to establish the aircraft inbound on the intermediate or
that is 180º out of phase with the primary current. This is
final approach segments.
a counterelectromotive force (CEMF).
covalent bond — A bond between two atoms that comes
counterrotating engine — An engine designed to allow
about when valence electrons are “shared” by atoms.
the crankshaft and other moving parts to rotate in the
direction opposite the manner of a conventional engine.

91

10001930-002_AviationDictionary_2012_BOOK.indb 91 3/27/2012 9:38:04 AM

 cowl flaps • crimping

cowl flaps — Movable doors on the air exit of an aircraft crater — A small pool of molten metal in the flame or arc
engine cowling. The cylinder head temperature can be during the process of welding.
controlled by varying the amount the flaps are opened.
craze — To produce minute cracks on the surface of a
cowl panels — The detachable coverings that cover areas material.
requiring regular access.
crazing — Region of ultrafine cracks, which may extend
cowl support ring — A large ring attached to a radial in a network on or under the surface of a resin or plastic
engine mount to provide firm support for cowl panels and material.
also for attachment of cowl flaps.
creep — A condition of permanent elongation in a material,
cowling — A removable cover or housing placed over or often due to stretching and high heat.
around an aircraft component or section, especially an
creeper — A platform with small wheels that allows a
engine.
person to lie prone and work on the undersurface of a
cowling, NACA — A cowling enclosing a radial air-cooled machine or vehicle being repaired.
engine, consisting of a hood, O-ring, and a portion of the
crepe masking tape — A paper tape with a crinkled surface
body behind the engine, so arranged that the cooling air
and adhesive on one side. Used to shield a surface from
smoothly enters the hood at the front and leaves through
paint spray.
a smooth annular slot between the body and the rear of
the hood; the whole forming a relatively low-drag body Crescent wrench — An adjustable open-end wrench
with a passage through a portion of it for the cooling air. manufactured by CrescentÒ. Often used incorrectly to
describe any adjustable wrench.
crab — The procedure of altering the heading of an aircraft
into the wind in order to maintain a desired course across crest — The surface of a thread that joins the flanks of the
the ground. thread and is farthest from the cylinder or cone from
which the thread projects.
crack — A partial separation of material usually caused
by vibration, overloading, internal stresses, defective crest clearance — As in a thread assembly, the distance,
assemblies, fatigue, or too rapid changes in temperature. measured perpendicular to the axis, between the crest of
a thread and the root of its mating thread.
crack arrester — A hole drilled into a material in order to
stop the spread of a crack. This hole, created by “stop crew member — A person assigned to perform duty in an
drilling,” distributes stresses over a larger area and keeps aircraft during flight.
the crack from continuing. Commonly used in both sheet
crew resource management (CRM) — The application of
metal and acrylic plastics.
team management concepts in the flight deck environment.
cradle — A support with pads used for cradling fuselage It was initially known as cockpit resource management,
and wings during assembly, disassembly, or repairs. but as CRM programs evolved to include cabin crews,
maintenance personnel and others, the phrase “crew
crankcase — The housing that serves as an engine’s
resource management” has been adopted. This includes
foundation and encloses the different mechanisms of the
single pilots, as in most general aviation aircraft. Pilots
engine.
of small aircraft, as well as crews of larger aircraft, must
crankpin — That part of a crankshaft to which the make effective use of all available resources; human
connecting rods attach. resources, hardware, and information. A current definition
includes all groups routinely working with the cockpit
crankshaft — A shaft with
crew who are involved in decisions required to operate
a series of throws used
a flight safely. These groups include, but are not limited
for transforming the
to, pilots, dispatchers, cabin crewmembers, maintenance
reciprocating motion of the
personnel, and air traffic controllers. CRM is one way
pistons into rotary motion
of addressing the challenge of optimizing the human/
used to turn the propeller of an aircraft.
machine interface and accompanying interpersonal
crankshaft runout — A measurement of how much a activities.
crankshaft is bent. The crankshaft is rotated and the
crewmember — A person assigned to perform duty in an
amount of “out-of-round” is measured using a dial
aircraft during flight time.
indicator.
crimping — Forming a series of small bends into a piece
crankshaft throw — The distance from the crankshaft
of sheet metal in order to shorten its length. Also used to
centerline to the centerline of the rod journal. Crankshaft
create a bend in angle stock by crimping the sock on one
throw is equal to half the stroke.
leg of the angle.

92

10001930-002_AviationDictionary_2012_BOOK.indb 92 3/27/2012 9:38:04 AM

 crimping tool • cross member

crimping tool — Device used to create small bends in sheet critical pressure — The highest compression of a fuel-air
metal for the purpose of shortening the sheet or bending mixture in a reciprocating engine that allows normal
angle stock. ignition of the mixture without premature spontaneous
detonation.
crimp‑on terminals — A solderless terminal placed on the
end of a wire and then squeezed around the wire to make critical strain — The strain at the yield point.
a solid electrical connection.
critical stress area — The area of a structure that would
crinkle finish — A protective finish that dries to a wrinkled first cause total failure of the structure when overstressed.
surface. Often used on surfaces that should not reflect
critical temperature — The highest temperature of a
light.
fuel-air mixture in a reciprocating engine that allows
criteria — Part of a performance-based objective. The normal ignition of the mixture without premature
standards against which the desired outcome is measured. spontaneous detonation.
criterion reference testing (CRT) — System of testing critique — Informal appraisals of student perfor­mance,
where students are graded against a measurable standard designed to quickly convey feedback. Use critiques to
or criterion rather than against each other. summarize and complete a lesson, as well as to prepare
students for the next lesson.
critical altitude — The maximum altitude at which a
turbocharged reciprocating engine can deliver its rated crocus cloth — A fabric embedded with abrasive compound,
horsepower. used to polish metal surfaces.
critical angle of attack — The angle of attack at which cross coat — A technique used in painting where a second
maximum lift is generated. Above this angle of attack, coat is sprayed on at a right angle to the first coat. This
an aircraft will stall. Also referred to as the stalling angle method is used to ensure full coverage of material.
of attack.
cross country — In soaring, any flight out of gliding range
critical compression ratio — On a diesel engine, the of the take-off airfield. Note that this is different than
lowest compression ratio that will still allow ignition of the definition in the FARs for meeting the experience
a particular fuel. requirements for pilot certificates and/or ratings.
critical coupling — In electricity, the relationship between cross feed — An assembly of valves installed in a fuel
primary and secondary windings of a transformer that system to allow any engine to receive fuel from any fuel
provides maximum transfer of electrical energy. tank, or to move fuel from one tank to another for fuel
balance.
critical engine — The engine that would have the most
adverse effect on controllability and climb performance cross firing — High voltage discharge from one ignition
if it were to fail. Multi-engine airplanes with propellers lead to another, causing a spark plug to fire at the incorrect
turning in the same direction are designed so the time.
descending blade of one engine is further from the
cross (fix) at (altitude) — Used by ATC when a specific
centerline of the aircraft than the descending blade of the
altitude restriction at a specified fix is required.
engine mounted on the other side. This makes the failure
of one engine more critical than the other because there cross (fix) at or above (altitude) — Used by ATC when an
is a greater yawing moment created by the engine that altitude restriction at a specified fix is required. It does
is producing thrust further from the aircraft centerline. not prohibit the aircraft from crossing the fix at a higher
To eliminate the critical engine, manufacturers use altitude than specified; however, the higher altitude
counter-rotating engines. In this case, the descending may not be one that will violate a succeeding altitude
propeller blades of both engines are the same distance restriction or altitude assignment.
from the aircraft centerline, and neither engine would
cross (fix) at or below (altitude) — Used by ATC when a
affect climb performance or controllability more than the
maximum crossing altitude at a specific fix is required.
other if it were to fail.
It does not prohibit the aircraft from crossing the fix
critical height — Lowest height in relation to an aerodrome at a lower altitude; however, it must be at or above the
specified level below which an approach procedure minimum IFR altitude.
cannot be continued in a safe manner solely by the aid
cross linking — In composites, with thermosetting and
of instruments.
certain thermoplastic polymers, the setting up of chemical
critical Mach number — That airspeed for a specific links between the molecular chains.
airframe where supersonic airflow is first encountered at
cross member — A structural member that joins two
any point on the aircraft.
longerons or other lengthwise structural members. It
critical part — That part in an assembly that would cause carries loads other than the primary loads.
total failure of the assembly.
93

10001930-002_AviationDictionary_2012_BOOK.indb 93 3/27/2012 9:38:04 AM

 cross modulation • cruise

cross modulation — The modulation of a desired signal by crosswind component — Component of the wind (in
an unwanted signal resulting in two signals in the output. knots) perpendicular to flight or taxi path of aircraft.
cross section — The representation on a drawing of a part’s crosswind landing — A landing where the wind is blowing
interior cut at right angles to the viewing axis. from other than parallel to the runway. Landings with small
crosswind angles or velocities are of little consequence
cross sectional area — The area of the plane section of an
and are not usually considered to be crosswind landings.
object cut at right angles to its length.
crosswind landing gear — Landing gear on an aircraft that
cross talk — In electronics, where signals in one portion
is specially adapted to landing in a crosswind. They are
of the equipment bleed over to another section where the
spring loaded on pivots to allow the gear to align with the
signal is not desired.
runway when the aircraft is landed in a crab.
cross-bleed — An assembly of valves installed in an
crowfoot wrench — An open or box-end wrench with a
air ducting system of a multi-engine turbine powered
short extension and a square drive to be driven with a
aircraft that allows bleed air from one engine to be used
ratchet and an extension bar. A crowfoot wrench allows a
in starting another engine.
fastener in a recess to be driven when a normal ratchet or
cross-brace wires — Wires arranged in an “X” fashion wrench would not work.
across rectangular sections in order to stiffen the
crucible steel — Steel made from heating iron and steel in
structures by triangulation.
a crucible until impurities have been boiled off. Alloying
cross-check — A systematic way of observing instrument elements are then added and the resulting high-grade
indications during attitude instrument flying. Also called steel is cast into ingots.
scanning, it requires logical and systematic observation
crude petroleum — Unrefined petroleum, in a raw or
of the instrument panel. It saves time and reduces the
natural condition, before being refined for use.
workload of instrument flying because the pertinent
instruments are observed as needed. cruise — 1. A moderate speed of travel at optimum speed
for sustained flight. 2. Used in an ATC clearance to
cross-country flying — Flying from one airport to another
authorize a pilot to conduct flight at any altitude from the
over a distance that requires some sort of navigation.
minimum IFR altitude up to and including the altitude
crosscut saw — A saw with closely spaced teeth used for specified in the clearance. The pilot may level off at any
cutting across the grain of wood. intermediate altitude within this block of airspace. Climb/
descent within the block is to be made at the discretion
crossed-control stall — A demonstration stall that a flight
of the pilot. However, once the pilot starts descent and
instructor shows a student pilot. This type of stall can occur
verbally reports leaving an altitude in the block, he
during a skidding turn, and is most likely to occur when a
may not return to that altitude without additional ATC
pilot tries to compensate for overshooting a runway during
clearance. Further, it is approval for the pilot to proceed
a turn from base to final while on landing approach.
to and make an approach at destination airport and can be
cross-hatching — A series of parallel lines on a mechanical used in conjunction with:
drawing. Denotes a section of the drawing has been
a. An airport clearance limit at locations with a standard/
removed. The style of the lines indicates the type of
special instrument approach procedure. The FARs
material depicted in the drawing
require that if an instrument letdown to an airport
crossover — A condition that exists in a helicopter rotor is necessary, the pilot shall make the letdown in
system in which the climbing and diving blades cross. accordance with a standard/special instrument
approach procedure for that airport, or
crossover tube — A small tube connecting multiple burner
cans together for the purpose of flame propagation during b. An airport clearance limit at locations that are within/
starting. below/outside controlled airspace and without a
standard/special instrument approach procedure. Such
cross-ply laminate — In composites, a laminate with plies
a clearance is NOT AUTHORIZATION for the pilot
usually oriented at 0° and 90° only.
to descend under IFR conditions below the applicable
cross-sectional view — A view in a mechanical drawing minimum IFR altitude nor does it imply that ATC is
that depicts the shape of a cross-sectional area of the exercising control over aircraft in Class G airspace;
object at an indicated point. however, it provides a means for the aircraft to proceed
to destination airport, descend and land in accordance
crosswind — Wind that is blowing across the flight or taxi
with applicable FARs governing VFR flight operations.
path of the aircraft. When used in conjunction with traffic
Also, this provides search and rescue protection until
patterns, the term is short for ‘crosswind leg.’
such time as the IFR flight plan is closed.

94

10001930-002_AviationDictionary_2012_BOOK.indb 94 3/27/2012 9:38:04 AM

 cruise climb • cure temperature

cruise climb — A climb technique employed by aircraft, crystal transducer — An electronic device that converts
usually at a constant power setting, resulting in an vibrations into electronic signals. A crystal transducer
increase of altitude as the aircraft weight decreases. uses a piezoelectric crystal that converts vibrations to a
minute alternating current.
cruise control — Engine operation procedures that allow
the best efficiency for power and fuel consumption crystal‑controlled oscillator — See crystal oscillator.
during cruising.
crystalline — Arranged in a definite pattern, with the
cruise power — Sixty percent to 70 percent of maximum atoms or molecules tending to be developed in precisely
continuous power; used for fuel economy and engine life oriented plane surfaces.
during cruising.
C-stage — In composites, the final stage in the curing of the
cruise propellers — A fixed-pitch propeller that provides mixed thermoset resin system. It cannot be softened by
the aircraft with the best performance during cruise flight. heat and is insoluble at this stage.
cruising altitude — An altitude or flight level maintained cube — A three dimensional geometric figure consisting of
during enroute level flight. This is a constant altitude and six congruent square sides.
should not be confused with a cruise clearance.
cube root — In mathematics, the cube root is the number
cruising level — See cruising altitude. that, when multiplied by itself twice, is the given number.
Example: The cube root of 27 is 3 (3 X 3 X 3).
crush gasket — A gasket usually formed of a sandwich of
copper with an asbestos core. When the gasket is crushed cumuliform — A term descriptive of all convective
between mating surfaces, it conforms to the surfaces and clouds exhibiting vertical development in contrast to the
creates a leak-proof seal. horizontally extended stratiform types.
cryogenic liquid — A gas that has been cooled to a cumulonimbus (Cb) — Deep convective clouds with a
temperature low enough for it to be liquefied. Liquid cirrus anvil and may contain any of the characteristics
oxygen and liquid nitrogen are commonly found of a thunderstorm: thunder, lightning, heavy rain, hail,
cryogenic liquids. strong winds, turbulence, and even tornadoes. Also
referred to as thunderclouds.
crystal — 1. A thin piece of piezoelectric material having a
specific resonant frequency used to control the frequency cumulous congestus — A cumulous cloud of significant
of an oscillator. 2. A small piece of galena or lead sulfide vertical extent and usually displaying sharp edges. In
that allows electron flow in only one direction. warm climates, these sometimes produce precipitation.
Also called towering cumulous, these clouds indicate that
crystal diode — An electronic component that passes
thunderstorm activity may occur soon.
electrons in one direction, but not the other. A crystal
diode is constructed from a germanium or silicon crystal. cumulus (Cu) — A principle cloud type having a flat
base and sharp rounded tops and sides. Clouds develop
crystal earphones — Earphones that reproduce sound by
vertically and tops often resemble a cauliflower.
use of piezoelectric crystals. Audio-frequency alternating
voltage is applied to the crystal and the crystal vibrates cumulus stage — The initial stage of a thunderstorm. The
in accord with the frequency of the voltage. The crystal cloud grows from cumulus to towering cumulus and
is attached to a sound diaphragm that causes the pressure usually lasts 10 or 15 minutes.
of the air to change in phase with the voltage. These
Cuno filter — The proprietary name of a fluid filter made
changes in air pressure are perceived by the ear as sound.
up of a stack of discs separated by scraper blades.
crystal filter — A crystal filter vibrates at a certain Contaminants collect on the edge of the discs and are
frequency. This absorbs vibrations at that frequency, but periodically scraped out and collected in the bottom of
passes frequencies above and below the frequency of the the filter case.
crystal.
cup washer — A cup-shaped, spring steel washer. When
crystal lattice — The basic pattern in which atoms are compressed, the spring action prevents the nut on a bolt
arranged, repeated throughout the solid. from loosening.
crystal microphone — A microphone making use of the cure — In composites, to change the physical properties
piezoelectric properties of a crystal, acted on by the of a material by chemical reaction, by the application of
pressure of sound waves. catalysts, heat and pressure, alone or in combination.
crystal oscillator — An electronic device that produces cure temperature — In composites, the temperature that
an alternating current. A crystal oscillator produces a the resin system attains for its final cure. Does not include
frequency determined by a crystal. the ramp up or down.

95

10001930-002_AviationDictionary_2012_BOOK.indb 95 3/27/2012 9:38:04 AM

 cure time • cyaniding

cure time — The time required for a resin to complete its cusp — The indentation on each side at the floor level when
solidification. a fuselage shape has a “figure eight” shape. The cusp
design is used to avoid unneeded width in this area.
curing agent — A catalytic or reactive agent that causes
polymerization when added to resin. Also referred to as cut off — To sever an object or to stop a flow.
a hardener.
cut thread — A thread produced by removing material
current — The flow of electricity. Technically, it is electrons from the surface with a form cutting tool.
that flow, but more commonly, this is called current-flow.
cut-away — Model of an object that is built in sections so it
Current-flow is measured in amperes.
can be taken apart to reveal the inner structure.
current amplifier — An electronic device whose output
cutaway drawing — A mechanical drawing with a portion
current is greater than its input current.
of the outside not drawn in order to show what the inside
current density — The amount of electrical current per of the object looks like.
cross-sectional area of a conductor. Expressed in amperes
cut-aways — Model of an object that is built in sections so
per square inch.
it can be taken apart to reveal the inner structure.
current flight plan [ICAO] — The flight plan, including
cutout switch — An electrical switch that interrupts the
changes, if any, brought about by subsequent clearances.
power to a motor or actuator when the limit of its desired
current limiter — A device that limits the generator output travel is reached.
to a level within that rated by the generator manufacturer.
cuts out — The intermittent operation of a magneto or
current plan — The ATC clearance the aircraft has received ignition system.
and is expected to fly.
cutting edge — The edge of a tool or device used to remove
current regulator — An electronic device in a circuit that material when some type of force is applied.
maintains a constant current .
cutting fluid — A fluid, often consisting of oil and water
current switch — A switch used to activate a separate that is flowed over the cutting surface of a cutting tool.
circuit in response to a specified current. When the AC Its purpose is to cool the surfaces, lubricate the cutting
current being monitored reaches or exceeds the switch device, flush chips away, and inhibit corrosion.
setting, the switch will conduct to activate another AC or
cutting plane — A line on an aircraft drawing that indicates
DC control circuit connected to that switch.
the surface of an auxiliary view.
current transformer — An electronic device used to
cutting speed — The speed at which a cutting tool moves
indicate the amount of current in an alternating current
across or through a material. The speed must be set
transmission line. The primary winding is connected in
according to the material being cut and the cutting tool
series with the line current and the secondary winding is
type in order to reduce wear and optimize the speed of
connected to an indicator that reads out in volts, which
the cutting procedure.
are proportionate to the amperage in the primary.
cutting torch — A torch used to cut metals. It consists of
current-fed antenna — A half-wave antenna fed in its
pre-heating jets to heat the work to near melting and a
center.
cutting jet to burn through the metal.
current‑limiting resistor — A resistor placed in an
CVFP (Charted Visual Flight Procedure) approach —
electronic circuit to limit the amount of amperage flowing
An approach conducted while operating on an instrument
in the circuit.
flight rules (IFR) flight plan which authorizes the pilot
curriculum — A set of courses in an area of specialization of an aircraft to proceed visually and clear of clouds to
offered by an educational institution. A curriculum for a the airport via visual landmarks and other information
pilot school usually includes courses for the various pilot depicted on a charted visual flight procedure. This
certificates and ratings. approach must be authorized and under the control of the
appropriate air traffic control facility. Weather minimums
curvature — The shape of a surface that has a smooth,
required are depicted on the chart.
bending surface.
cyaniding — A hardening metal where the heated metal is
curvic coupling — A circular set of gear-like teeth on each
introduced to a cyanide bath. The metal absorbs nitrogen
of two mating flanges that provide a positive engagement
and carbon from the cyanide and creates a hardened
when meshed together and bolted. Used to attach together
surface.
turbine wheels, compressor disks, etc.

96

10001930-002_AviationDictionary_2012_BOOK.indb 96 3/27/2012 9:38:04 AM

 cyanoacrylate • cylinder taper

cyanoacrylate — A single-component, polyester-type resin which the fuel is burned and in which the piston moves
that hardens by exposure to ambient moisture and surface up and down.
alkalinity.
cylinder barrel — That portion of the cylinder or a
cybernetics — The comparative study of the interaction of reciprocating engine in which the piston moves up and
biological, mechanical, and electrical systems. down.
cycle — A period of time during which a sequence of cylinder bore — The diameter of the cylinder barrel.
recurring events is completed. In aviation, a cycle can be
cylinder fins — Metal fins on a cylinder that increase the
one takeoff and one landing, one extension and retraction
area of metal exposed to air. Allows the heat to radiate
of the flaps, one retraction and extension of the landing
out into the air for cooling.
gear, etc.
cylinder flange — The base of a cylinder that incorporates
cycle — A complete series of events or operations that recur
a machined mounting flange by which the cylinder
regularly. The series ends at the same condition as it
assembly is attached to the crankcase.
started so that the next series of events can immediately
take place. cylinder head — The closed end of the combustion chamber
of a reciprocating engine.
cycles per second — A measure of how often something is
repeated or oscillates (cycles) per second. One cycle per cylinder head temperature — The temperature of the
second is called one hertz (Hz). cast-aluminum head of an air-cooled reciprocating
aircraft engine cylinder.
cyclic feathering — In rotorcraft, the mechanical change of
the angle of incidence, or pitch, of individual rotor blades cylinder honing — A machining process that trues the
independently of other blades in the system. inside surface of a cylinder. The process also prepares the
inner surface of a reciprocating engine cylinder to receive
cyclic pitch control — The control in the cockpit of a
proper lubrication.
helicopter with which the pilot can change the pitch of
the rotor blades at a specific point in their rotation. The cylinder pads — The machined surfaces on the crankcase
resulting change imparts lateral, forward, or backward of an aircraft engine on which the cylinders are mounted.
movement to the helicopter.
cylinder skirt — That portion of a reciprocating engine’s
cycling — The operation of a unit such as the landing gear cylinder that extends below the mounting flange.
retraction system through its full range of operation.
cylinder taper — Many reciprocating engine cylinders are
cycling switch — A switch that opens and closes the circuit, tapered so that the top portion of the cylinder (nearest the
permitting a unit to cycle on and off. combustion chamber) is slightly smaller than the opposite
end. This allows for increased expansion due to higher
cyclogenesis — Any development or strengthening of
temperatures and increased mass at the combustion end
cyclonic circulation in the atmosphere.
of the cylinder. Also referred to as a choke-bore cylinder.
cyclone — In meteorology, the closed circulation around
a low pressure area. The flow is counterclockwise in the
Northern Hemisphere and clockwise in the Southern
Hemisphere. Large tropical cyclones are referred to as
typhoons or hurricanes.
cyclonic flow — In the Northern Hemisphere the
counterclockwise flow of air around an area of
low pressure and a clockwise flow in the Southern
Hemisphere.
cyclostrophic wind — A wind in a circular path, in which
Coriolis acceleration is negligible as compared to
centrifugal forces and pressure gradient acceleration.
cylinder — 1. A geometric
shape having ends of a
circular form and parallel
sides. 2. That component
of a reciprocating engine in

97

10001930-002_AviationDictionary_2012_BOOK.indb 97 3/27/2012 9:38:05 AM

 D • dead

D Area” is not used in reference to areas within the United

States or any of its possessions or territories.
D check — The highest and most thorough level of d’Arsonval meter movement — Most commonly used
inspection in a Continuous Airworthiness Maintenance meter movement in DC measuring instruments. A
Program. Entails a complete teardown of the aircraft for movable coil on which a pointer is mounted rotates in the
inspection, repair, and replacement of worn components. field of a permanent magnet. The amount of current in the
the entire program consists of A, C, and D checks. coil determines the strength of the coil’s electromagnetic
Dacron® — Polyester fibers made by DuPont, Inc. field and the amount the pointer is deflected by the
magnetic field of the permanent magnet.
dado head — A woodworking tool used to cut a wide,
flat-bottomed groove. Usually consists of two normal dart leaders — An individual event in a return stroke that
blades separated by a wood-chipping blade. the eye cannot distinguish that occurs following the
initial discharge. See lightning.
dado plane — A narrow, woodworking plane used to cut a
wide, flat-bottomed groove in wood. dash numbers — Numbers following, and separated from,
a part number by a dash identifying the components of
Dalton’s law — One of the basic gas laws that explains the part.
partial pressures. The law states that the total pressure of
a gaseous mixture made up of two or more separate gases dashpot — A mechanical damper used to cushion or slow
is the sum of the partial pressures of each of the gases. down movement by restricting the flow of a viscous fluid.
This explains why, at high altitudes, the partial pressure data — Information available on a subject that is processed
of oxygen is not enough to allow the oxygen to enter for the purpose of reasoning, discussion, calculations,
the blood stream without assistance from supplemental etc. Computers process data and provide a desired output.
oxygen or pressurization.
data base — A grouping of data that can be easily searched
dampen — To deaden, depress, reduce, or lessen. for specific information and then processed or acted upon.
damper — A device used to limit movement. data block — See alphanumeric display.
damper valve — A plate in the flue of a furnace that data plate — A permanent identification plate affixed to an
regulates the draft. The plate fills the flue when turned aircraft, engine, or component.
perpendicular, shutting off the flow of gas. When the
plate is turned parallel to the flue, gases can freely flow. In data stamp — Information stamped on units or components
aviation, similar valves control the flow of fluid in a tube. providing information on the correct name, part number,
date of manufacture, and cure date, as applicable.
damper vane — A vane in a fuel flow meter used to dampen
fluctuations caused by erratic flow. database identifier — A specific geographic point in space
identified on an aeronautical chart and in a navigation
damper-type combustion air fuel valve — An database, officially designated by the controlling state
automatically actuated damper‑type valve located in authority or derived by Jeppesen. It has no ATC function
the combustion air inlet of an aircraft heater. The valve and should not be used in filing flight plans nor used
is held open by fusible links that melt and allow the when communicating with ATC.
valve to shut off the combustion air in case of a fire or
over-temperature condition. data-plate speed — The speed at which the manufacturer
determines “rated power” of a gas turbine engine.
damping action — An action that smoothes out pulsations Stamped on a data plate affixed to the engine. The engine
in the flow of an oscillation. is required to perform within a certain range of this value
damping tube — A short length of tubing with an throughout its service life.
extremely small inside diameter inside a manifold datum — An arbitrary reference line from which all
pressure gauge. It prevents a pressure surge (caused by measurements are made when determining the moments
the engine backfiring) from damaging the mechanism of used for weight and balance computations. Also called
the instrument. datum line.
danger area — A specified or specific area designated as Davis wing — A wing with a narrow chord and a thick
dangerous. Constitutes a potentially hazardous situation cross-section.
to persons or property.
DC amplifier — An electronic amplifier whose output is
danger area [ICAO] — An airspace of defined dimensions greater than and proportional to its DC input signal.
within which activities dangerous to the flight of aircraft
may exist at specified times. NOTE: The term “Danger dead — In electricity, having no potential difference or
current flow.

98

10001930-002_AviationDictionary_2012_BOOK.indb 98 3/27/2012 9:38:05 AM

 dead center • decision height (DH) (USA)

dead center — Either of the two positions at the ends of decelerate — To slow down the velocity of an object.
a stroke in a crank and connecting rod when the crank Opposite of accelerate.
throws and rod lie in a straight line. See bottom dead
deceleration — The rate of decrease in velocity.
center and top dead center.
deceleration check — A check made on an engine while
dead engine — An engine that is not running during flight.
retarding the throttle from the acceleration check. The
dead reckoning — Dead reckoning, as applied to flying, RPM should decrease smoothly and evenly with little or
is the navigation of an airplane solely by means of no tendency for the engine to after fire.
computations based on airspeed, course, heading, wind
deci — A metric prefix indicating one tenth the term shown.
direction, and speed, groundspeed, and elapsed time.
Example: decimeter or deciliter.
dead reckoning navigation — A method of navigating
decibel (dB) — 1. A measure of sound intensity equal to
from one location to another without the use of outside
1/10 of a bel. 2. A unit used to express the ratio between
navigation aids. Dead reckoning navigation relies on
two amounts of electrical or acoustical power and equal
calculating the effects of predicted winds on the course
to 10 times the logarithm of this ratio.
and speed of the aircraft.
DECIDE model — To assist in teaching pilots the elements
dead short — An electrical path with very low resistance,
of the decision-making process, a six-step model has
usually disastrous in nature.
been developed using the acronym “DECIDE.”
dead-stick landing — An aircraft landing accomplished
Detect the fact that a change has occurred.
without an operative engine. There is no capability to go
around from an inaccurate approach. Estimate the need to counter or react to the change.
dead-weight tester — A calibration device used to test Choose a desirable outcome for the success of the flight.
pressure gauges for accuracy.
Identify actions, which could successfully control the
de-aeration — The process of removing air from a liquid. change.
de-aerator chamber — In hydraulics, an area of a reservoir Do the necessary action to adapt to the change.
where de‑aeration takes place.
Evaluate the effect of the action.
de-aerator tray — A container that collects the return oil
decimal — A proper fraction in which the denominator is a
from the oil system of a turbine engine and allows the
power of ten. Usually expressed as a number divided by
air bubbles to separate out of the oil before it returns to
a decimal (period). Example: 12.345
the system.
decimal digit — One of the ten Arabic numerals 0, 1, 2, 3,
debarkation — The unloading of passengers and cargo.
4, 5, 6, 7, 8, or 9.
debooster — A unit used in the brake system to reduce
decimal number system — A number system that uses the
system pressure and give faster application and release
base of ten. Each number is expressed with one of the
of the brakes.
first nine integers or 0 in each place and each place value
debug — To troubleshoot electronic equipment or computer represents a power of 10.
programs and return to proper operation.
decimal point — The dot that separates a whole number
Deca (Deka) — A metric prefix indicating ten times the from its decimal fraction. Example: 19.44.
term shown. Example: decameter or decaliter.
decision altitude/decision height [ICAO] — A specified
decade resistance box — An electrical test device that altitude or height (A/H) in the precision approach
provides the capability to insert selected values of at which a missed approach must be initiated if the
resistance into a circuit. required visual reference to continue the approach has
not been established. NOTE 1: Decision altitude (DA) is
decades — A series of quantities in multiples of 10.
referenced to mean sea level (MSL) and decision height
decalage — The difference in the angle of incidence of two (DH) is referenced to the threshold elevation. NOTE 2:
aerodynamic surfaces of an aircraft. (Between wings of a The required visual reference means that section of the
biplane or between the wing and the horizontal stabilizer). visual aids or of the approach area which should have
been in view for sufficient time for the pilot to have made
decarbonizers — Potent solvents used to soften the bond of
an assessment of the aircraft position and rate of change
carbon to a metal part.
of position, in relation to the desired flight path.
decay — The gradual decrease in the amplitude of a
decision height (DH) (USA) — With respect to the
vibration or oscillation.
operation of aircraft, means the height at which a

99

10001930-002_AviationDictionary_2012_BOOK.indb 99 3/27/2012 9:38:05 AM

 decision-making process • de-icing equipment

decision must be made, during an ILS or PAR instrument defense mechanisms — Subconscious ego-protecting
approach, to either continue the approach or to execute a reactions to unpleasant situations.
missed approach.
defense visual flight rules (DVFR) — Rules applicable to
NOTE: Jeppesen approach charts use the abbreviation flights within an ADIZ conducted under the visual flight
DA(H). The decision altitude “DA” is referenced to mean rules in FAR 91.
sea level (MSL) and the parenthetical decision height
deferred item — An item on a Minimum Equipment List
(DH) is referenced to the TDZE or threshold elevation. A
(MEL) that can be inoperative under specified conditions.
DA(H) of 1,440 ft.. (200 ft.) is a Decision Altitude of
When an item is deferred, it is often accompanied by
1,440 ft. and a Decision Height of 200 ft.
some sort of flight limitation.
decision-making process — Involves an evaluation of risk
deflate — To decrease the amount of air or gas held by an
elements to achieve an accurate perception of the flight
object.
situation. The risk elements include the pilot, the aircraft,
the environment, the operation, and the situation. deflecting‑beam torque wrench — A hand‑operated torque
wrench in which the amount of torque applied to a bolt is
declination — The angular difference between magnetic
indicated by the amount the beam is bent. The indication
north and true north caused by the magnetic north pole
is read against a fixed scale on the handle of the wrench.
not being located at the same place as the true north pole.
In navigation for aircraft this is called variation. deflection — The movement of an electron beam up and
down or sideways in response to an electric or magnetic
decoder — The device used to decipher signals received
field in a cathode‑ray tube.
from ATCRBS transponders to effect their display as
select codes. degauss — To remove magnetism or magnetic field from an
object or piece of equipment.
decomposing — The process of a material being broken
down into its basic elements. Example: water breaking degeneration — Feedback of a portion of the output of a
down into oxygen and hydrogen by the process of circuit to the input in such a direction that it reduces the
electrolysis. magnitude of the input; also called negative feedback.
Degeneration reduces distortion, increases stability, and
decontamination — The removal or neutralization of
improves frequency response.
undesired material from an area, a piece of equipment, a
building, or a person. degreaser — A solvent used for removing oil or grease
from a part.
decouple — To release or disconnect a unit.
dehumidify — To reduce the amount of water vapor in the air.
dedicated computer — A computer that is used only for
one function. dehydrator — A piece of equipment or substance used to
remove water vapor from the air. Silica gel is often used
deductible — The amount that the policyholder is
to absorb water within a closed space.
responsible for in the event of a claim.
dehydrator plug — A plastic plug with threads screwed
de-energize — To turn off a piece of electrical equipment.
into a spark plug opening of an aircraft engine cylinder.
deep cycling — A treatment of nickel cadmium batteries These plugs are filled with silica‑gel and an indicator
in which the battery is completely discharged, the cells to remove moisture from the air inside the cylinder and
shorted out and allowed to “rest.” The battery is then indicate the condition of preservation of the cylinder.
recharged to 140% of its ampere‑hour capacity.
deicer — A system or substance that removes ice from an
deep discharge — The procedure of removing all electrical aircraft structure.
energy from a battery. After discharging a battery down
deicer boots — Inflatable rubber boots attached to the
to a low level, the cells are shorted out with shorting clips
leading edge of an airfoil. They can be sequentially
until all cells are completely discharged. This allows all
inflated and deflated to break away ice that has formed
cells to be recharged from the same starting condition.
over their surface.
deepening — A decrease in the central pressure of a
deicer tubes — The inflatable tubes in the deicer boot.
pressure system; usually applied to a low rather than to a
high, although technically, it is acceptable in either sense. deicing — Removing ice after it has formed.
defect — Any imperfection, fault, flaw, or blemish that may de-icing equipment — Aircraft equipment that is actuated
require repair or replacement of a part. to remove ice from the structure of the aircraft that has
already formed.
defective — Faulty. Not operating normally.

100

10001930-002_AviationDictionary_2012_BOOK.indb 100 3/27/2012 9:38:05 AM

 deicing fluid • departure control

deicing fluid — A liquid (usually heated) that is sprayed demonstration stalls — Stalls that the instructor
on an aircraft to remove ice. Deicing fluid prevents the demonstrates mainly as an in-flight portion of stall/spin
return of ice for a specified period of time. awareness training. The flight instructor PTS lists these
stalls, categorizes them, and explains the knowledge and
delaminate — In composites, the separation of layers due
skill associated with successful performance. Advise
to adhesive failure. This also includes the separation of
student pilots that demonstration stalls are not to be
the layers of fabric to a core structure. A delamination
practiced in solo flight. Like other flight maneuvers,
may be associated with bridging, drilling, and trimming.
perform demonstration stalls at an altitude that allows for
delaminated — 1. A condition caused by exfoliation recovery above 1,500 ft. AGL.
corrosion in which the layers of grain structure in an
demonstration-performance method — An educational
extrusion separate from one another. 2. Separation of the
presentation in which an instructor first shows the student
core and face sheets of a bonded structure along a bond
the correct way to perform an activity and then has the
line.
student attempt the same activity.
delay indefinite (reason if known) expect further
demulsibility — The measure of an oil’s ability to separate
clearance (time) — Used by ATC to inform a pilot when
from water.
an accurate estimate of the delay time and the reason
for the delay cannot immediately be determined; e.g., a demulsifier — A system or substance that causes an
disabled aircraft on the runway, terminal or center area emulsion (mixture) of two or more substances to break
saturation, weather below landing minimums, etc. down into component materials.
delay time — The amount of time that the arrival must lose denatured alcohol — Grain alcohol (ethyl alcohol or
to cross the meter fix at the assigned meter fix time. This ethanol) with substances added to make it unfit for human
is the difference between ACLT and VTA. consumption without affecting its use for other purposes.
delta — Greek letter (Δ) used in weight and balance denial of reality — A psychological defense mechanism
computations to indicate amount of change. where students may ignore or refuse to acknowledge
disagreeable realities. They may turn away from
delta connection — A method of connecting three
unpleasant sights, refuse to discuss unpopular topics, or
components to form a three‑sided circuit, usually drawn
reject criticism.
as a triangle, hence the term delta.
denier — A numbering system for filaments in the yarn
delta hinge — The hinge located at the root end of the rotor
used for weaving. The number is equal to the weight in
blade with its axis parallel to the plane of rotation of the
grams of 9,000 meters of yarn.
rotor that allows the blade to flap. The flapping blade
equalizes lift between the upwind and downwind sides denominate number — A number associated with a unit of
of the rotor disc. measurement.

delta winding — The denominator — The part of a fraction below the line
connection of the indicating division. It is an indication of the number of
windings of three‑­phase parts into which a number is divided.
AC machines. The three density — The mass of a substance per unit of its volume.
windings are connected The weight per unit volume expressed in pounds per
together to form a loop or cubic foot.
a single path through the
three windings. density altitude — Pressure altitude corrected for
nonstandard temperature variations.
delta wing — The triangular
wing planform of an dent — A depression in a surface usually caused by the
aircraft. surface being struck by another object.

demagnetize — To remove dented surface — A depression on a surface that usually

magnetic properties from affects a small area. Cams, tappet rollers, and ball and
an object. roller bearings are the parts most often involved.

demand oxygen system — Any oxygen system in which departure center — The ARTCC having jurisdiction for
the delivery of oxygen is metered according to the rate the airspace that generates a flight to the impacted airport.
and depth of a user’s breathing. departure control — A function of an approach control
demodulation — The recovery of the signal from a radio facility providing air traffic control service for departing
frequency carrier wave. Also referred to as detection. IFR and, under certain conditions, VFR aircraft.

101

10001930-002_AviationDictionary_2012_BOOK.indb 101 3/27/2012 9:38:05 AM

 departure end of runway (DER) • detents

departure end of runway (DER) — The end of runway desiccant bags — Cloth containers of a silica gel desiccant
available for the ground run of an aircraft departure. The packed with an engine or component that is placed in
end of the runway that is opposite the landing threshold, long‑term storage.
sometimes referred to as the stop end of the runway.
design load — The load for which a member is designed.
departure sequencing program — A program designed to It is usually obtained by multiplying a basic load by a
assist in achieving a specified interval over a common specified design load factor.
point for departures.
design maneuvering speed (VA) — The maximum speed
departure time — The time an aircraft becomes airborne. at which you can use full, abrupt control movement
without over stressing the airframe.
depletion area — That area on both sides of the junction of
a semiconductor that varies between acting as a conductor design size — That size from which the limits of size are
and an insulator. derived by the application of tolerances. When there is no
allowance, the design size is the same as the basic size.
depolarization — The absorption of generated gases in a
chemical cell especially during the “rest” periods. This designated — Being given the legal right and authority
may cause an apparent rejuvenation of the cell. to perform certain specified functions by the Federal
Aviation Administration.
deposition — The direct transformation of a gas to a solid
state, where the liquid state is bypassed. designated examiner — Any person authorized by the
Administrator to conduct a pilot proficiency test or a
depreservation — A procedure that includes a special
practical test for an airman certificate or rating issued
inspection and cleaning of aircraft parts removed from
under FAR Part 61. Also, a person authorized to conduct
storage prior to being installed on the aircraft or engine.
a knowledge test under FAR Part 61.
depressants — Drugs that reduce the body’s functioning
desired course — 1. True desired course — A predetermined
usually by lowering blood pressure, reducing mental
desired course direction to be followed (measured in
processing, and slowing motor and reaction responses.
degrees from true north). 2. Magnetic desired course —
depression — In meteorology, an area of low pressure, as in A predetermined desired course direction to be followed
a trough. Often used to describe the stage of development (measured in degrees from local magnetic north).
of a cyclone, as in “tropical depression.”
desired track — The planned or intended track between
depth gauge — A device used to measure the depth of a two waypoints. It is measured in degrees from either
hole, groove, or depression. magnetic or true north. The instantaneous angle may
change from point to point along the great circle track
depth micrometer — A form of micrometer caliper used to
between waypoints.
measure the depth of a recess.
destructive testing — Testing that results in the destruction
derate — To reduce the allowable power output of an engine
of the item being tested. For example, as a part of the
or motor in order to extend the life of the equipment.
certification process, aircraft wing structures are often
derichment — An automatic leaning of the fuel‑air mixture loaded until they fail.
ratio to a ratio that will produce maximum power
detail drawing — A drawing that describes a single part
regardless of the heat released. Derichment occurs when
in detail.
the anti‑detonation injection system injects liquid into the
cylinders to remove this excess heat. detail view — An auxiliary view incorporated into a
drawing to show additional details of a part.
descent — A reduction in altitude.
detailed inspection item — An item of a progressive
descent speed adjustments — Speed deceleration
inspection that requires close and careful inspection.
calculations made to determine an accurate VTA. These
May require disassembly or complete overhaul of a
calculations start at the transition point and use arrival
component or part.
speed segments to the vertex.
detector — That portion of an electronic circuit that
description of the skill or behavior — The first part of a
demodulates or detects the signal.
performance-based objective, which explains the desired
outcome of instruction in measurable concrete terms. detents — The points along a line of movement of a control
where distinct resistance to movement can be felt. These
desiccant — 1. Any form of absorbent material. 2. A
points are usually found at specific levels of importance
material used in a receiver‑dryer to absorb moisture from
to the operation of the controlled unit. An example would
the refrigerant.
be the flap control lever, where detents could be assigned
either to the number of degrees of travel (15º, 30º, and

102

10001930-002_AviationDictionary_2012_BOOK.indb 102 3/27/2012 9:38:05 AM

 detergent • diamond dressing tool

45º) or at specific performance points such as takeoff grass, as the near-surface layer of air cools faster than the
flaps and landing flaps. layers of air above it.
detergent — A cleansing material. An oil-soluble substance dew point — The temperature at which air becomes
that holds insoluble matter in suspension. Detergent saturated and produces dew or moisture.
is sometimes referred to as soap, though detergent is
Dewar flask — A double‑wall vacuum chamber used for
chemically different than soap.
the storage of liquid oxygen. Similar in principle to a
detergent oil — A mineral oil to which ash‑forming Thermos® bottle.
additives have been added to increase its resistance
dewaxed oil — A pure lubricating oil that has had waxy
to oxidation. Because of its tendency to loosen carbon
products removed during the refining process.
deposits, it is not used in aircraft engines.
dewpoint — The temperature to which air must be cooled
deteriorate — To become worse.
to become saturated with water vapor.
determiners — In test items, words that give a clue to
DF approach procedure — Used under emergency
the answer. Words such as “always” and “never” are
conditions where another instrument approach procedure
determiners in true-false questions. Since absolutes are
cannot be executed. DF guidance for an instrument
rare, such words usually make the statement false.
approach is given by ATC facilities with DF capability.
detonation — The sudden release of heat energy from
DF fix — The geographical location of an aircraft obtained
fuel in an aircraft engine caused by the fuel‑air mixture
by one or more direction finders.
reaching its critical pressure and temperature. Detonation
occurs as a violent explosion rather than a smooth DF guidance — Headings provided to aircraft by
burning process. facilities equipped with direction finding equipment.
These headings, if followed, will lead the aircraft to a
DETRESFA (distress phase) [ICAO] — The code word
predetermined point such as the DF station or an airport.
used to designate an emergency phase wherein there is
DF guidance is given to aircraft in distress or to other
reasonable certainty that an aircraft and its occupants
aircraft which request the service. Practice DF guidance
are threatened by grave and imminent danger or require
is provided when workload permits.
immediate assistance.
DF steer — See DF guidance.
Deutsch rivet — A type of
high-strength blind rivet. diagonal cutting pliers — A wire cutting tool that cuts by
chiseling action rather than by shearing.
developed width — Width
of the flat layout of a sheet diagram — A graphic representation of an assembly or
metal part. system.
developer — A powder that has been treated with a dial — An analog style instrument face.
penetrating dye. When sprayed on a surface, the powder
dial indicator — A precision linear measuring instrument
acts as a blotter, pulling penetrant out of any crack and
whose indication is amplified and read on a circular dial.
exposing the crack.
dial-indicating torque wrench — A hand‑operated,
development — The main body of an instructional lesson
deflecting beam‑type torque wrench that uses a dial
that contains a detailed listing of the subject matter.
indicator to measure the deflection of the beam and reads
Developing material in a structured way speeds up the
directly in foot‑pounds, inch-pounds, or meter‑kilograms
process and makes it easier to follow a logical progression.
of torque.
deviation — A compass error caused by magnetic
diamagnetic material — A material having extremely low
disturbances from electrical and metal components in
magnetic permeability and considered to be nonmagnetic.
the airplane. The correction for this error is displayed
on a compass correction card placed near the magnetic diameter — The length of a chord passing through the
compass in the airplane. center of a circular body.
deviations — 1. A departure from a current clearance, diamond — A hard substance consisting of nearly pure
such as an off course maneuver to avoid weather or carbon. Some are of gem quality while others, of
turbulence. 2. Where specifically authorized in the FARs industrial quality, are used as cutting surfaces.
and requested by the pilot, ATC may permit pilots to
diamond chisel — A cutting tool with a diamond shaped
deviate from certain regulations.
cutting face.
dew — Moisture that has condensed from water vapor.
diamond dressing tool — An industrial diamond mounted
Usually found on cooler objects near the ground, such as
in a tool and used to true a grinding wheel.

103

10001930-002_AviationDictionary_2012_BOOK.indb 103 3/27/2012 9:38:05 AM

 diamond-point cutting tool • diffuser vane

diamond-point cutting tool — A machine tool used for represent the same thing to every person. Confusion
machining very hard metals. The cutting face consists of results when the name of an object is not differentiated
an industrial grade diamond. from the characteristics of the object itself.
diaphragm switch — A switch whose position is controlled differences training — Training given to pilots who wish
by movement of a diaphragm. to transition between similar makes and models of a
given manufacturer. For example, transitioning from a
diaphragm type pump — A pump that uses a cam-operated
C-210 to a P-210 would require differences training for
flexible diaphragm to move fuel past spring-loaded
pressurization and turbocharging.
valves. The pump can have a single diaphragm that only
pumps on one direction of movement of the cam, or it differential aileron travel
can have a double diaphragm that operates on both the — The increased travel of
powered stroke and the spring return. the aileron moving up over
that of the aileron moving
diaphragm‑controlled — A mechanical movement
down. The up aileron
controlled by the action of a pressure or suction applied
produces extra parasite drag
to a diaphragm.
to compensate for the additional induced drag caused by
dibromodifluoromethane — A fire extinguishing agent. the down aileron. This balancing of the drag forces helps
Noncorrosive to aluminum, brass, and steel, it is less minimize adverse yaw.
toxic than CO2. It is one of the more effective fire
differential compression check — A test of the condition
extinguishing agents available. Halon 1202.
of an engine cylinder in which the amount of leakage past
dichromate solution — Cr2O7. Used with zinc as zinc the piston rings and valves is determined by measuring
dichromate, a protective coating on metal parts. the pressure drop across a calibrated orifice in the tester.
Sometimes referred to as gold iridite and found on many
differential heating — The heating of objects that have
brake components. Also found in sodium dichromate
dissimilar heat capacities. See heat capacity.
(Na2Cr2O7) and Potassium dichromate (K2Cr2O7).
Sodium dichromate is used to protect magnesium parts. differential pressure — A difference between two
pressures. The measurement of airspeed is an example of
die — 1. A tool used to shape or form metal or other
the use of a differential pressure.
materials. 2. A cutting tool used to cut threads on the
outside of round stock. differential pressure range of pressurization — The range
of cabin pressurization in which a constant differential is
die casting — Method by which molten metal is forced into
maintained between cabin pressure and the outside air
suitable permanent molds by hydraulic pressure in order
pressure.
to improve the grain structure of the resulting casting.
differential pressure switch — A diaphragm and electrical
dielectric — A material that will not conduct electricity.
microswitch arrangement that senses two pressures.
dielectric constant — Symbol: k. The characteristic of an If the difference in the two pressures exceeds a certain
insulator that determines the amount of electrical energy value, the microswitch illuminates a warning light.
that can be stored in electrostatic fields.
differential-voltage reverse‑current relay — Removes a
dielectric qualities — Insulating characteristics of a battery from and connects a generator to a load when the
material. generator voltage is higher than the battery voltage. If
the generator voltage falls below the battery voltage, the
dielectric strength — A measure of a dielectric’s ability to
battery will be reconnected.
withstand puncture by electrical stresses.
differentiating circuit — A circuit that produces an output
diesel engine — An internal combustion reciprocating
voltage proportional to the rate of change in input voltage.
engine whose ignition is achieved by the heat of
compression rather than with an electrical ignition. diffuser — 1. A duct used on a centrifugal flow turbine
engine to reduce the velocity of the air and increase its
diesel fuel — A fuel used in diesel engines. Very close in
pressure. 2. The divergent section of a gas turbine engine
grade to jet-fuel and kerosene.
used to convert velocity energy of compressor discharge
dieseling — The continued firing of a reciprocating engine air into pressure energy.
after the ignition has been turned off. Ignition is caused
diffuser vane — A turning or cascading vane in a centrifugal
by incandescent particles in the combustion chamber.
flow engine diffuser used to change air from a radial
difference between the symbol and the symbolized direction as it leaves the impeller to an axial direction as
object — The result of a word being confused with an it moves into the combustor.
unintended meaning. Words and symbols do not always

104

10001930-002_AviationDictionary_2012_BOOK.indb 104 3/27/2012 9:38:05 AM

 diffusion • direct altitude and identity readout

diffusion — 1. A process where particles of liquids, gases, dimpling — A process used

or solids move from a region of higher concentration to to indent the hole into
one of lower concentration. 2. The scattering of light by which a flush rivet is to be
a rough surface or by transmission through a translucent installed. Some metals such
material. as the harder aluminum alloys cannot be dimpled while
diffusion welding — A method of fusing materials to the metal is cold because it is likely to crack. This type
each other that relies on the two materials being pressed of metal must be hot dimpled. Hot dimpling equipment
together under high pressure and the joint heated to less consists of a pair of electrically heated dies with a pilot
than melting temperature. The two pieces fuse together that is inserted into the rivet hole. The pilot is passed
without the strength degradation found with normal through the hole and the heated dies are pressed together.
welding. The dies heat the metal enough to soften it and force it
into the shape of the die.
digital readouts — The presentation of information by an
instrument in a digital form such as light emitting diodes diode — A device that allows a flow of electrons in one
or drums, rather than by the movement of a pointer over direction but not the opposite. Also referred to as an
a numbered dial. electron check valve.

digital voltmeter — A voltage measuring device that reads dip — A vertical attraction between a compass needle and
out in digital form rather than an analog dial. the magnetic poles. The closer the aircraft is to the pole,
the more severe the effect. In the Northern Hemisphere a
digitize — To change an analog reading to digital format weight is placed on the south-facing end of the compass
(binary) that can be used by a computer. needle; in the Southern Hemisphere a weight is placed on
dihedral — The positive acute angle between the lateral the north-facing end of the compass needle to somewhat
axis of an airplane and a line through the center of a wing compensate for this effect.
or horizontal stabilizer. dip coating — A process of coating various products with
dikes — A common expression for diagonal cutting pliers. a soft, rubber-like, plastic coating applied by dipping the
product into a container of plastic coating. Often used to
diluent — A material used to change the concentration of insulate the handles of hand tools.
some other substance without changing the characteristics
of the base material. Common diluents include water- DIP (Dual Inline Packaging) — A standard configuration
used to dilute salt water solutions and water-based paints used for chips, DIP switches, etc., used on computer
and paint thinners used to dilute oil-based paints. circuit boards.

diluter-demand oxygen system — An oxygen system dip soldering — A process of lowering a printed circuit
that delivers oxygen mixed or diluted with air in order board onto the top of a container of molten solder in order
to maintain a constant oxygen partial pressure as the to solder the leads of components that extend through the
altitude changes. board.

dilution air — The portion of combustion secondary air dipole antenna — A center-fed, half-wave antenna.
used to control the gas temperature immediately prior to dipping — A method of paint application in which a part is
its entry into the turbine nozzle area. dipped into a tank of finishing material.
dimension — A measurement of length, width, thickness, dipstick — A bayonet-type gauge used for measuring the
size, or degree listed within a drawing. quantity of fluid in a reservoir.
dimension line — A light solid line broken at its midpoint direct — Straight line flight between two navigational aids,
for insertion of measurement indications. Dimension fixes, points or any combination thereof. When used by
lines typically have outward pointing arrowheads at each pilots in describing off-airway routes, points defining
end to show origin and termination of a measurement. direct route segments become compulsory reporting
dimensional inspection — The physical measurement of points unless the aircraft is under radar contact.
a part against a recognized standard to determine the direct altitude and identity readout — The DAIR
amount of wear or deformation of the part. System is a modification to the AN/ TPX-42 Interrogator
dimmer — A device that controls illumination. Can be System. The Navy has two adaptations of the DAIR
either a simple rheostat or a variable pulse control. System - Carrier Air Traffic Control Direct Altitude
and Identification Readout System for Aircraft Carriers
dimming relay — A relay that allows a light or lights in a and Radar Air Traffic Control Facility Direct Altitude
circuit to be dimmed. and Identity Readout System for land based terminal
dimming rheostat — A rheostat used to control the degree operations. The DAIR detects, tracks, and predicts
of brilliance of a lighting circuit. secondary radar aircraft targets. Targets are displayed by

105

10001930-002_AviationDictionary_2012_BOOK.indb 105 3/27/2012 9:38:06 AM

 direct control • discharge indicator disk

means of computer generated symbols and alphanumeric ground-based transmitters, both of which can be
characters depicting flight identification, altitude, ground identified on his chart. UDF’s receive signals in the ultra
speed, and flight plan data. The DAIR System is capable high frequency radio broadcast band; VDF’s in the very
of interfacing with ARTCCs. high frequency band; and UVDF’s in both bands. ATC
provides DF service at those air traffic control towers
direct control — In rotorcraft, the ability to maneuver a
and flight service stations listed in the Airport/Facility
rotorcraft by tilting the rotor disc and changing the pitch
Directory and the DOD Flip IFR En Route Supplement
of the rotor blades.
and the Jeppesen Radio Aids Section.
direct current (DC) — A flow of electrons in one direction
directional antenna — An antenna that either transmits
throughout a circuit.
or receives signals in a field pattern other than
direct question — A question used for follow-up purposes, omnidirectional. Usual patterns for waves that are longer
but directed at a specific individual. than microwaves are either cardioid or figure-eight.
Microwave antennae usually have narrow field patterns.
direct route — A requested route published on a Jeppesen
Enroute or Area chart to assist pilots who have previous directional gyro — An instrument used to determine
knowledge of acceptance of these routes by ATC. Use of heading in an aircraft. It does not indicate magnetic
a direct route may require prior ATC approval and may direction, but is gyro-stabilized to indicate direction after
not provide ATC or Advisory services, or be acceptable being set with reference to a magnetic compass.
in flight plans.
directional reference — In gas turbine engines, an industry
direct shaft turbine — A turbine engine in which the standard to describe engine locations. The orientation is
compressor and power section are mounted on a common to look from the rear towards the front of the engine and
driveshaft. use standard twelve hour clock reference points. Right
Side and Left Side are also determined in this manner.
direct user access terminal service (DUATS) — A
computer-based program providing NWS and FAA directional stability — Stability about the vertical axis
weather products that are normally used in pilot weather of an aircraft, whereby an aircraft tends to return, on
briefings. its own, to flight aligned with the relative wind when
disturbed from that equilibrium state. The vertical tail is
direct-cranking electric starter — A high‑torque,
the primary contributor to directional stability, causing an
direct‑current electric motor used to rotate a reciprocating
airplane in flight to align with the relative wind.
aircraft engine for starting.
dirigible — A lighter-than-air aircraft. Dirigibles are
direct-current amplifier — An electronic amplifier whose
constructed of a lightweight metal framework supporting
output is greater than and proportional to its DC input
a fabric gas envelope filled with helium (early dirigibles
signal.
used flammable hydrogen). Dirigibles are propelled
direct-current electricity — Electricity that flows in one by engine-driven propellers and are capable of being
direction only. The current from solar cells, chemical cells maneuvered as opposed to balloons that drift with the
(batteries), and thermocouples are direct-current (DC). prevailing wind.
direct-current generator — Electrical generator that has disbond — In composites, the separation of a bond from
a DC output rather than an AC output. Since generators one structure to another. Many times this term is used for
naturally produce AC, an electronic rectifier or a referring to the separation of the laminate skin to the core
commutator (mechanical rectifier) must convert the AC structure. It is also used for a separation from a fitting to
output to DC. the skin.
direct-current motor — A motor that operates on direct disc area — In rotorcraft, the area swept by the blades of
current (DC). the rotor. It is a circle with its center at the hub and has a
radius of one blade length.
direction finder — A radio receiver equipped with a
directional sensing antenna used to take bearings on a disc loading — The total helicopter weight divided by the
radio transmitter. Specialized radio direction finders are rotor disc area.
used in aircraft as air navigation aids. Others are ground
discharge indicator disk — An indicator disk on the
based primarily to obtain a “fix” on a pilot requesting
exterior of an aircraft that indicates the status of the
orientation assistance, or to locate downed aircraft. A
onboard fire protection system. If the system has been
location “fix” is established by the intersection of two
discharged normally, a yellow disk is blown out, and if
or more bearing lines plotted on a navigational chart
the system has discharged because the system overheats,
using either two separately located Direction Finders
a red disk is blown out.
to obtain a fix on an aircraft or by a pilot plotting the
bearing indications of his DF on two separately located

106

10001930-002_AviationDictionary_2012_BOOK.indb 106 3/27/2012 9:38:06 AM

 discharge nozzle • distance measuring equipment (DME)

discharge nozzle — The portion of a carburetor that sprays dispersant — A substance that keeps particles suspended
the fuel into the intake airstream. Serves to atomize the in solution. An example is ashless dispersant (AD)
fuel for best combustion. oil. It contains a substance that causes ash and other
contaminants suspended in the oil to be filtered out.
disconnect — To remove a load from a source of power or
the removal of one electrical device from another by the displaced threshold — When the landing area begins at
use of a manually-operated switch or an automatic relay. a point on the runway other than the beginning of the
runway.
discontinuity — In meteorology, a condition where there
is a rapid change from one type of weather phenomena display tube — An electron tube in which a stream of
or air mass to another. A cold front is an example of a electrons (cathode rays) from an electron gun impinges
discontinuity. upon a fluorescent screen, thus producing a bright spot
on the screen. The electron beam is deflected electrically
discreet — Showing good judgment in conduct or speech.
or magnetically to produce patterns on the screen. Also
discrete — Not linear. A single action rather than action referred to as a cathode ray tube (CRT).
changing through a range.
dissimilar metal corrosion — Corrosion caused by the
discrete beacon code — See discrete code. different atomic structures of metals. All metals are
listed on a nobility chart from the most vulnerable to
discrete code — As used in the Air Traffic Control Radar
corrosion (least noble) to the least vulnerable (most
Beacon System (ATCRBS), any one of the 4096 selectable
noble). Magnesium and Zinc are the most vulnerable to
Mode 3/A aircraft transponder codes except those ending
corrosion, while gold and platinum are the least. When
in zero zero; e.g., discrete codes: 0010, 1201, 2317, 7777;
two metals are in contact with each other, the farther apart
non-discrete codes: 0100, 1200, 7700. Non-discrete codes
they are on the nobility chart, the more likely dissimilar
are normally reserved for radar facilities that are not equipped
metal corrosion will occur. All that is necessary is for an
with discrete decoding capability and for other purposes such
electrolyte (usually water) to contact the area where they
as emergencies (7700), VFR aircraft (1200), etc.
touch for corrosion to occur.
discrete frequency — A separate radio frequency for
dissipate — To lessen in concentration or intensity. Smoke
use in direct pilot-controller communications in air
can dissipate due to mixing with surrounding cleaner air.
traffic control which reduces frequency congestion
Electrical power can be dissipated by being changed to
by controlling the number of aircraft operating on a
heat by a motor, transformer, or resistor.
particular frequency at one time. Discrete frequencies are
normally designated for each control sector in enroute/ dissipating stage — Thirty minutes or so after a single-cell
terminal ATC facilities. Discrete frequencies are listed on airmass thunderstorm begins, downdrafts spread
Jeppesen charts. throughout the lower levels of the cell. Without the
necessary source of energy, (heat and moisture), the
discrimination — 1. In knowledge testing, able to detect
end of the thunderstorm is near and the clouds take on a
small differences in understanding of material tested. 2.
strataform appearance.
In a measuring instrument, means being able to detect
small differences in understanding of material between dissipation contrail (distrail) — A streak of clearing that
individuals. occurs behind an aircraft as it flies near the top of, or just
within a thin cloud layer.
discriminator — In a radio receiver, a demodulator that
derives an audio signal from an incoming frequency- or dissolve — To change form from a solid to become part of
pulse-modulated RF signal. a liquid into which the solid is placed, so as to pass into
solution. A crystal of salt dissolves when placed in water
disengage — To break the connection between mechanical
to become a new liquid, salt water.
or electronic components.
dissymmetry of lift — On a helicopter in forward flight,
dish antenna — A parabolic-shaped antenna used for
the advancing blade develops more lift at a given angle
transmitting and receiving microwave signals.
of attack than does the retreating blade. This is because
disk area — A description of an area swept by the blades the effective velocity of the relative wind is greater on the
of a helicopter. advancing blade. The blades of a helicopter are designed
to flap in order to compensate for this.
disk brake — A brake that achieves brake action with a disk
or disks attached to the rotating wheel being squeezed distance measuring equipment (DME) — Equipment
between brake pucks and caliper attached to the aircraft (airborne and ground) to measure, in nautical miles,
gear structure. the slant range distance of an aircraft from the DME
navigation aid.
disk loading — A ratio of the gross weight of a helicopter
to the disk area.

107

10001930-002_AviationDictionary_2012_BOOK.indb 107 3/27/2012 9:38:06 AM

 Distant Early Warning Identification Zone (DEWIZ) • diving blade

Distant Early Warning Identification Zone (DEWIZ) — disturbance — In meteorology, another name for an area
An ADIZ (Air Defense Identification Zone) located over that shows indications of cyclonic development, along
the coastal waters of Alaska. with associated weather such as clouds and precipitation.
distillate fuel — A liquid hydrocarbon fuel that has been disuse — A theory of forgetting that suggests a person
condensed from vapors of crude petroleum. forgets those things which are not used.
distillation — A process whereby a liquid is heated until dither signal — A varying signal that is mixed into a
gases boil off, and the gases are then cooled until they command signal and increases sensitivity of control.
condense back into a liquid. The process is used to purify Dithering the commands to a stepper motor enables
water or to select certain petroleum products from a base response with lessened hysteresis. The least significant
liquid of crude oil. Distillation of individual petroleum bit of an analog-to-digital signal converter can be dithered
products is possible since each boils off at a different to lessen ambiguity.
temperature.
diurnal effects — A daily variation (may be in temperature,
distilled water — Water that has been heated until it boils moisture, wind, cloud cover, etc.) especially pertaining
and is then condensed back into a liquid. The effect to a cycle completed within a 24-hour period, and which
purifies the water, leaving the non-water products behind. recurs every 24 hours.
distortion — An undesired change in the waveform of the diurnal variation — Daily, especially pertaining to a cycle
output of a circuit –as compared with the input. completed within a 24‑hour period, and which recurs
every 24 hours.
distractions — During training flights, an instructor should
interject realistic distractions to determine if students can dive — A steep, nose-down descent.
maintain aircraft control while their attention is diverted.
dive brake — An auxiliary control that slows an aircraft
distractors — Incorrect responses to a multiple-choice test during descent. Used to limit speed or to minimize
item. “shock cooling” on reciprocating engines by allowing
higher power settings during descent. Also referred to as
distress — A condition of being threatened by serious and/or
a speed brake.
imminent danger and of requiring immediate assistance.
dive flaps — Devices used on an airplane to produce drag
distress frequencies — Radio frequencies used for
without an attendant increase in lift. Also referred to as
broadcasting distress signals. In aviation, the frequencies
speed brakes.
are 121.5 MHz, 243.0 MHz, and 406.0 MHz.
divergence — In meteorology, the condition that exists
distributed pole motor — An electric motor that has the
when the distribution of winds within a given area is such
stator windings wound into slots in the motor frame
that there is a net horizontal flow of air outward from the
rather than on discrete pole shoes.
region. The opposite of convergence.
distributor — That part of a high-tension magneto that
divergent duct — A cone‑shaped passage or channel in
distributes the high voltage to each spark plug at the
which a gas can be forced to flow from its smallest area
proper time. Distributors for low-tension ignition
to its largest area resulting in decreased velocity and
systems distribute the low voltage to the transformers at
increased pressure.
each spark plug at the proper time for air-fuel ignition.
diverse vector area — In a radar environment, that area
distributor block — A dielectric block in a magneto that
in which a prescribed departure route is not required
contains stationary electrodes to pick up the voltage from
as the only suitable route to avoid obstacles. The area
a rotating distributor brush or finger and deliver it to the
in which random radar vectors below the MVA/MIA,
proper ignition lead.
established in accordance with the TERPS criteria for
distributor brush — A carbon brush used on a low‑tension diverse departures obstacles and terrain avoidance, may
magneto to distribute the voltage to the distributor block be issued to departing aircraft.
as it rotates.
dividend — A number to be divided.
distributor finger — A rotating conductor in the distributor
dividers — A measuring tool having two movable legs,
of a high-tension magneto that delivers voltage to the
each with sharp points. Dividers can be used to transfer
distributor electrodes.
measurements or to divide straight or uniformly curved
distributor valve — A device that controls the inflation lines into an equal number of parts.
sequence of deicer tubes.
diving blade — A blade track of a helicopter’s main rotor that
lowers with an increase in revolutions per minute (RPM).

108

10001930-002_AviationDictionary_2012_BOOK.indb 108 3/27/2012 9:38:06 AM

 divisor • double magneto

divisor — The number by which a dividend is divided. with germanium or silicon in semiconductors to create
diodes and transistors.
DME fix — A geographical position determined by
reference to a navigational aid which provides distance donor impurity — The elements added to germanium or
and azimuth information. It is defined by a specific silicon to create diodes and transistors.
distance in nautical miles and a radial, azimuth, or course
dope — The finishing material used on fabric surfaces that
(i.e., localizer) in degrees magnetic from that aid.
tautens, strengthens, and weatherproofs the fabric.
DME separation — Spacing of aircraft in terms of
dope proofing — Coating the structural elements of a
distances (nautical miles) determined by reference to
fabric-covered aircraft to protect them from the solvents
distance measuring equipment (DME).
in the dope.
dock — An enclosed work area where airplanes can be
dope roping — A condition in the application of dope in
placed for repairs.
which the surface dries while the dope is being brushed.
docking — Placing an airplane in a hangar where dock This results in a stringy, uneven surface.
platforms are used to facilitate maintenance.
doped-in panel — An entire panel between ribs and from
DOD FLIP — Department of Defense Flight Information the trailing edge to the leading edge that is doped in
Publications used for flight planning, enroute, and place, but includes rib stitching on sections over the ribs.
terminal operations. FLIP is produced by the National
doped-on fabric repair — Repair of a small section of a
Imagery and Mapping Agency (NIMA) for worldwide
fabric structure. Typically applied by doping on a patch
use. United States Government Flight Information
over a small hole or tear in the fabric.
Publications (enroute charts and instrument approach
procedure charts) are incorporated in DOD FLIP for use doped-on fabric repair — The repair of small damage to
in the National Airspace System (NAS). a fabric covered aircraft by doping a patch directly to the
fabric covering using no other attachment
doghouse — A mark on a turn and slip indicator that
resembles a doghouse. It is located one needle width dope-proof paint — A paint applied to protect structure
away from the center and when the pointer aligns with it from being damaged by the solvents in the dope.
a standard rate of turn is being made.
Doppler effect — The effect where any oscillating
dolly — A low mobile platform on wheels or casters used frequency, whether sound or radar beams, are compressed
for moving heavy aircraft components. (increased in frequency) as the source and the receiver
move closer to each other and decompressed (lowered in
dolly block — Variously shaped anvils used to form and
frequency) when moving apart.
finish sheet metal parts.
Doppler radar — A radar system that indicates speed by
dolphin flight — In gliders, straight flight following
measuring the amount of Doppler shift and equating it to
speed-to-fly theory. Glides can often be extended and
the speed that the measured object is moving toward or
average cross-country speeds increased by flying faster
away from the measuring point.
in sink and slower in lift without stopping to circle.
dorsal — Situated near the rear or on the back of an object.
domain — Spheres of magnetic influence around molecules
of metals containing iron. Magnetic fields. dorsal fin — A fixed vertical control surface on the upper
surface of an aircraft. Usually on the rear of an aircraft
domains of learning — In addition to the four basic levels
and tapering into the vertical stabilizer, it increases the
of learning, psychologists have developed three domains
directional stability of the aircraft.
of learning: cognitive, psychomotor, and affective.
These domains represent what is to be gained during the double flare — On rigid fluid
learning process, either knowledge, skills, or attitudes. lines, a connecting flare
where the tubing is bent back
domestic airspace — Airspace which overlies the
on itself creating a double
continental land mass of the United States plus Hawaii
thickness. Only al­lowed
and U.S. possessions. Domestic airspace extends to 12
on soft materials in small
miles offshore.
diameters.
donor — An impurity used in a semiconductor to provide
double magneto — A single magneto housing that holds
free electrons as current carriers. A semiconductor with a
one rotating permanent magnet and one cam with two
donor impurity is said to be type N.
sets of breaker points, two condensers, two coils, and two
donor atom — An atom of a material that has more distributors. For all practical purposes, this constitutes
electrons than needed for normal covalent bonding. Used two ignition systems. Also called a dual magneto.

109

10001930-002_AviationDictionary_2012_BOOK.indb 109 3/27/2012 9:38:06 AM

 double spread • draftsman

double spread — -The spreading of an adhesive equally Dow 19 treatment — An acid treatment for magnesium
divided between the two surfaces to be joined. alloy parts, which produces an oxide film that inhibits the
formation of harmful corrosion.
double-acting actuator — An actuator that uses hydraulic
or pneumatic power to move the piston in both directions. Dow metal — A series of magnesium alloys produced by
the Dow Chemical Corporation.
double-acting hand pump — A hydraulic hand pump
that moves fluid with both the forward and rearward dowel — A short wood or metal rod used to hold objects
movement of the handle. together.
double-backed tape — Adhesive tape that is sticky on both downburst — A strong downdraft which induces an
sides. outburst of damaging winds on or near the ground.
Damaging winds, either straight or curved, are highly
double-cut file — A file with two sets of parallel grooves,
divergent. The sizes of downbursts vary from 1/2 mile or
cut at an angle to each other.
less to more than 10 miles. An intense downburst often
double-cut saw — A saw with teeth shaped so that it cuts in causes widespread damage. Damaging winds, lasting 5
both the down and return strokes. to 30 minutes, could reach speeds as high as 120 knots.
double-loop rib-stitching — Attachment of fabric to the downdraft — Any downward flow of air, for example, the
aircraft structure using a double loop of rib‑stitch cord at flow downwind of buildings or hills, or the sinking air
each stitch. near thunderstorms especially in areas of precipitation.
double-pole, double-throw (DPDT) switch — A switch downdraft carburetor — A carburetor mounted on top
that controls two circuits, selecting either of two positions of the engine in which the flow of air into the engine is
(and sometimes a third, off position) for each circuit. downward through the venturi.
double-pole, single‑throw (DPST) switch — A switch that downlock pin — A landing gear safety device consisting
controls two circuits, selecting either off or on. of a pin that, when placed into a hole in the landing gear
apparatus, prevents the gear from retracting or collapsing
doubler — In aircraft sheet metal, a thickness of metal
while on the ground. The downlock pin must be removed
attached to the skin of an aircraft to strengthen it. Often
before flight.
used on the inside of the fuselage to strengthen the skin
where an antenna is attached. downlocks — Mechanical locks that hold a retractable
landing gear in the “on” or “down” position, preventing
doubler plies — In composites, a patch that extends over
its retracting when the hydraulic pressure is released.
the sanded out area to the existing structure which
strengthens the repair. A doubler can also be used where downslope wind — Wind moving down a slope, the
fasteners are used or where there are abrupt load transfers. wind can be either a cold downslope wind or a warm
downslope wind.
double-row radial engine — A radial engine having two
rows of cylinders and using two master rods attached to a downtime — The time an airplane is out of commission.
single crankshaft having two throws.
downwash — 1. Air deflected perpendicular to the motion
double-sided tape — Tape with adhesive on both sides. of the airfoil. 2. Air that has been accelerated downward
by the action of the main rotor of a helicopter.
double-tapered wing — A wing where both the chord and
the thickness ratio vary along the span. downwash angle — The
angle the air is deflected
double-throw switch — A switch that selects one circuit
downward by an airfoil. It is
from two possible circuits. Can have a center “off”
the difference between the
position.
angle of air approaching the
dovetail — A method of joining two materials where one airfoil and the air leaving it.
has a base shaped like a widened, inverted, triangle that
downwind — The direction in which the wind is blowing.
fits into a similarly shaped cutout in the adjoining piece.
Often found in attaching turbine and compressor blades downwind landing — Landing in a direction so that the
to rotor disks. wind is coming from behind the aircraft.
dovetail fit — A shape similar to a cabinet maker’s downwind leg — A flight path parallel to the landing runway in
interlocking “dovetail joint.” Primarily used to fit the direction opposite to landing. The downwind leg normally
compressor blades into a compressor disk. extends between the crosswind leg and the base leg.
draftsman — A person who makes mechanical drawings.

110

10001930-002_AviationDictionary_2012_BOOK.indb 110 3/27/2012 9:38:06 AM

 drag • drip pan

drag — An aerodynamic force on a body acting parallel draw filing — A method of hand filing in which the file
and opposite to the relative wind. The resistance of the is grasped with both hands and moved crosswise over
atmosphere to the relative motion of an aircraft. Drag the work. Draw filing produces an exceptionally smooth
opposes thrust and limits the speed of the airplane. surface.
drag brace — 1. In main landing gears, a device that acts as draw knife — A knife with handles on either end, designed
side support for shock strut. 2. An adjustable brace used to be pulled (drawn) toward the user.
to position the main rotor in a fixed position preventing
draw set — A riveting tool used to force sheets of metal
movement of the blade at the attached point on semi‑rigid
together before they are riveted.
rotors.
drawing — A graphic method of conveying information.
drag chute — A relatively small parachute attached to
the rear of an aircraft. Drag chutes are deployed during drawing number — The number assigned to each drawing
landing rolls to help slow an aircraft and sometimes in in a set of drawings and located in the lower right-hand
flight to increase drag. corner of the title block. It identifies the drawing and is
usually associated with the part number of the component
drag coefficient — One of the aerodynamic characteristics
or part depicted in the drawing.
of an airfoil section that illustrates the increase in induced
drag as the angle of attack is increased. drift angle — The horizontal angle between the longitudinal
axis of an aircraft and its path relative to the ground.
drag demonstration — The demonstration of the effects of
drag on a multi-engine airplane from landing gear, flaps, drift magnet — A small permanent magnet in a fixed-coil
and windmilling propellers. ratiometer indicator. Used to drift or pull the pointer off
scale when the instrument is not energized.
drag hinge — The hinge on a helicopter rotor blade parallel
to the axis of rotation of the blade. It allows the blade to drift punch — A pin punch with a long straight shank.
move back and forth on a horizontal plane, minimizing
driftdown — The unavoidable descent due to the loss of an
the blade vibrations.
engine when above the engine-out absolute ceiling of an
drag wire — A diagonal, load‑carrying member of a Pratt airplane. If the airplane is above its engine-out altitude
truss wing. It runs from the front spar inboard to the rear limits, it is incapable of maintaining altitude with one
spar outboard and carries tensile loads that tend to drag engine inoperative, and the airplane will drift down to
back on the wing. the engine-out absolute ceiling.
dragging brakes — Brakes that have not fully released and drill — 1. A rotary cutting tool driven with a drill motor or
that maintain some friction as the wheel rolls. Dragging a drill press. 2. To sink a hole with a drill, usually a twist
brakes cause serious overheating. drill. 3. A pointed, rotating cutting tool.
drain — The electrode in a field effect transistor (FET) that drill bushing — Hardened steel sleeves inserted in jigs,
corresponds to a collector of the ordinary transistor. fixtures, or templates to provide a guide for drills so holes
will be straight and in the proper location.
drain can — A container to catch fuel drained from the
main fuel manifold after shutdown of a turbine engine. drill chuck — The clamp on the spindle of a drill motor or
drill press into which the drill bit is fastened.
drain hole — A hole placed in the lower surface of a wing
or other sealed component to provide ventilation and drill jig — A device that holds parts or units in the proper
allow the drainage of any accumulated moisture. position while holes are being drilled.
drain plug — A removable plug located at the lowest point drill press — A power‑driven drilling device that includes
of a system used for drainage purposes. a table for holding the material, a chuck for holding the
drill bit, a motor for driving the chuck, and a means of
drain valve — A spring‑opened and burner pressure‑closed
feeding the drill into the material.
mechanical valve located in the lower portion of the
combustor outer case, installed to drain off puddled fuel drill rod — A high carbon tool steel. It has a combination
after an aborted start or after shutdown. Also referred to of hardness and toughness for good wear characteristics.
as a drip valve.
drilling burrs — Sharp ragged particles of metal left by the
drainage wind — A shallow, small scale current of cold drill when a hole is made.
dense air accelerated down a slope by gravity.
drip pan — A shallow pan placed beneath an engine to
drape — In composites, the ability of a fabric or pre-preg to catch dripping fluids.
conform to a contoured surface.

111

10001930-002_AviationDictionary_2012_BOOK.indb 111 3/27/2012 9:38:06 AM

 drip valve • dry air

drip valve — A spring‑opened and burner pressure‑closed to equilibrium with the weaker spring force and
mechanical valve located in the lower portion of the consequently slightly less speed results. The inability of
combustor outer case, installed to drain off puddled fuel the engine power to increase as the rotor pitch is increased
after an aborted start or after shutdown. Also referred to causes the rotor to slow down.
as a drain valve.
droop compensator — In helicopters, a device that
drip-stick gauge — A stick used as a visual means of automatically adds power when collective pitch is
checking the fuel level from beneath the wing of a large increased in order to compensate for the increased load
jet transport aircraft. The stick is released and pulled placed on the engine.
downward until fuel drips from its end, signifying that
droop restraint — A device used to limit the droop of the
the inside is even with the top of the fuel in the tank. The
main rotor blades at low RPM.
fuel quantity is read where the drip‑stick enters the wing.
drop cloth — A plastic or fabric sheet used to protect floors,
drive coupling — A coupling between the accessory section
furniture, or other objects from paint drips or overspray
of an engine and the component that is driven. It is used
from painting operations.
to absorb torsional shock or to serve as a safety link that
will shear in case the component seizes. drop forging — A process of forcing semi‑molten metal
to flow into a mold or die under the pressure of repeated
drive fit — A fit between mating parts in which the part
hammer blows.
to be inserted into the hole is larger than the hole and
therefore must be driven or forced together with the other drop hammer — A large, heavy, hammer-type,
part. Also referred to as an interference fit. metal‑forming machine that uses sets of matched dies to
form compound curved sheet metal parts. The metal is
drive gear — In a gear train, the gear nearest the power
placed over the female die and the male die is dropped
source. Meshes with and drives (turns) the driven gear.
into it, forcing the metal to conform to the shape of the
drive screws — Plain‑headed, self‑tapping screws used two dies.
for attaching name plates to castings or to plug holes in
drop tank — An externally mounted fuel tank designed to
tubular structures through which rust‑preventative oil has
be dropped in flight.
been forced.
drop-forged part — A steel part that has been formed by
driven gear — In a gear train, the gear being driven (turned)
the drop-forging process.
by the drive gear.
droplets — Tiny drops of liquid.
driver — In electronics, a device that supplies input power
to an output device. drop-out voltage — In electricity, the minimum voltage
that can be applied to a device without it dropping
driver head — A head on a bolt or screw designed for driving
from the circuit. Usually used in referring to relays that
the fastener by means of a tool such as a screwdriver or
de-energize when control voltage drops below a certain
Allen wench rather than a conventional wrench.
drop-out voltage.
drizzle — A form of precipitation. Very small water drops
dropping resistor — A resistor used to decrease the voltage
that appear to float with the air currents while falling in an
in a circuit.
irregular path (unlike rain, which falls in a comparatively
straight path, and unlike fog droplets which remain drum brake — A friction device used on some aircraft
suspended in the air). landing gear. Consists of a cylindrical metal drum attached
to the wheel and shoe-shaped friction pads attached to the
drogue — A device that provides drag to a moving body.
landing gear. This device is applied against the inner side
For boats, a sea anchor provides drag that stabilizes the
of the drum when braking action is desired.
position of the boat in relation to current. In aircraft a
drogue chute stabilizes or slows the airplane. A drogue dry adiabat — A line on a thermodynamic chart representing
receptacle for refueling is a basket-shaped device into a rate of temperature change at the dry adiabatic lapse rate.
which another aircraft can insert a probe to receive fuel
dry adiabatic lapse rate (DALR) — The rate of decrease
from an aerial refueling tanker.
of temperature with height of unsaturated air lifted
drone — An unmanned aircraft guided by remote control. adiabatically (not heat exchange). Numerically the value
Newest terminology refers to these vehicles as UAVs is 3C or 5.4F per 1000’.
(Unmanned Aerial Vehicles) and RPVs (Remote Piloted
dry adiabatic process — The cooling of an unsaturated
Vehicles).
parcel of air by expansion and the warming of a parcel of
droop — Refers to the RPM loss that occurs when a fuel air by compression.
control flyweight governor speeder spring is extended
dry air — Air that contains no water vapor. Dry air weighs
and weakened. It takes less flyweight force to come
0.07651 pounds per cubic foot under standard sea level
112

10001930-002_AviationDictionary_2012_BOOK.indb 112 3/27/2012 9:38:06 AM

 dry air pump • dump valve

atmospheric conditions of 59°F (15°C) and a barometric to the pressure pump by gravity. After it has lubricated
pressure of 14.69 PSI, or 29.92 inches of mercury. the engine, the oil is pumped back into the tank by an
engine‑driven scavenger pump.
dry air pump — An engine-driven air pump using carbon
vanes and that does not require any lubricating oil in the dry-sump system — An oil system in which the oil is
pump for sealing or cooling. contained in a separate tank and circulated through the
engine by pumps.
dry bulb — A name given to an ordinary thermometer
used to determine temperature of the air; also used as a dual controls — Two sets of flight controls for an aircraft
contraction for dry-bulb temperature. Compare wet bulb. that allow the airplane to be flown from either of two
positions.
dry clearance — Clearance adjusted in adjusting valve
tappets without any oil in the tappet body. dual indicator — An aircraft instrument that provides
two sets of indications on one dial. For example, the oil
dry fiber — In composites, a condition in which fibers are
pressure of both engines can be shown on one indicator
not fully encapsulated by resin during pultrusion.
using one dial and two pointers.
dry ice — Frozen carbon dioxide (CO2). Dry ice sublimates
dual magneto — A single magneto housing that holds one
from solid to gas without becoming a liquid. It is used
rotating permanent magnet and one cam with two sets
for non-mechanical cooling of perishables or for cooling
of breaker points, two condensers, two coils, and two
parts for an interference fit.
distributors. For all practical purposes, this constitutes
dry laminate — In composites, a laminate con­taining two ignition systems.
insufficient resin for complete bonding of the
dual rotor system — The rotor system of a helicopter in
reinforcement.
which there are two separate main rotors spinning in such
dry line — The moisture boundary, where the moisture a direction that they tend to cancel the torque of each
content of the air changes rapidly from one side to the other.
other.
dual-spool compressor — A turbine engine with two
dry operation — The operation of an aircraft engine separate compressors, each with its own stage of turbine.
equipped with a water injection system, but operating The low-pressure compressor is N1 and the high-pressure
without the benefit of water injection. compressor is N2.
dry rot — The condition of wood attacked by fungus. duckbill pliers — Flat‑nosed pliers used extensively in
Causes brittleness and decay. safety wiring.
dry wash — Aircraft cleaning method in which cleaning duct — A hollow tube used to transmit and direct the flow
material is applied by spray, mop, or cloth and removed of air through an aircraft.
by mopping or wiping with a clean, dry cloth. It is used
duct support systems — Methods and apparatus used to
to remove airport film, dust, and small amounts of dirt
support cabin air supply ducts.
and soil.
ducted-fan engine — An engine-propeller combination that
dry-bulb temperature — The temperature of the air
has the propeller enclosed in a radial shroud. Enclosing
without the effect of water evaporation.
the propeller improves the efficiency of the propeller.
dry-cell battery — Common name for a carbon-zinc,
ductility — The property that allows metal to be drawn into
single-cell battery. D-, C-, AA-, and AAA-cells are
thinner sections without breaking.
all dry-cell batteries. They are not rechargeable or
serviceable. ductwork — The channels or tubing through which the
cabin air supply is distributed.
dry-charge battery — The common way of shipping a
lead-acid battery. The battery is fully charged, drained, due regard — A phase of flight wherein an aircraft
and the cells are washed and dried. The battery is sealed commander of a State-operated aircraft assumes
until it is ready to be put into service. Electrolyte is added responsibility to separate his aircraft from all other
and the battery is given a freshening charge, making it aircraft.
ready for service.
dump chute — In an aircraft fuel system, a device designed
dry-chemical fire extinguisher — An extinguishing agent to carry dumped fuel away from the aircraft to prevent it
such as sodium bicarbonate used as a compressed, from being ignited by static electricity or engine exhaust.
non-flammable gas as a propellant. Dry-chemical fire
dump valve — The valve that allows the fuel in a tank to be
extinguishers are usually rated for multiple purpose use.
dumped in flight in order to decrease the landing weight
dry-sump engine — An engine in which most of the of the aircraft.
lubricating oil is carried in an external tank and is fed
113

10001930-002_AviationDictionary_2012_BOOK.indb 113 3/27/2012 9:38:07 AM

 duo-servo brakes • dynamic load

duo-servo brakes — Brakes that use the momentum of the DVFR flight plan — A flight plan filed for a VFR aircraft
aircraft to wedge the lining against the drum and assist which intends to operate in airspace within which the
in braking when the aircraft is rolling either forward or ready identification, location, and control of aircraft are
backward. required in the interest of national security.
duplex bearing — A matched pair of bearings with a DVOR (Doppler VOR) — Provides increased accuracy
surface ground on each to make contact with the other compared to a conventional VOR. Employed in areas
matched surface. When three bearings are used they such as mountainous terrain.
are called triplex bearings; when four bearings are used
Dwell angle — In ignition systems, the time that the ignition
they are called quadplex bearings, and so on. These are
points remain closed. During this time, the magnetic field
usually ball bearings.
builds in the primary coil. When the points open, the
duplex fuel nozzle — A turbine engine fuel nozzle that has magnetic field collapses, creating a much higher voltage
two different spray patterns: one for low airflow and one in the secondary coil, which is connected to the spark
for high airflow. This keeps the flame pattern centered in plugs.
the combustor section.
dye — A material added to a substance to add or change
duplex operation — In communications, the capability its color. In aviation, dye is added to aviation fuels to
of all stations to transmit and receive simultaneously. identify the grade of fuel.
Telephone communication is a duplex operation. For
dye penetrant inspection — An inspection method for
radio communication to be a duplex operation, two
surface cracks in which a penetrating dye is allowed to
frequencies are required.
enter any cracks present and is pulled out of the crack by
duplexer — A circuit that makes it possible to use the same an absorbent developer. A crack appears as a line on the
antenna for transmitting and receiving without allowing surface of the developer.
excessive power to flow to the receiver.
dynafocal engine mount — A mount that attaches an
durability — The ability to withstand hard wear. aircraft engine onto the airframe in which the extended
center line of all of the mounting bolts would cross at the
Dural® — A high strength, low weight alloy consisting of
center of gravity of the engine and propeller combination.
95% aluminum, 4% copper, and 1% magnesium.
dynamic — Continuous review, evaluation, and change to
Duralumin — The original name of the aluminum alloy
meet demands.
now known as 2017. First produced in Germany and used
in its Zeppelin fleet of WWI. dynamic balance — The condition that exists in a rotating
body in which all of the rotating forces are balanced
dust — Small soil particles suspended in the atmosphere.
within themselves and no vibration is produced by the
dust devil — An unusual, frequently severe weather body in motion.
condition characterized by strong winds and dust-filled
dynamic braking — A method of slowing the rotation
air over an extensive area.. A small vigorous circulation
of equipment driven by an electric motor. Braking is
that can pick up dust or other debris near the surface to accomplished by disconnecting electrical power from the
form a column hundreds or even thousands of feet deep. motor and replacing it with a resistance load. The inertia
At the ground, winds can be strong enough to flip an of the motor/equipment causes the motor to become a
unattended aircraft. Dust devils mark the location where generator and the resistance absorbs the electrical output
a thermal is leaving the ground. of the motor and thus resists and slows the rotation.
Dutch roll — A combination of rolling and yawing dynamic damper — A counterweight on the crankshaft of
oscillations that normally occurs when the dihedral an aircraft engine. It is attached in such a way that it can
effects of an aircraft are more powerful than the rock back and forth while the shaft is spinning and absorb
directional stability. dynamic vibrations. In essence, it changes the resonant
duty cycle — The comparison of the time a piece of frequency of the engine/propeller combination.
equipment can operate to how long it must cool before dynamic factor — The ratio between the load carried
being operated again. A device that can operate one by any part of an aircraft when accelerating and the
minute before having to cool off for four minutes would corresponding basic load.
have a 25% duty cycle.
dynamic load — The effective weight of an aircraft. It is the
duty runway — See runway in use and active runway. actual weight of the aircraft multiplied by the load factor
D-value — Departure of true altitude from pressure altitude; (G-load). When an aircraft is sitting on the ramp, the load
obtained by algebraically subtracting true altitude from factor is one and the dynamic load equals the weight of
pressure altitude. the aircraft. In flight, if the aircraft is experiencing a load
factor of two (as it would be if in a level 60º bank turn)

114

10001930-002_AviationDictionary_2012_BOOK.indb 114 3/27/2012 9:38:07 AM

 dynamic microphone • Dzus fastener

the dynamic load would be twice the actual weight of the

aircraft.
dynamic microphone — A device used to convert acoustic
pressure waves into electrical waves. Incoming sound
impinges a movable diaphragm that has a coil of wire
on it. The coil is in a magnetic field and its movement
produces an electrical signal that correlates to the sound.
dynamic pressure — The product 1/2 p V2, where p is the
density of the air and V is the relative speed of the air.
dynamic restrictions — Those restrictions imposed by
the local facility on an “as needed” basis to manage
unpredictable fluctuations in traffic demands.
dynamic rollover — The tendency of a helicopter to
continue rolling when the critical angle is exceeded, if
one gear is on the ground, and the helicopter is pivoting
around that point.
dynamic stability — The property of an aircraft that
causes it, when disturbed from straight and level flight,
to develop forces or moments that restore the original
condition of straight and level.
dynamometer — An instrument used to measure torque
force or power.
dynamotor — A machine with two windings on a single
armature that simultaneously operates as a motor with
one of the windings and as a generator with the other. The
armature windings are usually different so that the voltage
on the generator side is different from the voltage on the
motor side and the machine acts as a rotary transformer.
dynatron effect — The area of operation in a tetrode
electron tube where plate current decreases as plate
voltage increases. This effect is caused by secondary
electrons to the screen grid.
dyne — A unit of force. Dyne is the amount of force required
to accelerate one gram of mass one centimeter per second
squared. In science, the term is slowly becoming obsolete.
dynode — The elements in a multiplier tube that emit
secondary electrons.
Dzus fastener — A patented form of cowling fastener in
which a slotted stud is forced over a spring steel wire and
rotated to lock the wire in a cam.

115

10001930-002_AviationDictionary_2012_BOOK.indb 115 3/27/2012 9:38:07 AM

 E • effective value

E eddy — In meteorology, an organized movement of air in a

circulation of a particular size. The organization is more
early warning radar — Long-range radar used to detect obvious in the larger scale circulations.
incom ing aircraft or missiles soon enough to be eddy current — A current induced into the core of a coil,
intercepted by defensive aircraft or missiles. transformer, or the armature core of a motor or generator
earplug — A rubber, wax, or soft plastic device worn in the by current flowing in the winding. Eddy currents cause
canal of the ear to keep loud noises from damaging the power loss and are minimized by laminating the iron
ear and to help prevent hearing loss. cores.
earth connection — An electrical connection with a ground. eddy current inspection — A nondestructive inspection
The United Kingdom uses “earth” for the electrical term used to locate surface or subsurface defects in a metal
“ground.” part. This is a comparison‑type inspection, based on the
difference in conductivity of a sound and a defective part.
earth ground — In electricity, a ground connected directly
to Earth. This connection is usually achieved by attaching eddy current losses — The
a grounding clamp to a metal water pipe or to a grounding electrical losses in the
rod driven into the ground. The third plug in a three-wire core of a transformer or
system is usually connected to earth ground. other electrical machine.
The induction of eddy
Earth induction compass — A direction indicator in an currents into the core robs
aircraft that derives its signal from the lines of flux of the the machine of some of its
Earth cutting across the windings of the flux valve. power.
Earth’s magnetic field — The magnetic lines of flux that edge distance — The distance from the center of a bolt or
surround the Earth. These lines enter and exit the Earth at rivet hole to the edge of the material.
the magnetic north and south poles, close to, but not at,
the geographic poles. edge thickness — The thickness of the edge of a material.
easy-out — A screw extractor used to remove broken edge-grain wood — Wood that has been sawed from the tree
screws or studs. It is made of hard steel and has a point in such a way that the edges of its grain are visible in the
with a tapered, left‑hand spiral‑like thread. A hole is wide part of the plank. Also referred to as quarter-sawed
drilled in the shank of the broken screw and the easy‑out wood.
is screwed into it by turning it counter-clockwise. Edison effect — The emission of electrons from a heated
eccentric — A disk or filament attached to an electrode placed in an evacuated
wheel having its axis tube. The discovery of Thomas A. Edison in 1883.
of revolution dis­placed eductor — A jet pump used in some aircraft fuel systems
from its center so that it to remove fuel from a vent‑drain tank and return it to the
is capable of im­parting main tank.
recipro­cating motion.
effect — A principle of learning, which states that learning
eccentric cam — A circular is strengthened when accompanied by a pleasant or
cam with a displaced satisfying feeling, and that learning is weakened when
axis. As the shaft rotates about its axis, the outside of the associated with an unpleasant feeling.
eccentric cam rises and falls, changing rotary motion into
reciprocating motion. effective pitch — The actual distance a propeller moves
through the air in one revolution. It is the difference
echo — In radar terminology, the energy reflected or between the geometric pitch of the propeller and the
scattered by a target and the radar scope presentation of propeller slip.
the return from a target.
effective thread — The effective (or useful) thread includes
economizer system — A power compensator or a power the complete thread and that portion of the incomplete
enrichment system in a carburetor or fuel injection system thread having crests not fully formed.
that adds additional fuel. It enriches the fuel mixture at
high power engine operations. The economizer is closed effective value — The root mean square (RMS) value of
during cruising speeds. sine wave AC. It is equivalent to 0.707 times the peak
value and corresponds to the DC value that will produce
E-core — The laminated core of an electric transformer the same amount of heat.
cut in the shape of the letter “E.” The coil windings are
mounted on the core.

116

10001930-002_AviationDictionary_2012_BOOK.indb 116 3/27/2012 9:38:07 AM

 effective voltage • electric strain gauge

effective voltage — The equivalent direct current (DC) elasticity — The capability of an object or material to
voltage in an alternating current system. It is calculated be stretched and to recover its size and shape after
as .707 times the peak sinusoidal waveform voltage deformation.
value. In a non-sinusoidal waveform, it is the root mean
elastomeric bearing — A metal and rubber composite
square voltage value.
bearing used to carry oscillating loads where complete
efficiency — A measure of a system’s effectiveness or a rotation is not needed. The bearing is made of alternate
mechanism found by dividing the output of the mechanism layers of an elastomer and metal bonded together.
by its input. It is usually expressed as a percentage. Elastomeric bearings can be designed to take radial,
axial, and torsional loads.
effort arm — The distance from the input to the fulcrum on
a lever. The distance from the fulcrum to the output point elastomers — A rubber or synthetic rubber used in the layers
is referred to as the load arm. between the metal in an elastomeric bearing. Elastomers
can be stretched to twice their original length and can
E‑gap angle — The number of degrees of magnet rotation
return to their original size and shape when released.
beyond its neutral position at which the primary magneto
breaker points open. It is at this point that the primary E-layer — A layer of ionized air in the ionosphere found
current flow is the greatest and, therefore, the rate of approximately 55 to 90 miles above Earth.
collapse of the primary field will induce the greatest
elbow — A fluid line fitting used to join two pieces of tubing
voltage into the secondary winding.
at an angle of 90°.
E-glass — In composites, a type of fiberglass. The E stands
Elcon connector — A slip-on type terminal, held in place
for electrical. It is used primarily when there could be
with a hand screw, for aircraft battery installation. It is
interference to radio signals such as with a radome.
similar to the Cannon connector.
egoistic needs — Basic personal needs that relate
electret — A permanently polarized dielectric material.
to a student’s self-esteem and are directly linked
to self-confidence, independence, achievement, electret microphone — A device that changes sound
competence, and knowledge. Another type relates pressure into an electrical signal. It consists of a
to a student’s reputation, such as status, recognition, diaphragm made of a thin foil of electret placed next to
appreciation, and respect of associates. a metal coated plate. Sound pressure that is picked up by
the microphone vibrates the diaphragm causing a voltage.
eight-harness satin — In composites, a type of fabric
The waveform of this voltage is a copy of the waveform
weave. The fabric has a seven-by-one weave pattern
of the sound that vibrated the diaphragm.
in which a filling thread floats over seven warp threads
and then under one. Like the crowfoot weave, it looks electric bonding — The connecting of metal structural parts
different on one side than on the other. This weave is together with electrical conductors in order to keep them
more pliable than any of the others and is especially at the same electrical potential. Bonding eliminates static
adaptable to forming around compound curves, such as electricity build-up, which causes radio interference.
on radomes.
electric discharge machining — A process of machining
ejection seat — An emergency escape seat found in military complex metal shapes by a controlled electric arc that
aircraft that, when used, is propelled or shot from the erodes the metal.
aircraft and parachutes to the ground.
electric drill motor — An electric motor, usually of
ejector pump — A pump that produces a low hydraulic the universal type, which is geared down to provide
pressure. The low pressure is used to eject or move fluid additional torque and is equipped with a chuck to hold
from one place to another. See also eductor. a twist drill.
elastic limit — The maximum load (in PSI) a metal can electric inertia starter — An electric starter motor for
withstand without causing a permanent deformation. If a aircraft reciprocating engines that spins a small flywheel
metal hasn’t reached its elastic limit, it will return to its to a high speed. The energy in the flywheel, when coupled
original dimensions when the load is removed no matter to the engine crankshaft, turns or “cranks” the engine.
how many times the load is applied.
electric strain gauge — A device used to measure the
elastic stop nut — A self‑locking nut with a collar of elastic amount of physical strain placed on a piece of conductive
material and an inside diameter slightly smaller than the material. A strain gauge is made of a piece of very fine wire
outside diameter of the bolt or stud it fits. The collar fills that is bonded to the material in which the strain is to be
the bolt threads and prevents the nut from backing out measured, and the two ends of the wire are connected into
inadvertently. a sensitive, resistance‑measuring bridge circuit. When the
material on which the strain gauge is mounted is strained,
the wire in the strain gauge is stretched. It becomes longer

117

10001930-002_AviationDictionary_2012_BOOK.indb 117 3/27/2012 9:38:07 AM

 electric wave • electrodynamic damping

and thinner. When its length and its cross sectional area electrical strength — The maximum amount of voltage
changes, its resistance changes. The change in resistance that can be placed on an insulator before the insulator
of the strain gauge is proportional to the amount of strain breaks down and allows electrons to flow through it.
in the material, and the amount of strain is proportional to
electrical symbols — The graphic symbols used in aircraft
the amount of stress that caused it.
drawings to represent electrical wiring or components.
electric wave — One of the components of a radio wave
electrical zero — A designated rotor position in synchro
produced along the length of the antenna.
systems. It is a reference position for meshing gears and
electrical bus — An electrical distribution point to which for installing indicators.
many circuits can be connected.
electrically detonated squib — An explosive charge,
electrical charge — An excess (negative charge) or usually installed in fire extinguisher systems, that is
deficiency (positive charge) of electrons in a body. ignited by electrical methods.
electrical diagram — A diagram or drawing showing the electrically suspended gyroscope — A gyroscope with a
relationship of electrical components within a system. rotor supported in an electromagnetic field. This allows
the rotor to spin with an absolute minimum of friction.
electrical energy — The energy possessed by a substance
or device because of a difference in electrical potential. electricity — The physical phenomena arising from the
This can exist because of electromagnetic or electrostatic existence of positive and negative electrical charges.
forces. Electricity can be observed in the attracting and repelling
of objects electrified by friction and in natural phenomena
electrical equipment — An electrical unit or combination
(lightning and aurora borealis). Usually employed in the
of units that make up the electrical system.
form of electrical currents generated by a mechanical
electrical filter — An arrangement of a choke coil and generator device that forces the flow of electrons from
condenser used in an electrical circuit to create a steady an area having an excess of electrons to an area with a
current flow. shortage of electrons. In the process, heat is produced,
and a magnetic field surrounds the conductor.
electrical generator — A mechanical device that converts
mechanical energy into electrical energy. electroacoustic transducer — A device that converts
variations in sound pressure into variations of voltage,
electrical insulator — A material that prevents the passage
or vice versa.
of electricity. The material’s outer electrons are so forcibly
held to the nucleus that they cannot be dislodged to flow electrochemical action — The corrosive results of the
in a circuit. Glass is an example of a good insulating potential difference of two different metals in contact
material. with each other in the presence of an electrolyte.
electrical lines — The wiring used for transporting electrical electrochemical series — A list of metallic elements that
energy to electrical equipment. ranks them according to the ease with which they give
up electrons. All metals are listed on an electrochemical
electrical resistance welding — The fusion of metals by
series or nobility chart from the most vulnerable to
clamping them together and passing a high amperage
corrosion (least noble) to the least vulnerable (most
electrical current through the joint. The resulting heat
noble). See also dissimilar metal corrosion.
melts the metal, and the pressure causes the two pieces
to fuse together. Spot and seam welding are forms of electrochemistry — The branch of chemistry that deals
electrical resistance welding. with the electrical voltages existing within a substance
because of its chemical composition.
electrical shield — A housing made of a conductive material
that encloses an electrical circuit. The shield picks up any electrode — A terminal element in an electric device or
electrical energy radiated from the circuit and carries it to circuit. Examples are the plates in a storage battery, the
ground so it cannot interfere with any other electrical or elements in an electron tube, and the carbon rods in an
electronic equipment. arc light.
electrical short — An unintentional electrical system fault electrode potential — A voltage that exists between
connection that provides a low-resistance path across an different metals and alloys because of their chemical
electrical circuit. Electrons can flow through the short to composition. An electrical current will flow between
ground without passing through the load. these materials when a conductive path is provided.
electrical steel — A low-carbon steel alloy that contains up electrodynamic damping — The diminishing of
to 5% silicon and is used in the form of thin laminations oscillations of the pointer of an electrical meter by the
for the cores of transformers and the armatures of generation of electromagnetic fields in the frame of the
electrical motors and generators. moving coil.

118

10001930-002_AviationDictionary_2012_BOOK.indb 118 3/27/2012 9:38:07 AM

 electrogalvanizing • electronic emission

electrogalvanizing — -The process of coating metal with electron — 1. A subatomic particle with a negative electric
zinc by electroplating. charge. It spins around the nucleus of an atom, and under
certain conditions, can be caused to move from one atom
electro‑hydraulic control — A hydraulic control that is
to another. Electrons that travel in this manner are called
electrically actuated.
free electrons. 2. The negatively charged part of an atom
electrolysis — A chemical change produced in an electrolyte of which all matter is made. Electrons circle around the
by an electric current. nucleus of an atom in orbits or shells.
electrolyte — A nonmetallic conductor, such as a liquid or a electron beam — A narrow beam of free electrons in a
gas, in which current is carried by the movement of ions. vacuum. In cathode-ray tubes (CRTs), the electron beam
strikes luminescent phosphors, causing them to emit
electrolytic — The action of conducting electrical current
light. CRTs are used in TV receivers, radar, computer
through a nonmetallic conductor by the movement of
monitors, and some instrument displays.
ions.
electron beam welding — A process of welding metal by
electrolytic capacitor — A capacitor that uses metal foil
the heat that is produced when a high-speed stream of
for the electrodes and a thin film of metallic oxide as the
electrons strike the metal.
dielectric. The sheets of metal foil are separated by a piece
of porous paper that is impregnated with an electrolyte. electron current flow — The flow of electrons from
The capacity is affected by the thickness of the dielectric. negative to positive in a circuit outside of the source.
electromagnet — A magnet produced by electrical current electron drift — The relatively slow natural movement of
flowing through a coil of wire. The coil is often wound individual electrons that move from atom to atom within
around a soft iron core that concentrates the lines of flux the conductor.
and intensifies the magnetic field.
electron force — The force causing electrons to move
electromagnetic emission — The radiation of through a conductor (electromagnetic force). The symbol
electromagnetic energy that is produced when electricity “E” is used in calculations until the actual number of
flows through a conductor. volts is determined.
electromagnetic induction — A transfer of electrical electron gun — The combination of an electron-emitting
energy from one conductor to another by means of a cathode together with accelerating anodes and
moving electromagnetic field. A voltage is produced in beam-forming electrodes to produce the electron beam in
a conductor as the magnetic lines of force cut or link a cathode-ray tube.
with the conductor. The value of the voltage produced by
electron spin — The rotation of an electron about its own
electromagnetic induction is proportional to the number
axis.
of lines of force cut per second. An emf (electromagnetic
force) of 1 volt will be induced when 100,000,000 lines electron tube — 1. A device consisting of an evacuated or
of force are cut per second. gas‑filled envelope containing electrodes for the purpose
of controlling electron flow. The electrodes are usually a
electromagnetic radiation — An electrical energy of
cathode “electron emitter,” a plate “anode,” and one or
extremely high frequency and short wavelength that will
more grids. 2. A vacuum tube. It consists of a cathode
penetrate solid objects and expose photographic film.
and its heater, the grids, and plate that are usually housed
electromagnetic vibrator — A device that interrupts the in a glass envelope. The tube may also be filled with an
flow of DC through a set of contacts and changes it into inert gas.
pulsating DC. The contacts will vibrate between open
electron-flow — The current‑flow in a circuit is actually
and closed as long as the vibrator is connected to a source
the flow of electrons. Electrons flow from negative to
of DC electricity.
positive in the external circuit.
electromagnetic waves — A resonance of electric and
electronic counter‑countermeasures — Methods
magnetic fields that move at the speed of light.
used by the military to counter the ECM (Electronic
electromagnetism — The magnetic field emanating from Countermeasures) of the enemy and decrease the
a conductor carrying electrical current. Its strength effectiveness of the enemy’s countermeasures. See also
is determined by the amount of current flowing in the electronic countermeasures.
conductor.
electronic countermeasures — Methods of de­creasing the
electromechanical frequency meter — An instrument that effectiveness of enemy communications or radar.
uses the resonant frequency of a vibrating metal reed
electronic emission — The freeing of electrons from the
to measure the frequency of alternating current. Also
surface of a material usually produced by heat.
referred to as a vibrating-reed frequency meter.

119

10001930-002_AviationDictionary_2012_BOOK.indb 119 3/27/2012 9:38:07 AM

 electronic leak detector • emergency locator transmitter (ELT)

electronic leak detector — An electronic oscillator device that person is feeling threatened since most of a person’s
that emits an audible tone if any refrigerant gas is picked effort is focused on whatever is threatening them.
up in its sensor tube. When a refrigerant leak is detected,
elevator — A horizontal, movable control surface on the
the tone changes.
tail of an airplane. It is used to rotate the airplane about
electronic moisture indicator — A device for checking its lateral axis.
moisture in a material. It operates on the principle of
elevator angle — The angular displacement of the elevator
measuring the conductivity of the material.
from its neutral position.
electronic oscillator — 1. An electronic device used in a
elevator control tab — A metal tab located on the elevator
leak detector that emits a changing audible tone when a
that helps the pilot control the elevator.
leak is detected. 2. An electronic circuit that converts DC
into AC electricity. elevator trim stall — A demonstration stall that a flight
instructor shows a student pilot. It simulates the danger
electronic voltmeter — An electronic instrument used to
zone defined by a rejected landing or go-around, and is
measure voltage.
demonstrated at altitude with the airplane configured and
electronics — 1. The branch of science that deals with trimmed for a typical final approach to landing.
electron flow and its control. 2. In physics, the study and
elevon — A control surface that combines the functions
use of the movement and effects of free electrons and
of both ailerons and elevators. Movement of the control
with electronic devices.
wheel to the right or left causes the elevons to move
electroplating — An electrochemical method of depositing differentially. (When the left elevon moves up, the right
a thin layer of metal on some object. The object to be elevon moves down.) The differential movement of the
plated is the cathode, the metal that will be deposited is elevons causes the airplane to rotate about its longitudinal
the anode, and the electrolyte is a nonmetallic conductor (roll) axis.
that will form ions of the plating metal.
ellipse — An oval. A curve generated by a point moving
electrostatic charge — A stationary electrical charge on an such that the sum of its distances from two fixed points
object caused by an accumulation of electrons or by a (foci) is a constant. It is the plane cross-section of a
depletion of electrons. cylinder at other than a right angle or a right cone at other
than parallel to the base.
electrostatic deflection control — A method of controlling
the position of a beam of electrons on the face of a elliptical — Of or having the form of an ellipse. An
cathode-ray tube. The beam of electrons that forms the elongated oval shape.
trace or picture on a cathode-ray tube can be deflected to
elongate — To stretch or lengthen.
the correct position on the screen by electrostatic charges
on plates that are placed above, below, and on each side e-mail — Electronic mail. Mail sent and received between
of the beam. computers.
electrostatic energy — In a capacitor, the energy stored embarkation — The loading of passengers and cargo onto
when two opposing electrical charges act across the the airplane.
dielectric.
embedded circulation — A relatively small scale
electrostatic field — A field of force that exists around a circulation embedded in, and driven by, a larger scale
charged body. Also referred to as a dielectric field. circulation.
electrostatic stress — The electrical force that tends to embossing — The process of raising a boss or protuberance
puncture an insulator. It is caused by an accumulation of on the surface.
electrical charges on a body.
emergency — A distress or an urgency condition.
electrostatics — The branch of physics that deals with the
emergency air pressure — The compressed air stored in
attraction and repulsion of static electrical charges.
high‑strength steel cylinders used to provide emergency
electrovalent or ionic bond — The bond formed by two landing gear extension and emergency braking in the
atoms when one atom gives up one or more valence event of the failure of the main power system.
electrons to the other. The bond is based on the attraction
emergency descent — A maneuver designed to allow the
between the positive and negative ions thus formed.
aircraft to descend to a lower altitude at the fastest, most
element — The basic chemical substances that cannot be practical airspeed, in the event of an engine fire, loss of
divided into simpler substances by chemical means. cabin pressure, or other emergency.
element of threat — A perception factor that describes emergency locator transmitter (ELT) — A radio
how a person is unlikely to easily comprehend an event if transmitter attached to the aircraft structure which

120

10001930-002_AviationDictionary_2012_BOOK.indb 120 3/27/2012 9:38:07 AM

 emery paper • engine controls

operates from its own power source on 121.5 MHz, 243.0 enclosed relay — An electrical relay in which both the coil
MHz, and 406 MHz. It aids in locating downed aircraft and the contacts are enclosed in a protective housing.
by radiating a downward sweeping audio tone, 2-4 times
encode — In electronics, to put an analog signal into digital
per second. It is designed to function without human
format.
action after an accident. The 406 MHz ELT broadcasts
an identification signal and is capable of broadcasting encoding altimeter — A pneumatic altimeter that provides
location if linked to a GPS receiver. a signal to the transponder that indicates the altitude on
the radar operator’s screen.
emery paper — A fine abrasive paper composed of
pulverized corundum or aluminum oxide and used for end spanner — A socket wrench that has a series of raised
polishing. lugs around its end rather than splines broached inside.
emery wheel — A wheel consisting of a fine abrasive end voltage — The voltage across a chemical cell when the
material composed of pulverized corundum or aluminum cell should be discarded or recharged. The end voltage
oxide and used for grinding and polishing. of a particular type of cell is usually defined by the
manufacturer. Also referred to as an end‑of‑life voltage.
emitter — The electrode of a transistor that corresponds
to the cathode of a vacuum tube. Conventional current endurance — The length of time an aircraft can remain
enters a transistor through the emitter. in the air. The power produced by the engines can be
regulated to give the aircraft the greatest speed, the
empennage — The rear or tail portion of an airplane.
greatest range, or the greatest endurance.
empty field myopia — The normal tendency of the eye
energy — Inherent power or the capacity for performing
to focus at only 10 to 30 feet when looking into a field
work. When a portion of matter is stationary, it often has
devoid of objects, contrasting colors, or patterns.
energy due to its position in relation to other portions of
empty weight — The weight of an aircraft, its power plant, matter. This is called potential energy. If the matter is
and all of the fixed equipment. It includes unusable fuel moving, it is said to have kinetic energy, or energy due
and undrainable oil for aircraft not certified under FAR to motion.
Part 23 (aircraft certified under FAR Part 23 include full
engaging solenoid — A solenoid used to engage an inertia
oil as part of empty weight).
starter with the engine.
empty weight center of gravity (EWCG) — The center of
engine — A machine that converts energy into mechanical
gravity of an airplane that includes all fixed equipment,
power.
the unusable fuel, and undrainable oil for aircraft not
certified under FAR Part 23 (aircraft certified under FAR engine analyzer — An electronic instrument using a
Part 23 include full oil as part of empty weight). cathode ray oscilloscope as an indicator to analyze the
condition of the ignition system and to visually display
empty weight center of gravity range — The range
the vibrations in the engine.
determined so that the empty weight center of gravity
limits will not be exceeded under standard specifications engine breather — The vent for the crankcase of a
loading arrangements. reciprocating engine. It allows fumes to escape from
the crankcase and prevents pressure build‑up inside the
empty weight moment — The moment of an aircraft at its
engine.
empty weight.
engine compartment — The area of an aircraft in which the
emulsion‑type cleaner — A chemical cleaner that mixes
engine and its components and accessories are located.
with water or petroleum solvent to form an emulsion. It is
used to loosen dirt, soot, or oxide films from the surface engine compressor — The section of a turbine engine in
of an aircraft. which the air is compressed before it enters the burner
section.
En Route Automated Radar Tracking System (EARTS)
— An automated radar tracking system that combines engine conditioning — An integrated system of engine
inputs from multiple short- and long-range radars into checks and tests whereby engines can be brought up to or
one display. kept in top operating condition. Two of the most important
checks of engine conditioning are the compression test
enamel — A material whose pigments are dispersed in a
and the cold cylinder check.
varnish base. The finish cures by chemical changes
within the base. engine controls — The controls required for the proper
operation of an aircraft engine. They include the throttle,
encapsulate — To completely surround or cover something.
mixture control, propeller pitch control, carburetor heat,
encased — Enclosed in a housing. engine cowl flap control, and the ignition switch.

121

10001930-002_AviationDictionary_2012_BOOK.indb 121 3/27/2012 9:38:07 AM

 engine cycle • enrich

engine cycle — 1. The cycle of events that must be engine pressure ratio (EPR) — In gas turbine engines, the
accomplished in the transformation of chemical energy ratio of turbine discharge pressure divided by compressor
into mechanical energy. The two most common cycles of inlet pressure. Displayed in the cockpit as an indication
events are the Otto cycle, which describes the events of of engine thrust.
the reciprocating engine, and the Brayton cycle, which
engine ratings — The engine power ratings as type
describes the transformation taking place in a turbine
certificated by the FAA. These ratings list thrust or shaft
engine. 2. One takeoff and landing as recorded by an
horsepower at takeoff, cruise, etc.
airline. Also described as one start and one stop of the
engine or sometimes as one full advance and retard of engine ring cowl — The ring‑shaped covering over the
the throttle. The latter two situations require special cylinders of a radial engine for the purpose of streamlining
recording procedures for maintenance runs if cycle times and improving the airflow through the engine.
are needed.
engine seizure — The locking‑up or stopping of an engine
engine gauge unit — A three‑in‑one instrument used to because of some internal malfunction.
show the operating condition of an engine. It houses a
engine stations — In gas turbine engines, numbered
fuel pressure, oil pressure, and oil temperature gauge in
locations along the engine length, or along the gas
one case.
path used for the purpose of identifying pressure and
engine history recorder — An electronic data collection temperature points, component locations and the like.
device on some newer engines which records the number
engine stroke — In a reciprocating engine, the distance a
of times certain normal operating parameters such as
piston travels from bottom dead center (BDC) to top dead
speed and temperature are reached.
center (TDC). Engine stroke is equal to two times the
engine inoperative loss of directional control crankshaft throw.
demonstration — This demonstration is required during
engine sump — The lowest point in the engine from which
a multi-engine practical test to show the control pressures
the oil may be drained.
necessary to maintain directional control with one engine
inoperative. This demonstration should be accomplished engine trimming — The adjustment of the fuel control unit
within a safe distance of a suitable airport, and the entry of a gas-turbine engine.
altitude should allow completion no lower than 3,000 feet
engine-driven air pump — An air pump driven from
AGL. Since actual VMC varies with existing condition,
an accessory drive on the engine. Also referred to as a
the pilot should not try to duplicate the published VMC,
vacuum pump.
which was established during initial certification. Pilots
should expect a loss of directional control at a speed that engineer — A person who practices the profession of
may be higher than the published VMC. Remember, as engineering. In the United Kingdom an engineer is an
altitude increases, actual VMC decreases, and under aircraft maintenance technician.
some weight and altitude combinations, VMC and stall
engineered performance standards — A mathematically
speed are the same. This means that the loss of directional
derived runway capacity standard. EPS’s are calculated
control demonstration cannot be accomplished safely.
for each airport on an individual basis and reflect that
Pilots should be prepared to recover at the first indication
airport’s aircraft mix, operating procedures, runway
of stall or loss of directional control, whichever occurs
layout, and specific weather conditions. EPS’s do not give
first. The bottom line is that the intent of the engine-out
consideration to staffing, experience levels, equipment
loss of directional control demonstration is to demonstrate
outages, and intrail restrictions as does the AAR.
the onset of control limits. Normally, this occurs when the
nose begins to move even though full rudder is applied. enhanced training materials — While aviation instructors
are expected to be familiar with all regulatory training
engine logbook — A record book of an aircraft engine’s
requirements, use of instructor-oriented training
time in service, maintenance performed, inspections, etc.
materials, which are enhanced for regulatory compliance,
engine mount — The structure used to attach an engine in are beneficial for ensuring that required training is
the airframe. It normally includes shock mounts. accomplished, endorsed, and properly documented.
Examples of these materials may include training syllabi,
engine mounting pads — The shock absorbing units
maneuver guides or handbooks, and computer-based
connected between the engine and the engine mount.
training.
engine nacelle — The streamlined, enclosed housing on a
enrich — To make a fuel‑air mixture ratio richer. When
wing or fuselage in which the engine is mounted.
the amount of fuel metered into the engine is increased
engine performance — The relationship between power, without increasing the amount of air, the mixture is
RPM, fuel consumption, and manifold pressure of an enriched.
engine.

122

10001930-002_AviationDictionary_2012_BOOK.indb 122 3/27/2012 9:38:08 AM

 enroute air traffic control services • equalization

enroute air traffic control services — Air traffic control entrained air — The foam or bubbles in the scavenged oil
service provided aircraft on IFR flight plans, generally caused by heat and the centrifugal action of the oil‑wetted
by centers, when these aircraft are operating between parts. Oil with large quantities of entrained air is a poor
departure and destination terminal areas. When lubricant. This air has to be removed.
equipment, capabilities, and controller workload permit,
entrained water — The water held in suspension in aircraft
certain advisory/assistance services may be provided to
fuel. It is in such tiny droplets that it passes through filters
VFR aircraft.
and will do no damage until the temperature of the fuel
enroute charts — a. Enroute Low Altitude Charts – drops to the point that these tiny particles accumulate or
Provide aeronautical information for enroute instrument coalesce to form free water in the tank.
navigation (IFR) in the low altitude stratum. Information
envelope — A pre‑sewn cover made of aircraft fabric that is
includes the portrayal of airways, limits of controlled
slipped over the structure and attached.
airspace, position identification and frequencies of radio
aids, selected airports, minimum enroute and minimum envelope method of recovering — A method of recovering
obstruction clearance altitudes, airway distances, an aircraft structure in which a pre‑sewn fabric envelope
reporting points, restricted areas, and related data. Area is slipped over the structure and attached. The opening is
charts, which are a part of this series, furnish terminal closed either by cementing the fabric to the structure or
data at a larger scale in congested areas. b. Enroute High by hand sewing.
Altitude Charts — Provide aeronautical information for
envelope power — In electricity, a measurement of average
enroute instrument navigation (IFR) in the high altitude
power supplied to an antenna by a radio transmitter.
stratum. Information includes the portrayal of jet routes,
identification and frequencies of radio aids, selected environmental — The conditions surrounding an object.
airports, distances, time zones, special use airspace, and
environmental control systems — In an aircraft, the
related information.
systems, including the supplemental oxygen systems,
enroute descent — Descent from the enroute cruising air conditioning systems, heaters, and pressurization
altitude which takes place along the route of flight. systems, which make it possible for an occupant to
function at high altitude.
enroute flight advisory service — A service specifically
designed to provide, upon pilot request, timely weather environmental stress cracking (ESC) — In composites,
information pertinent to his type of flight, intended route the susceptibility of a resin to cracking or crazing when
of flight and altitude. The FSSs providing this service are in the presence of surface-active chemicals.
listed in the Airport/Facility Directory.
Eonnex — A fabric woven from polyester fibers.
enroute high altitude charts — Provide aeronautical
epicyclic gear train — An arrangement of gears in which
information for enroute instrument navigation (IFR)
one or more gears travel around the circumference of
in the high altitude stratum. Information includes the
another gear.
portrayal of jet routes, identification and frequencies
of radio aids, selected airports, distances, time zones, epoxy — A flexible, thermosetting resin made by the
special use airspace, and related information. polymerization of an epoxide. It is noted for its durability
and chemical resistance.
enroute low altitude charts — Provide aeronautical
information for enroute instrument navigation (IFR) epoxy primer — A two‑part catalyzed paint material used
in the low altitude stratum. Information includes the to provide a good bond between a surface and the topcoat.
portrayal of airways, limits of controlled airspace, position
epoxy resin — A common thermoset material used in aircraft
identification and frequencies of radio aids, selected
construction. Used as the bonding matrix to distribute the
airports, minimum enroute and minimum obstruction
stresses to the fibers, and hold the fibers together. When
clearance altitudes, airway distances, reporting points,
mixed with a catalyst, they are adhesive, resistant to
restricted areas, and related data. Area charts, which are
chemicals, are water resistant, and are unaffected by heat
a part of this series, furnish terminal data at a larger scale
or cold. One part of a two-part system which combines
in congested areas.
the resin and the catalyst to form the bonding matrix. In
enroute minimum safe altitude warning — A function of composites, the term “resin” is often used to describe the
the NAS Stage A enroute computer that aids the controller two parts mixed together.
by alerting him when a tracked aircraft is below or
EPR-rated gas turbine — A method of expressing the
predicted by the computer to go below a predetermined
thrust of a gas turbine engine in terms of engine pressure
minimum IFR altitude (MIA).
ratio (EPR).
enroute spacing program — A program designed to assist
equalization — The process of restoring all of the cells of a
the exit sector in achieving the required in-trail spacing.
nickel‑cadmium battery to a condition of equal capacity.

123

10001930-002_AviationDictionary_2012_BOOK.indb 123 3/27/2012 9:38:08 AM

 equalizer circuit • evaluation

All of the cells are discharged, shorted out, and allowed escutcheon — A reinforcement around a hole or opening
to “rest.” The battery is then said to be equalized and in a material that helps prevent tearing out of the base
ready to receive a fresh charge. material.
equalizer circuit — A circuit in a multiple‑generator established — To be stable or fixed on a route, route
voltage‑regulator system that tends to equalize the segment, altitude, heading, etc.
current output of the generators by controlling the field
estimated ceiling — A ceiling value that derives from an
currents of all the generators in the system.
estimate made by an observer or when the method of
equilibrium — A condition that exists within a body when determining ceiling does not fall definitively in any other
the sum of the moments of all of the forces acting on the category.
body is equal to zero.
estimated elapsed time [ICAO] — The estimated time
equilibrium level — The altitude where the updraft required to proceed from one significant point to another.
temperature is equal to its surroundings.
estimated off-block time [ICAO] — The estimated time at
equinox — Noon on the day when the sun’s rays are which the aircraft will commence movement associated
perpendicular to the earth’s surface at the equator. with departure.
equipment — Any item that is secured in a fixed location to estimated position error (EPE) — A measure of the current
the aircraft and is to be utilized in the aircraft. estimated navigational performance. Also referred to as
Actual Navigation Performance (ANP).
equipment ground — In electricity, a ground connected to
the case or chassis of electronic equipment. The chassis estimated time enroute — The estimated flying time from
is in turn, connected to an earth ground. See also earth departure point to destination (lift-off to touchdown).
ground.
estimated time of arrival — The time the flight is estimated
equipment list — A comprehensive list of equipment to arrive at the gate (scheduled operators) or the actual
installed on a particular aircraft. This includes the runway on times for nonscheduled operators.
required and optional equipment.
etch — To chemically remove a part of a material. Clad
equivalent airspeed (EAS) — The calibrated airspeed, aluminum alloy sheets are etched before painting to
shown on the airspeed indicator, corrected for errors that microscopically roughen them so that the primer can
are caused by the compressibility of the air inside, the bond tightly to their surface.
pitot tube, or by the installation of the instrument.
etching — A process of detecting defects in aluminum alloy
equivalent circuit — A circuit containing only one or by use of a caustic soda and nitric acid solution.
two components that has the same properties as a
ethylene dibromide — A chemical compound of bromine
more complex circuit. Used to more easily analyze the
that is added to aviation gasoline. Used to convert the
characteristics of the circuit.
lead deposits from the tetraethyl lead into lead bromides
equivalent flat plate area — The area of a square flat that are volatile enough to vaporize and pass out the
plate, normal to the direction of motion, which offers exhaust rather than foul the spark plugs.
the same amount of resistance to motion as the body or
ethylene glycol — A viscous form of liquid alcohol (C2HS02)
combination of bodies under consideration.
used as a coolant for high‑powered, liquid-cooled
equivalent monoplane — A monoplane wing with equal engines.
lift and drag properties as a combination of two or more
eutectic metal — A metal alloy whose melting point, due to
wings.
the proportion of its components, is lower than would be
equivalent shaft horsepower (ESHP) — A unit of measured possible before the mixture of the components.
power output of turboprops and some turboshaft engines.
evacuated bellows — A set of bellows from which most of
Where ESHP equals SHP plus HP from jet thrust (HP
the air has been removed and the bellows sealed. They
from jet thrust equals static thrust divided by 2.6).
serve as the sensitive element in an aneroid barometer for
erosion — The removal of material by abrasion, dissolution, measuring atmospheric pressure.
and/or corrosion.
evaluation — Measures a demonstrated performance
escape velocity — The speed an aircraft or missile must against a criteria or standard, such as a grade of at
reach in order for it to escape from the gravitational field least 70% to pass a written test. Formal evaluations are
of the Earth. typically in the form of written tests, oral quizzing, or
check flights, and are used to measure performance and
document whether the course objectives have been met.

124

10001930-002_AviationDictionary_2012_BOOK.indb 124 3/27/2012 9:38:08 AM

 evaporation • expel

evaporation — Change of state from liquid to vapor. expand — To increase the dimensions of.
evaporator — The unit in a vapor‑cycle air conditioning expanded plastic — The increase in the volume of
system in which liquid refrigerant absorbs heat from the plastic resin generated when the materials that make up
cabin to change the refrigerant into a vapor. Air blown the plastic are mixed. The volume is increased by gas
over the evaporator loses its heat and is cooled. bubbles.
execute missed approach — Instructions issued to a pilot expander-tube brake — A nonservo brake in which the
making an instrument approach which means continue composition blocks are forced out against a rotating drum
inbound to the missed approach point and execute by hydraulic fluid, expanding a synthetic rubber tube on
the missed approach procedure as described on the which they rest.
Instrument Approach Procedure Chart or as previously
expansion boots — Inflatable deicer boots.
assigned by ATC. The pilot may climb immediately to
the altitude specified in the missed approach procedure expansion coefficient — A number that describes the
upon making a missed approach. No turns should be change in linear dimensions of a material with a specified
initiated prior to reaching the missed approach point. change in its temperature.
When conducting an ASR or PAR approach, execute the
expansion reamers — A
assigned missed approach procedure immediately upon
precision cutting tool used
receiving instructions to “execute missed approach.”
to enlarge and smooth the
(Refer to AIM)
inside circumference of a
exercise — A principle of learning that those things most drilled hole. The diameter
often repeated are best remembered. of the reamer can be
changed by an adjustable
exhaust contrails — Forms when the water vapor added
wedge inside the blades.
from an aircraft exhaust is sufficient to saturate the
atmosphere. expansion turbine — A turbine wheel in an air‑cycle air
conditioning system used to extract some of the energy
exhaust gas temperature (EGT) — In gas turbine engines,
from the bleed air. The energy of the bleed air drives the
temperature taken at the turbine exit. Often referred to
turbine and the air is further cooled by expansion.
as Tt7.
expansion wave — The change in velocity and density
exhaust manifold — A pipe with several apertures used
of the air as it passes over the thickest part of an airfoil
to collect exhaust gases from reciprocating engines. The
moving through the air at speeds greater than the speed
manifold attaches to the individual exhaust ports and
of sound.
carries the exhaust gases overboard through a common
discharge. expect (altitude) at (time) or (fix) — Used under certain
conditions to provide a pilot with an altitude to be used
exhaust nozzle — The rear opening of a turbine engine
in the event of two-way communications failure. It also
exhaust duct. The nozzle acts as an orifice, the size of
provides altitude information to assist the pilot in planning.
which determines the density and velocity of the gases as
they emerge from the engine. expect further clearance (time) — The time a pilot can
expect to receive clearance beyond a clearance limit.
exhaust port — The hole in the cylinder of a reciprocating
engine through which the exhaust gases are expelled. expect further clearance via (airways, routes or fixes) —
Used to inform a pilot of the routing he can expect if
exhaust stacks — The short, individual pipes attached
any part of the route beyond a short range clearance limit
to the exhaust ports of the cylinders of reciprocating
differs from that filed.
engines, through which the exhaust gases are discharged
overboard. expected departure clearance time — The runway release
time assigned to an aircraft in a controlled departure time
exhaust stroke — The stroke of the Otto cycle where the
program and shown on the flight progress strip as an EDCT.
exhaust gases are forced out of the cylinder as the piston
is moving away from the crankshaft and the exhaust expedite — Used by ATC when prompt compliance is
valve is open. required to avoid the development of an imminent
situation. Expedite climb/descent normally indicates to
exhaust valve — The valve in an aircraft engine cylinder
a pilot that the approximate best rate of climb/descent
through which the burned gases leave the combustion
should be used without requiring an exceptional change
chamber.
in aircraft handling characteristics.
exit guide vanes — The fixed airfoils at the discharge end of
expel — To force or drive out.
an axial flow compressor that straighten out the swirling
air caused by the rotating rotors so that the air leaves the
engine in an axial direction.
125

10001930-002_AviationDictionary_2012_BOOK.indb 125 3/27/2012 9:38:08 AM

 expendable weight • extratropical cyclone

expendable weight — The weight that is decreased in more than 50 nautical miles from an off-shore heliport
flight. The fuel on board is an expendable weight as it is structure.
used in flight.
extension lines — The lines on a technical drawing that
experimental category — A grouping for aircraft that extend from a view for the purpose of identifying a
do not have type certificates or do not conform to their dimension.
type certificates. Special airworthiness certificates
extent of damage — An amount of damage sustained by a
may be issued in the experimental category for the
unit of equipment.
following purposes: research and development, showing
compliance with regulations, crew training, exhibition, exterior angle — The angle between one of the sides of a
air racing, market surveys, operating amateur-built polygon and an extension to an adjacent side.
aircraft, or operating kit-built aircraft.
exterior view — A view of an object showing only its outer
explode — To make a violent change in chemical or visible surfaces.
composition. To violently release chemical, mechanical,
external combustion engine — A heat engine in which the
or nuclear energy. Usually accompanied by loud noise, a
chemical energy in the fuel is converted into heat energy
flash of light and a great deal of heat.
released to the outside of the engine. Heating water to
explosion-proof motor — An electric motor sealed in a produce steam that is put to mechanical use is a form of
way that prevents explosive gases from being ignited by an external combustion engine.
electrical sparks within the motor.
external inspection — A visual inspection done externally
explosion-proof switch — An electric switch sealed in a to the airframe, engine, or unit component without having
way that prevents explosive gases from being ignited by to inspect the internal mechanism by disassembly.
electrical sparks within the switch.
external load — A load that is carried or extends outside
explosive atmosphere — A gaseous environment of an aircraft.
containing explosive vapors or explosive concentrations
external resources — Many potential resources exist
of fine dust that can be ignited.
outside the cockpit such as air traffic controllers,
explosive bolt — A special bolt that contains an explosive charge maintenance technicians, and flight service personnel.
that can be ignited when the bolt must instantly release. Used
external tooth lock washer — A
to allow instant release of expended rocket stages.
thin, spring steel, shake‑proof
explosive charge — A quantity of explosive that can be lock washer with twisted teeth
used to break a seal and discharge a substance. around its outside circumference
that holds pressure between the
explosive rivet — A patented blind rivet manufactured
head of a screw or bolt and the
by the DuPont Company. Its hollow end is filled with
metal surface to prevent the
an explosive and sealed with a cap. When the rivet is
fastener from loosening.
heated, it explodes, swelling its end and clamping the
metal together. external-control surface locks —
The locks applied on the exterior of the control surfaces
exponent — In mathematics, a number superscripted above
of a parked aircraft to prevent movement in windy
and to the right of a base number. It indicates the power to
conditions.
which the base number is to be multiplied. In the example
23, the base number is 2 while the exponent is 3. This is external-load attaching — The structural components
stated as two cubed (or two to the third power) and is used to attach an external load to an aircraft, including
shown as 2 X 2 X 2 = 8. external-load containers, the backup structure at the
attachment points, and any quick-release device used to
extend — To move away from the normal or closed
jettison the external load.
position. When landing gear is extended, it is moved
from its retracted position to the “gear down” position. extinguishing agent — The agent used in a fire extinguishing
Flaps can be extended from their stowed position to full system to either cool the fuel below its kindling point or
extension or to some point in between. to exclude oxygen from the surface of the fire.
extended over-water operation — 1. With respect to extra-flexible control cable — A special metal cable
aircraft other than helicopters, an operation over water flexible enough to pass around pulleys. It consists of
at a horizontal distance of more than 50 nautical miles seven strands of wire with 19 wires in each strand.
from the nearest shoreline. 2. With respect to helicopters,
extratropical cyclone — A macroscale low-pressure
an operation over water at a horizontal distance of more
disturbance that develops outside the tropics.
than 50 nautical miles from the nearest shoreline and

126

10001930-002_AviationDictionary_2012_BOOK.indb 126 3/27/2012 9:38:08 AM

 extrude • eyelet

extrude — To form by forcing through a die of the desired

shape.
extrusion — A strip
of metal, usually
of aluminum or
mag­nesium, that
has been forced
through a die in its
plastic state. This
can pro­duce complex
cross-sectional shapes required for modern aircraft
construction.
eye — 1. The hole of an eyebolt. 2. In meteorology, the
roughly circular area of calm or relatively light winds
and comparatively fair weather at the center of a
well‑developed tropical cyclone. A wall cloud marks the
outer boundary of the eye.
eye wall — The cloudy region embedded with cumulonimbus
(CB) clouds immediately adjacent to the eye of an intense
tropical cyclone.
eyebolt — A bolt that has a flattened head with a hole in it.
An eyebolt is used to attach a cable to a structure.
eyebrow lights — Small shielded lights positioned over
the top corners of an instrument on an aircraft instrument
panel. The lights illuminate the dials of the instrument,
but they do not shine in the eyes of the pilot.
eyelet — A flanged tubular fastener designed for securing
by curling or splaying the end.

127

10001930-002_AviationDictionary_2012_BOOK.indb 127 3/27/2012 9:38:08 AM

 F • fail-safe

F fabric warp face — That side of a woven fabric on which

the greatest number of yarns are parallel to the selvage.
FAA air carrier operations specifications — Document fabricate — To construct or build something.
issued to users operating under Federal Aviation
Administration Regulations (FAR) Parts 121, 125, 127, fabrication — The assembling of parts to make a complete
129, and 135. Operations Specifications are established unit or a structure.
and formalized by FARs. The primary purpose of FAA face of a propeller — The flat side of a propeller blade.
Air Carrier Operations Specifications is to provide a
legally enforceable means of prescribing an authorization, face of the drawing — The surface of an object as seen
limitation and/or procedures for a specific operator. from the front view.
Operations Specifications are subject to expeditious face shield — A transparent protective guard covering the
changes. These changes are usually too time critical to entire face to protect against flying objects or liquid spray.
adopt through the regulatory process.
face-end spanner — A type of semicircular, open‑end
FAA Form 337 — Major Repair and Alteration Form. wrench having short pins extending from its face and
FAA Form 8500-8 — Application for airman medical used to turn special circular t­ype nuts.
certificate, or airman medical and student pilot certificate. faceplate, lathe — Used for turning metal. A heavy, steel
FAA Form 8710-1 — Application for an airman certificate disk with a smooth face mounted on the headstock of the
and/or rating. lathe and is turned by it.
FAA-approved data — Data that can be used as face-to-face bearings — Bearing sets installed in such
authorization for the techniques or procedures necessary a way that one set carries thrust loads in one direction
to make a repair or an alteration to a certificated aircraft. while the other bearing set carries thrust loads in the
Approved data can consist of documents such as opposite direction.
Manufacturer’s Service Bul­letins, Manufacturer’s kit facing — A machining operation on the end, flat face, or
instructions, Airworthiness Directives, or specific details shoulder of a part.
of a repair issued by the engineering department of the
manufacturer. facsimile — A copy of a document that is transmitted over
telephone lines or radio waves by a facsimile machine to
FAA-PMA — The identifying letters required on an aircraft be recreated by a facsimile machine at the other end. Also
part or com­ponent to signify it as being manufactured referred to as a fax.
under a Federal Aviation Administration Parts
Manufacturing Approval. factor of safety — The ratio of the ultimate strength of a
member to the probable maximum load. This ratio is
fabric — Individual fibers woven together to produce cloth. larger than one.
Unidirectional or matted fibers may be included in this
classification. fading — 1. A decrease in the friction applied by a
drum‑type brake when it is hot. As the drum is heated,
fabric material — A cloth used to cover aircraft structures. it expands in a bellmouth fashion and part of it moves
The basic fabric is Grade‑A long staple cotton, but Irish away from the lining. This decreases the friction area and
linen is sometimes used interchangeably. Synthetic causes a loss of breaking action. 2. A decrease in strength
fabrics made of polyester resins and spe­cially treated of a received radio signal.
glass fibers also can be used in place of cotton.
fahnstock clip — An electrical type of spring clip connector
fabric punch test — A test performed to measure the used to temporarily connect a wire to an electrical circuit.
condition of fabric covering material on fabric-covered
aircraft. The tester determines fabric condition by Fahrenheit (F) — A temperature scale on which pure water
measuring the resistance of the fabric to a sharp punch freezes at 32° and boils under standard atmospheric
pressed against the fabric until it pierces. pressure conditions at 212°.
fabric punch tester — A hand tester used to give an fail hardover — A failure of an automatic flight control
indication of the relative strength of aircraft fabric. It system in which a steady signal is produced that drives
measures the force required to press a specially shaped the controls to the extreme end of their travel and holds
pointed plunger a specific distance into the fabric. them there.
fabric repair — The repair made to a fabric-covered fail-safe — A design feature that transmits the loads into
structure that produces the same strength and tautness in a secondary portion of the structure in the event of the
the fabric as it originally had. primary structure failure.

128

10001930-002_AviationDictionary_2012_BOOK.indb 128 3/27/2012 9:38:08 AM

 fail-safe control • feathering axis

fail-safe control — A type of control that automatically puts fastener — A device such as a rivet, screw, or bolt used to
the control­led device in a safe condition if the control fasten two objects together.
system should fail.
fatigue — The weakening and eventual failure of a metal
faired curve — A smoothly curved object. due to continued reversal or repeated stresses beyond the
fatigue limit.
fairing — A smooth covering over a joint or a junction in
an aircraft structure to provide a smooth surface for the fatigue crack — A crack in a structural member caused by
airflow. Its primary purpose is to reduce drag. flexing or vibration.
fairlead — Wood or plastic guides for aircraft control fatigue failure — The failure of a material due to flexing
cable, used to hold straight runs of cable away from the or vibration.
structure.
fatigue limit — The amount of flexing or vibration a body
fallstreaks — Ice crystals that descend from cirrus clouds. can withstand before fatigue failure occurs.
false rib — Short, semi‑rib extending from the spar to the fatigue resistance — The property that enables a metal
leading edge of the wing. It is used to give rigidity and to withstand repeated loads or reversals of loads and
better shape to the leading edge of fabric covered wings. vibrations.
false spar — A partial spar in an aircraft wing to which the fatigue strength — The ability of a material to withstand
aileron hinges attach. vibration and flexing.
false start — A condition in starting a turbine engine in fault — A defect in an electrical circuit.
which ignition occurs but the RPM will not increase.
fault tree — A chart used to determine the possible causes
This condition is usually caused by the engine not being
of some undesired event. The chart includes the undesired
turned fast enough by the starter when ignition occurs.
occurrence with the possible causes listed below it. A fault
fan — A feature of some turbojet engines. It is, in effect, tree is also referred to as a logic chart since the branches
a ducted, multi-bladed propeller driven by a gas turbine of the “tree” are connected through the use of logic gates.
engine. It can be constructed as an extension of some
faying strip — The strip along the edge of a sheet metal
of the turbine blades (aft fan), but it is more commonly
skin where a lap joint is formed. This inaccessible area is
an extension of compressor blades or powered by gears
highly susceptible to the formation of corrosion.
from the compressor or turbine sections (forward fan).
These fans pull large volumes of air around the outside faying surface — The overlapping area of adjoining
of the gas generator portion of the engine. surfaces.
fan air — The portion of airflow through a turbofan engine FDC NOTAM — A NOTAM issued by the National
that is acted upon by the fan stages of the compressor. Flight Data Center which contains information of a
regulatory nature such as temporary flight restrictions
fan marker — An aircraft directional radio signal
or amendments to instrument approach procedures and
transmitted vertically upward from a transmitter located
other current aeronautical charts.
along a naviga­tional radio range. It is heard only when
the aircraft is directly over the transmitter. feather — To change the angle of propeller blades so that
the chords become approximately parallel to the line of
Farad (f) — The basic unit of capacitance. A capacitor of
flight.
one farad will hold one coulomb (6.28 x 1018 electrons)
under a pressure of one volt. feather edge — A very thin, sharp edge of a material.
Susceptible to damage as a result of bending or breaking.
Faraday’s law of electrolysis — The amount of chemical
change produced by current during electrolysis is feathered propeller — A propeller whose blades have been
proportional to the quantity of electricity used. rotated so that the leading and trailing edges are nearly
parallel with the aircraft flight path to stop or minimize
Faraday’s law of electromagnetic induction — When
drag and engine rotation. Normally used to indicate
there is relative motion between a conductor and a
shutdown of a reciprocating or turboprop engine due to
magnetic field, or when there is a change in magnitude of
malfunction.
the magnetic field, electrons are induced to flow through
the conductor. feathering — In rotorcraft, the action that changes the pitch
angle of the rotor blades by rotating them around their
fast file — A system whereby a pilot files a flight plan via
feathering (spanwise) axis.
telephone that is tape recorded and then transcribed
for transmission to the appropriate air traffic facility. feathering axis — In rotorcraft, the axis about which the
Loca­tions having a fast file capability are contained in pitch angle of a rotor blade is varied. Sometimes referred
the Air­port/Facility Directory. (Refer to AIM) to as the spanwise axis.

129

10001930-002_AviationDictionary_2012_BOOK.indb 129 3/27/2012 9:38:08 AM

 feathering propeller • ferry permit

feathering propeller — A controllable pitch propeller with proceed from the enroute structure to the initial approach
a pitch range sufficient to allow the blades to be turned fix (IAF).
parallel to the line of flight. This reduces drag and helps
feedthrough capacitor — A capacitor used to block low
prevent further damage to an engine that has been shut
frequencies while passing radio frequencies. Some
down after a malfunction.
magnetos use a feed-through capacitor to serve as the
feathering solenoid — A locking, electrical solenoid used normal capacitor to minimize arcing of the points. They
with a Hamil­ton Standard Hydromatic propeller. The also decrease the amount of radio interference caused by
solenoid keeps the feather­ing pump running after the electrical energy being radiated from the ignition switch
feathering button has been momentarily depressed. The lead.
solenoid is de-energized when the propeller be­comes
feedthrough connector — A connector used to carry a
fully feathered.
group of conductors through a bulkhead.
feathering switch — Hydromatic propellers are standard
feel — The feedback from a power‑controlled flight control
equipment on certain models of airplanes, i.e., the D18C
or brake system. This “feel” allows the pilot to sense how
and D18C-T airplanes. These propellers are controlled
much pressure is needed for the operation of the system.
by individual, single-acting, Hamilton Standard propeller
governors, and feathering or unfeathering action is feeler gauge — A measuring tool consisting of a series of
accomplished by individual, electric motor-driven pump precision ground steel blades of various thicknesses. It
feathering systems. The pumps are controlled by a is used to determine the clearance or separation between
feathering switch. parts.
Federal Airways — See Low Altitude Airway Structure. fence — A fixed vane that extends chordwise across the
wing of an airplane. Fences prevent air from flowing
Federal Aviation Administration (FAA) — An
along the span of the wing.
organization within the Department of Transportation.
The FAA establishes aviation rules and regulations as Fenwal spot‑type fire detection system — A fire detection
well as enforces those policies. The purpose of the FAA system utiliz­ing bimetallic thermal switches. A fire or
is to set the standards for civil aircraft in the interest of overheat condition closes the switches and signals the
public safety. presence of the fire or overheat.
Federal Aviation Regulations (FAR) — The rules, ferrite — A magnetic substance that consists of ferric oxide
regulations, and guidelines established by the FAA to combined with the oxides of one or more metals. Ferrite
govern the operation of aircraft, airways, airmen, and the has high magnetic permeability and high electrical
safe operation of civil aircraft. resistance.
Federal Communications Commission (FCC) — A ferritic stainless steel — Straight chromium carbon and
government board, made up of seven commissioners, low‑alloy steels that are strongly magnetic.
responsible for regulating all interstate electrical
ferromagnetic materials — Magnetic materials composed
communications, including foreign communications that
largely of iron.
originate in the United States.
ferrous metal — Iron or any alloy containing iron.
feedback — 1. Another way to gauge whether students are
receiving the correct message. Students must interpret ferrule resistor — A group of resistors that have metal
and evaluate the information received and then respond. bands (ferrules) around each end so that they can be
The transmission of evaluative or corrective information mounted in standard fuse clips.
to the original or controlling source about an action,
ferrule terminals — The terminals on each end of a tubular
event, or process. 2. In rotorcraft, the transmittal of
fuse. Used for making connections with the circuit.
forces, which are initiated by aerodynamic action on rotor
blades, to the cockpit controls. 3. A portion of the output ferry — The movement of an aircraft from one location to
signal of a circuit that is returned to the input. Positive another.
feedback occurs when the feedback signal is in phase
ferry flight — A flight for the purpose of returning an
with the input signal. Negative feedback occurs when the
aircraft to base; delivering an aircraft from one location to
feedback signal is out of phase with the input signal.
another; or moving an aircraft to and from a maintenance
feeder fix — The fix depicted on instrument approach base. Ferry flights, under certain conditions may be
procedure charts which establishes the starting point of con­ducted under terms of a special flight permit.
the feeder route.
ferry permit — Commonly used name for Special Flight
feeder route — A route depicted on instrument approach Permit. A Special Flight Permit issued by the FAA allows
procedure charts to designate routes for aircraft to an unlicensed aircraft to be flown from one location to
another location.
130

10001930-002_AviationDictionary_2012_BOOK.indb 130 3/27/2012 9:38:08 AM

 fiber • files, classification

fiber — A single strand of material, used as a reinforcement field maintenance — The maintenance performed on
because of its high strength and stiffness. aircraft remotely or semi‑remotely from the home station.
Typically, there are few tools or equipment to implement
fiber bridging — In composites, reinforcing fiber material
normal main­tenance procedures.
that bridges an inside-radius of a pultruded product. This
condition is caused by shrinkage stresses around such a field strength — 1. The intensity of the magnetic strength
radius during cure. of a magnet or electromagnet. 2. The intensity of the
electromagnetic field emanating from a radio transmitter
fiber content — The amount of fiber in a composite
antenna.
expressed as a ratio to the matrix. The most desirable
fiber content is a 60:40 ratio. This means there is 60% field strength meter — An electrical instrument that
fiber and 40% matrix material. measures the strength of an electromagnetic field
radiating from a radio transmitting antenna.
fiber direction or orientation — In composites, the
orientation of the fibers in a laminate to the 0º reference filament — 1. The heated element in a light bulb or electron
designated by the manufacturer. tube. In an electron tube, the heat speeds up the molecular
movement in the cathode that emits electrons. 2. The
fiber locknut — A type of self‑locking fastener with a fiber
smallest unit of a fibrous material.
insert that puts pressure on the threads to lock the nut in
place. This prevents the nut from turning when installed filament winding — In composites, a manufacturing
in areas subject to vibration. method in which long continuous fiber is wound around
a mandrel to produce a structure.
fiber optics — The transmission of light through a bundle
of fiber rods. Often used in areas where light must be file — A hand‑operated cutting tool made of high‑carbon
transmitted, but where it is inconvenient or dangerous steel and fitted with rows of very shallow teeth extending
to use electrical transmission. An optical device called diagonally across the width of the tool.
a Borescope uses tiny glass rods that conduct light and
filed — Normally used in conjunction with flight plans,
vision to make inspection around corners practicable.
meaning a flight plan has been submitted to ATC.
Fiber optics are also used to transmit information from
one electronic device to another. filed enroute delay — Any of the following pre­planned
delays at points/areas along the route of flight which
fiber reinforced plastics (FRP) — Term used
require special flight plan filing and handling tech­niques.
interchangeably for advanced composites
a. Terminal Area Delay. A delay within a terminal area
fiberglass — Extremely thin fibers of glass. May be woven
for touch-and-go, low approach, or other terminal area
into a cloth or lightly packed into a mat. Used to reinforce
activity.
epoxy or polyester resin for aircraft structure.
b. Special Use Airspace Delay. A delay within a Mili­tary
fiberglass reinforcement — In composites, fiberglass used
Operating Area, Restricted Area, Warning Area, or
as a reinforcement in a plastic matrix.
ATC Assigned Airspace.
fidelity — The degree of similarity between the input and
c. Aerial Refueling Delay. A delay within an Aerial
output waveforms of an electronic circuit.
Refueling Track or Anchor.
field — A space in which magnetic or electric lines of force
filed flight plan — The flight plan as filed with an ATS unit
exist.
by the pilot or his designated representative with­out any
field coil — Coil or winding used to produce a magnetic subsequent changes or clearances.
field.
files, classification — The teeth on a file vary from very fine
field effect transistor (FET) — A special form of to coarse in the following sequence:
semiconductor device with high input impedance.
a. Dead‑smooth cut
Electron flow between its source and drain is controlled
by a voltage applied to the gate. b. Smooth cut
field elevation — See Airport Elevation c. Second cut
field excitation — DC supplied to the field of an alternator d. Bastard cut
or generator to produce magnetic flux, which is cut by the
e. Coarse cut
conductors in the armature or stator.
Files with a single set of cutting teeth are called single‑cut
field frame — The main structure of a generator or motor
files. A file that has a second set of cutting teeth crossing
on which field poles and windings are mounted.
the first set is called a double‑cut.

131

10001930-002_AviationDictionary_2012_BOOK.indb 131 3/27/2012 9:38:08 AM

 filiform corrosion • final approach fix (FAF) (Australia)

filiform corrosion — A thread- or filament‑like corrosion film strength — A lubricant’s ability to maintain a
that forms on aluminum skins beneath a covering of continuous lubricating film under mechanical pressure
protective coating. without breaking down.
fill — The direction across the width of fabric. filter — 1. A device for straining out unwanted solid particles
in a fluid. 2. An electrical circuit arranged to pass certain
fill threads — Threads running across the width of a piece
frequencies while blocking all others. A high pass filter
of fabric from one selvage edge to the other. Also referred
passes high frequencies and blocks low frequencies.
to as weft or woof threads.
filter capacitor — A low-impedance capacitor attached
filler — In composites, material added to the mixed resin
across the output of a DC power supply to filter any
to increase viscosity, improve appearance, and lower the
ripple to ground, leaving the DC untouched.
density and cost.
filter choke — An inductor placed in series with the output
filler material — Any material mixed or added to a base
of a DC power supply to reduce the amount of ripple
material in order to give body to the base material.
while allowing the DC to pass.
filler metal — A metal used to increase the area of a weld.
filtering — The separation of unwanted components from
Normally supplied in the form of the welding rod or the
either a fluid flow or an electrical flow.
electrode used in arc welding.
fin — 1. The vertical stabilizer of an airplane to which the
filler neck — Usually, a cylinder‑shaped neck or tube
rudder is hinged. It produces directional stability. 2. A
leading into a reservoir for replenishing fluids.
key under the head of a fastener that serves to keep the
filler plug — The plug installed in a sheet metal or wood fastener from turning during assembly and use.
structural repair to make the surface of the repair coincide
final — Commonly used to mean that an aircraft is on the
with the original skin contour. The filler plug is used
final approach course or is aligned with a landing area.
only to make the surface aerodynamically smooth. The
(See Final Approach Course) (See Final Approach - IFR)
strength of the repair comes from the doubler inside the
(See Traffic Pattern) (See Segments of an Instrument
structure.
Approach Procedure)
filler ply — In composites, an additional patch to fill in a
final approach — A flight path of a landing aircraft in the
depression in the repair, or to buildup an edge.
direction of landing along the extended runway centerline
filler rod — A thin metal rod or wire used in welding to from the base leg or straight in to the runway.
provide the necessary filler metal. Used to provide
final approach - IFR (USA) — The flight path of an aircraft
additional strength to the weld.
which is inbound to an airport on a final instrument
filler valve — A readily accessible valve that provides approach course, beginning at the final approach fix or
a means of servicing an installed oxygen, air, or fluid point and extending to the airport or the point where a
system. circle-to-land maneuver or a missed approach is executed.
fillet — A rounded‑out addition at the intersection of two final approach course — A bearing/radial/track of an
plane surfaces to produce a smooth junction where the instrument approach leading to a runway or an extended
two surfaces meet. Fillets produce a smooth aerodynamic runway centerline all without regard to distance.
junction between the wing and the fuselage of an airplane.
final approach fix (FAF) — The fix from which the final
filling — An increase in the central pressure of a pressure approach (IFR) to an airport is executed and which
system; opposite of deepening; more commonly applied identifies the beginning of the final approach segment.
to a low rather than a high. It is designated in the profile view of Jeppesen Terminal
charts by the Maltese Cross symbol for nonprecision
fillister‑head screw — A machine screw whose shape
approaches and by the glide slope/path intercept point on
consists of a rounded top surface, cylindrical sides, and a
precision approaches. The glide slope/path symbol starts
flat bearing surface.
at the FAF. When ATC directs a lower-than-published
film adhesive — In composites, a synthetic resin adhesive, Glide Slope/Path Intercept Altitude, it is the resultant
usually of the thermosetting type, in the form of a thin, actual point of the glide slope/path intercept.
dry film of resin.
final approach fix (FAF) (Australia) — A specified
film resistor — A resistor formed by coating a ceramic, point on a non-precision approach which identifies
glass, or other insulating cylinder with a metal oxide or the commencement of the final segment. The FAF is
other thin resistive film. designated in the profile view of Jeppesen Terminal
charts by the Maltese Cross symbol.

132

10001930-002_AviationDictionary_2012_BOOK.indb 132 3/27/2012 9:38:09 AM

 final approach (ICAO) • fireproof structure

final approach (ICAO) — That part of an instrument finger brake — A metal-forming machine similar to a leaf
approach procedure which commences at the specified (cornice) brake. It is used to form all four sides of a box.
final approach fix or point, or where such a fix or point The sides that have been bent up fit between the fingers
is not specified, 1. at the end of the last procedure turn, of the clamp while the last bends are being made. Also
base turn or inbound turn of a racetrack procedure, if referred to as a box brake.
specified; or 2. at the point of interception of the last
finger patch — A form of
track specified in the approach procedure; and ends at a
welded patch to go over
point in the vicinity of an aerodrome from which: a. a
a cluster in a steel tube
landing can be made; or b. a missed approach procedure
fuselage. Fingers ex­tend
is initiated.
along all of the tubes in the
final approach point — The point, applicable only to a cluster.
nonprecision approach with no depicted FAF (such as
finger screen — A finger‑shaped filter screen used on fuel
an on-airport VOR), where the aircraft is estab­lished
tank standpipes. Used to screen or filter out large pieces
inbound on the final approach course from the proce­dure
of contamination.
turn and where the final approach descent may be
commenced. The FAP serves as the FAF and identifies finish — In composites, a material that is applied to the
the beginning of the final approach segment. fabric after it is woven to improve the bond of the fiber
to the resin system.
final approach point (FAP) (Australia) — A specified
point on the glide path of a precision instrument approach finish turning — A final smoothing process in the
which identifies the commencement of the final segment. machining of a metal part in which the part is turned to
NOTE: The FAP is co-incident with the FAF of a localizer its correct dimension.
based non-precision approach.
finite life — The length of usefulness of a limited-life
final approach segment — That segment of an instrument part. The part should not be used past the end of its
approach procedure in which alignment and descent for predetermined operating life.
landing are accomplished.
fire alarm relay — A relay actuated by a fire detection
final controller — The controller providing information and system. Provides energy for the fire warning bell and the
final approach guidance during PAR and ASR approaches fire warning lights in the cockpit.
utilizing radar equipment. (See Radar Approach)
fire detection system — A system in an aircraft that informs
final monitor aid — A high resolution color dis­play that the pilot of a fire on board the aircraft.
is equipped with the controller alert system hard­ware/
fire extinguisher — Any device containing an extinguishing
software which is used in the precision runway monitor
agent used to either cool a material below its kindling
(PRM) system. The display includes alert algo­rithms
point or to exclude oxygen from its surface.
providing the target predictors, a color change alert
when a target penetrates or is predicted to penetrate the fire extinguishing agent — Any approved chemical used to
no transgression zone (NTZ), a color change alert if the extinguish a fire by either reducing the temperature of the
air­craft transponder becomes inoperative, synthesized fuel to a temperature that is below its kindling point or by
voice alerts, digital mapping, and like features contained excluding oxygen from the fire.
in the PRM system. (See Radar Approach)
fire point — The temperature at which the vapors given off
final monitor controller — Air Traffic Con­trol Specialist by a sub­stance will ignite and continue to burn when a
assigned to radar monitor the flight path of aircraft during flame is passed above it.
simultaneous parallel and simultaneous close parallel
fire valve — A valve that automatically shuts off the supply
ILS approach operations. Each runway is assigned a
of com­bustion air to a combustion‑type cabin heater in
final monitor controller during simultaneous parallel
the event of a fire or overheat condition.
and simultaneous close parallel ILS approaches. Final
monitor controllers shall utilize the Precision Runway fire zone — An area or region of an aircraft designated by the
Monitor (PRM) system during simultaneous close manufac­turer to require fire detection, fire extinguishing
parallel ILS approaches. equipment, and a high degree of inherent fire resistance.
fineness ratio — The ratio of the length to the maximum fireproof — The capacity to withstand the heat associated
diameter of a streamlined body such as an airship hull. with fire without being destroyed.
fine-wire spark plug — A spark plug using platinum or fireproof structure — A structure constructed of
iridium electrodes. The small electrodes allow the firing nonflammable materials.
end cavity to be open resulting in better scavenging of the
lead oxides from the plug. The heat transfer characteristics
of the fine wires prevent their overheating.
133

10001930-002_AviationDictionary_2012_BOOK.indb 133 3/27/2012 9:38:09 AM

 fire‑resistant structure • flag

fire‑resistant structure — A structure capable of resisting fit — The range of tightness in the design of mating
fire or ex­posure to high temperature for a specified period parts. Tightness of fit is the result of applying specific
of time without being destroyed or structurally damaged. combinations of al­lowances and tolerances.
firewall — A fire‑resistant bulkhead that must be installed fitting — A part used to join or attach assemblies together.
between an engine compartment and the rest of the
five-hour rating — The ampere‑hour rating of a battery
aircraft structure.
that will discharge the battery in five hours. This is the
firewall shutoff valve — A valve located on the airframe side most commonly used rating for aircraft batteries.
of a firewall that will completely shut off the flow of fuel,
five-minute rating — A rating of the ampere‑hour capacity
oil, or hydraulic fluid to the engine during an engine fire.
of batteries normally used to indicate the capacity of a
firing order — The order or sequence in which the cylinders battery for high current drains such as starting current.
of an internal combustion engine fire in a normal cycle of The five‑minute rating of a battery is an indication of
operation. the way the battery will function under the severe loads
required by the engine starter.
firing position — The position of the piston in the cylinder
of a reciprocating engine at the time ignition should fix — A geographical position determined by visual
occur. Igniting the mixture at this position allows the reference to the surface, by reference to one or more radio
peak cylinder pressure to occur shortly after the piston navaids, by celestial plotting, or by another navigational
passes top center. device. (Note, fix is a generic name for a geographical
position and is referred to as a fix, waypoint, intersection,
firmer chisel — A woodworking chisel that has a thin, flat
reporting point, etc.)
blade.
fix balancing — A process whereby aircraft are evenly
firmware — A computer program contained permanently
distributed over several available arrival fixes reduc­ing
in a computer. Usually contained in read-only memory
delays and controller workload.
(ROM).
fixed — The state of a permanently installed system in
first solo — A student pilot may not operate an aircraft in
contrast to any type of portable equipment system.
solo flight unless that student has met the requirements of
FAR Part 61. “Solo flight,” refers to the flight time that a fixed cowl flap — Fixed or ground adjustable doors on the
student pilot is the solo occupant of the aircraft, or when air exit of an aircraft engine cowling. The cylinder head
the student performs the duties of a pilot in command of a temperature can be controlled by varying the amount the
gas balloon or airship requiring more than one pilot flight flaps are opened if ground adjustable.
crewmember. “First solo” refers to the very first time a
fixed equipment — Non-movable, attached equipment.
student embarks on a solo flight.
fixed landing gear — Landing gear that is not retractable.
first tier center — The ARTCC immediately adjacent to the
impacted center. fixed tail surfaces — Surfaces, mounted rigidly to the
fuselage, that stabilize aircraft during takeoff, flights, and
first‑class lever — A lever in which the fulcrum or pivot
landing. Fixed tail surfaces also provide anchorage for
point is posi­tioned between two forces that act in opposite
the rudder and elevators. Often referred to as stabilizers.
directions.
fixed-base operator (FBO) — An entrepreneur on an
fisheyes — Isolated areas on a surface that have rejected the
airfield that conducts business involved with general
material’s finish because of wax or silicone contamination.
aviation. Often sells aviation fuel, aircraft and aircraft
fishmouth splice — A parts, aviation related goods, repairs aircraft, and
welded splice in steel conducts flying training.
tube structure in which
fixed-pitch propellers — Propellers with fixed blade
one tube telescopes over the other. The outside tube is
angles. Fixed-pitch propellers are designed as climb
cut into a “V,” resem­bling an open fishmouth, to provide
propellers, cruise propellers, or standard propellers.
additional area for the weld.
fixed‑wing aircraft — An airplane with rigidly attached
fishtail — A method no longer used to decrease the speed
wings, as distinguished from a helicopter or autogyro.
of an airplane on its approach for landing. Fishtailing
consists of alternately skidding the airplane to the left and fixture — A small jig or device for holding parts in the
right by using the rudder while keeping the wings level proper position for assembly.
with the control stick.
flag — A warning device incorporated in certain air­borne
fissure — A scratch or crack. navigation and flight instruments indicating that: 1.
instruments are inoperative or otherwise not operat­ing

134

10001930-002_AviationDictionary_2012_BOOK.indb 134 3/27/2012 9:38:09 AM

 flag alarm • flashing off

satisfactorily, or 2. Signal strength or quality of the flare — 1. A flight maneuver

received signal falls below acceptable values. made by pulling back on the
flag alarm — See flag. control wheel just before
touchdown to reduce speed
flame out — In gas turbine engines, an unintentional loss of and settle the airplane onto
combustion due to a blowout (too much fuel) or die-out the runway with the least
(too little fuel). amount of vertical speed. 2.
flame spraying — In flame spraying, molten metal is A signal device that was, at
sprayed onto a base material. The combustion of a fuel one time, carried in most airplanes in the event of a crash
gas is used to melt a metal. Melted particles are propelled landing. The flare was usually fired into the air from a
toward the base material by a high-pressure gas where specially designed gun and signaled the general location
they are quenched very rapidly. This process allows a of the downed aircraft’s position. 3. A 37° cone‑shaped
high wear resistant or high temperature resistant coating expansion at the end of a piece of tubing. A sleeve and
to be applied to a surface that normally does not have nut are slipped over the tubing prior to using a special
these characteristics. cone‑shaped flaring tool to form the flare. 4. In rotorcraft,
a maneuver accomplished prior to landing to slow down
flameout — A condition in the operation of a gas turbine the aircraft.
engine in which the fire in the engine goes out due to either
too much or too little fuel sprayed into the combustors. flareless fitting — A form of fluid line fitting used on some
hydraulic lines. Instead of using a formed flare on the
flameout pattern — An approach normally con­ducted by end of the tube, a compression sleeve is forced into the
a single-engine military aircraft experiencing loss or tube. A fluid‑tight sealing surface is formed when the
anticipating loss of engine power or control. The standard compression sleeve is tightened onto a recess in the
overhead approach starts at a relatively high alti­tude attachment fitting.
over a runway (“high key”) followed by a continuous
180 degree turn to a high, wide position (“low key”) flaring — An operation used to expand the end of a length
fol­lowed by a continuous 180 degree turn final. The of tubing designed to produce a tight seal when coupled
standard straight-in approach with a high rate of descent to another unit.
to the run­way. Flameout approaches terminate in the type flaring block — A split clamp, usually made of hardened
approach requested by the pilot (normally fullstop). steel, used to hold tubing while it is being flared.
flammable — Any material that will burn or support flaring tool — A split block with chamfered holes to clamp
combustion. the various sizes of tubing while a hardened and polished
flammable liquid — Any liquid that gives off easily ignited, cone is forced into the end of the tubing to form it against
combustible vapors. the chamfer.

flange — Any design of a machine, motor, or other flash — The thin fin of metal along the sides or around
mechanism having a ridge that sticks out from the device. the edges of a forged or upset section. It is caused when
It is generally used for attaching something to the device metal flows out between the edges of the forging dies.
or for connecting two or more devices together. flash line — A raised line along the boundary of a cast part.
flaperon — A type of control used on airplanes that serves flash plating — A very thin deposit of metal sufficient to
as both aileron and wing flap. give a solid color.
flapper valve — A type of check valve that allows fluid to flash point — The temperature at which a fluid will
flow through it in the direction of flow, forcing the valve momentarily ignite (flash), but not sustain combustion
off of its seat. It does not allow fluid to flow in the opposite when a small flame is passed above its surface.
direction since this causes the flapper valve to close.
flashback — A malfunction in an oxyacetylene torch in
flapping — In rotorcraft, the vertical movement of a blade which the gases burn inside the mixing head. Flashback
about a flapping hinge. is very dangerous and can cause an explosion unless the
flapping hinge — In rotorcraft, the hinge that permits the gases are immediately shut off at the regulator. This stops
rotor blade to flap and thus balance the lift generated by the fire inside the torch from burning back through the
the advancing and retreating blades. hoses to the supply tanks.

flaps — Hinged portion of the trailing edge between the flasher mechanism — An automatic electrical switching
ailerons and fuselage. In some aircraft ailerons and flaps device used for the flashing operation of lights.
are interconnected to produce full-span ‘flaperons.’ In flashing off — The drying process of a finish to which
either case, flaps change the lift and drag on the wing. solvents have been added for proper spray paint viscosity.

135

10001930-002_AviationDictionary_2012_BOOK.indb 135 3/27/2012 9:38:09 AM

 flashing the field • flight director system

Although the surface feels dry to the touch, the film is flatnose pliers — Pliers with deep, square jaws and a firm
not completely dry until the proper cure time has been hinge, used to produce a sharp, neat bend in sheet metal
established. and to make flanges along the edge of a part.
flashing the field — A procedure in which a battery is fleet weight — The average weight of several aircraft of the
momentarily connected to the field coil of an aircraft DC same model and with the same equipment. This weight
generator. Current flows through it for a few seconds to may be used for weight and balance calculations by FAR
make a permanent magnet of the field frame. This process Part 121 and 135 operators.
restores the residual magnetism.
flex hose — The colloquial term for flexible tubing used in
flashover — A condition inside the distributor of a an aircraft plumbing system to allow relative movement
high‑tension magneto in which the spark jumps the between the two ends of the hose.
air gap to the wrong electrode. This may be caused by
flexibility — A material characteristic that allows it to be
moisture inside the distributor or by a dirty distributor
repeatedly bent, stretched, or twisted within its elastic
block.
limits and still return to its original condition each time
flash‑resistant — Not susceptible to burning violently the bending, stretching, or twisting force is removed.
when ignited.
flexible control cable — A steel aircraft control cable
flat file — A file slightly tapered toward the point in both consisting of seven strands of steel wire, each strand
width and thickness. Cuts on all sides. Double-cut on having seven separate wires. Also referred to as
both sides and single-cut on both edges. seven‑by‑seven cable.
flat lacquer — Any lacquer that dries with a non‑glossy or flight — 1. Travel through the air. An aircraft is considered
flat finish. to be in flight from the time it airplane departs from the
ground until it lands. 2. To take flight physically, students
flat machine tip — Compressor or turbine blade tips that
may develop symptoms or ailments that give them
have a constant cross section, as opposed to a squeeler‑tip
acceptable excuses for avoiding lessons. More frequent
or a shrouded‑tip configuration.
than physical flights are mental flights, or daydreaming.
flat rating — A current means of referring to “rated thrust” Mental flight provides a simple escape from problems.
at a specific temperature above Standard Day value.
flight assist — Help given to a pilot when the pilot takes
flat spin — A dangerous flight condition or flight maneuver the precaution of requesting assistance from Air Traffic
in which the aircraft is yawing around the vertical axis Control (ATC). A flight assist report (FAA Form 7230-6)
with a pitch attitude approximately level with the horizon. is filed by ATC personnel in order to help other pilots
learn from the incident. This form is not used to initiate
flat washer — A flat, thin ring used under the head of a bolt
enforcement action.
or nut in order to protect the surface of the material from
damage. Also referred to as a plain washer. flight check — A call-sign prefix used by FAA air­craft
engaged in flight inspection/certification of naviga­tional
flat‑compounded generator — A generator that has both a
aids and flight procedures. The word “recorded” may be
series and a parallel winding. The series field is adjusted
added as a suffix; e. g, “Flight Check 320 recorded” to
by a regulator to keep the output voltage of the generator
indicate that an automated flight inspection is in progress
constant from a no‑load condition to the maximum load
in terminal areas. (See Flight Inspection) (Refer to AIM)
the generator can produce.
flight control surfaces — The movable airfoils used to
flathead pin — A high‑strength steel pin with a flat head on
change the attitude of the aircraft in flight.
one end and a hole for a cotter pin on the other end. Used
as a hinge for control surfaces or for attaching a cable to a flight controller — The command unit of an autopilot
control horn. Also referred to as a clevis pin. Clevis pins system. It is manually operated to generate signals
are designed to take shear loads only. that cause the aircraft to climb, descend, or perform
coordinated turns.
flathead rivet — An AN442
rivet used for internal flight deck — The area in an aircraft that houses all of
structure where the head the occupants who fly the aircraft, along with all of the
of the rivet will not be controls used in flight. It includes the flight stations for
exposed to the airstream. the pilot, copilot, flight engineer, navigator, and radio
Flathead rivets are usually operator as required.
driven with an automatic riveting machine.
flight director system — A form of automatic flight control
in which all of the information is displayed to the pilot
rather than being used to actuate control servos.

136

10001930-002_AviationDictionary_2012_BOOK.indb 136 3/27/2012 9:38:09 AM

 flight engineer • flight simulator

flight engineer — The member of the flight crew responsible flight management system procedure — An arrival,
for the mechanical operation of the aircraft in flight. departure, or approach procedure developed for use by
aircraft with a slant E (/E) or slant F(/ F) equipment suffix.
flight following — See traffic advisories.
flight manual — Approved information that must be carried
flight following — A radar traffic information service
in an airplane. This includes the speeds, engine operating
which routinely provides traffic information for IFR
limits, and any other information vital to the pilot.
aircraft. However, when available, VFR aircraft may
request flight following and be alerted, by ATC, to air flight path — A line, course, or track along which an aircraft
traffic which is relevant to the flight. is flying or intended to be flown.
flight idle — Engine speed, usually in the 70% to 80% flight plan — Specified information relating to the intended
range, for minimum flight thrust. flight of an aircraft that is filed orally or in writing with
an FSS or an ATC Facility.
flight information region — An airspace of defined
dimensions within which Flight Information Ser­vice and flight plan area — The geographical area assigned by
Alerting Service are provided. regional air traffic divisions to a flight service station for
the purpose of search and rescue for VFR air­craft, issuance
a. Flight Information Service – A service provided for
of notams, pilot briefing, in-flight services, broadcast,
the purpose of giving advice and information useful
emergency services, flight data processing, inter­national
for the safe and efficient conduct of flights.
operations, and aviation weather services. Three letter
b. Alerting Service – A service provided to notify identifiers are assigned to every flight service station.
appropriate organizations regarding aircraft in need of
flight recorder — A general term applied to any instrument
search and rescue aid, and to assist such organiza­tions
or device that records information about the per­formance
as required.
of an aircraft in flight or about conditions encountered
flight inspection — Inflight investigation and evaluation in flight. Flight recorders may make records of airspeed,
of a navigational aid to determine whether it meets outside air temperature, vertical acceleration, engine
established tolerances. (See Navigational Aid) (See RPM, manifold pressure, and other pertinent vari­ables
Flight Check) for a given flight Housed in a crash‑proof container, the
flight recorder is used to determine the probable cause of
flight instructor refresher course (FIRC) — An
any accident the aircraft should be involved in..
educational seminar for flight instructors, which consists
of ground training or flight training or a combination of flight review — An industry-managed, FAA monitored
both. The FIRC must be completed within the 3 calendar currency program designed to assess and update a pilot’s
months preceding the expiration month of the current knowledge and skills.
flight instructor certificate, and usually consists of at least
flight service stations — Air traffic facilities which provide
16 hours of ground and/or flight training.
pilot briefing, enroute communications and VFR search
flight level — A level of constant atmospheric pressure and rescue services, assist lost aircraft and air­craft in
related to a reference datum of 29.92 inches of mercury. emergency situations, relay ATC clearances, origi­nate
Flight levels are stated in three digits, representing Notices to Airmen, broadcast aviation weather and NAS
hundreds of feet. For example, flight level 250 represents information, receive and process IFR flight plans, and
a pressure altitude of 25,000 ft. monitor NAVAIDs. In addition, at selected locations, FSSs
provide Enroute Flight Advisory Service (Flight Watch),
flight line — 1. The area of an airfield where airplanes
take weather observations, issue airport advisories, and
are parked. Also referred to as a ramp or tarmac. 2.
advise Customs and Immigration of transborder flights.
A term used to describe the precise movement of a
civil photogrammetric aircraft along a pre­determined flight simulator — A device that is a full-size aircraft
course(s), at a predetermined altitude, during the actual cockpit replica of a specific type of aircraft, or make,
photographic run. model, and series of aircraft; includes the hardware and
software necessary to represent the aircraft in ground
flight management system — A computer system that uses
operations and flight operations; uses a force cueing
a large data base to allow routes to be pre­programmed
system that provides cues at least equivalent to those cues
and fed into the system by means of a data loader. The
provided by a 3 degree freedom of motion system; uses a
system is constantly updated with respect to position
visual system that provides at least a 45 degree horizontal
accuracy by reference to conventional navigation aids.
field of view and a 30 degree vertical field of view
The sophisticated program and its associated data base
simultaneously for each pilot; and has been evaluated,
insures that the most appropriate aids are automatically
qualified, and approved by the Administrator.
selected during the information update cycle.

137

10001930-002_AviationDictionary_2012_BOOK.indb 137 3/27/2012 9:38:09 AM

 flight standards district office (FSDO) • fluctuating arc

flight standards district office (FSDO) — An FAA overcharge. For a lead-acid battery, this potential is about
field office serving an assigned geographical area. Its 14.2 volts for a 12 volt battery.
staff of flight standards personnel serves the aviation
floated battery — A permanently installed storage battery
industry and the general public on matters relating to
posi­tioned across the output of a generator. The generator
the certification and operation of air carrier and general
carries the normal electrical load and keeps the battery
aviation aircraft. Activities include general surveillance
fully charged at all times.
of operational safety, certification of airmen and aircraft,
accident prevention, investigation, and enforcement floating ground — A ground not attached directly to an
action, among other duties. earth ground. See also chassis ground or equipment
ground.
flight test — A flight for the purpose of:
floating waypoint — An airspace fix at a point in space
a. Investigating the operation/flight characteristics of an
not directly associated with a conventional airway. In
aircraft or aircraft component.
many cases, it may be established for such purposes as an
b. Evaluating an applicant for a pilot certificate or rat­ing. ATC metering fix, holding point, RNAV-direct routing,
gateway waypoint, STAR origination point leaving the
flight time — The time from the moment an aircraft first
enroute structure, and SID terminating point joining the
moves under its own power for the purpose of flight until
enroute structure.
the moment it comes to rest at the next point of landing.
float-type carburetor — A fuel metering device which that
flight training devices (FTD) — A full-size replica of
a float-operated needle valve to maintain a constant fuel
the instruments, equipment, panels, and controls of an
metering pressure or head.
aircraft, or set of aircraft, in an open flight deck area or in
an enclosed cockpit. A force (motion) cueing system or flock — Pulverized wool or cotton fibers attached to screen
visual system is not required. wire used as an air filter. The flock‑covered screen is
lightly oiled to prevent dirt and dust from entering the
flight visibility — The average forward horizontal distance,
engine.
from the cockpit of an aircraft in flight, at which
prominent unlighted objects can be seen and identified flood valve — A control valve used to direct the flow of
by day and prominent lighted objects can be seen and extinguishing agent in a CO2 fire extinguisher system.
identified by night.
flow control — Measures designed to adjust the flow of traffic
flight watch — A shortened term for use in air-ground into a given airspace, along a given route, or bound for a
contacts to identify the flight service station provid­ing given aerodrome (airport) so as to ensure the most effective
Enroute Flight Advisory Service; e.g., “Oakland Flight utilization of the airspace. (See Quota Flow Control)
Watch.”
flow control valve — A valve that controls the direction or
flight-path angle — The angle between the flight path of amount of fluid flow.
the aircraft and the horizontal.
flow indicator — A device in an oxygen system that
flint lighter — A flint and steel friction lighter used to ignite provides users with a positive indication that oxygen is
an oxyacetylene torch for welding. flowing.
FLIP — Department of Defense Flight Information flow meter — An autosyn electrical transmitter that
Publications used for flight planning, enroute, and provides a signal to a cockpit instrument. This indicator
terminal operations. FLIP is produced by the National shows pounds per hour of fuel flow being consumed by
Imagery and Mapping Agency (NIMA) for worldwide an operating engine.
use. United States Government Flight Information
flow reverser — A mechanical device placed in the tail pipe
Publications (enroute charts and instrument approach
of a turbojet engine to deflect the exhaust gases forward.
procedure charts) are incorporated in DOD FLIP for use
This decreases the aircraft landing roll.
in the National Airspace System (NAS).
flowchart — A diagram that uses symbols connected
flip-flop — An electronic device capable of assuming
by lines to indicate the sequence of steps that must be
either of two stable states. Term used to describe a
followed in order to achieve a desired end result.
communications radio set up with two frequencies
entered and the pilot is able to switch back and forth fluctuate — 1. The swing or oscillation of a dial from low to
(flip-flop) between them. high. 2. To continually change or vary in an irregular way.
float charging potential — A charging potential that fluctuating arc — A malfunction in an inert‑gas arc welding
can be left connected across the poles of a chemical system caused by improper grounding.
cell on standby service without damage or destructive

138

10001930-002_AviationDictionary_2012_BOOK.indb 138 3/27/2012 9:38:09 AM

 fluid • fly-by-wire

fluid — 1. A substance, either gaseous or liquid, that will flush repairs — Metal repairs designed to maintain an
conform to the shape of the container that holds it. A aircraft’s skin original contour.
gaseous fluid will expand to fill the entire container,
flush rivet — A countersunk rivet in which the manufactured
while a liquid fluid will fill only the lower part of the
head is flush with the surface of the metal when it is
container. 2. Any material whose molecules are able to
properly driven.
flow past one another without destroying itself. Gases
and liquids are both fluids. flush riveting — Riveting using countersunk‑head rivets.
Pro­duces a perfectly smooth outside skin.
fluid mechanics — The science and technology of forces
produced by fluids. flute — A groove that is cut or formed in a material.
fluid ounce — A liquid volume equal to 1/16 liquid pint or flutes — Spiral-cut grooves in a drill bit that extend from
1.8 cu. in. the point to the shank and allow chips to move from
the hole being drilled and for lubrication to flow to the
fluid power — The transmission of force by the movement
cutting edges.
of a fluid. The best examples are hydraulics and
pneumatics. flutter — The rapid and uncontrolled oscillation of a flight
control resulting from an unbalanced surface. Flutter
fluidics — The branch of science that studies the various
normally leads to a catastrophic failure of the structure.
shapes of ducts to sense, measure, and control physical
conditions. flux — 1. A material used in soldering, brazing, or welding
to clean the surface of oxides and prevent oxides from
fluidity — The ability of a liquid or gas to flow easily and
forming. Helps ensure good adhesion or fusion of
smoothly.
surfaces. 2. Magnetic lines of force.
fluorescent — A substance that will glow or fluoresce
flux density — The number of lines of magnetic force per
when excited. Some types of dye penetrant material use
unit area.
fluorescent dyes, which can be observed under ultraviolet
light. flux valve — A special transformer that develops a signal
whose char­acteristics are determined by the unit’s
fluorescent finish — A highly light‑reflecting aircraft finish.
position in relation to the Earth’s magnetic field. It is part
fluorescent lamp — A lamp that emits light as the result of of an Earth inductor compass system.
the glowing of a fluorescent coating on the inside surface
flux valve spider — The framework around which the three
of a tube rather than from the glowing of an incandescent
pick‑up coils of a flux valve are wound. The spider’s
filament.
highly permeable material accepts the lines of flux from
fluorescent penetrant inspection — A form of the Earth’s magnetic field.
nondestructive inspec­tion in which a part is thoroughly
fly — To travel through the air as a pilot or passenger in an
cleaned and immersed in a vat of penetrating oil. When
aircraft.
the part has soaked for a sufficient time, it is removed and
the oil is washed from the surface and the part is dried. fly cutter — A cutting tool used to cut round holes in sheet
The part is then covered with a developer that draws the metal. It is turned by a drill press and the cutting is done
oil out from any crack into which it may have seeped. by a tool bit held in an adjustable arm.
The part is inspected under ultraviolet light, which causes
fly heading (degrees) — Informs the pilot of the heading he
the crack to appear as a vivid green line.
should fly. The pilot may have to turn to, or continue on,
fluorescent pigment — A paint pigment that can absorb a specific compass direction in order to com­ply with the
visible or non‑visible electromagnetic radiation and instructions. The pilot is expected to turn in the shorter
release it as energy in a wavelength. direction to the heading, unless otherwise instructed by
ATC.
fluorine — A gaseous element with the symbol F and an
atomic number of 9. fly-by waypoint — A fly-by waypoint requires the use of
turn anticipation to avoid overshoot of the next flight
fluoroscope — An instrument used for observing the
segment.
internal structure of an object by means of X rays.
fly-by-wire — A system that moves aircraft controls by
flush — To clean, wash, or empty out with a sudden flow of
use of electro-mechanical servos and controls them
solvent or other cleaning agent.
by electrical signals from control inputs such as yoke,
flush patch — A type of sheet metal repair that leaves a rudders, or autopilot. Control devices and servos are
smooth surface maintaining the skin’s original contour. connected only by electrical wires with no mechanical
The repair is reinforced on the inside and the damaged linkage between them.
area is filled with a plug patch.

139

10001930-002_AviationDictionary_2012_BOOK.indb 139 3/27/2012 9:38:10 AM

 flying boat • forging

flying boat — A form of seaplane whose fuselage serves as fogger oil jet — An air and oil spray mist device used on
the boat hull. some engines for lubricating main bearings as opposed to
a fluid stream‑type oil jet.
flying wires — Wires used to hold the wings in position
during flight and landing loads. There are three types of foil — A form of metal such as that used in common
flying wires: Standard flying wires keep the wing from household aluminum foil that has been rolled out into
moving upward during flight and go from the upper outer very thin sheets.
wing strut fitting to the lower portion of the fuselage.
folded fell seam — A type of machine‑sewn seam
Landing wires go from the top of the inner cabin strut
recommended for use in sewing aircraft fabric.
down to the lower outer wing fitting near the location
of the bottom attach fittings of the “N” strut and keep folding — To make sharp, angular bends in sheets of
the wing from flexing downward on landing loads. Drag material.
wires go from the firewall to the top of the wing strut
follow-up question — In the guided discussion method, a
area and keep the wings from pivoting rearward due to
question used by an instructor to get the discussion back
the air drag. Flying wires are also used to reinforce the on track or to get the students to explain something more
attachment of the vertical fin and stabilizer to the fuselage. thoroughly.
fly-over waypoint — A fly-over waypoint precludes any foot‑ pound (ft-lb) — 1. A unit of work: One pound of
turn until the waypoint is overflown and is followed by force moved through a distance of one foot. 2. A unit of
an intercept maneuver of the next flight segment.
torque: The amount of torque produced when a force of
fly-over waypoint — A fly-over waypoint pre­cludes any one pound is applied one foot from the pivot point.
turn until the waypoint is overflown and is fol­lowed by
foot-candle — The unit of luminance on a surface that is one
an intercept maneuver of the next flight segment.
foot from a uniform point source of light of one candle.
flyweights — The L‑shaped speed sensing units pivoted Equal to one lumen per square foot. In science, the lux,
on the outer edges of a rotating disc. When rotational one lumen per square meter, is in more common usage.
speed is high enough, centrifugal force moves them
force — The energy applied to an object that attempts to
to an angular position. This motion is utilized for
cause the object to change its direction, speed, or motion.
various applications, including propeller governors and
mechanical tach­ometers. forced exhaust mixer — A long duct design for a turbofan
that causes fan air and hot exhaust streams to mix. Used
flywheel — A heavy wheel or weight used to smooth out the
for sound attenuation primarily. Also referred to as mixed
pulsations in a drive system.
exhaust.
flywheel effect — In electronics, a parallel LC circuit that
forced landing — Any landing necessitated by a malfunction
permits a continuing flow of current even though only
of the aircraft, engine, or improper flight planning.
small pulses of energy are applied to the circuit.
forceps — A small tool used to grasp or hold things.
foam rubber — A form of rubber containing millions of tiny
air bubbles beaten into the latex before being vulcanized foreflap — The first flap in a triple-slotted segmented flap.
foamed plastic — A synthetic resin filled with millions of foreign object damage (FOD) — Internal gas turbine
tiny bubbles. Foamed plastics are characteristically light engine damage that occurs from the injection of foreign
weight and resilient. Also referred to as expanded plastic. objects into the engine. FOD includes ground debris or
objects in the air such as birds or flying debris.
foaming — An undesirable condition in a lubrication
system in which oil passing through the engine picks foreign particle — A material or particle that can cause
up air, causing tiny air bubbles to form in the oil. Oil serious damage or contamination if it enters a fluid
foaming reduces the ability of the oil to lubricate and to system.
absorb heat as it should.
forge — A method of forming metal parts by heating the
Foehn — A warm, dry, downslope wind, the warmness metal to a plastic state (nearly, but not quite melted) and
and dryness being due to adiabatic compression upon hammering it to shape.
de­scent; characteristic of mountainous regions. See
adia­batic process, Chinook, Santa Ana. forge welding — The joining of metal by forging.

fog — Cloud consisting of numerous minute water droplets forging — The process of forming a product by hammering
and based at the surface; droplets are small enough to or pressing. When the material is forged below the
be suspended in the earth’s atmosphere indefinitely. recrystallization temperature, it is said to be cold forged.
(Unlike drizzle, it does not fall to the surface; differs When worked above the recrystallization temperature, it
from cloud only in that a cloud is not based at the surface; is said to be hot forged.
distinguished from haze by its wetness and gray color.)

140

10001930-002_AviationDictionary_2012_BOOK.indb 140 3/27/2012 9:38:10 AM

 fork lift • free electrons

fork lift — A steerable machine with two long steel fingers forward current — The amount of current that flows
that can be positioned under a pallet for lifting and through a semiconductor device when it is forward-biased.
moving heavy loads.
forward fan — Turbofan with the fan located at the front
form drag — Skin friction caused by turbulence induced of the com­pressor. It can be a part of the compressor or a
by the shape of the aircraft. separate rotor.
form factor — The ratio of the length of a wire coil to its forward slip — A slide used to dissipate altitude without
diameter. increasing the glider’s speed, particularly in gliders
without flaps or with inoperative spoilers.
form of thread — In threaded fasteners, the profile of a
thread in an axial plane for a length of one pitch. fossil fuels — Lubricants, fuels, and other petroleum
products derived from oil extracted from the Earth.
formal lecture — An oral presentation where the purpose
is to inform, persuade, or entertain with little or no verbal fouled spark plug — The condition of the spark plug
participation by the listeners. electrodes when they are contaminated with foreign
matter. This condition provides a conductive path for the
formation flight — More than one aircraft which, by prior
high voltage to leak off to ground rather than building up
arrangement between the pilots, operate as a single
enough potential to jump the electrode gap.
aircraft with regard to navigation and position reporting.
Separation between aircraft within the formation is the four-harness satin — A fabric weave. Also called crowfoot
responsibility of the flight leader and the pilots of the satin because the weaving pattern resembles the
other aircraft in the flight. This includes transition periods imprint of a crow’s foot. In this type of weave there is a
when aircraft within the formation are maneuvering to three-by-one interlacing.
attain separation from each other to effect individual
four-stroke engine — The four‑stroke, five‑event cycle
control and during join-up and breakaway.
consists of five separate mechanical processes occurring
a. A standard formation is one in which a proximity of no in the following order: First, the intake stroke, in which
more than 1 mile laterally or longitudinally and within the piston moves inward with the intake valve open.
100 feet vertically from the flight leader is maintained Second, the compression stroke when the piston moves
by each wingman. outward with both valves closed. Third, ignition occurs
near the top of the compression stroke. Fourth, the power
b. Nonstandard formations are those operating under any
stroke is an inward stroke of the piston with both valves
of the following conditions:
closed, and finally, the exhaust stroke occurs when the
1. When the flight leader has requested and ATC has piston moves out­ward with the exhaust valve open. At
approved other than standard formation dimensions. this point, the cycle begins again.
2. When operating within an authorized altitude Fowler flap — Wing flaps that are lowered by sliding from
reservation (ALTRV) or under the provisions of a the trailing edge of the wing on a track. Fowler flaps
letter of agreement. modify the shape of the airfoil and increase the area of
the wing.
3. When the operations are conducted in airspace
specifically designed for a special activity. (See fractional distillation — A process of oil refining in which
Altitude Reservation) (Refer to FAR 91) the crude oil is heated to the boiling point. As each type
of hydrocarbon rises through the distillation column,
former — A frame of light wood or metal that attaches to
the heavier components begin to cool and condense into
the truss of the fuselage or wing in order to provide the
liquids. Lighter fractions such as propane and butane
required aerodynamic shape.
continue to rise and condense later. As a result, different
forming — The process of shaping a part. fractions are separated by a process of condensing, or
distilling, at different temperatures.
forming block — A block, usually made of hardwood,
around which metal parts are formed. fractions — The various components of a hydrocarbon fuel
separated by the distillation process.
forming machine — A hand‑operated or power‑driven
machine used to shape sheet metal. frame — A former ring that provides shape and rigidity to a
semi­-monocoque or monocoque structure.
forward bias — The polarity relationship between a power
supply and a semiconductor that allows conduction. free balloon — A lighter‑than‑air, helium‑filled device used
in weather observations to find the height of the base of
forward center of gravity limit — The most forward
the lower layer of clouds.
location allowed for the center of gravity of an aircraft in
its loaded condition. free electrons — Those electrons so loosely bound in the
outer shells of some atoms that they are able to move

141

10001930-002_AviationDictionary_2012_BOOK.indb 141 3/27/2012 9:38:10 AM

 free fit • friction brake

from atom to atom when an electro motive force is freezing level chart — A chart depiction of the freezing
applied to the material. levels, reported in hundreds of feet.
free fit — A loose fit between moving parts such as a nut freezing point — The temperature at which a liquid will
that turns easily on the threads of a screw or bolt. change into a solid.
free power turbine — In gas turbine engines, a turbine freezing rain — Rain that freezes upon contact with the
wheel which drives a power output gearbox rather than a ground or other objects, such as trees, power lines and
compressor. Found in Turboprop and Turboshaft engines. aircraft.
free turbine — A turboshaft engine with no physical French fell seam — A type of machine‑sewn seam.
connection between the compressor and power output Recommended for sewing together sheets of aircraft
shaft. fabric.
free water — Liquid water that has condensed out and is no Freon — A fluorinated hydrocarbon compound used as a
longer entrained in a turbine engine fuel. fire extinguish­ing agent or a refrigerant for vapor‑cycle
air conditioning systems. A registered trademark of E.I.
free-air wire — A wire completely open to air circulation
DuPont de Nemours & Company.
and not in a bundle.
frequency — The number of waves that pass some fixed
free‑running multivibrator — An oscillator that alternates
point in a given time interval, measured in cycles per
between two different output voltage levels during the
second (cps) or Hertz (Hz).
time it is on. The output remains at each voltage level for
a definite period of time. Produces a continuous square frequency converter — A circuit device that changes the
or rectangular waveform. The free-running multivibrator frequency of an alternating current.
has two outputs, but no inputs. Also referred to as an
frequency meter — An electronic instrument that measures
astable multivibrator.
and indicates the frequency of an alternating current on a
freewheeling unit — In rotorcraft, a component of the dial or digital display.
transmission or power train that automatically disconnects
frequency modulation (FM) — A radio wave transmission
the main rotor from the engine when the engine stops or
method where information is transmitted by varying the
slows below the equivalent rotor r.p.m.
modulation signal in proportion to the audio signal.
freeze — 1. The process in which a liquid changes into a
frequency multiplier — Circuit designed to double, triple,
solid due to the removal of heat energy. 2. The stoppage
or quadruple the frequency of a signal by harmonic
of a mechanical device due to binding of the mechanical
conversion.
mechanism.
frequency synthesizer — An electronic circuit used to
freeze calculated landing time — A dynamic parameter
produce AC with an accurately controlled frequency.
number of minutes prior to the meter fix calculated time
of arrival for each aircraft when the TCLT is frozen fresh annual inspection — An annual inspection recently
and becomes an ACLT (i.e., the VTA is updated and performed on an airplane. Sometimes this is used as a
consequently the TCLT is modified as appro­priate until selling point for an airplane. The skill and integrity of the
FCLT minutes prior to meter fix calculated time of arrival, person performing the inspection determines the value in
at which time updating is suspended and an ACLT and a a purchase situation.
frozen meter fix crossing time (MFT) is assigned).
freshening charge — The charge given a dry‑charged
freeze speed parameter — A speed adapted for each battery to bring it up to its rated capacity.
aircraft to determine fast and slow aircraft. Fast air­craft
fretting — Surface erosion caused by a slight movement
freeze on parameter FCLT and slow aircraft freeze on
between two overlapping parts.
parameter MLDI.
fretting corrosion — Corrosion damage between parts that
freeze/frozen — Terms used in referring to arrivals which
are allowed to rub together. The rubbing removes the
have been assigned ACLT’s and to the lists in which they
protective oxide films and allows the metals to corrode.
are displayed.
friction — The force that resists the relative motion of two
freezing — Change of state from liquid to solid.
bodies in contact.
freezing drizzle — Drizzle that freezes on contact.
friction brake — Any of a number of different mechanisms
freezing level — A level in the atmosphere at which the used with a rotating wheel or shaft in which friction is
temperature is 32° F (0° C). used to slow its rotation.

142

10001930-002_AviationDictionary_2012_BOOK.indb 142 3/27/2012 9:38:10 AM

 friction clutch • fuel evaporation ice

friction clutch — A mechanism used to connect a motor to lower surface and produces some parasite drag,
a mechanical load. decreasing the amount of adverse yaw.
friction damper — A rubber insert used to limit excessive front — The boundary between two different airmasses.
movement in a pedestal‑type dynafocal engine mount.
front spar — The foremost spar of a multispar wing.
friction error, instrument — The error caused by friction
frontal cyclone — A low pressure area and associated
in an instrument mechanism.
counterclockwise winds (Northern Hemisphere) that
friction horsepower — The amount of horsepower required develops on the polar front and moves west to east as a
to turn the engine against the friction of the moving parts macroscale eddy embedded in the prevailing westerlies.
and to compress the charges in the cylinders. Also called a frontal low or wave cyclone.
friction loss — The loss of mechanical energy in a device frontal lifting — The lifting of a warm airmass over a
caused by the friction that is incidental to changing relative cold airmass.
mechanical energy into heat.
frontal wind shear — The change of wind speed or
friction mean effective pressure (FMEP) — The average direction per unit distance across a frontal zone.
working pres­sure within an engine used to overcome
frontal zone — A narrow region of transition between two
friction. IMEP - BMEP = FMEP (IMEP is Indicated
airmasses.
Mean Effective Pressure and BMEP is Brake Mean
Effective Pressure). frost — Ice crystal deposits formed by sub­limation when
temperature and dewpoint are below freezing.
friction measurement — A measurement of the friction
characteristics of the runway pavement surface using frustrum — The portion of a cone from which the top has
continuous self-watering friction measurement equip­ment been removed.
in accordance with the specifications, procedures and
fuel — A substance that, when combined with an oxidizer,
schedules contained in AC 150/5320-12, Measurement,
will burn and produce heat.
Construction, and Maintenance of Skid-Resistant Airport
Pavement Surfaces. fuel boost pump — An auxiliary electrically operated
pump located within a fuel tank to force the fuel from
friction stir welding — A new technology welding method
the tank to the engine. Usually a centrifugal-type pump.
that joins materials by plasticizing and consolidating
Provides vapor-free fuel with a slight head pressure to
them along the weld line. The process involves a rotating
the main pump.
pin forced down into the seam between two sheets of
metal. The pin continues rotating and moves forward in fuel cell — The compartment in an aircraft where engine
the direction of welding. As the pin proceeds, the friction fuel is stored.
heats the surrounding material producing a plasticized
fuel consumption — The actual amount of fuel consumed
area around the pin As the pin moves along the seam, the
by an engine under a specified set of conditions. Fuel
plasticized material consolidates behind the pin and cools
consumption can be expressed in either pounds per hour
to form a bond. No melting occurs and the weld is left in
or gallons per hour.
a fine-grained condition with none of the oxide and gas
entrapment problems of more conventional welds. fuel control unit — In gas turbine engines, the main fuel
scheduling device which receives a mechanical input
friction tape — Cloth, electrical, insulating tape
signal from the power lever and various other signals,
impreg­nated with a black tar-like material.
such as Pt2, Tt2, etc. These signals provide for automatic
friction welding — A method of joining materials by scheduling of fuel at all ambient conditions of ground
vigorously rubbing one mating surface against another and flight operation.
while forcing them together with a large amount of pressure.
fuel dump system — A portion of the fuel system of large
friction-lock Cherry rivet — A jet transport aircraft that allows fuel to be dumped in
patented blind rivet made by Cherry flight. This is sometimes necessary to reduce the weight
Rivet, a division of Textron Inc., in of the aircraft to below maximum landing weight or to
which the stem locks in the hollow minimize fuel in the event of an emergency landing.
shank by friction.
fuel evaporation ice — Ice formed due to the cooling
Frise-type ailerons — An aileron effect of the fuel evaporating after it is sprayed into
having the nose portion projecting the induction system of reciprocating engines. This
ahead of the hinge line. When the trailing edge of the evaporation process causes carburetor and induction
aileron moves up, the nose projects below the wing’s system parts to become very cold and allows moisture in

143

10001930-002_AviationDictionary_2012_BOOK.indb 143 3/27/2012 9:38:10 AM

 fuel flow • full annealing

the air to condense, collect and freeze on them. This type fuel remaining — A phrase used by either pilots or
of ice is most troublesome in float‑type carburetors. controllers when relating to the fuel remaining on board
until actual fuel exhaustion. When transmitting such
fuel flow — The rate at which fuel is consumed by the engine
infor­mation in response to either a controller question
in pounds per hour (PPH) or gallons per hour (GPH).
or pilot initiated cautionary advisory to air traffic
fuel flowmeter — A cockpit instrument used to indicate the control, pilots will state the APPROXIMATE NUMBER
rate of the fuel consumed by the engine during flight. OF MINUTES the flight can continue with the fuel
remaining. All reserve fuel SHOULD BE INCLUDED
fuel grade — A classification of aviation gasoline according
in the time stated, as should an allowance for established
to its anti-­detonation characteristics.
fuel gauge system error.
fuel heater — A radiator‑like device that has fuel passing
fuel shut‑off valve — A valve in an aircraft fuel system that
through its core. A heat exchange occurs to keep the fuel
shuts off all fuel flow to the engine.
temperature above the freezing point of water. This keeps
entrained water from forming ice crystals and blocking fuel siphoning — Unintentional release of fuel caused by
fuel flow. overflow, puncture, loose cap, etc.
fuel injection manifold valve — A valve used in a fuel fuel strainer — A device that removes dirt, water, and other
injection system that distributes fuel from the fuel control foreign particles from the fuel. It is usually located in the
unit to the various injection nozzles. The valve provides fuel tank outlets or at the lowest point of an aircraft’s fuel
a metering force for conditions of low fuel flow and a system.
positive fuel shut off when the engine is shut down.
fuel system — The system that stores fuel and delivers the
fuel injection system — A fuel metering system used on proper amount of clean fuel at the right pressure to meet
some aircraft reciprocating engines utilizing a constant the demands of the engine.
flow of fuel to the injection nozzles. Fuel injectors are
fuel tank vent — A vent in a fuel tank that allows the air
located in the heads of all cylinders just outside of the
pressure above the fuel to be the same as the surrounding air.
intake valve. It differs from sequential fuel injection that
uses a timed charge of high‑pressure fuel sprayed directly fuel venting — See fuel siphoning
into the combustion chamber of the cylinder.
fuel-air combustion starter — A fuel engine-starting
fuel load — That part of the useful load of an aircraft accessory that utilizes a combustion section similar to
consisting of the usable fuel on board. a turbine engine. Com­bustion products are exhausted
through a turbine connected to a reduction gearbox to
fuel manifold — A pipe-like fitting that distributes fuel flow
create starting torque.
to the individual fuel injection nozzles. The manifold
contains one single fuel line when used with single‑line fuel-air mixture ratio — The weight ratio in pounds of the
duplex nozzles and two lines for dual‑line duplex nozzles. fuel and air that are mixed together creating a combustible
mixture to be burned in an engine.
fuel metering device — Any apparatus such as a carburetor,
fuel injector, or fuel control unit, that mixes fuel with fuel-oil cooler — A heat exchange device that heats the fuel
intake air in the correct proportions and delivers the and cools the oil. It is a radiator‑like unit. Fuel passes
mixture to the engine. through the cores and oil passes around the cores. The oil
flow is controlled by a thermostatic valve that routes the
fuel nozzle — In gas turbine engines, a device used to spray
oil through the cooler only when a certain oil temperature
fuel into a combustion liner. The two most common types
is reached. On some engines, no fuel heater is required
are the atomizing nozzle and the vaporizing nozzle.
due to the exchange rate of this oil cooler.
fuel nozzle ferrule — The receptacle in the combustion
fuel-oil heat exchanger — A heat exchanging device used
liner of a gas-turbine engine where the fuel nozzle tip is
on turbine engines to take heat from the engine oil and
inserted.
put it into the fuel. It is a radiator‑like unit directing fuel
fuel pressure — The pressure of fuel within a fuel system. through the tubes that pass through the hot engine oil.
The most common measurement location is at the point Heat from the oil raises the fuel temperature, and at the
where fuel is delivered to the fuel control unit. same time, lowers the temperature of the oil.
fuel pressure gauge — A gauge that indicates the fuel fulcrum — A point on which a lever is supported, balanced,
pressure delivered to the carburetor. or about which it turns.
fuel pump — An electrical or engine‑driven pump used to full annealing — A process used to produce a fine grained,
provide a positive volume of fuel under pressure to the soft, ductile metal without internal stresses or strains. To
engine. fully anneal a metal, the temperature of the metal is raised
to its critical temperature followed by controlled cooling.

144

10001930-002_AviationDictionary_2012_BOOK.indb 144 3/27/2012 9:38:10 AM

 full fuel • fusion

full fuel — The amount of fuel in an aircraft when all fuel funneling effect — An increase in winds due to airflow
tanks are filled to the quantity called for in the aircraft through a narrow mountain pass.
specifications.
furrow — A deep groove.
full oil — The quantity of oil shown as oil capacity in
fuse — An aircraft electrical circuit protection device. It
aircraft specifications.
consists of a link of low-melting-point metal that melts
full rudder — The movement of the rudder to its extreme and opens the circuit when an ex­cessive amount of
limit. current flows through it.
full throw — The full range of control surface travel. fuse holder — A device mounted to an electrical fuse panel
that holds tubular fuses and makes connections to both
full-register position — The position of the rotating
ends.
magnet in a mag­neto when the poles are fully aligned
with the pole shoes of the magneto frame. At this point, fuse link — A strip of low‑melting‑point metal used in an
the maximum number of lines of flux flow in the frame. electrical circuit fuse device to protect a circuit. When
excessive current flows through the circuit the fuse link
full-rich — That position of the mixture control that allows
melts and opens the circuit.
the maxi­mum amount of fuel to flow to the engine
relative to air flow. fuselage — The area of an airplane aft of the firewall and
forward of the empennage. The cabin or cockpit, is
full-scale drawing — A drawing of a part that is the same
located in the fuselage. It may also provide room for
size as the part.
cargo and attachment points for other major airplane
full-wave rectifier — A form of rectifier that inverts one components.
half of the input AC signal and provides a pulsating DC
fuselage stations — Distances measured along the
output having twice the frequency of the input alternating
lon­gitudinal axis of an airplane. Represents distances
current.
from the datum in inches.
fully articulated rotor — A rotor that is attached to a
fusible alloy — A filler material that melts at approximately
helicopter rotor hub in such a way that the pitch angle
160°F. Used to prevent kinking during tube bending. The
of each blade can change, and each blade is free to move
alloy is heated in hot water and poured inside the tubing.
up and down and back and forth in its plane of rotation.
Once the alloy has cooled and set, the tube can be bent
fumes — Vaporized liquids. by hand around a forming block or bender. After the tube
is bent, it is reheated in hot water to remove the fusible
functional check — A check for proper operation of the
alloy.
aircraft and systems. Required before returning an
aircraft to service after an annual or 100-hour inspection. fusible plug — A hollow plug in an aircraft wheel filled
with a material having a specific melting point. If the
functional test — A method of testing a system through
melting point is reached due to brake heat, the filler will
its normal operating range to determine whether or not it
melt out and deflate the tire rather than allow the pressure
functions properly.
to increase to the point that would cause a blowout.
fundamentals of instruction — Includes the learning
fusion — The melting together of metal parts.
process, elements of effective teaching, student evaluation
and testing, course development, lesson planning, and
classroom training techniques.
fungicidal paste — A paste mixed with clear dope and
applied as a first coat on cotton. The fungicidal agent
soaks into the fibers and prevents the formation of mold
or fungus.
fungus spores — The seed of certain fungi that attach to
organic materials such as cotton or linen and cause the
material to rot.
funnel cloud — A tornado cloud extending downward from
the parent cloud but not reaching the ground.

145

10001930-002_AviationDictionary_2012_BOOK.indb 145 3/27/2012 9:38:10 AM

 G • gas generator

G 18.
19.
Nickel (active)
76NI-16Cr-7Fe alloy (active)
gain — The increase in signal power through a circuit. 20. Yellow brass
21. Admiralty brass
galling — Fretting or chafing of a mating surface by sliding 22. Aluminum bronze
contact with another surface or body. The heat friction 23. Red brass
causes the material from one surface to be welded or 24. Copper
deposited onto the other surface, ultimately damaging 25. Silicon bronze
the surface area. 26. 70-30 cupro-nickel
gallon — 1. Imperial: A unit of liquid measurement used 27. G-Bronze
outside of the United States. One Imperial gallon is equal 28. M-Bronze
to 277.4 cu. in., 4.55 liters, or 1.201 U.S. gallons. 2. U.S.: 29. Silver solder
A unit of liquid measurement used in the United States. 30. Nickel (passive)
One U.S. gallon is equal to 231 cu. in., 128 fl. oz., or 31. 75NI-16Cr-7Fe alloy (passive)
3.785 liters. 32. 7NI-33Cu alloy
33. 13 percent chromium stainless steel, type 410
galvanic action — Electron flow because of a difference of (passive)
electrode potential between different substances. 34. Titanium
galvanic corrosion — Corrosion due to the presence 35. 18-8 Stainless steel, type 304 (passive)
of dissimilar me­tals in contact with each other in the 36. 18-8-3 Stainless steel, type 316 (passive)
presence of an electrolyte such as water. 37. Silver
38. Graphite
galvanic couple — Dissimilar metals that produce an 39. Gold
electrical voltage when they are both in contact with 40. Platinum
the same electrolyte. When dissimilar metals are in this
condition, one metal forms the anode and the other metal galvanizing — A method of protecting steel parts from
forms the cathode, thereby producing a current between corrosion by dipping them in a vat of molten zinc or by
the two metals. electroplating them. The protection actually comes from
sacrificial corrosion of the zinc.
galvanic electricity — The electricity produced by chemical
action such as that produced in a dry‑cell battery or galvanometer — An electrical measuring instrument in
storage battery. which electrical current is measured by the reaction of its
electromagnetic field to the field of a permanent magnet.
galvanic grouping — An arrangement of metals in a series
according to their electrode potential difference. gamma rays — Electromagnetic radiation that results from
nuclear fission.
galvanic metal electrical series — The hierarchical
arrangement of metals in order of their chemical activity. ganged tuning — A mechanical arrangement that permits
The following list of metals indicates their hierarchical the simul­taneous tuning of two or more electronic
chemical activity, and acts as the anode in any electrolytic circuits.
action to those that follow: gap — The distance between two objects.
1. Magnesium
2. Zinc garnet paper — An abrasive polishing paper consisting of
3. Galvanized steel a sheet of flexible paper with a layer of finely crushed
4. Aluminum 6053 garnet.
5. Alcad gas — 1. A fluid that assumes the shape of the container
6. Cadmium it is placed in and fills the container. 2. The physical
7. Aluminum 2024 condition of matter in which a material takes the shape
8. Mild steel of its container and expands to fill the entire container.
9. Cast iron Oxygen and nitrogen are two chemical elements that
10. 13 percent chromium stainless steel, type 410 are gases at normal room temperature and pressure. The
(active) air we breathe is a physical mixture of gases, primarily
11. 18-8 Stainless steel, type 304 (active) nitrogen and oxygen.
12. 18-8-3 Stainless steel, type 316 (active)
13. Lead gas generator — The basic power producing portion of a
14. Tin gas turbine engine excluding sections such as the inlet
15. Muntz metal duct, the fan section, free power turbines, and the tailpipe.
16. Manganese bronze Each manufacturer designates what is included in the gas
17. Naval brass generator, but generally it consists of the compressor,
diffuser, com­bustor, and turbine.
146

10001930-002_AviationDictionary_2012_BOOK.indb 146 3/27/2012 9:38:10 AM

 gas generator turbine • gear backlash

gas generator turbine — In gas turbine engines, high gassing, battery — The release of hydrogen and oxygen as
pressure turbine wheel(s) which drive the compressor of a free gas during the charging cycle of lead‑acid storage
a turboshaft or turboprop engine. batteries.
gas path — The airflow or open portion of the engine gate — 1. A logic device having one or more inputs and/or
front to back where air is compressed, combusted, and outputs. The condition of the inputs determines whether
exhausted. or not a voltage is present at the outputs. 2. The electrode
of a silicon‑controlled rectifier or a triac through which
gas path analysis (GPA) — A computer analysis of engine
the trigger pulse is applied.
parameters on some airliners. It is designed to assist the
modular maintenance and on‑condition maintenance gate hold procedures — Procedures at selected airports
concepts by giving continuous on‑condition data. Also that require aircraft to hold at the gate or other ground
used for predicting engine com­ponent airworthiness. locations whenever departure delays exceed or are
anticipated to exceed 15 minutes. Departure sequence
gas storage cylinders — Long bottles of high‑strength steel
is maintained in accordance with initial call-up unless
used to store compressed gases.
modi­fied by flow control restrictions. Pilots should
gas turbine — Engine consisting of a compressor, monitor the ground control/clearance delivery frequency
combustor and turbine, using a gaseous fluid as a working for engine start/taxi advisories or new proposed start/taxi
medium and producing either shaft horsepower, jet thrust, times if the delay changes.
or both. The four common types of Gas Turbine Engines
gate-type check valve — A one‑way flow valve having
are Turbojet, Turbofan, Turboprop and Turboshaft.
a swinging gate or flapper. The gate-type check valve
gas turbine engine — A heat engine in which burning fuel can isolate one of the vacuum pumps in a multi‑engine
adds energy to compressed air and accelerates the air aircraft from the rest of the system in the event of a
through the remainder of the engine. Some of the energy failure of the pump.
is extracted to turn the air compressor, and the remainder
gateway fix — A navigation aid or fix where an aircraft
accelerates the air to produce thrust. A portion of this
transitions between the domestic route structure and the
energy can be converted into torque to drive a propeller
oceanic route airspace.
or a system of rotors for a helicopter.
gauge — Any of a variety of measuring instruments. Some
gas welding — The method of fusing metals together by a
are used to indicate the amount of air pressure, the
flame using gas as fuel. The most common types of gas
depth of a hole or a groove, or possibly the thickness or
welding use oxygen and acetylene gas (oxyacetylene)
clearance between close‑fitting parts of a machine, etc.
and oxygen and hydrogen (oxyhydrogen).
gauge pressure — Pressure measured relative to the
gascolator — A device that removes dirt, water, and other
existing atmospheric pressure. Engine oil pressure and
foreign particles from the fuel. It is usually located in the
hydraulic pressure are normally measured as gauge
fuel tank outlets or at the lowest point of an aircraft’s fuel
pressure. If gauge pressure is measured in pounds per
system.
square inch, it is referred to as PSIG (pounds per square
gaseous — Having the nature or form of gas. inch, gauge). Two other types of pressure that are often
used are differential pressure (PSID) and absolute
gaseous breathing oxygen — Oxygen that is 99.5% pure
pressure (PSIA). Differential pressure is the difference
and contains prac­tically no water vapor.
between two pressures and absolute pressure is a value
gaseous fuel — Any mixture of flammable gases used for compared to zero pressure.
fuel.
gauss — The unit of magnetomotive force. It is equal to one
gas-filled tube — An electron tube with gas introduced maxwell per cm2.
into the envelope to produce certain desired operating
gear — A toothed wheel or disc that meshes with another
characteristics.
toothed wheel or disc to transmit motion.
gasket — The static, stationary seal between two flat
gear and pinion mechanism — A mechanical amplifying
surfaces.
mechanism consisting of two gears, one being a pinion,
gasoline — A volatile, highly flammable liquid mixture which is much smaller than the other. The mechanical
of hydrocarbons produced by the fractional distillation advantage of the mechanism is deter­mined by the ratio
of petroleum and used as fuel in internal‑combustion between the number of teeth on the pinion and the
engines. number of teeth on the large gear. Often the large gear
is only a portion of the wheel and is called a sector gear.
gasoline combustion heaters — Aircraft cabin heaters that
burn gasoline from the aircraft fuel tanks to produce the gear backlash — The measured clearance between the
required heat. teeth of meshed gears.

147

10001930-002_AviationDictionary_2012_BOOK.indb 147 3/27/2012 9:38:10 AM

 gear indicators • gerotor pump

gear indicators — Indicators in the cockpit of an airplane one of the windings and as a generator with the other.
having retrac­table landing gear to inform the pilot of The armature windings are usually different so that the
the position of the gear. It will indicate whether they are voltage on the generator side is different from the voltage
down and locked, in transit, or up and locked. on the motor side and the machine acts as a rotary
transformer. Also referred to as a dynamotor.
gear preload — The pressure with which two gears mate
or mesh together. general aviation — The portion of the aviation industry
that covers all of aviation with the exception of military,
gear-driven supercharger — An internal, engine‑driven
public-use aircraft, and the airlines.
supercharger on a reciprocating engine driven from the
crankshaft through a gear arrangement. General Aviation District Office (GADO) — Designated
FAA Field Offices staffed to serve the general public and
geared fan — A design that allows a fan to rotate at a
aviation industry on matters pertaining to the certification,
different speed than the compressor rotor. The fan being
maintenance, and operation of general aviation.
geared down allows for higher speeds in the compressor
without creating excessive tip speeds on the fan. general circulation — The wind system that extends over
the entire globe; it is a macroscale phenomena with a
geared fan gas turbine engine — A turbofan engine that
typical horizontal dimension of 10,000 nautical miles.
uses a set of reduction gears between the first stage of the
gas generator compres­sor and the fan. generator — A mechanical device consisting of a conductor
being turned within a magnetic field. Produces electricity
geared propeller — A propeller driven from the crankshaft
by electromagnetic induction.
through a series of reduction gears. This allows the
engine to operate at an efficient speed while holding the generator current limiter — A special high-current fuse
propeller RPM in its efficient range. capable of carrying momentary current overloads.
However, it will melt and open the circuit under current
gear-type pump — A
flows that might damage the generator. These are used in
power‑driven fluid
generator installations that are not protected by automatic
pump, usually a constant
current limiters.
displace­ment-type pump,
driven by the engine GEO map — The digitized map markings associated with
accessory drive and used to the ASR-9 Radar System.
pump fluid under pres­sure.
geodetic construction — A form of aircraft construction in
The gear‑type pump is
which the stress carrying portion of the skin is made up
made up of two meshed
of a lattice work of thin metal or wood strips.
spur gears mounted in a
close‑fitting housing. Fluid is taken into the inlet side of geographic poles — The poles of the axis about which the
the housing and fills the space between the teeth of both Earth rotates. They form true north and true south.
gears. As the fluid is carried around the housing of the
geometric pitch — The distance a propeller should advance
rotating gears to the discharge side of the pump, the gear
in one revolution without any slip.
teeth mesh and the fluid is forced out of the outlet side of
the pump. geostrophic balance — The balance of forces that exists
when Coriolis force and pressure gradient force are equal
gel — A jelly-like substance formed by the coagulation of a
in magnitude but in the opposite direction.
solution into a solid phase.
geostrophic wind — The wind that occurs when Coriolis
gel coat — In composites, a coating of resin, generally
force and pressure gradient are equal and opposite.
pigmented, applied to the mold or part to produce a
smooth finish. Considered a nonstructural finish. German silver — Metals of the copper/nickel/zinc alloy
family. Also referred to as nickel silver.
gel time — In composites, the period of time from the initial
mixing of the reactants of a liquid material composition germanium — A grayish‑white metallic chemical with a
to the point in time when gelation occurs, as defined by a symbol of Ge and an atomic number of 32. Often it is
specific test method. used in the manufacturing of semiconductor devices such
as diodes and transistors.
gelatinous — Having the consistency of gelatin or jelly.
gerotor pump — A form of constant displacement pump
gelled cell battery — A lead‑acid battery that has a gelling
using a spur gear driven by the engine and turning inside of
agent added to the electrolyte to make it non‑spillable
an internal tooth gear. The internal tooth gear has one more
and retain a high level of electrolyte in the battery.
space than teeth on the drive gear. As the pump rotates, the
genemotor — A machine with two windings on a single volume at the inlet port increases while the volume at the
armature that operates simultaneously as a motor with outlet decreases, moving fluid through the pump.

148

10001930-002_AviationDictionary_2012_BOOK.indb 148 3/27/2012 9:38:11 AM

 Giga • glideslope intercept altitude

Giga — Billion. glide path (ICAO) — A descent profile determined for

vertical guidance during a final approach.
Gigacycle — Gigahertz.
glide ratio — The ratio of the forward distance the airplane
Gigahertz — One billion hertz.
travels to the vertical distance the aircraft descends when
gilbert — The unit of magnetomotive force equal to operating at low power or without power.
approximately 0.7968 amp‑turn.
glide slope / glide path intercept altitude — The
gill-type cowl flap — A cowl flap used on the trailing edge minimum altitude to intercept the glide slope/path on
of each cowling of a horizontally opposed engine. Its a precision approach. The intersection of the published
purpose is to regulate the flow of air through the engine intercept altitude with the glide slope/path, designated on
for cooling. Jeppesen Terminal charts by the start of the glide slope/
path symbol, is the precision FAF; however, when ATC
gimbal — The frame in which a gyro spins. It is designed
directs a lower altitude, the resultant lower intercept
in such a way that it allows a gyroscope to remain in an
position is then the FAF.
upright condition while the base is tilted. Rate gyros use
a single gimbal, while attitude gyros are mounted in a glide slope (GS) — Provides vertical guidance for aircraft
double gimbal. during approach and landing. The glide slope/glidepath is
based on the following:
gimlet point — A threaded cone point usually having a
point angle of 45° to 50°. It is used on thread-forming a. Electronic components emitting signals which provide
screws such as Type A tapping screws, wood screws, lag vertical guidance by reference to airborne instruments
bolts, etc. during instrument approaches such as ILS/MLS; or
girt bar — Part of the emergency evacuation slide/raft b. Visual ground aids, such as VASI, which provide
assembly on transport category aircraft. The girt bar vertical guidance for a VFR approach or for the visual
enables the slide to deploy when the door is “armed” and portion of an instrument approach and landing.
allows the door to be opened without deploying when the
c. PAR, used by ATC to inform an aircraft making a PAR
door is “disarmed.”
approach of its vertical position (elevation) relative to
glacier winds — One of the cold downslope winds. A the descent profile.
shallow layer of cold, dense air that rapidly flows down
glidepath — See glideslope.
the surface of a glacier.
glidepath [ICAO] — A descent profile determined for
glareshield — Dark, non-reflective cover of the space
vertical guidance during a final approach.
between the instrument panel and the windshield. Also
used to describe the area surrounding the sides and top of glidepath intercept altitude — See glideslope intercept
the instrument panel. altitude.
glass cloth — An aircraft fabric made from fine spun glass glider — A heavier‑than‑air aircraft supported in flight by
fila­ments woven into a strong, tough fabric. These fabrics the dynamic reaction of the air against its lifting surfaces.
are used for reinforcing plastic resins to mold various Its free flight does not depend on power generated from
types of products. an engine.
glass fiber — Filaments of fine spun glass woven into glideslope — Provides vertical guidance for aircraft during
cloth or packed together into a mat used for thermal and approach and landing. The glide slope/glide path is based
acoustical insulation. on the following:
glaze — 1. The hard, smooth surface of a finishing system. a. Electronic components emitting signals which provide
Glaze must normally be “broken” or roughened before vertical guidance by reference to airborne instruments
another coat of material will adhere to it. 2. A hard, during instrument approaches such as ILS/MLS, or
glass‑like surface that forms on the rotating disks of a
b. Visual ground aids, such as VASI, which provide
multiple‑disk brake. Glaze forms when the sintered
vertical guidance for a VFR approach or for the visual
material surface is locally overheated. This slick surface
portion of an instrument approach and landing.
does not produce uniform friction and will cause the
brakes to chatter or squeal if not removed. c. PAR. Used by ATC to inform an aircraft making a PAR
approach of its vertical position (elevation) relative to
glide — 1. A slow descent of an aircraft without the aid of
the descent profile.
the engine. 2. To descend at a normal angle of attack with
little or no engine power. glideslope intercept altitude — The minimum altitude to
intercept the glideslope/path on a precision approach.
glide path — The path of an aircraft relative to the ground
The intersection of the published intercept altitude with
while approaching a landing.

149

10001930-002_AviationDictionary_2012_BOOK.indb 149 3/27/2012 9:38:11 AM

 gliding angle • goniometer antenna

the glideslope/path, designated on Government charts by blowing through the coil is ignited to initiate combustion
the lightning bolt symbol, is the precision FAF; however, in the combustor section.
when the approach chart shows an alternative lower
glue — A liquid adhesive capable of holding materials
glideslope intercept altitude, and ATC directs a lower
together after drying.
altitude, the resultant lower intercept position is then the
FAF. glue blocks — Wood blocks used as backing support when
making repairs to a wooden structure. They distribute
gliding angle — The angle between the flight path during a
clamp pressure evenly over the area being glued.
glide and a horizontal axis relative to the ground.
glue joint — Glued wood joints. Two pieces of wood joined
gliding ratio — The ratio of the horizontal distance an
using glue rather than a mechanical fastener.
aircraft travels while gliding for every unit of vertical
distance it descends. Glyptal — A registered trade name of an insulating varnish
used in electrical machinery.
g-load — Gust load, the incremental change in vertical
acceleration of an aircraft. go ahead — Proceed with your message. Not to be used for
any other purpose.
global circulation system — In meteorology, the
combination of the general and monsoon circulations. go around — 1. To abort a landing. 2. Instructions for a
pilot to abandon his approach to landing. Additional
global navigation satellite systems (GNSS) — An
instructions may follow. Unless otherwise advised by
“umbrella” term adopted by the International Civil
ATC, a VFR aircraft or an aircraft conducting visual
Aviation Organization (ICAO) to% encompass any
approach should overfly the runway while climbing to
independent satellite navigation system used by a pilot
traffic pattern altitude and enter the traffic pattern via the
to perform onboard position determinations from the
crosswind leg. A pilot on an IFR flight plan making an
satellite data.
instrument approach should execute the published missed
global positioning system (GPS) — A space-base radio approach procedure or proceed as instructed by ATC,
positioning, navigation, and time-transfer system. The e.g., “Go around” (additional instructions, if required).
system provides highly accurate position and velocity
goals and values — A perception factor that describes how
information, and precise time, on a continuous global
a person’s perception of an event depends on beliefs.
basis, to an unlimited number of properly equipped
Motivation toward learning is affected by how much
users. The system is unaffected by weather, and provides
value a person puts on education. Instructors who have
a worldwide common grid reference system. The GPS
some idea of the goals and values of their students will be
concept is predicated upon accurate and continuous
more successful at teaching them.
knowledge of the spatial position of each satellite in the
system with respect to time and distance from a transmitting go-around power or thrust setting — The maximum
satellite to the user. The GPS receiver automatically allowable in-flight power or thrust setting identified in
selects appropriate signals from the satellites in view and the performance data.
translates these into three dimensional position, velocity,
gold — A malleable, ductile, yellow corrosion-resistant
and time. System accuracy for civil users is normally 100
chemical ele­ment with a symbol of Au and an atomic
meters horizontally.
number of 79. Used on critical electrical contacts because
globules — A tiny ball of liquid often found in suspension of its resistance to corrosion.
with some other liquid.
gold leaf — Pure gold rolled into extremely thin sheets.
glow coil igniter — An ignition igniter. Around a pin
Gold Seal Flight Instructor Certificate — A flight
extending from the body of the igniter is a resistance
instructor certificate printed with a distinctive gold seal
wire wound into a coil. Direct current causes the coil
to recognize excellence in flight training based on a CFI’s
to become red hot, igniting the fuel/air mixture until
record of performance. To obtain a gold seal certificate,
the device is operating at a temperature sufficient to
a CFI must have trained and recommended at least 10
maintain the flame. At this point current to the glow coil
students for practical tests within the previous 24 months,
is automatically turned off.
and at least 8 of these students must have passed on their
glow discharge tube — A glass tube with a gas such as first attempt. A CFI must also hold a ground instructor
neon under low pressure. Two electrodes are embedded certificate with an advanced or instrument rating.
in opposite ends of the tube. When a sufficiently high
goniometer antenna — A fixed-loop antenna used by
potential difference is applied be­tween the electrodes, the
automatic direc­tion finding equipment, consisting of two
gas will ionize and glow.
coils oriented 90° to each other. It measures the angle
glow plug igniter — An igniter that uses a coil of wire between a known reference and the direction from which
heated by high‑voltage DC electricity. Air and fuel the radio signal is being received.

150

10001930-002_AviationDictionary_2012_BOOK.indb 150 3/27/2012 9:38:11 AM

 go/no-go gauge • grid minimum off-route altitude (grid MORA)

go/no-go gauge — A measuring gauge consisting of a pull. The acceleration rate of a freely falling object is
part having two dimensions: the minimum size and the 32.2 ft./second 2, or 980.7 cm./second 2.
maximum size. An opening of the correct dimension
gravity — 1. The force of attraction between any two
will allow one side to go, or pass through, and the other
objects containing mass. This force is proportional to the
dimension will not.
mass of the objects. Large objects exhibiting forces of
gouge — A cut, groove, or hole in a material. Considered gravity are the Earth, moon, and planets. 2. One of the
to be a defect. four main forces acting on an aircraft. Equivalent to the
actual weight of the rotorcraft. It acts downward toward
gouging — A furrowing condition in which surface material
the center of the earth.
is displaced or damaged. Usually caused by foreign
material between tight fitting, moving parts. gravity waves — A small-scale wave of air moving in
vertical oscillations caused by gravity. Occurring in a
governor — A control that limits the maximum rotational
stable atmosphere gravity plays the major role in forcing
speed of a device.
the air parcels to return to their equilibrium level.
grade-A cotton — Long‑staple cotton fabric with 80
great circle — The largest circle which can be drawn on the
threads per inch in both the warp and fill directions. It
earth’s surface. The shortest distance between two points
is the standard material for covering aircraft structures.
on a sphere.
gradient — A consistent rate of change, both increasing
green run — The first run of a new or freshly overhauled
and decreasing. This term can be applied to the ascent or
engine.
descent of an aircraft or changes in temperature, pressure,
or concentration levels. greenhouse effect — The capture of terrestrial radiation by
certain atmospheric gases. These gases are commonly
gradient system — A device used to give “artificial feel” to
called greenhouse gases.
hydraulically boosted flight controls.
Greenwich mean time (GMT) — The time at the 0°
grain boundary — The lines in metal that are formed by
meridian located at the Royal Observatory, London,
the surfaces of the grains in the metal.
England. Also referred to as Zulu time.
grains — The individual crystals of a material.
greige Dacron — A synthetic, polyester fabric in its natural
gram (g) — The unit of weight or mass in the metric system. condi­tion as it comes from the loom.
One gram equals 1/1,000 kg or about 0.035 ounce.
grid — 1. The electrode of a vacuum tube where the signal
granular — Containing or consisting of grains or granules. is applied. 2. The framework of a plate in a lead‑acid
battery cell. It is made of lead and antimony with the
graph — A pictorial presentation of data, equations, and
actual plate material (spongy lead or lead peroxide)
formulas.
attached. 3. The electrode in an electron tube between the
graphic plan display (GPD) — A view available with cathode and the anode. It is used to control the amount,
URET CCLD (User Request Evaluation Tool Core shape, and velocity of the electron stream between the
Capability Limited Deployment) that provides a graphic cathode and the anode.
display of aircraft, traffic, and notification of predicted
grid minimum off-route altitude (grid MORA) —
conflicts. Graphic routes for Current Plans and Trial
An altitude derived by Jeppesen or provided by State
Plans are displayed upon controller request.
Authorities. The Grid MORA altitude provides terrain
graphite — 1. A soft, black form of carbon that usually and manmade structure clearance within the section
has a greasy feel. Graphite is commonly used as a dry outlined by latitude and longitude lines. MORA does not
lubricant. Graphite is also known as black lead and is provide for NAVAID signal coverage or communication
used in making pencils. 2. A carbonized fiber used as a coverage. 1.) Grid MORA values derived by Jeppesen
reinforcement. The graphitization is accomplished by clear all terrain and manmade structures by 1000 feet in
heating the carbon fiber to temperatures up to 5400ºF. areas where the highest elevations are 5000 feet MSL
See also carbon fiber and carbon/graphite fiber. or lower. MORA values clear all terrain and manmade
structures by 2000 feet in areas where the highest
graupel — White, round or conical ice particles 1/8” to 1/4”
elevations are 5001 feet MSL or higher. When a Grid
in diameter. They often form as a thunderstorm matures
MORA is shown as “Unsurveyed” it is due to incomplete
and indicate the likelihood of lightning. Also referred to
or insufficient information. Grid MORA values followed
as soft hail or snow pellets.
by a  denote doubtful accuracy, but are believed to
gravitational acceleration — The acceleration of a provide sufficient reference point clearance. 2.) Grid
free‑falling object caused by the Earth’s gravitational MORA (State) altitude supplied by the State Authority

151

10001930-002_AviationDictionary_2012_BOOK.indb 151 3/27/2012 9:38:11 AM

 grind • ground resonance

provides 2000 feet clearance in mountainous areas and takeoff. Pilots will use four “key clicks” on the VHF
1000 feet in nonmountainous areas. radio to contact the appropriate ATC facility or six “key
clicks” to contact the FSS. The GCO system is intended
grind — The process of removing metal from a part with an
to be used only on the ground.
abrasive stone or wheel.
ground controlled approach — A radar approach system
grinder — A machine with an abrasive wheel used to
operated from the ground by air traffic control personnel
remove material from a part.
transmitting instructions to the pilot by radio. The
grinding wheel — An abrasive wheel used on grinders to approach may be conducted with surveillance radar
remove ex­cess material. (ASR) only or with both surveillance and precision
approach radar (PAR). Usage of the term “GCA” by pilots
grip length — The length of the unthreaded shank of a bolt.
Also, the length of a blind rivet between the manufactured is discouraged except when referring to a GCA facility.
head and the maximum extent of the pulled head. It is the Pilots should specifically request a “PAR” approach
maximum thickness of material that can be joined by a when a precision radar approach is desired or request an
fastener. “ASR” or “surveillance” approach when a nonprecision
radar approach is desired.
grip range — The difference between the maximum and
minimum thickness of material that may be joined by a ground crew — The people who maintain, service, and
fastener.
 prepare the aircraft before and after flight.

grit blasting — A process for cleaning metal in which ground delay — The amount of delay attributed to ATC,
abrasive materials such as sand, rice, baked wheat, encountered prior to departure, usually associated with a
plaster pellets, glass beads, or crushed walnut shells are CDT program.
forcefully blown onto the part’s surface. ground effect — The condition of slightly increased air
grommet — 1. A metal or plastic eyelet used for reinforcing pressure below an airplane wing or helicopter rotor
holes in aircraft fabric. 2. A small ring of metal, rubber, or system that increases the amount of lift produced. It exists
plastic used as a fairlead and protector for tubing or wire within approximately one-­half wing span or one‑half of
going though a hole in a metal structure. the rotor diameter from the ground.

grooved surface — A shallow, smooth channel wider than ground fog — In the United States, a fog that is generally
a scratch resulting from wear caused by concentrated less than 20 feet deep
contact stress. Abnormal relative movement between ground idle — A gas turbine engine speed usually in the
contact sur­faces or by foreign material on contact 60% to 70% of the maximum RPM range, used as a
surfaces creates the contact stress. The parts usually minimum thrust setting for ground operations.
affected include cylinder barrels, valve faces, and oil seal
outer sleeves. ground loop — 1. The sudden reversal of direction of travel
on the ground of an airplane having a tailwheel-type
gross thrust — The thrust developed by an engine, not
landing gear. The center of gravity swings around ahead
taking into consideration any pressure of initial air mass
of the wheels. 2. An undesirable flow of electrical current
momentum. Also referred to as static thrust (Fg).
through the braid around a shielded wire.
gross weight — The total weight of a fully loaded aircraft
ground plane — The reflector used in a quarter‑wave radio
including the fuel, oil, and cargo it is carrying.
antenna. Serves as an additional quarter‑wave element.
ground — 1. A reference point for voltage measurement in
ground potential — The zero potential (no voltage
an electrical circuit. 2. To connect a part or component to
difference) of electrical circuits.
the electrical ground (normally the airframe).
ground power unit — A small gas turbine whose purpose is
ground clutter — A pattern produced on the radar scope by
to provide either electrical power, air pressure for starting
ground returns which may degrade other radar returns in
aircraft engines, or both. A ground unit is connected to
the affected area. The effect of ground clutter is minimized
by the use of moving target indicator (MTI) circuits in the the aircraft when needed. Similar to an aircraft installed
radar equipment resulting in a radar presentation which auxiliary power unit.
displays only targets which are in motion. ground resonance — On rotorcraft, an aerodynamic
ground communication outlet (GCO) — An unstaffed, phenomenon associated with fully-articulated rotor
remotely controlled, ground/ground communications systems. Ground resonance develops when the rotor
facility. Pilots at uncontrolled airports may contact ATC blades move out of phase with each other and cause the
and FSS via VHF to a telephone connection to obtain an rotor disc to become unbalanced. This condition only
instrument clearance or close a VFR or IFR flight plan. occurs when the rotorcraft is in contact with the ground
They may also get an updated weather briefing prior to and can cause the craft to self-destruct in a matter of

152

10001930-002_AviationDictionary_2012_BOOK.indb 152 3/27/2012 9:38:11 AM

 ground return electrical circuit • gyro

seconds. At high RPM, immediate lift-off will stop the guide vanes — In a turbine engine, stationary airfoil
resonance. At low RPM, immediate closing of the throttle sections positioned radially around the inside of the
and lowering of the collective will stop the resonance. engine. The airfoils direct the flow of air or gases from
one major part to another.
ground return electrical circuit — An electrical circuit that
uses the structure of the aircraft as one of the conductors guided discussion — An educational presentation where
in the circuit. the topic to be covered by a group is introduced and
the instructor participates only as necessary to keep the
ground speed — The speed of an aircraft relative to the
group focused on the subject.
surface of the earth.
guided discussion method — An educational presentation
ground support equipment (GSE) — Equipment separate
typically used in the classroom where the topic to be
from the aircraft but used in direct support to facilitate
covered by a group is introduced and the instructor
maintenance. GSE can include such items as engine hoist,
participates only as necessary to keep the group focused
auxiliary power units, testing equipment, compressed air
on the subject.
units, etc.
guncotton — Nitrocellulose. A nitrated cotton fiber used in
ground visibility — Prevailing horizontal visibility near the
nitrate dope.
earth’s surface as reported by the United States National
Weather Service or an accredited observer. G-unit — The unit of acceleration as a measure of the force
of gravity. One G‑unit is the attraction of gravity for a
ground wave — The portion of a radio wave that travels to
body.
the receiver along the surface of the Earth.
Gunk — A chemical degreaser used for loosening grease
ground‑adjustable propeller — A propeller with a pitch
and soft carbon from the surface of metal parts.
that can be ad­justed and locked on the ground when the
engine is not operating but cannot be changed during gusset — A small reinforcing member used to support the
flight. corners of a structure.
ground-boost engine — An engine that, because of gust — A sudden brief increase in wind; according to U.S.
supercharging (including turbocharging), can develop weather observing practices, gusts are reported when the
more power at sea level than it could without the variation in wind speed between peaks and lulls is at least
supercharging. 10 knots.
ground-controlled landing approach — A directed gust front — The sharp boundary found on the edge of a
approach to landing through instructions provided by a pool of cold air that is fed by the downdrafts and spreads
ground controller The controller watches the aircraft on a out below the thunderstorm. A gust front is the key to the
radar scope showing the relative position of the aircraft to long life of a multicell thunderstorm.
the glide slope and its horizontal position. The controller
gust lock — Locks used to prevent controls from being
gives the pilot instructions necessary for keeping the
damaged by wind gusts while an airplane is parked on
aircraft on its intended path until it lands.
the ground. External locks are positioned between the
grounded — To declare an aircraft or airman unfit for flight. movable surfaces and the fixed aircraft structure. They
are usually painted red and will have a warning streamer
groundspeed — Speed of the aircraft in relation to the
to indicate their installation. Internal control surface
ground.
locks are set in the cockpit.
group task — Part of cooperative, or group learning. Each
gustnadoes — A tornado-like vortex that sometimes occurs
activity your students engage in is known as a group task.
near gust fronts and the edge of a downburst.
growler — Test equipment used to check generator and
guttered surface — Severe erosion confined to narrow
starter arma­tures for shorts. The growler forms the
areas in the direction of the gas flow. One cause is
primary of a transformer and the armature forms the
improper valve seating that allows escape of combustion
secondary. Shorts show up since they cause vibration in
gases through a narrow area. Areas affected are valve
a thin piece of metal, such as a hacksaw blade, held over
seats, cylinder heads, pistons, and valve and spark plug
the armature.
inserts.
guarded switch — A switch protected against accidental
Guy-Lussac’s law — The volume of gas is directly
move­ment by having a guard or shroud located directly
proportional to the absolute temperature, provided the
over the switch. The guard must be raised before the
pressure is held constant.
switch can be actuated.
gyro — Short for gyroscope. A wheel or disk mounted to
gudgeon pin — British for wrist pin. See wrist pin.
spin rapidly about a specific axis while rotating freely

153

10001930-002_AviationDictionary_2012_BOOK.indb 153 3/27/2012 9:38:11 AM

 gyro horizon • gyroscopic precession

about all axes. The gyroscope exhibits rigidity in space;

therefore, it remains in the same relative position to space
even as the vehicle it is mounted in changes position.
gyro horizon — An attitude gyroscopic instrument that
indicates rota­tion about the pitch and roll axes.
gyrocompass — A navigational instrument that uses a
gyro­scope as a stable reference to keep the compass from
oscillating.
Gyrocopter — Trademark applied to gyroplanes designed
and produced by the Bensen Aircraft Company.
gyrodyne — A rotorcraft whose rotors are normally
engine‑driven for takeoff, hovering, and landing, and
forward flight through part of its speed range. Its means of
propulsion, consisting usually of conven­tional propellers,
is independent of the rotor system.
gyroplane — A rotorcraft whose rotors are not engine-driven,
except for initial starting, but are made to rotate by action
of the air when the rotorcraft is moving; and whose
means of propulsion, consisting usually of conventional
propellers, is independent of the rotor system.
gyroscopic precession — An inherent quality of rotating
bodies, which causes an applied force to be manifested
90° in the direction of rotation from the point where the
force is applied.

154

10001930-002_AviationDictionary_2012_BOOK.indb 154 3/27/2012 9:38:11 AM

 H • hand snips

H halo — A circle of light that appears around the moon when

seen through a thin layer of cirrostratus clouds. The halo
hacksaw — A hand‑operated metal cutting saw with appearance is caused by tiny ice crystals in the cloud that
narrow, replace­able blades. The replaceable blade is held scatter the light passing through it.
in the hacksaw frame under tension. halogen — One of the five chemical elements (fluorine,
hailstones — Precipitation formed by drops of water carried chlorine, bromine, iodine, and astatine) in Group VII of
by upward currents of wind inside a cumulonimbus cloud the periodic table of chemical elements. Used in some
to a level where the temperature is low enough to freeze fire extinguishing systems.
the drops into ice. When the hailstones are too heavy to Halon — Low-toxicity, chemically stable compounds used
be carried in the cloud, they fall to the ground. in fire protection systems. In aviation, Halon 1301 is
hairline — A very thin line. most commonly used. The benefit of using Halon fire
extinguishers is that they do not leave liquid or solid
hairline crack — A nearly imperceptible crack on the residues when discharged; therefore, they are preferred
surface of a piece of material. for sensitive areas and can be used in the presence of
hairspring — A flat, coiled spring used in aircraft humans, which is important in closed areas. Halons are
instruments as either a calibrated restraint or a preloading being phased out since they are a chlorofluorocarbon
device for the gears. (CFC) and damage the ozone layer.
halation — A distortion on a cathode-ray tube that shows hammer — A hand-tool consisting of a heavy head and a
up as a blurred area around an image. handle. It is used for pounding, driving, or shaping.
half hitch — A knot used for lacing wire bundles. hammer welding — A forge welding in which the edges of
two pieces of metal are heated red‑hot and then fused by
half life — One half‑life is the measure of the time a beating with a hammer.
particular radioactive material loses one half of its
radioactivity. At each half‑life interval, the material loses hand drill — A hand‑operated, eggbeater‑type tool used to
one half more of its remain­ing life and so on. turn a twist drill.
half view — An aircraft drawing that shows only one‑half hand driving — A method of forming rivets in which the
of a sym­metrical view. Center lines and break lines are head is driven with a hand set and hammer, and the shank
used to show that there is more of the object than is is bucked with a bucking bar.
shown in the drawing. hand file — A hand‑operated cutting tool made of
half-duplex communication — Communication in which high‑carbon steel and fitted with rows of very shallow
sig­nals can be sent in one direction at a time, but cannot teeth extending diagonally across the width of the tool.
be sent in both directions at the same time. hand forming — The process of shrinking, stretching,
half-life inspection — A jet engine inspection required or forming sheet metal by using soft‑faced mallets
under conditions of warranty, completed at half the time or hammers to force the metal down against suitable
between overhaul (TBO) interval. It includes primarily forming blocks or into dies.
a hot section disassembly, inspection, and repair as hand inertia starter — An inertia starter for reciprocating
necessary. engines in which the flywheel is brought up to speed by a
half-round file — A hand file that is flat on one side and hand‑operated crank.
curved on the other. hand lay-up — In composites, assembling layers of
half-section — A view in which the cutting plane extends reinforcement by hand. This includes the working the
only halfway across the object, leaving the other half of resin into the fabric, as well as using a pre-preg fabric.
the object as an exterior view. hand pump — A pump operated by hand to create a flow
half-wave radio antenna — An antenna with an electrical of fluid.
length that is approximately one half of the wavelength hand rivet set — A rivet set that can be clamped into a
of the frequency for which the antenna is tuned. vise to hold the manufactured head of the rivet while the
half-wave rectifier — A rectifier that changes AC into shank is upset with a hammer and a flat punch.
pulsating DC using one diode and producing only one hand snips — Compound-action hand shears used for
half of the AC wave in its output. cutting sheet metal. They normally come in sets of three:
Hall-effect generator — An electronic device used to one that cuts to the left, one that cuts to the right, and one
measure the intensity of a magnetic field. Converts that cuts straight.
magnetic field to a low-level electrical signal.

155

10001930-002_AviationDictionary_2012_BOOK.indb 155 3/27/2012 9:38:11 AM

 hand tools • hazardous inflight weather advisory service (HIWAS)

hand tools — A general name for all of the hand‑operated hardened steel — Steel that has been hardened by a process
tools used in the performance of maintenance. of heating the steel above its critical temperature then
quenching it in brine, water, or oil. Although the hardened
hand-bending tools — A hand‑operated, tube-bending tool
steel is very strong, it is also brittle.
consisting of a clamp, a radius block, and a sliding bar.
It is used to bend thin‑wall aluminum alloy or copper hardener — A chemical constituent of an adhesive that
tubing in such a way that it does not collapse the tube. promotes its setting and hardening.
handbook — A manual that describes simple operations or hardening — 1. A heat treatment of metal that increases
a system of operations. A handbook normally does not its brittleness as well as its resistance to abrasion while
contain specific detailed information on the maintenance it decreases its ductility and malleability. 2. Aluminum:
of such systems. The process of increasing the strength and hardness of
aluminum after it has been solution-heat treated. Age
hand-cranked inertia starter — A starter that uses a hand
hardening takes several days at room temperature until
crank to store energy in a spinning flywheel. The crank is
the metal reaches its full hard state. 3. Steel: A process
geared to the flywheel through a high‑ratio gear system
so that the flywheel can be spun at a high speed. The whereby steel is made hard and brittle by heating it
flywheel is coupled by a clutch to the crankshaft of the to a temperature above its critical temperature and
engine for starting. immediately quenching it in water or oil.

handoff — An action taken to transfer the radar identification hard-facing — A process of welding, plating, or spraying
of an aircraft from one controller to another if the aircraft a hard material such as carbide on the surface of a tool to
will enter the receiving controller’s airspace and radio increase its hardness and to keep the tool from wearing.
communications with the aircraft will be transferred. hardness — The property of a metal that enables it to resist
hangar — A building used for the purpose of housing and penetration, wear, or cutting actions.
main­taining aircraft. hardness test — An evaluation of the hardness of a material
hangar queen — Slang, for an aircraft that is frequently by measur­ing the depth of penetration of a specially
non-airworthy and spends a lot of time in the hangar. shaped probe under a specified load. The surface
In the military or commercial aviation, these aircraft hardness of aluminum alloy parts such as brake housings
are frequently robbed of parts to keep other aircraft and wheels can be measured to determine whether or not
airworthy, thus prolonging the status of the hangar queen. their heat treatment has been affected by overheating.
Also referred to as an orphaned airplane. hardware — The nuts, bolts, screws, rivets, etc. necessary
hard — The condition of a material when it is compact, for assem­bling parts.
solid, and difficult to bend or deform. hardwood — A wood with compact texture.
hard landing — An improper landing of an aircraft that has harmonic — A frequency of vibration that is an even
trans­mitted undue stresses into the structure. The degree multiple of the fundamental of another vibration
of a landing’s hardness determines the type of special frequency.
inspection that will be performed to determine if there is
structural damage to the aircraft. harness satin — A weaving pattern producing a satin
appearance. See also eight-harness satin and four-harness
hard X-rays — The degree of the penetration power of satin.
an X‑ray as determined by the amount of voltage that
is applied to the anode of the X‑ray tube. The higher the Hartley oscillator — An electronic oscillator that produces
voltage, the greater its penetrating power. its feedback through a tapped inductor.
hardboard — A wood composition material manufactured have numbers — Used by pilots to inform ATC that they
by bonding sawdust and chips of wood with an adhesive have received runway, wind, and altimeter information
under heat and pressure. only.
hard-drawn copper wire — Copper wire that has hazardous attitudes — Studies have identified five
been pulled through dies to reduce its diameter to a hazardous attitudes that can interfere with a pilot’s
predetermined size. Pulling the wire also hardens the ability to make sound decisions and exercise authority
wire and increases its tensile strength. properly. The five hazardous attitudes are anti-authority,
impulsivity, invulnerability, macho, and resignation.
hardenability — In a ferrous alloy, the property of metal
that determines the depth and distribution of hardness hazardous inflight weather advisory service (HIWAS) —
induced by heat treatment and quenching or by cold Continuous recorded hazardous inflight weather forecasts
working. broadcasted to airborne pilots over selected VOR outlets
defined as an HIWAS Broadcast Area.

156

10001930-002_AviationDictionary_2012_BOOK.indb 156 3/27/2012 9:38:11 AM

 hazardous weather information • heavy ends

hazardous weather information — Summary of heat load — The amount of heat that an air conditioner is
significant meteorological information (SIGMET/ WS), required to remove from an airplane cabin in order to
convective significant meteorological information, maintain a constant cabin temperature.
(convective SIGMET/WST), urgent pilot weather reports
heat of compression — The heat generated when a gas is
(urgent PIREP/UUA), center weather advisories (CWA),
com­pressed.
airmen’s meteorological information (AIRMET/WA) and
any other weather such as isolated thunderstorms that are heat pump — Moves heat from one location to another. A
rapidly developing and increasing in intensity, or low heat pump can generally be reversed so that it either adds
ceilings and visibilities that are becoming widespread heat (acts as a heater) or takes heat away (acts as an air
which is considered significant and are not included in a conditioner).
current hazardous weather advisory.
heat sink — 1. A device on which semiconductors can be
haze — Fine dust or salt particles dispersed through a mounted to absorb the heat that would normally tend to
portion of the atmosphere; particles are so small they damage them. 2. A heavy plate of conductive material
cannot be felt or individually seen with the naked eye (as that will absorb or carry away heat. Especially useful in
compared with the large particle of dust), but diminish welding.
the visibility; distinguished from fog by its bluish or
heat treatment of a plastic resin — The operation in
yellowish tinge.
which a cemented joint in a thermoplastic resin is held
heading — The direction in which the longitudinal axis at an elevated temperature so the entrapped solvent can
of the airplane points with respect to true or magnetic diffuse into a greater volume of the resin. This decreases
north. Heading is equal to course plus or minus any wind its concentration and increases the strength of the joint.
correction angle.
heat treatment of metals — Any operation in which
heads up display (HUD) — A system that displays flight the physical char­acteristics of a metal are changed by
information on a transparent display in the line-of-sight heating. This includes anneal­ing, hardening, tempering,
of the pilot so that information can be read without and normalizing.
looking down into the cockpit. Newest terminology is
heat value — The heat energy available per unit volume
Head-up Guidance System (HGS).
of a fuel.
head-up guidance system (HGS) — See heads up display.
heater — Any device that produces controlled heating.
headwind component — That portion of the wind which
heating element — An electrical resistance wire that glows
acts straight down the runway toward the airplane on
red‑hot to produce heat.
takeoff or parallel to the line of flight when airborne.
heat-shrinkable — A quality in a synthetic fiber that allows
headwork — Conscious, rational thought process when
a fabric to shrink when heat is applied.
making decisions.
heatshrinkable fabric — An inorganic fabric used to
heat — Energy associated with the motion of molecules
cover light aircraft structures. The fabric is sewn and put
within a material. The more heat energy there is in a
on the aircraft structure so that it is taut but not tight.
material, the faster its molecules move.
After securing the fabric to the structure with a special
heat capacity — The amount of heat energy required to adhesive, it is shrunk to the correct tautness by ironing it
raise the temperature of a substance 1ºC. with an ordinary household electric iron or by heating it
with a high wattage hair dryer. The material is then given
heat dissipation — The loss of heat or the transfer of heat
a coating of non‑tautening dope.
into another object or substance.
Heaviside atmospheric layer — A layer of ionized particles
heat energy — Energy associated with the motion of the
that surrounds the Earth. The ionosphere.
molecules within a substance.
heavy (aircraft) — For the purposes of Wake Turbulence
heat engine — Any mechanical device that converts
Separation Minima, ATC classifies aircraft as Heavy,
heat energy into mechanical energy. For example,
Large, and Small. Heavy aircraft are capable of takeoff
reciprocating and turbine engines are heat engines.
weights of more than 255,000 pounds whether or not
heat exchanger — Any device used to transfer heat from they are operating at this weight during any particular
one body to another. phase of flight. See Aircraft Classes
heat lamp — An incandescent lamp that produces a heavy ends — In the fractional distillation process, the last
maximum of in­frared radiation with a minimum of parts of crude petroleum refining that have the highest
visible light rays. Used for drying paint or for applying boiling points.
heat to glued parts to decrease curing time.

157

10001930-002_AviationDictionary_2012_BOOK.indb 157 3/27/2012 9:38:12 AM

 heavy snow warning • heterogeneous mixture

heavy snow warning — A warning that snowfall may heliport — An area of land, water, or structure used
exceed four inches or more in a 12-hour period or six or intended to be used for the landing and takeoff of
inches in a 24-hour period. helicopters and includes its buildings and facilities, if any.
Hecto — One hundred. heliport reference point (HRP) — The geographic center
of a heliport.
hedge-hopping — An aircraft flying very near the Earth’s
surface yet avoiding obstructions on the ground. helium — An inert, gaseous, chemical element with a
symbol of He and an atomic number of 2. Used to inflate
height above airport (HAA) — The height of the Minimum
lighter­-than‑air aircraft.
Descent Altitude (MDA) above the published airport
elevation. This is published in conjunction with circling henry — The standard unit of inductance. It is the amount
minimums. of inductance in which a current change of one ampere
per second will induce a voltage of one volt. Named for
height above landing — The height above a designated
Joseph Henry, an American physicist.
helicopter landing area used for helicopter instrument
approach procedures. heptane — A liquid hydrocarbon material (C7H17) having
a low critical pressure and temperature and whose
height above touchdown (HAT) — The height of the
detonation characteristics are used in determining the
Decision Height or Minimum Descent Altitude above
octane rating of aviation gasoline.
the highest runway elevation in the touchdown zone
(first 3,000 feet of the runway). HAT is published on heptode — A vacuum tube that has seven active electrodes,
instrument approach charts in conjunction with all including the anode, cathode, control grid, and four other
straight-in minimums. special-purpose grids such as screen grids, suppressor
grids, and beam-forming grids.
height band — In gliders, the altitude range in which the
thermals are strongest on any given day. Remaining with hermaphrodite calipers — A tool used to scribe lines
the height band on a cross-country flight should allow the equidistant from an edge. Consists of a caliper with one
fastest average speed. pointed leg and one with a hook on the end as with an
outside caliper. The hook is placed on the edge of the
height gradient — The rate of change of height per unit of
material, and the point is used to scribe a line.
distance on a constant pressure chart.
hermetically sealed — A method of protecting an aircraft
Heliarc — A welding process used extensively on aircraft
instrument by exhausting all of the air from its case and
parts. It is a gas-shielded process to prevent oxidation
sealing it so that no moisture can get in.
of the base metal. The two types of Heliarc welding are
tungsten inert‑gas (TIG) welding and metal inert‑gas hermetically sealed integrating gyro (HIG) — A gyro
(MIG) welding. mounted in a sealed case with a viscous damping medium.
The output is there­fore an indication of the total amount
helical — A line or form that winds around a cylinder or the
of angular displacement of the vehicle in which the gyro
line of threads on a bolt.
is installed rather than the rate of angular displacement.
helical potentiometer — A potentiometer with a resistance
Hertz antenna — A half‑wave radio antenna.
element made in the form of a spiral. The wiper is moved
over the element by turning a multi‑turn screw. hertz (Hz) — A unit used for measuring the frequency of
vibrations or of AC electricity. It is used for the frequency
helical spline — A spline that winds around a shaft. Helical
of any type of repeating cycles of motion. One hertz is
splines are used to change the linear motion of the device
equal to one cycle per second. Named for Hein­rich Hertz,
that rides on the splines into the shaft’s rotary motion on
a German physicist.
which the splines are cut.
heterodyne — To mix or beat together two frequencies in
helical spring — A spring wound in the form of a spiral.
order to produce an intermediate frequency.
Helicoil — A special helical steel insert screwed into
heterodyne-type frequency meter — A frequency
specially cut threads to restore threads that have been
meter that beats (heterodynes) an unknown-frequency
stripped out or to provide durable threads in soft castings.
signal against a locally-produced signal from a
helicopter — A rotorcraft that, for its horizontal motion, variable-frequency generator. When the beat is of zero
depends principally on its engine-driven rotors. frequency, the frequency of the incoming signal can be
read from a dial or a digital display showing the frequency
helipad — A small, designated area, usually with a prepared
of the local generator.
surface, on a heliport, airport, landing/ takeoff area,
apron/ramp, or movement area used for takeoff, landing, heterogeneous mixture — A mixture composed of
or parking of helicopters. dissimilar ingredients.

158

10001930-002_AviationDictionary_2012_BOOK.indb 158 3/27/2012 9:38:12 AM

 hexadecimal number system • high-pressure compressor

hexadecimal number system — A number system that high speed exit — See high speed taxiway.
uses the base 16. (The decimal system uses the base ten).
high speed taxiway — A long radius taxiway designed and
hexagon — A figure that has six sides. provided with lighting or marking to define the path of
aircraft, traveling at high speed (up to 60 knots), from
hexagon head bolt — A bolt head shaped with six sides (a
the runway center to a point on the center of a taxiway.
hexagon).
Also referred to as long radius exit or turn-off taxiway.
hexode — An electron tube having six active elements. The high speed taxiway is designed to expedite aircraft
turning off the runway after landing, thus reducing
HF communications — See high frequency communications.
runway occupancy time.
hidden surfaces — Any surface represented on an aircraft
high speed taxiway / turnoff (HST) — A long radius
drawing that cannot be seen in a particular view but is
taxiway designed and provided with lighting or marking
represented in outline form with hidden lines.
to define the path of an aircraft, traveling at high speed
hierarchy of human needs — A listing by Abraham Maslow (up to 60 knots), from the runway center to a point on the
of needs from the most basic to the most fulfilling. These center of a taxiway. Also referred to as long radius exit
range from physical through safety, social, and ego to or turnoff taxiway. The high speed taxiway is designed
self-fulfillment. to expedite aircraft turning off the runway after landing,
thus reducing runway occupancy time.
high — An area of high barometric pressure, with its
attendant system of winds; an anticyclone. Also referred high speed turnoff — See high speed taxiway.
to as a high-pressure system.
high strength steel — Steel that has a tensile strength of
high altitude checkout — FAR 61.31(f) requires specific between 50,000 and 100,000 PSI.
ground and flight training for a pilot to act as PIC
high-bypass turbofan — Turbine engines with 4:1
of a pressurized airplane that has a service ceiling
fan‑to‑engine bypass ratio or higher. That is, four or more
or maximum operating altitude, whichever is lower,
times as much air flows through the fan as through the
above 25,000 MSL. High-altitude checkouts require
core engine.
both ground and flight training. Included in the ground
training is a thorough review of the physiological aspects high-bypass turbofan engine — A turbofan engine in
of high-altitude flight. An overview of these effects is which the mass airflow in pounds per second that passes
contained in Chapter 8 of the Aeronautical Information through the fan can be four times or more greater than
Manual (AIM) and AC 61-107, Operations of Aircraft that which is moved by the gas generator or core of the
at Altitudes Above 25,000 Feet MSL and/or MACH engine.
Numbers (Mmo) Greater Than .75. AC 61-107 contains
high-carbon steel — Steel that contains more than 0.5%
a recommended outline for a high-altitude training
carbon.
program. An instructor needs a logbook endorsement
for high-altitude operations to give flight instruction high-frequency communications — Radio communication
in a pressurized airplane that has a service ceiling or at a frequency that is above the upper end of the
maximum operating altitude above 25,000 feet MSL. commercial AM broadcasting band.
high blower — The high-speed operation of a single‑stage, high-level language — The language of computer
two -speed, internal supercharger system. Usually about instruction a computer can understand.
10:1 ratio.
high-lift device — Any lift‑modifying device such as a slot,
high cycle fatigue — A condition seen as cracking or slat, or any of the forms of flaps that are used to allow an
stretching caused by vibration stresses above the design airfoil to achieve a higher angle of attack before airflow
limit of the engine. separation occurs.
high frequency — The frequency band between 3 and 30 high-pass filter — An electronic filter that allows AC, above
MHz. a certain frequency, to pass with little or no opposition.
high frequency communications — High radio frequencies high-potential ignition lead test — A test performed on the
(HF) between 3 and 30 MHz used for air-to-ground voice spark plug electrical wires of an aircraft ignition system
communication in overseas operations. to see if there is a voltage leak to ground.
high performance airplane — An airplane with an engine high-pressure compressor — The rear section of a
of more than 200 horsepower. dual‑spool com­pressor. Also referred to as an N2
compressor or high speed compressor.
high pressure turbine — In gas turbine engines, the turbine
rotor which drives the high pressure compressor in a dual
or triple spool axial flow gas turbine engine.

159

10001930-002_AviationDictionary_2012_BOOK.indb 159 3/27/2012 9:38:12 AM

 high-pressure oxygen system • holding procedure

high-pressure oxygen system — Gaseous oxygen systems Hi-Shear rivet — A threadless

whose cylinders carry between 1,000 and 2,000 PSI bolt used for high‑speed,
pressure. high‑strength, lightweight
high-pressure system — In gaseous systems, maximum construction of an aircraft.
pressure between 1,000 and 2,000 PSI. In liquid systems, A steel pin is held into the
it refers to approximately 300 PSI pressures. structure by an aluminum or
mild‑steel collar swaged into a groove around the end of
high-pressure turbine — The forward most turbine wheels, the pin.
also called the N2 turbine or high‑speed turbine, that drive
the high‑speed compressor in a two‑spool, axial-flow gas HIWAS area — Hazardous Inflight Weather Advisory
turbine engine. Service. Continuous recorded hazardous inflight weather
forecasts broadcasted to airborne pilots over selected
high-rate discharge — See cold-cranking amps. VOR outlets defined as an HIWAS Broadcast Area.
high-resistance connection — An electrical connection HIWAS broadcast area — A geographical area of
with excessive resistance. Usually caused by a poor responsibility including one or more HIWAS outlet areas
solder joint or loose fastener. assigned to an AFSS/FSS for hazardous weather advisory
high-speed steel — Alloys of steel that maintain their broadcasting.
strength when operating at red‑hot temperatures. They HIWAS outlet area — An area defined as a 150 NM radius
are used for metal‑cutting tools. of a HIWAS outlet, expanded as necessary to provide
high-speed taxiway exit or turnoff — A wide radius coverage.
turn-off from the runway to allow an aircraft to turn off at hold for release — Used by ATC to delay an aircraft for
a higher rate of speed than would be possible on a normal traffic management reasons; i.e., weather, traffic volume,
right angle turn-off. etc. Hold for release instructions (including departure
high-strength fastener — A fastener with high tensile delay information) are used to inform a pilot or a
and shear strengths attained through combinations of controller (either directly or through an authorized relay)
materials, work‑harden­ing, and heat treatment. that an IFR departure clearance is not valid until a release
time or additional instructions have been received.
high-tension magneto — A self‑contained magneto
ignition system used to provide a high potential voltage hold procedure — A predetermined maneuver which keeps
to the spark plugs. The magneto consists of a rotating aircraft within a specified airspace while awaiting further
magnet, cam, breaker points, capacitor, and a coil with clearance from air traffic control. Also used during
a primary and a secondary winding. The output of the ground operations to keep aircraft within a specified area
secondary winding goes to a distributor, then to the spark or at a specified point while awaiting further clearance
plugs. from air traffic control.

high-voltage igniter plug — An igniter plug utilizing an hold/holding procedure — A pre-determined maneuver
air gap between its center electrode and its outer casing. which keeps aircraft within a specified airspace while
Used to start the engine combustion process. awaiting further clearance from air traffic control. Also
used during ground operations to keep aircraft within
high-voltage ignition system — A main system with a a specified area or at a specified point while awaiting
voltage output in the range of approximately 5,000 to further clearance from air traffic control.
30,000 volts delivered to the igniter plug.
holding coil — An auxiliary coil in an electrical relay that
high-wing airplane — A monoplane with a single airfoil keeps the relay energized after the current that caused the
mounted on top of the fuselage. relay to close has stopped flowing through the main coil.
hinge — A fastener that allows one of the connected pieces holding fix — A specified fix identifiable to a pilot by
to pivot with respect to the other. NAVAIDs or visual reference to the ground used as
hinge point — The pivot point about which a control a reference point in establishing and maintaining the
surface or a door hinges. position of an aircraft while holding.

Hipernik — A magnetic alloy made of 50% iron and 50% holding point [ICAO] — A specified location, identified by
nickel. visual or other means, in the vicinity of which the position
of an aircraft in flight is maintained in accordance with
air traffic control clearances
holding procedure — An aircraft maneuver in which a pilot
is in­structed by air traffic control to maintain a specified
air space until given further instruction.

160

10001930-002_AviationDictionary_2012_BOOK.indb 160 3/27/2012 9:38:12 AM

 hold-short point • horizontal needle of the cross‑point indicator

hold-short point — A point on the runway beyond which of years in their hangars, garages, and even basements.
a landing aircraft with a LAHSO clearance is not These airplanes are known as homebuilts. An airplane is
authorized to proceed. This point may be located prior to considered amateur built if the builder constructs at least
an intersecting runway, taxi-way, predetermined point, or 51% of the aircraft. Manufacturers of homebuilt kits may
approach/departure flight path. not construct more than 49% of the total airplane.
hold-short position lights — Flashing in-pavement white homing — A method of navigating to an NDB by holding a
lights located at specified hold-short points. zero relative bearing. The result of homing in a crosswind
is a curved course.
hold-short position marking — The painted runway
marking located at the hold-short point on all LAHSO hone — A fine abrasive stone used to sharpen cutting tools
runways. or create a finished surface.
hold-short position signs — Red and White holding honeycomb — A material made up of hexagonal-shaped
position signs located alongside the hold-short point. cells. Constructed of thin metal, paper, or plastic and
used as a core material for sandwich structures. Named
hole — 1. The vacancy in the valence structure of an element
after a bee’s honeycomb because of its appearance.
that will accept an electron from an outside source. 2.
The absence of an electron at a point where one might honeycomb shroud ring — Honeycomb material into
be expected. For most purposes, a hole may be treated which a rotating airfoil can cut without degrading its
as a positive charge. 3. A serious discrepancy, flaw, or air-sealing function. Usually in the hot section. Also
weakness. 4. An opening in which something is missing. referred to as an abradable shroud.
hole finder — A tool used in sheet metal work to determine honing — The process of removing a very small amount
the rivet hole locations to be drilled in a piece of sheet of material to produce a smooth finish on a surface or to
metal so they will match those in the piece of metal being produce a sharp edge on a cutting tool such as a knife or
overlapped. a chisel.
hole punch — A hollow punch resembling a sharp‑edged hook rule — A steel scale with a hook or projection on one
tube. It is used to punch holes in gasket material. end so the rule can be used to measure accurately from
the edge of materials.
holist — A learning style that focuses on the overall object
first and then examines the individual components, using hook spanner — A semicircular spanner wrench with the
a top to bottom approach. handle on one end and a hook on the other. The hook
engages notches in the outside circumference of a
hollow drill — A drill with a hole through its center making
ring‑type nut.
it easier for the drill to be lubricated.
Hooke’s law — A law of physics that deals with the
hollow-mill collar cutter — A tool used to remove collar
relationship between stress and strain in a material.
material from pin rivets so the rivet can be tapped out of
It states that stress in a ductile material is directly
the work.
proportional to the strain until the limit of elasticity of
home study course — Under FAR 61.35, a home study the material is reached.
course may be used to meet the prerequisites for a
hopper — A funnel‑shaped container used for storing the
knowledge test. Home study curriculums may be
abrasive in a sand-blasting machine. The container has
developed individually by students from material
an opening in the top for loading and a smaller opening
described in the applicable FAA knowledge test guide.
in the bottom for dumping.
Usually, home study courses are designed by pilot
schools, colleges and universities, aviation organizations, hopper-type oil tank — A container within an oil tank used
publishers, or individual ground or flight instructors. The to hold oil diluted with gasoline for cold weather starting.
home study course may feature printed material, video, The use of a hopper minimizes the amount of oil that
or computer-based training provided on CDs or accessed must be diluted.
over the Internet. Regardless of the medium, students must
horizon — The line of sight boundary between the Earth
show that the course has been satisfactorily completed
and the sky.
and obtain an endorsement from an authorized instructor.
Refer to Certification: Pilots and Flight Instructors (AC horizontal — Parallel to the Earth’s horizon or to the base
61-65), which describes several methods that students can line of an object.
use to show evidence of having satisfactorily completed
horizontal needle of the cross‑point indicator — The
home study courses.
glide slope indicator of the standard ILS indicator (cross
homebuilt airplane — An aircraft constructed by an point indicator). The horizontal bar is also referred to the
amateur builder. Such builders buy kits and/or plans horizontal needle and indicates the position of the aircraft
for the aircraft and assemble the airplane over a period on the ILS glideslope.
161

10001930-002_AviationDictionary_2012_BOOK.indb 161 3/27/2012 9:38:12 AM

 horizontal pressure gradient force • hot-tank oil system

horizontal pressure gradient force — The force that arises principle is used in many fire detection systems. The cold
because of a horizontal pressure gradient. junction is sometimes referred to as the reference junction.
horizontal stabilizer — A fixed horizontal airfoil attached hot section — The portion of a turbine engine aft of the
to the rear of the fuselage to provide stability in pitch. diffuser where combustion takes place.
horizontal wind shear — The change in wind direction hot section distress — Any of the metal deterioration
and/or speed over a horizontal distance. conditions found in the hot section such as warping or
creeping.
horizontally opposed engine — A reciprocating engine
with the cylinders arranged in two horizontal rows, hot section inspection — An inspection of the hot section
one on either side of the crankshaft. The cylinders are of a gas turbine engine.
slightly staggered, with the cylinders in one bank slightly
hot shearing — A method of cutting heavy sheets of
ahead of those in the other bank. Staggering the cylinders
magnesium alloys in which the metal is cut while hot.
allows each piston to be connected to a separate throw of
This improves the smoothness of the cut.
the crankshaft.
hot spark plug — A spark plug with a long‑nose insulator
horn — A lever or device fastened or connected to a control
in which the heat transferring from the center electrode
surface to which an operating cable or rod is attached.
into the shell has a long path to travel. Hot spark plugs
horse latitudes — Approximately 30° to 35° north and are used in engines that operate relatively cool, and
south latitudes. An area of high barometric pressure and they keep the center insulator hot enough to prevent the
light, changeable winds. accumulation of lead oxides.
horsepower (HP) — The standard unit of power used for hot sparks — Localized areas in the cylinder of an internal
mechanical measurement. It is equal to 33,000 ft.‑lbs. of combustion engine that are overheated to the point
work done in one minute, or 550 ft.‑lbs. of work done in where they become incandescent or glow. They cause
one second. Electrically, it is equal to 746 watts. pre-ignition.
horseshoe magnet — A magnet shaped like the letter “U” hot spots — Localized discoloration on hot section parts
(or a horseshoe). indicating a breakdown of cooling air or harmful
concentration of fuel at that point. This often is the result
hose — A flexible plumbing line used in place of rigid
of a malfunctioning fuel nozzle.

tubing in areas subject to movement or vibration.
hot stamping — A method of identifying or imprinting
hose clamp — A metal clamp used to hold a rubber hose
plastic materials, cloth, or paper by using heated metal
onto a piece of rigid tubing.
dies.
hot air muff — A jacket installed around a tail pipe.
hot start — In gas turbine engines, a start which occurs
Air routed through the hot air muff picks up heat by
with normal engine rotation, but exhaust temperature
convection through the tail pipe material. This heated air
exceeds prescribed limits. This is usually caused by an
is then routed to the cabin.
excessively rich mixture in the combustor. The fuel to the
hot bond repair — In composites, a repair made using a hot engine must be terminated immediately to prevent engine
patch bonding machine to cure and monitor the curing damage.
operation. Hot bonding equipment typically includes
hot streak ignition — An afterburner ignition system
both the heat source and the vacuum source.
in which a stream of raw fuel continues to burn while
hot corrosion — Corrosion occurring in hot sections from passing through the turbine section and provides ignition
a chemical reaction between sulfur in the fuel and salt in for afterburner fuel supply.
the air stream. This condition is more of a problem when
hot valve clearance — The clearance between the valve
operating near salt water.
stem and the rocker arm when all of the engine parts have
hot dimpling — A coin dimpling or countersinking of metal reached their operating temperature.
for flush rivets or screws. A heating unit heats the metals
hot wire — A wire connected directly to the power source.
to prevent cracking around the hole.
hot-tank lubrication system — A gas turbine engine
hot forming — Working operations such as bending and
lubrication system in which hot oil returns directly from
drawing sheet and plate, forging, pressing, and heading,
the engine to the tank without being cooled because the oil
performed on metal heated to temperatures above room
cooler is in the pressure portion of the lubrication system.
temperature.
hot-tank oil system — A lubrication system where the oil
hot junction — One end of a thermocouple. When combined
cooler is located in the pressure oil subsystem and the
with a cold junction, a small current is generated. The same
scavenge oil returns to the oil tank uncooled.

162

10001930-002_AviationDictionary_2012_BOOK.indb 162 3/27/2012 9:38:12 AM

 hot-wire ammeter • hydraulic booster unit

hot-wire ammeter — A current measuring instrument looking down into the cockpit. Newest terminology is
for measuring high frequency alternating current. The Head-up Guidance System (HGS).
ammeter uses the heating effect of the high frequency
hue — 1. The gradation of colors. 2. The characteristics of a
current to heat a wire and change its length. As the wire
color that differentiates between red, blue, or yellow and
lengthens, it moves a pointer across a dial to show the
any of the inter­mediate colors.
amount of current flowing through the wire.
human factors — The study of how people interact with
hot-wire anemometer — A wind speed indicator that
their environments. In the case of general aviation, it
measures the amount of heat the wind removes from a
is the study of how pilot performance is influenced by
heated wire. The speed of the wind is proportional to the
such issues as the design of cockpits, the function of
amount of heat removed.
the organs of the body, the effects of emotions, and the
hourmeter — An odometer‑type instrument used to interaction and communication with other participants in
measure hours of operating time. When incorporated into the aviation community, such as other crew members and
a mechanical tachometer, it is accurate only at a specified air traffic control personnel.
RPM.
human factors related — The phrase “human factors
housing — A frame, box or casing that contains a part or related” more aptly describes an accident since it is not
mechanism. usually a single decision that leads to an accident, but a
chain of events triggered by a number of factors. The poor
hover — The action of a helicopter maintaining a constant
judgment chain, sometimes referred to as the error chain,
position over a selected point. Hovering allows the
is a term used to describe this principle of contributing
helicopter to sustain flight with no movement in relation
factors in a human factors related accident.
to the ground.
humidifier — A device used to increase the humidity of
hover check — Used to describe when a helicopter/
the air. Humidifiers are primarily used in air‑cycle air
VTOL aircraft requires a stabilized hover to conduct a
conditioning systems to increase the comfort within the
performance/power check prior to hover taxi, air taxi,
cabin.
or takeoff. Altitude of the hover will vary based on the
purpose of the check. humidity — The amount of water vapor in the air.
hover taxi — Used to describe a helicopter/VTOL aircraft hung start — In gas turbine engines, a condition of normal
movement conducted above the surface and in ground light off but with rpm remaining at some low value rather
effect at airspeeds less than approximately 20 knots. The than increasing to the normal idle rpm. This is often the
actual height may vary and some helicopters may require result of insufficient power to the engine from the starter.
hover taxi above 25 feet AGL to reduce ground effect In the event of a hung start, the engine should be shut
turbulence or provide clearance for cargo slingloads. down.
hovering ceiling — The maximum altitude at which a hunting — 1. An undesirable oscillation above and below
helicopter can support itself without forward motion. a desired value in a control system. 2. An oscillatory
motion of an articulated rotor’s blades about the Alpha
hovering outside of ground effect — Hovering greater
Hinge caused by coriolis forces.
than one rotor diameter distance above the surface.
Because induced drag is greater while hovering out of hurricane — A tropical cyclone in the Western Hemisphere
ground effect, it takes more power to achieve a hover out with winds in excess of 65 knots.
of ground effect.
hurricane eye — The circular, nearly cloud free region
how do you hear me? — A question relating to the approximately 10 to 20 nautical miles in diameter,
quality of the transmission or to determine how well the located in the center of the storm.
transmission is being received.
hurricane warning — The warning issued within 24 hours
hub — In helicopters, the part of a propeller or rotor system of the arrival of hurricane conditions.
that attaches to the main driving shaft and to which the
hurricane watch — Issued when hurricane conditions are
blades are fastened.
expected in a particular area within a day or more.
Huck Lockbolt — A patented, threadless bolt used in
hybrid — In composites, the combination of two or
the production of aircraft where quickly installed
more types of reinforcing materials into the composite
high‑strength, lightweight fasteners are required.
structure.
HUD — Heads up display. A system that displays flight
hydraulic booster unit — A unit for moving the flight
information on a transparent display in the line-of-sight
controls in a large, high‑speed aircraft. It is actuated by
of the pilot so that information can be read without
the normal cockpit controls but greatly amplifies the
force the pilot exerts.
163

10001930-002_AviationDictionary_2012_BOOK.indb 163 3/27/2012 9:38:12 AM

 hydraulic brake • hydrostatic testing

hydraulic brake — An aircraft brake operated by means of hydrogen embrittlement — A brittle condition caused
hydraulic fluid under pressure. by the metal absorbing hydrogen while it is being
electroplated.
hydraulic filter — A unit that removes foreign particles
from the hydraulic system. hydrogen fuel — A proposed jet fuel of the future that
could be stored as a gas or cryogenic liquid. The present
hydraulic fluid — A liquid used to transmit and distribute
high cost and storage problems prevent its current use.
forces to various units being actuated.
hydrogen peroxide — H2O2. An unstable compound used
hydraulic fuse — A unit designed to stop the flow of
as an oxidizing agent, antiseptic, and a fuel for rocket
hydraulic fluid if a leak occurs downstream of the fuse.
engines.
hydraulic lock — A condition that occurs in a reciprocating
hydrological cycle — The movement of moisture from the
engine having cylinders below the crankcase. Oil leaks
earth to the atmosphere and back to the earth again.
past the piston rings and fills the cylinder with an
incompressible fluid. The engine cannot then be rotated hydromechanical fuel control — A fuel control that
without damage. utilizes hydraulic and mechanical forces to operate its
fuel scheduling mechanisms.
hydraulic motor — A motor driven by a flow of hydraulic
fluid. hydrometeor — Atmospheric water vapor. Liquid or solid
water formation that is suspended in, or falling from, the air,
hydraulic pump — An engine-driven, electric motor‑driven,
including clouds, fog, ice fog, mist, rain, and hail also any
or hand‑operated pump used to move hydraulic fluid
water particles blown by the wind from the Earth’s surface.
through a system.
hydrometer — A device used to
hydraulic reservoir — A container for the hydraulic fluid
measure specific gravity of a
supply in an aircraft.
liquid. It consists of a weighted
hydraulic system — An aircraft’s entire fluid power system, float with a long stem in the
includ­ing the reservoir, pump, control valves, actuators, enlarged glass tube of a syringe.
and all of the associated plumbing. Liquid is pulled up into the tube
and the float rides vertically on
hydraulic valve lifter — The hydraulic units in the
the surface. The amount the float
valve train of a reciprocat­ing aircraft engine used to
is submerged is a function of the
automatically adjust for any changes in dimensions of
density of the liquid. The number
the engine caused by expansion and also to keep the
on the float’s stem opposite the liquid level is the specific
operating clearance in the valve mechanism at zero.
gravity.
hydraulics — The branch of science that deals with the
hydroplaning — A condition that exists when landing
transmission of power by incompressible fluids under
on a surface with standing water deeper than the tread
pressure.
depth of the tires. When the brakes are applied, there is a
hydrocarbon — An organic compound that consists possibility that the brake will lock up and the tire will ride
mostly of carbon and hydrogen. The vast majority of on the surface of the water, much like a water ski. When
our fossil fuels, including gasoline and turbine fuel, are the tires are hydroplaning, directional control and braking
hydrocarbons. action are virtually impossible. An effective anti-skid
system can minimize the effects of hydroplaning.
hydrodynamics — The study of forces produced by
incompres­sible fluids in motion. hydropneumatic — Mechanical equipment that uses both
hydraulic and pneumatic forces in order to accomplish its
hydrofoil — An airfoil‑shaped plate attached to the bottom
intended purpose.
of an airplane or boat that lifts the vehicle out of the water
by hydrodynamic action when the vehicle is moved hydro-ski — A hydrofoil mounted below the hull of a
through the water at high speed. flying boat, which hydrodynamically produces lift by the
hydro‑ski. As the flying boat begins to move through the
hydrogen — A basic element with a symbol of H and an
water, the hydro‑ski helps to lift the hull out of the water.
atomic number of 1. In chemical formulas, free hydrogen
appears as H2 because there must be two atoms of hydro-sorb — A hydraulic shock absorber used in a bungee
hydrogen to form one molecule of free hydrogen gas. shock cord landing gear to prevent rebound.
hydrogen bomb — A nuclear weapon that produces heat hydrostatic testing — The method of pressure‑testing
and light from the fusion of hydrogen atoms. compressed gas cylinders with high‑pressure water rather
than a compressible fluid such as air. Water is used for
hydrogen brazing — Braze welding in which hydrogen is
safety reasons.
used as the fuel gas.

164

10001930-002_AviationDictionary_2012_BOOK.indb 164 3/27/2012 9:38:12 AM

 hydroxide • hysteresis loop

hydroxide — A chemical compound made up of a metal

or a non‑metal (acid) base and a negative hydroxyl ion
(OH).
hygrometer — An instrument used to determine the amount
of mois­ture in the air.
hygroscopic material — A material such as silica gel that
absorbs moisture from the air.
hypergolic — A self-igniting reaction upon contact of the
components, without the presence of a spark.
hypersonic — A regime of flight where speeds of Mach
5.00 are exceeded.
hypersonic engine — An engine designed to operate in the
speed range above Mach 5. One possibility is the variable
cycle engine. This engine functions as a turbojet up to
perhaps Mach 3, then as doors close off the compressor
inlet, it operates from a ramjet-type duct surrounding the
engine.
hypersonic flight — Flight at speeds of Mach 5 or above.
hypersonic flow — Flow at very high supersonic speeds.
Mach 5 or above.
hyperventilation — Breathing at such an excess rate that
the normal amount of carbon dioxide is depleted from
the blood.
hypotenuse — The side of a 90° (right) triangle opposite
the right angle.
hypoxia — A lack of sufficient oxygen reaching the body
tissues.
hysteresis loop — A graph of the magnetic characteristics
of a material.

165

10001930-002_AviationDictionary_2012_BOOK.indb 165 3/27/2012 9:38:12 AM

 I • idle thrust

I anti-icing equipment is not utilized unless encountered

for an extended period of time (over 1 hour).
I beam — A structural beam Light – The rate of accumulation may create a problem
constructed of extruded metal if flight is prolonged in this environment (over 1 hour).
or wood, whose cross section Occasional use of deicing/anti-icing equipment
resembles the letter I. removes/prevents accumulation. It does not present a
I say again — During problem if the deicing/anti-icing equipment is used.
communications, this indicates Moderate – The rate of accumulation is such that even
that the message will be repeated. short encounters become potentially hazardous and
ice — The solid state or condition of water when the use of deicing / anti-icing equipment or flight diversion
tempera­ture is 0°C or 32°F. is necessary.
ice crystal process — The process by which cloud particles Severe – The rate of accumulation is such that deicing/
grow to precipitation size. This can only occur where ice anti-icing equipment fails to reduce or control the
crystals and water droplets coexist and the temperature hazard. Immediate flight diversion is necessary.
is below 0º C. ideal cycle — A cycle in which no pressure loss occurs
ice crystals — Small ice particles that float in the air in clear across the combus­tion section. However, this is not
cold weather. Also referred to as ice needles. practical for the gas turbine where a slight pressure loss
is needed for correct cooling air.
ice fog — Fog composed of minute suspended par­ticles of
ice; occurs at very low temperatures. ident — A request for a pilot to activate the aircraft
transponder identification feature. This will help the
ice light — A light mounted on an aircraft in such a way that controller to confirm an aircraft identity or to identify an
it shines on the leading edge of the wing, allowing the aircraft.
pilot to see the buildup of ice on the wing at night.
ident feature — The special feature in the Air Traffic
ice needles — Small ice particles that float in the air in clear Control Radar Beacon System (ATCRBS) equipment. It
cold weather. Also referred to as ice crystals. is used to immediately distinguish one displayed beacon
ice pellets — Small, transparent or translucent, round or target from other beacon targets. See also ident.
irregularly shaped pellets of ice. They can be hard grains Identification, Friend or Foe (IFF) — A transponder
that rebound on striking a hard surface or pellets of snow feature that allows a classified code to be set into selected
encased in ice. transponders to identify friendly aircraft to interrogating
icebox rivet — Rivets made of 2024 or 2017 aluminum units.
alloy, which are too hard to drive unless they are in a identification symbol — A symbol used in an aircraft
softened condition. These rivets must be heat‑treated, drawing to correlate a specific item with its description in
quenched, and held in a subzero icebox until they are the bill of materials or the revision block.
driven.
idiot light — A slang term for warning lights that are used
ice-up — A condition in flight in which ice forms on the instead of digital or analog instruments to indicate the
aircraft structure. condition or pressure of a system.
icing — The accumulation of airframe ice. idle — In gas turbine engines, a percent rpm setting, the
a. Types of icing are: value of which changes from engine to engine. It is the
lowest engine operating speed authorized.
Rime Ice — Rough, milky, opaque ice formed by the
instantaneous freezing of small supercooled water idle cut off — That position of the mixture control in which
droplets. fuel is prevented from flowing from the metering system
into the engine.
Clear Ice — A glossy, clear, or translucent ice formed
by the relatively slow freezing of large supercooled idle mixture — A fuel‑air mixture used by an aircraft engine
water droplets. to provide proper operation at the idle RPM.
Mixed — A mixture of clear ice and rime ice. idle speed — The RPM of an aircraft engine when the
throttle or power control lever is fully closed.
b. Intensity of ice includes:
idle thrust — The jet thrust obtained with the engine power
Trace — Ice becomes perceptible. Rate of accumulation control lever set at the stop for the least thrust (idle stop)
is slightly greater than the rate of sublimation. Deicing/ position.

166

10001930-002_AviationDictionary_2012_BOOK.indb 166 3/27/2012 9:38:13 AM

 idler gear • ILS categories

idler gear — A gear used in a gear train to drive another the symbol used to alert the pilot to nonstandard takeoff
gear in a reverse direction of rotation without changing minimums and departure procedures. When departing
the speed of rotation and without adding to or taking IFR from such airports, or from any airports where there
away power from the gear train. are no departure procedures, DPs, or ATC facilities
available, pilots should advise ATC of any departure
idler pulley — The idler pulley changes angular
limitations. Controllers may query a pilot to determine
relationships between pulleys but does not change the
acceptable departure directions, turns, or headings after
direction of rotation of either pulley. An idler pulley is
takeoff. Pilots should be familiar with the departure
also used to adjust the tension on the belt that joins a
procedures and must assure that their aircraft can meet or
drive pulley with a driven pulley.
exceed any specified climb gradients.
idling current — A low output or operating current that
igniter — The electrical device used to provide the spark
flows in an electronic circuit when there is no input signal
for starting combustion in a turbine engine. Some igniters
or output signal.
resemble spark plugs while others, called glow plugs,
if no transmission received for (time) — Used by ATC have a coil of resistance wire that glows red hot when
in radar approaches to prefix procedures that should be electrical current flows through the coil.
followed by the pilot in event of lost communications.
igniter plug — In gas turbine engines, an electrical sparking
IF/IAWP — Intermediate Fix/Initial Approach Waypoint. device used to start the burning of the fuel-air mixture in
The waypoint where the final approach course of a T a combustor.
approach meets the crossbar of the T. When designated
ignition — The process whereby the fuel‑air mixture in
(in conjunction with a TAA) this waypoint will be used
either a turbine or reciprocating aircraft engine is ignited.
as an IAWP when approaching the airport from certain
directions, and as an IFWP when beginning the approach ignition harness — The complete set of wires that carry
from another IAWP. high‑voltage current from the magneto to the spark plugs.
IFR aircraft — An aircraft conducting flight in accordance ignition timing — The timing of the fuel‑air mixture’s
with instrument flight rules. ignition in the cylinders of a reciprocating engine that
ensures the mixture will be burning before the piston
IFR conditions — Weather conditions below the minimum
reaches the top of its stroke and the maximum pressure
for flight under visual flight rules.
will be produced in the cylinder as the piston starts
IFR departure procedure — See IFR takeoff minimums downward.
and departure procedures.
illumination — The light output of a light source.
IFR flight — See IFR aircraft.
illustrated parts catalog (IPC) — A required document
IFR landing minimums — See landing minimums. produced by a manufacturer. It has an exploded view of
the parts and the part numbers for identification. It does
IFR military training routes (IR) — Routes used by the
not contain approved data.
Department of Defense and associated Reserve and Air
Guard units for the purpose of conducting low-altitude illustrated parts list (IPL) — An exploded‑view drawing
navigation and tactical training in both IFR and VFR in­cluded in a service manual showing every part of a
weather conditions below 10,000 feet MSL at airspeeds component, along with its proper name, part number, and
in excess of 250 knots IAS. [Jeppesen does not chart number required for assembly. This is FAA‑approved
these routes.] data and using parts not in­cluded in this list jeopardizes
the airworthiness of the component.
IFR over-the-top — With respect to the operation of
aircraft, means the operation of an aircraft over-the-top illustrated talk — An oral presentation where the speaker
on an IFR flight plan when cleared by air traffic control to relies heavily on visual aids to convey ideas to the
maintain “VFR conditions” or “VFR conditions on top.” listeners.
IFR takeoff minimums and departure procedures — ILS categories —
Federal Aviation Regulations, Part 91, prescribes standard
a. ILS Category I – An ILS approach procedure which
takeoff rules for certain civil users. At some airports,
provides for approach to a height above touchdown of
obstructions or other factors require the establishment of
not less than 200 feet and with runway visual range of
nonstandard takeoff minimums, departure procedures, or
not less than 1,800 feet.
both, to assist pilots in avoiding obstacles during climb
to the minimum enroute altitude. Those airports are listed b. ILS Category II – An ILS approach procedure which
in NOS/DOD Instrument Approach Charts (IAPs) under provides for approach to a height above touchdown of
a section entitled “IFR Takeoff Minimums and Departure not less than 100 feet and with runway visual range of
Procedures.” The NOS/DOD IAP chart legend illustrates not less than 1,200 feet.

167

10001930-002_AviationDictionary_2012_BOOK.indb 167 3/27/2012 9:38:13 AM

 ILS categories (ICAO) • impedance matching transformer

c. ILS Category III – I’M SAFE checklist — Personal Checklist ― I’m

physically and mentally safe to fly; not being impaired
1. IIIA – An ILS approach procedure which provides
by illness, medication, stress, alcohol, fatigue, or eating.
for approach without a decision height minimum
and with runway visual range of not less than 700 image frequency — The image produced in a super
feet. heterodyne receiver when an unwanted signal of a
specific frequency is mixed with the oscillator frequency,
2. IIIB – An ILS approach procedure which provides
it produces an intermediate frequency equal to the
for approach without a decision height minimum
intermediate frequency of the desired input frequency.
and with runway visual range of not less than 150
feet. immediately — Used by ATC or pilots when such action
compliance is required to avoid an imminent situation.
3. IIIC – An ILS approach procedure which provides
for approach without a decision height minimum immersion heater — An electrical heater used to heat
and without runway visual range minimum. liquids by immersing the heater in the liquid to keep it
warm. Insures adequate temperature and flow during cold
ILS categories (ICAO) —
weather operations.
a. ILS Category I – An ILS approach procedure which
immersion-type oil heater — An electrical heater
provides for an approach to a decision height not
immersed in the engine oil reservoir to keep the oil warm
lower than 200 feet (60m) and a visibility not less than
when the engine is not operating and ensure an adequate
2400 feet (800m) or a runway visual range not less
flow of lubricant for starting in extremely cold weather.
than 1800 feet (550m).
immiscible — Liquids that do not mix with each other such
b. ILS Category II (Special authorization required) –
as oil and water.
An ILS approach procedure which provides for an
approach to a decision height lower than 200 feet impact area — That portion of a damaged structure that has
(60m) but not lower than 100 feet (30m) and a runway received the majority of the damage from a collision or
visual range not less than 1200 feet (350m). other impact.
c. ILS Category III (Special authorization required) – impact extrusion — Metal forming in which hard metal is
forced through a die by striking it with a hard blow.
1. IIIA – An ILS approach procedure which provides
for approach with either a decision height lower impact ice — Ice that forms on the wings and control
than 100 feet (30m) or with no decision height and surfaces or on the carburetor heat valve, the walls of the
with a runway visual range of not less than 700 feet air scoop, or the carburetor units during flight. Impact ice
(200m). collecting on the metering elements of the carburetor can
upset fuel metering or stop carburetor fuel flow.
2. IIIB – An ILS approach procedure which provides
for approach with either a decision height lower impact pressure — In pitot-static systems, the difference
than 50 feet (15m) or with no decision height and between pitot pressure and static pressure.
with a runway visual range of less than 700 feet
impact test — A test to determine the energy absorbed in
(200m) but not less than 150 feet (50m).
fracturing a test bar at high velocity. The test may be in
3. IIIC – An ILS approach procedure which provides tension or in bending, or it may properly be a notch test if
for approach with no decision height and no runway a notch is present, creating multi­-axial stresses.
visual range limitations.
impact wrench — A power wrench, usually air‑driven, used
d. Some areas require special authorization for ILS to spin nuts onto bolts. Its torque forces are in a series
Category I approaches. In these areas, an additional of blows or impacts. Because of the uneven torque it
category of approach called ILS is available without produces, it should not be used for any threaded fastener
special authorization. These ILS approaches have where the amount of torque is critical.
minimums higher than a decision height of 200 feet
impedance coupling — The use in electronics of an
and a runway visual range value of 2600 feet. Jeppesen
impedance matching transformer to connect a power
approach charts, at these locations, will have a notation
source with a load that has a different impedance.
in the chart heading or in the minimum box titles.
impedance matching — The matching of the impedance
ILS PRM approach — An instrument landing system (ILS)
of a source of electrical power with the impedance of the
approach conducted to parallel runways whose extended
load that uses the power. Allows maximum transfer of
centerlines are separated by less than 4,300 feet and the
power to occur.
parallel runways have a Precision Runway Monitoring
(PRM) system that permits simultaneous independent impedance matching transformer — An electronic device
ILS approaches. used to connect a load and a source of electrical power

168

10001930-002_AviationDictionary_2012_BOOK.indb 168 3/27/2012 9:38:13 AM

 impedance triangle • inclusions

that differ in their impedance. It consists of a transformer impulsive — A learning style where a student makes a quick
with a primary winding that matches the impedance of assessment and then decides to take action. Impulsive
the source and a secondary winding that matches the students may not read each question or all of the answer
load. choices entirely. As a result, they tend to select the first
choice that appears correct.
impedance triangle — The graphical repre­sentation of
resistance, reactance, and impedance in an electrical impurities — 1. Undesired foreign objects in a fluid. 2. A
circuit. Resistance in ohms is drawn as the horizontal base chemical element such as arsenic or phosphorus that is
of the triangle and reactance in ohms is drawn vertically added to silicon or germanium to give them some desired
at 90 degrees to the resistance. Impedance in ohms is electrical characteristic.
the hypotenuse of the triangle. The angle between it and
in ground effect (IGE) hover — In rotorcraft, hovering
horizontal is called the “phase angle.”
close to the surface (usually less than one rotor diameter
impedance (Z) — The vector sum of the opposition to distance above the surface) under the influence of ground
the flow of AC caused by circuit resistance, capacitive effect.
reactance, and inductive reactance.
in phase — A condition in an electrical circuit where the
impeller — A vaned disc that picks up and accelerates the voltage and current rise and fall together. In an AC circuit,
air out­wardly to increase the pressure in a supercharger the two pass through 0° and 180° at the same time, going
for a reciprocating engine, or to provide the pressurized in the same direction.
air for a centrifugal‑type turbine engine. inactive aircraft — An aircraft that is no longer operational.
impingement starting — A turbine engine starting process inboard — Toward the center of the aircraft.
requiring no engine­ mounted starter. Air from a source
separate from the engine to be started is directed onto the incandescent — Glowing because of intense heat.
turbine wheel(s) to cause engine rotation for starting and incandescent lamp — An electric lamp that produces light
then the air source is removed. by a white ­hot filament enclosed in a glass bulb from
implode — To burst inward. The reverse of explosion. which the air has been removed and replaced with an
inert gas.
impregnate — In reinforcing plastics, to saturate the
reinforcement with a resin. incerfa (uncertainty phase) [ICAO] — A situation
wherein uncertainty exists as to the safety of an aircraft
impulse — A change in momentum caused by a surge or and its occupants.
pulse of energy.
inches of mercury (in. Hg) — A measurement of air
impulse coupling — A spring‑loaded coupling between pressure., normally used for atmospheric pressures. 1 in.
a magneto and its drive gear that causes the magneto Hg. is equal to approximately l/2 PSI.
to produce a hot and late spark for starting the engine.
When the engine is being turned over slowly, the magnet inches per second (ips)
is restrained by stops, and the spring is wound. At the — A velocity measurement. Used in electronic balancing.
proper time for the starting spark to occur, the spring is
released and the magnet is spun, producing a hot, late incidence board — A device used to measure the angle of
spark. When the engine starts, centrifugal force holds the incidence of a wing.
coupling engaged so that it acts as a solid unit. incipient stage — The time when frontal cyclone
impulse turbine — A development begins, pressure falls at some point along
stator vane and rotor the original stationary front and counterclockwise
blade arrange­ment circulation is generated.
whereby the vanes form inclined plane — A machine used to gain a mechanical
conver­gent ducts and advantage. It consists of a flat surface positioned at an
the blades form straight angle with the horizon.
ducts. The rotor is then
turned by impulse inclinometer — An instrument consisting of a curved glass
as gases impinge on tube, hous­ing a glass ball, and damped with a fluid similar
the blades. A design to kerosene. It may be used to indicate inclination, as a
common to turbine driven accessories such as air starters. level, or, as used in the turn and slip indicator, to show the
relationship between gravity and centrifugal force in a turn.
impulse-reaction turbine — A stator vane and rotor blade
arrangement whereby the base area is an impulse design inclusions — The impurities con­tained in a material.
and the tip is a reaction design. This design is common
to flight engines.

169

10001930-002_AviationDictionary_2012_BOOK.indb 169 3/27/2012 9:38:13 AM

 incompressible fluids • inductive kick

incompressible fluids — Any liquid such as oil or water. inductance — The property of a conductor that causes an
Liquids cannot be compressed but can be used in a electromo­tive force or voltage to be generated when lines
regulated fluid power system such as a hydraulic system of magnetic force cut across it.
to gain a mechanical advantage.
inductance bridge — An electronic device used to
Inconel — A chromium‑iron alloy similar to stainless steel, accurately measure an unknown inductance by comparing
but which cannot be hardened by heat treatment. it to a known inductance. An inductance bridge is similar
to the Wheatstone bridge used to measure resistance.
increase speed to (speed) — See speed adjustment.
inductance coil — A coil designed to introduce inductance
incrementally — Moving in steps rather than in continuous
into a circuit.
motion.
induction compass — A direction indicator that derives its
indefinite ceiling — A ceiling classification denoting
signal from the lines of flux of the Earth cutting across
vertical visibility into a surface based obscuration.
the windings of the flux valve mounted in the airplane.
indicated air temperature (IAT) — Is the temperature
induction furnace — An electric furnace that melts metal
of the air as measured by the temperature probe on the
by the induction of high‑frequency electromagnetic
outside of the aircraft.
energy.
indicated airspeed — The airspeed as indicated on the
induction heating — A method of heating a conducting
airspeed indicator with no corrections applied.
material by passing high frequency alternating current
indicated altitude — The altitude shown by an altimeter set through it.
to the current altimeter setting.
induction icing — The formation of ice on aircraft air
indicated horsepower (IHP) — The total horsepower induction ports and air filters.
developed in the engine. It is the sum of the brake
induction motor — An AC electric motor that has the AC
horsepower delivered to the propeller shaft and the
line voltage connected across stationary windings in the
friction horsepower required to drive the engine.
motor housing. Current induced into the rotor causes a
indicated mean effective pressure (IMEP) — The average magnetic field that reacts with the field of the stator, and
measured pressure inside the cylinder of an engine during this reaction causes the rotor to turn.
the power stroke. Expressed in pounds per square inch.
induction period — The time period after catalyzed
indicating fuse — A fuse assembly that has a small neon material is mixed in which the material is allowed to
light installed in parallel with the fuse that shows when begin curing before being sprayed onto a surface.
the fuse has blown.
induction system — The complete system of air passages
indicating instrument — A device such as a gauge, dial, or in a reciprocating engine, from the air filter inlet to the
pointer that measures or records and also visibly indicates. intake valve of the cylinder.
An apparatus that shows fluid pres­sures, temperatures, or
induction system fire — A fire in the carburetor or air
quantities.
inlet system of a reciprocating engine usually caused by
indicator — See indicating instrument. flooding and a backfire.
indirect light — Light reflected onto a surface from another induction vibrator — A coil and set of contact points
surface. that produce pulsating DC from straight DC. Pulsating
DC can be used in the primary winding of a magneto to
induced current — The electrical current that is generated
produce a high voltage in the secondary winding.
in a conductor when it is crossed by magnetic lines of flux.
induction welding — A method of welding in which the
induced drag — That part of the total drag that is created
metal is melted by the induction of high‑frequency
by the production of lift.
electromagnetic energy.
induced flow — In rotorcraft, the component of air flowing
inductive circuit — An AC circuit in which the capacitive
vertically through the rotor system resulting from the
reactance lags behind the inductive reactance.
production of lift.
inductive kick — A slang term used for inductive reactance
induced voltage — The voltage generated by a conductor
in a coil of wire. It is a high voltage produced across a
when lines of magnetic flux cut across it.
coil when current stops flowing through the coil. When
inducer — The center inlet portion of a centrifugal impeller, current flows through a coil, a magnetic field is set up
sometimes made of a different, harder metal than the around each of the turns of wire in the coil. But when
impeller for FOD protection. the current stops flowing, the magnetic field collapses

170

10001930-002_AviationDictionary_2012_BOOK.indb 170 3/27/2012 9:38:13 AM

 inductive reactance • inhibitive film

across the coil producing many times the voltage that energy. The drive motor is disengaged and the work
was originally in the coil. This high voltage is called an pieces are forced together by the friction welding force.
inductive kick. This causes the faying surfaces to rub together under
pressure. The kinetic energy stored in the rotating
inductive reactance — An opposition to the flow of AC
flywheel is dissipated as heat through friction at the weld
caused by the generation of an induced voltage whose
interface as the flywheel speed decreases.
polarity is opposite to that of the voltage that created it.

inertial navigation — Navigation by means of a
inductive time constant — A measurement of the amount
self-contained, airborne device that senses changes of
of time needed for the current induced into an inductive
direction or acceleration and automatically corrects for
circuit to reach 63.2% of its maximum value.
deviations in a planned course.
inductive tuning — A method of selecting or changing the
inertial navigation system — An RNAV system which is a
resonance of a radio frequency circuit by changing the
form of self-contained navigation.
inductance. The circuit is tuned by rotating a tuning coil
that increases or decreases the inductance. inflammable — Able to burn and support combustion;
easily inflamed. A word that has been replaced with
inductor — A coil or other device used to introduce
“flammable” to avoid confusion.
inductance into a circuit.
inflight refueling — A procedure used by the military to
industrial diamond — A diamond used as a cutting tool.
transfer fuel from one aircraft to another during flight.
inert agent — A fire extinguishing agent that extinguishes
inflight weather advisory — See weather advisory.
fire by exclud­ing the oxygen from its surface.
informal lecture — A lecture style that lends itself to active
inert gas — A gas such as argon or helium that does not
student participation.
form other chemical compounds when it comes into
contact with other elements. information request — A request originated by an FSS for
information concerning an overdue VFR aircraft.
inert gas arc welding — A process of arc welding in which
the arc is submerged in an envelope of an inert gas such infrared guidance — A guidance system used on
as argon to exclude the oxygen from the molten metal heat-seeking missiles to hone in on the infra-red signature
and prevent the formation of oxides. of a target.
inertia — The tendency of a mass at rest to remain at rest, infrared (IR) — Electromagnetic radiation having
or if in motion to remain in motion, unless acted upon by wavelengths longer than red light.
some external force.
infrared lamp — An incandescent lamp that produces light
inertia anti-icer — A movable vane in the induction air ener­gy in the infrared range.
system that, in the extended position, causes the velocity
infrared radiation — Electromagnetic radiation having
of the incoming air to increase and change direction,
wavelengths longer than red light and shorter than
thereby discharging the heavier ice overboard while
microwaves.
directing the lighter, ice‑free air into the engine plenum.
infrasonic frequencies — Frequencies below the audio
inertia force — A force due to inertia, or the resistance to
frequency range. Also referred to as subsonic frequencies.
acceleration or deceleration.
ingest — To pull in something such as air or to ingest FOD
inertia starter — A starter for large reciprocating engines
in a gas turbine engine.
that uses the energy stored in a flywheel, spinning at a
high rate of speed, to turn the engine for starting. ingot — A large cast bar of metal, as poured, with no
working.
inertia switch — An electrical switch built into an
emergency locator transmitter (ELT). Designed to close inherent stability — That built‑in characteristic of an
and start the ELT when there is a sudden change in its aircraft that causes it, when disturbed from straight and
velocity. level flight, to return to straight and level flight.
inertia welding — An advanced technology process of inhibited sealer — A material used to exclude moisture and
welding through use of high speed rubbing friction. air from a honeycomb repair. In addition to sealing, it
Developed to join super alloys that are difficult to weld inhibits the formation of corrosion.
with traditional methods. In inertia welding, one of the
inhibitive film — A film of material on the surface of a
work pieces is connected to a flywheel and the other is
metal that inhibits or retards the formation of corrosion.
restrained from rotating. The flywheel is accelerated to
It does this by providing an ionized surface that will not
a predetermined rotational speed, storing the required
allow the formation of corrosive salts on the metal.

171

10001930-002_AviationDictionary_2012_BOOK.indb 171 3/27/2012 9:38:13 AM

 inhibitor • inner marker

inhibitor — 1. An agent added to a resin to retard its curing inlet gearbox — An auxiliary gearbox driven from and
and increase its shelf life. 2. Any substance that slows or located in front of the compressor in the engine inlet area.
prevents a reaction. Not all engines are configured with this gearbox.
initial approach fix (IAF) — The fixes depicted on inlet guide vane — In gas turbine engines, stationary airfoil
instrument approach procedure charts that identify the which precedes the first stage compressor rotor blades.
beginning of the initial approach segment(s). These guide vanes form straight through passages and
are present to direct air onto the blades at the optimum
initial approach segment — The segment between the
angle.
initial approach fix and the intermediate fix or the point
where the aircraft is established on the intermediate inlet particle separator — An inlet device on some
course or final approach course. turbine powered rotorcraft that prevents sand and other
FOD-causing debris from entering the engine. On some
initial approach segment [ICAO] — That segment of separators, the trap has to be cleaned while, on others, the
an instrument approach procedure between the initial debris is directed overboard.
approach fix and the intermediate approach fix, or where
applicable, the final approach fix or point. inlet pressure (Pt2) — The pressure total taken in the
engine inlet as a measure of air density, a parameter sent
initial climb area (ICA) — The ICA is the segment of the
to the fuel control for fuel scheduling purposes.
departure procedure that starts at the departure end of the
runway and proceeds along the runway centerline extended inlet screen — An anti-FOD screen used on turbine powered
to allow the aircraft sufficient distance to reach an altitude rotorcraft and most stationary turbines. Not generally
of 400 feet above departure end runway elevation, and used on other aircraft installations due to icing and other
to allow the establishment of positive course guidance aerodynamic problems that can result.
by all navigation systems. A typical straight departure
inlet spike — A moveable inlet device used to control inlet
ICA extends 2-5 nautical miles from the departure end of
geometry and shock waves. This inlet design diffuses
runway along the runway centerline extended. It is 500
supersonic airflow and reduces it to subsonic speed for
feet wide each side of the runway centerline at departure
entry into the engine.
end of runway, then splays out at 15º.
inlet strut assembly — The spoke‑like stationary airfoils
initial lift — One of the two requirements for the production
that are part of the inlet case. They are used to support
of a thunderstorm, the other is potential instability.
the front bearing housing and provide passageways for
initialization — To facilitate the start-up of a program. oil and air line routing from outside the engine to inside.
In computers it is the start-up of computer language
instructions that the computer understands in order to inlet temperature (Tt2) — The temperature signal taken in
operate as intended. the en­gine inlet to measure air density. Used by the fuel
control unit as a fuel scheduling parameter.
injection molding — A method of forming thermoplastics
by forcing resin, under high pressure, into a mold and in-line engine — An engine with all of the cylinders in a
allowing it to harden. single line. The crankcase may be located either above or
below the cylinders. If it is above, it is called an inverted
injection pump — A high pressure fuel pump used in a in‑line engine.
reciprocat­ing engine fuel injection system. Fuel is
pumped, under high pres­sure, into the combustion in-line reciprocating engine — An engine in which all of
chamber of the engine where it is atomized and ignites as the cylinders are arranged in a straight line, with each
it leaves the injector nozzle. cylinder piston connected to a separate throw of the
crankshaft.
inland navigation facility — A navigation aid on a North
American Route at which the common route and/ or the inner exhaust cone — The conical‑shaped portion of a
noncommon route begins or ends. turbine engine exhaust system that is used to produce
the proper area increase for the gases as they leave the
inlet buzz — An audible sound that sometimes occurs in engine.
inlets of supersonic aircraft when shock waves alternately
move in and out. This condition appears when design inner liner — Refers to can‑annular combustion liner; the
speeds are exceeded. innermost section.
inlet case — The front compressor supporting member, inner marker — A marker beacon used with an ILS (CAT
usually one single casting. II) precision approach located between the middle marker
and the end of the ILS runway, transmitting a radiation
inlet duct — That portion of the structure of a pattern keyed at six dots per second and indicating to the
turbine‑powered aircraft that directs the air into the pilot, both aurally and visually, that he is at the designated
engine compressor. decision height (DH), normally 100 feet above the

172

10001930-002_AviationDictionary_2012_BOOK.indb 172 3/27/2012 9:38:13 AM

 inner marker beacon • instrument approach procedure

touchdown zone elevation, on the ILS CAT II approach. Inspection Authorization (IA) — An authorization issued
It also marks progress during a CAT III approach. by the FAA to experienced A&P technicians meeting
certain requirements. This authorization allows them
inner marker beacon — See inner marker.
to return aircraft to service after annual inspections or
inner tube — An air‑tight rubber tube that has a stem for certain major repairs.
inflating it. Used inside a pneumatic tire to hold the air
inspection door — A small door or hinged plate on the
that inflates the tire.
surface of an aircraft structure that can be opened for
inoperative — Not working. inspecting the interior of the aircraft.
inoperative components — The lowest landing minimums inspection hole — A hole in the skin of an aircraft, closed
on an approach are authorized when all components with an inspection plate that is held in place with screws
and visual aids are operating. If some components are on metal skins and with friction clamps on fabric skins.
inoperative, higher landing minimums may be required. The hole can be opened for inspection or repair inside the
If more than one component is inoperative, apply only structure.
the greatest increase in altitude and/or visibility required
inspection plate — A cover over an inspection hole that is
by the failure of a single component.
held in place with screws on metal skins and with friction
inoperative equipment — Equipment in the aircraft that is clamps on fabric skins.
not functional.
instability — 1. The characteristic of an aircraft that causes
input capacitance — Capacitance measured across the it, when dis­turbed from a condition of level flight, to
input terminals of a circuit. depart further from this condition. 2. In meteorology, a
general term to indicate various states of the atmosphere
input circuit — A circuit that provides appropriate power
in which spontaneous convection will occur when
and impedance matching between an input device and
prescribed criteria are met; indicative of turbu­lence. See
the signal source.
also absolute instability, conditionally unstable air.
input impedance — Impedance measured across the input
installation drawing — A drawing that shows all of the
terminals of a circuit.
parts in their proper relationship for installation.
input transformer — An electronic device that isolates
installation error — An error in pitot static instruments
a signal source from an input device and matches the
(the airspeed indicator, the altimeter, and the rate of
impedance. See also impedance matching transformer.
climb indicator) caused by a change in alignment of the
inrush current — The high current that flows in an electrical static pressure port with the airflow as the aircraft’s angle
machine or circuit when the switch is first closed. of attack changes.
inside caliper — A measuring instrument with two instantaneous rate of climb indicator (IVSI) — A vertical
adjustable legs used to determine an inside measurement. speed indicator that uses internal accelerometer‑type
Once the distance has been established, the actual air pumps to overcome the inherent lag of this type of
measurement is made with a steel scale, a micrometer, or instrument and to provide an instantaneous indication of
a vernier caliper. altitude changes due to pitch attitude changes.
inside diameter — The diameter measured from one inside instructional aids — Devices that assist an instructor in
surface, through center, and to the opposite inside surface. the teaching-learning process. They are supplementary
training devices and are not self-supporting.
inside micrometer — -A micrometer caliper used to
measure the inside diameter of a circular object such as instrument — A device using an internal mechanism to
a cylinder bore. It measures in increments of l/1,000” show visually or aurally the attitude, altitude, or operation
or smaller. It works on the same principle as an outside of an aircraft or aircraft part. It includes electronic devices
micrometer caliper. for automatically controlling an aircraft in flight.
insight — The grouping of perceptions into meaningful instrument approach — See instrument approach
wholes. Creating insight is one of the instructor’s major procedure.
responsibilities.
instrument approach procedure — A series of
insolation — Solar radiation received at the surface of the predetermined maneuvers for the orderly transfer of
Earth. an aircraft under instrument flight conditions from
the beginning of the initial approach to a landing or to
inspect — To determine the condition of something by
a point from which a landing may be made visually.
sight, feel, measurement, or other means.
It is prescribed and approved for a specific airport by
competent authority.

173

10001930-002_AviationDictionary_2012_BOOK.indb 173 3/27/2012 9:38:13 AM

 instrument approach procedure [ICAO] • instrumentation

a. U.S. civil standard instrument approach procedures Instrument Flight Rules (IFR) flight — Aircraft flight
are approved by the FAA as prescribed under FAR 97, con­ducted entirely by reference to instruments and radio
and are available for public use. navigation.
b. U.S. military standard instrument approach procedures instrument ground instructor — A person certificated by
are approved and published by the Department of the FAA who is authorized to provide the following: ground
Defense. training in the aeronautical knowledge areas required for
issuance of an instrument rating under Part 61; ground
c. Special instrument approach procedures are approved
training required for an instrument proficiency check;
by the FAA for individual operators, but are not
and a recommendation for a knowledge test required for
published in FAR 97 for public use.
issuance of an instrument rating under Part 61.
instrument approach procedure [ICAO] — A series
instrument interpretation — One of the fundamental skills
of predetermined maneuvers by reference to flight
of basic attitude instrument flying. The three fundamental
instruments with specified protection from obstacles
skills include: instrument cross-check, instrument
from the initial approach fix, or where applicable, from
interpretation, and aircraft control. Interpretation involves
the beginning of a defined arrival route to a point from
an awareness of the instrument indications that represent
which a landing can be completed and thereafter, if a
the desired pitch and bank attitudes for the aircraft.
landing is not completed, to a position at which holding
or enroute obstacle clearance criteria apply. instrument landing system (ILS) — A precision instrument
approach system that consists of the following electronic
instrument approach procedures charts — Portray
components and visual aids:
the aeronautical data which is required to execute an
instrument approach to an airport. These charts depict a. Localizer
the procedures, including all related data, and the airport
b. Glide Slope
diagram. Each procedure is des­ignated for use with a
specific type of electronic nav­igation system including c. Outer Marker
NDB, TACAN, VOR, ILS/ MLS, and RNAV. These
d. Middle Marker
charts are identified by the type of navigational aid(s)
which provide final approach guidance. e. Approach Lights
instrument approach waypoint — Fixes used in defining instrument meteorological conditions (IMC) —
RNAV IAPs, including the feeder waypoint (FWP), Meteorological conditions expressed in terms of
the initial approach waypoint (IAWP), the intermediate visibility, distance from cloud, and ceiling less than the
waypoint (IWP), the final approach waypoint (FAWP), minima specified for visual meteorological conditions.
the RWY WP, and the APT WP, when required.
instrument panel — A panel, typically located in front of
instrument departure procedure (DP) — A preplanned the pilot, that holds all of the indicating instruments that
instrument flight rule (IFR) air traffic control departure show the condition of the aircraft flight and mechanical
procedure printed for pilot use in graphic and/or textual systems.
form. DP’s provide transition from the terminal to the
instrument proficiency check — An evaluation ride based
appropriate enroute structure.
on the instrument rating practical test standard. Required
instrument departure procedure (DP) charts — Charts to regain instrument flying privileges when the privileges
designed to expedite clearance delivery and to facilitate have expired due to lack of currency.
transition between takeoff and enroute operations. Each
instrument runway — A runway equipped with electronic
DP is presented as a separate chart and may serve a single
and visual navigation aids for which a precision or
airport or more than one airport in a given geographical
nonprecision approach procedure having straight-in
location.
landing minimums has been approved.
instrument flight rules (IFR) — Rules that govern the
instrument shunt — An electrical shunt used with an
procedure for conducting flight in instrument weather
ammeter to make it possible for it to measure current.
conditions. When weather conditions are below the
minimums prescribed for VFR, only instrument‑rated instrument training — That time in which instrument
pilots may fly in accordance with IFR. training is received from an authorized instructor under
actual or simulated instrument conditions.
Instrument Flight Rules (IFR) conditions — Weather
conditions considered unsafe for flight under visual flight instrumentation — The installation or use of indicating
rules. instruments.

174

10001930-002_AviationDictionary_2012_BOOK.indb 174 3/27/2012 9:38:13 AM

 insulated gate field effect transistor (IGFET) • interface

insulated gate field effect transistor (IGFET) — A outside visual references. Handling of the controls is the
semiconductor whose gate is insulated from the channel. same regardless of whether flight instruments or outside
The IGFET is now called a MOSFET (Metal Oxide Field references are being used.
Effect Transistor). The MOSFET has an extremely large
integrating circuit — A network circuit whose output is
input impedance. Because the insulating oxide layer is
proportional to the sum of its instantaneous inputs.
extremely thin, the MOSFET is susceptible to destruction
by electrostatic charges. Special precautions are necessary integrity — The ability of a system to provide timely
when handling or transporting MOS devices. warnings to users when the system should not be used
for navigation.
insulating electrical tape — A flexible, adhesive‑backed
tape made of a polyvinylchloride material used as intensity — A principle of learning where a dramatic or
insulation over wire terminals and wire splices. exciting learning experience is likely to be remembered
longer than a boring experience. Students experiencing
insulation — A heavy material used in an aircraft to prevent
the real thing will learn more than when they are merely
the conduction of heat into or out of any of its operating
told about the real thing.
components.
intensity control — A cathode-ray tube control that meters
insulation blanket — 1. A layer of fireproof insulating
the quan­tity of electrons in the beam that strikes the
material used to keep the heat of a jet engine tail pipe
phosphores­cent screen inside the cathode=ray tube. The
from radiating into the engine compartment. 2. Any
more electrons that strike the screen, the brighter the
material such as fiberglass or aluminum used to insulate
display.
against sound, heat, or cold.
interactive video — Software that responds quickly to
insulation grip — A plastic‑covered, thin metal reinforcing
certain choices and commands by the user. A typical
sleeve on a pre-insulated terminal lug that grips the
system consists of a compact disc, computer, and video
insulation of the wire when the lug is crimped, adding
technology.
strength and durability to the installation.
intercom — A communication system within an airplane
insulation resistance — The electrical resistance of an
for the purpose of communicating between flight crew
insulating material separating two conductors.
members or to passengers.
insulation strength — A statement of the electrical
interconnector — A small tube connecting multiple burner
insulating property of a substance. Usually stated as
cans together for the purpose of flame propagation during
the voltage an insulator can withstand without breaking
starting.
down.
intercooler — A devise used to reduce the temperatures
insulator — A material or device used to prevent passage
of the compressed air before it enters the fuel metering
of heat, electricity, or sound from one medium to another.
device. The resulting cooler air has a higher density,
intake valve — A reciprocating engine valve, located in which permits the engine to be operated with a higher
the head of a cylinder, which provides the passage of the power setting.
fuel‑air mixture into the combustion chamber.
intercostal — A longitudinal structure similar to a stringer,
integral fuel tank — A portion of the aircraft structure, but which is attached to a wing rib or fuselage frame and
usually a wing, which is sealed off and used as a fuel ends at an adjacent rib or frame. Intercostals are usually
tank. When a wing is used as an integral fuel tank, it is used to support access doors, equipment, etc.
called a “wet wing.”
intercylinder baffles — Sheet metal air deflectors installed
integrated circuit (IC) — A microminiature circuit between and around air‑cooled cylinders to aid in uniform
incorporated on a very small chip of semiconductor cooling.
material through solid state technology. A number of
interelectrode — The capacitive effect between two
circuit elements such as transistors, diodes, resistors,
elements in an electron tube. At high frequencies, signals
and capacitors are build into the semiconductor chip by
can be fed across the interelectrode capacitance between
means of photography, etching, and diffusion.
the plate and a grid.
integrated engine pressure ratio (IEPR) — Used on some
interelectrode capacitance — The capacitance that exists
turbofans to include fan discharge total pressure and
between two electrodes in an electron tube.
compressor inlet total pressure.
interface — A surface that forms the common boundary
integrated flight instruction — A technique of flight
between two parts of matter such as water interfaces in
instruction where students are taught to perform flight
jet fuel and crystal interfaces in metals.
maneuvers by reference to flight instruments and to

175

10001930-002_AviationDictionary_2012_BOOK.indb 175 3/27/2012 9:38:14 AM

 interference • internal wrenching bolt

interference — 1. A theory of forgetting where a person forgets intermediate position — The position of some movable unit
something because a certain experience overshadows it, or that lies in between the extreme positions of movement.
the learning of similar things has intervened. 2. Barriers to
intermediate turbine temperature (ITT) — The
effective communication that are caused by physiological,
temperature taken usually at a station between the high
environmental, and psychological factors outside the direct and low pressure turbine wheels.
control of the instructor. The instructor must take these
factors into account in order to communicate effectively. Intermediate-Range Ballistic Missile (IRBM) — A
ballistic missile with a range generally between 1,500
interference fit — A fit between two parts in which the part and 3,437 statute miles.
being put into a hole is larger than the hole itself. In order
to fit them together, the hole is expanded by heating and intermittent fault — An occasional condition in which a
the part is shrunk by chilling. After being united, when fault in a system does not occur with consistency.
the two parts reach the same temperature, they will not intermittent load — A load that is not continually on the
separate. The area around the hole is subject to tensile system.
stress and thus vulnerable to stress corrosion.
intermittent‑duty relay — An electrical relay that cannot
intergranular corrosion — The formation of corrosion be energized over long periods of time. This precludes
along the grain boundaries within a metal alloy. their use for master relays or for lighting circuits.
interim summary — An interim summary can be made internal air pressure — Air pressure within a vessel or
immediately after each topic to bring ideas together, container.
create an efficient transition to the next topic, divert
internal baffles — The deflector plates installed inside a
the discussion to another member of the group, or keep
tank or reservoir to prevent the fluid from sloshing or
students on track.
surging in flight.
interlock — An automatic control device that prevents an
internal combustion engine — An engine that obtains its
action until the device that is protected with the interlock power from heat produced by the combustion of a fuel air
is actuated. mixture within the cylinder of the engine.
intermediate approach segment — The segment of an internal control lock — A device used to lock a control
instrument approach procedure between the intermediate surface in place when the airplane is parked. It is actuated
fix or point and the final approach fix. from a control in the cockpit.
intermediate approach segment [ICAO] — That segment internal damage — Damage that occurs inside a part,
of an instrument approach procedure between either the component, or mechanism that is not visible externally.
intermediate approach fix and the final approach fix or
point, or between the end of a reversal, race track or dead internal resistance — The resistance of the battery to the
reckoning track procedure and the final approach fix or flow of current. It causes a voltage drop proportional to
point, as appropriate. the amount of current flow.
internal resources — During pilot operations, these are
intermediate case — The high-pressure compressor outer
sources of information found within the airplane such
case on a turbine engine.
as the pilot’s operating handbook, checklists, aircraft
intermediate compressor — On a triple-spool turbine equipment, aeronautical charts, the instructor, another
engine, the N2 compressor. pilot, and passengers, as well as one’s ingenuity,
knowledge, and skills.
intermediate fix — The fix that identifies the beginning
of the intermediate approach segment of an instrument internal supercharger — A gear-driven centrifugal blower
approach procedure. The fix is not normally identified on in the accessory section of a reciprocating aircraft engine.
the instrument approach chart as an intermediate fix (IF). Used to increase the pressure of the induction system air.

intermediate frequency — A frequency generated in a internal thread — A thread on the internal surface of a
superhetro­dyne receiver equal to the difference between hollow cylinder or cone.
the received radio frequency signal and that produced by internal timing — The timing of the relationship of the
the local oscillator. E‑gap position of the rotating magnet and the opening of
the breaker points in a magneto.
intermediate landing — On the rare occasion that this
option is requested, it should be approved. The departure internal wrenching
center, however, must advise the ATCSCC so that the bolt — A
appropriate delay is carried over and assigned at the high-strength
intermediate airport. An intermediate landing airport steel bolt with its
within the arrival center will not be accepted without head re­cessed to
coordination with and the approval of the ATCSCC. allow the insertion of an Allen wrench.
176

10001930-002_AviationDictionary_2012_BOOK.indb 176 3/27/2012 9:38:14 AM

 international airport • interstage transformer

international airport — Relating to international flight, it candela, degrees Kelvin, hertz, radian, newton, joule,
means: a. An airport of entry which has been designated watt, coulomb, volt, ohm, farad, tesla, and weber.
by the Secretary of Treasury or Commissioner of Customs
Internet — An electronic network which connects
as an international airport for customs service. b. A
computers around the world.
landing rights airport at which specific permission to land
must be obtained from customs authorities in advance interphone system — A communication system normally
of contemplated use. c. Airports designated under the carried out between in‑flight crew members using
Convention on International Civil Aviation as an airport microphones and earphones.
for use by international commercial air transport and/or
international general aviation. interplane struts — Struts that run vertically near the wing
tips be­tween the wings of a biplane.
international airport (ICAO) — Any airport designated
by the Contracting State in whose territory it is situated interpolation — The estimation of an intermediate value
as an airport of entry and departure for international of a quantity that falls between marked values in a series.
air traffic, where the formalities incident to customs, Example: In a measurement of length, with a rule that
immigration, public health, animal and plant quarantine is marked in 1/8’s of an inch, the value falls between
and similar procedures are carried out. 3/8 inch and ½ inch. The estimated (interpolated) value
might then be said to be 7/16 inch.
International Civil Aviation Organization [ICAO] —
A specialized agency of the United Nations whose interpole — A field pole in a compound‑wound electrical
objective is to develop the principles and techniques of generator used to correct for armature reaction. Armature
international air navigation and to foster planning and reaction is the distortion of the generator field flux by the
development of international civil air transport. current flowing in the windings of the armature.

ICAO Regions include: interrib bracing — The reinforcing tape of a fabric‑covered

wing that runs diagonally from the top of one wing rib to
1. AFI African-Indian Ocean Region the bottom of the next throughout a truss‑type wing to
2. CAR Caribbean Region hold the ribs upright and in line until the rib‑stitching is
done.
3. EUR European Region
interrogator — The ground-based surveillance radar
4. MID/ASIA Middle East/Asia Region beacon transmitter-receiver, which normally scans in
5. NAM North American Region synchronism with a primary radar, transmitting discrete
radio signals which repetitiously request all transponders
6. NAT North Atlantic Region on the mode being used to reply. The replies received are
7. PAC Pacific Region mixed with the primary radar returns and displayed on the
same plan position indicator (radar scope). Also applied
8. SAM South American Region to the airborne element of the TACAN/DME system.
international flight information manual — A publication intersecting runways — Two or more runways that cross
designed primarily as a pilot’s preflight planning guide or meet within their lengths. See also intersection.
for flights into foreign airspace and for flights returning
to the U.S. from foreign locations. intersection — 1. Typically, the point at which two VOR
radial position lines cross on a route, usually intersecting
International Morse Code — Dots and dashes used in at a good angle for positive indication of position,
combination for transmitting messages. Each combination resulting in a VOR/VOR fix. 2. A point defined by any
represents a letter of the alphabet or a numeral. combination of courses, radials or bearings of two or
international phonetic alphabet — A list of words used more navigational aids. 3. Used to describe the point
to denote the letters of the alphabet. Agreed upon by where two runways, a runway and a taxiway, or two
all nations, the use minimizes confusion regarding the taxiways cross or meet.
speaker’s intent. intersection departure — A departure from any runway
international standard atmosphere (ISA) — A intersection except the end of the runway.
hypothetical atmosphere based on averages in which intersection takeoff — See intersection departure.
the surface temperature is 59°F (15°C), the surface
pressure is 29.92 in. Hg (1013.2 Mb) at sea level, and interstage transformer — A transformer used to prevent
the temperature lapse rate is approximately 2°C per 1,000 the flow of DC from one stage of a multi-stage transformer
feet. system to the other. Provides the correct amount of
impedance for the AC output of one stage and for the AC
international system of units — The system of metric input of the following stage.
units that includes: meter, kilogram, second, ampere,

177

10001930-002_AviationDictionary_2012_BOOK.indb 177 3/27/2012 9:38:14 AM

 interstate air commerce • iris exhaust nozzle

interstate air commerce — The carriage by aircraft of invert — To reverse the position, order, or condition of
persons or property for compensation or hire, or the something.
carriage of mail by aircraft, or the operation ornavigation
inverted engine — A reciprocating engine whose crankshaft
of aircraft in the conduct or furtherance of a business or
and crankcase are above the cylinders.
vocation, in commerce between a place in any State of
the United States, or the District of Columbia, and a place inverted spin — A maneuver having the characteristics of
in any other State of the United States, or the District of a normal spin except that the airplane is in an inverted
Columbia; or between places in the same State of the United attitude.
States through the airspace over any place outside thereof;
inverter — An electrical device that changes DC to AC.
or between places in the same territory or possession of
the United States, or the District of Columbia. investment casting — Casting as in a vacuum furnace or
spin chamber to produce a denser, better quality material.
interstate air transportation — The carriage by aircraft of
Used to produce some steels in turbine engines.
persons or property as a common carrier for compensation
or hire, or the carriage of mail by aircraft in commerce: a. iodine — A poisonous element with a symbol of I and an
Between a place in a State or the District of Columbia and atomic number of 53.
another place in another State or the District of Columbia,
ion — An atom that has either gained or lost an electron. If
b. Between places in the same State through the airspace
an atom has a shortage of electrons, it is a positive ion.
over any place outside that State; or c. Between places in
If it possesses an excess of electrons, it is a negative ion.
the same possession of the United States; Whether that
commerce moves wholly by aircraft of partly by aircraft ion engine — A reaction engine that ejects a stream of
and partly by other forms of transportation. Intrastate air ionized particles to produce a forward thrust.
transportation means the carriage of persons or property
ionic charges — The charges in solid-state junctions caused
as a common carrier for compensation or hire, by
by the dissimilarity of the junction materials. The charges
turbojet-powered aircraft capable of carrying thirty or more
create “barrier voltages.” In order for a diode to rectify, it
persons, wholly within the same State of the United States.
must be presented with an AC voltage whose peak value
intertropical convergence zone — The boundary zone exceeds its barrier voltage.
between the trade wind system of the Northern and
ionize — To convert totally or partially into ions.
Southern Hemispheres; it is characterized in maritime
climates by showery precipitation with cumulonimbus ionosphere — A series of atmospheric layers of ions that begins
clouds sometimes extending to great heights. ap­proximately 25 miles above the surface of the Earth.
introduction — The first element of an instructional IR — 1. Voltage. Since E (voltage) = I (current) times R
lesson that sets the stage for the rest of the lesson by (resistance), IR is another way of stating E, or voltage. 2.
relating the coverage of the material to the entire course. Routes used by the Department of Defense and associated
The introduction itself is typically composed of three Reserve and Air Guard units for the purpose of conducting
elements: attention, motivation, and an overview of what low-altitude navigation and tactical training in both IFR
is to be covered. and VFR weather conditions below 10,000 feet MSL at
airspeeds in excess of 250 knots IAS. [Jeppesen does not
Invar — A nickel‑iron alloy with an extremely small
chart these routes.]
temperature coefficient of expansion.
IR drop — The amount voltage drops in a given conductor
inverse peak voltage — The amount of inverse voltage a
due to the resistance of the conductor. The IR drop is found
device can withstand without breakdown.
by the formula: I x R=E (voltage), or by multiplying the
inverse square law — In physics, a given physical quantity amount of current (I) in amps, by the amount of resistance
varies inversely with the square of another physical (R) in ohms.
quantity (usually distance). For example, if the distance
IRAN — An acronym used by the military services for a
from a magnet doubles, the strength of magnetism
form of main­tenance known as Inspect and Repair As
decreases to one fourth of its original value.
Necessary.
inverse voltage — The amount of voltage seen by a rectifier
iridium — An extremely hard and brittle metallic element
during the half cycle of AC being blocked to create
of the platinum group, with a symbol of Ir and an atomic
pulsed DC.
number of 77. Used for electrodes of fine‑wire spark plugs
inversion — In meteorology, an increase in temperature that must operate in extreme lead-fouling conditions.
with height — a re­versal of the normal decrease with
iris exhaust nozzle — In turbine engines, a nozzle design
height in the tropo­sphere; may also be applied to other
similar to a camera shutter. It can be a two-position,
meteorological properties.
partially‑open/fully‑open or a variable opening type. The
widest opening is for afterburner mode. The variable
178

10001930-002_AviationDictionary_2012_BOOK.indb 178 3/27/2012 9:38:14 AM

 Irish linen • isotopes

opening type is controlled to continuously seek the isoheight — A line that shows contours of equal height on a
optimum position for existing conditions. constant-pressure weather chart.
Irish linen — A strong fabric made from flax used to cover isohumes — Lines of equal relative humidity.
many of the older aircraft. It is still popular in Europe,
isolation mount — A rubber and metal composite used to
but it is no longer readily available in the United States.
prevent vibration transfer from one component to another.
It may be used as a direct replacement for grade‑A cotton.
isolation transformer — An electrical transformer with
iron — A heavy, malleable, ductile, magnetic, silver‑white
equal numbers of turns in the primary and secondary
metallic ele­ment with a symbol of Fe and an atomic
coils. This type transformer is used to isolate a piece of
number of 26. It is used in the production of steel and all
equipment from its power source.
ferrous metals.
isolation valve — A valve in an aircraft pneumatic system
iron-constantan thermocouple — A low temperature
that can be shut off to isolate the components from the
thermocouple that operates up to about 800º C. Used in
source of air pressure so maintenance can be performed
aviation primarily to measure cylinder head temperature.
without discharging the system.
iron-core coil — An inductor that consists of a soft
isoline — A line on a weather chart showing contours of
laminated iron core around which wire is wound.
equal values of some quantity. It could be equal height
iron-core transformer — An electrical transformer that (isoheight), barometric pressure (isobar), temperature
has coils wound around soft iron cores. The cores cut (isotherm), wind (isotach), etc.
down on eddy-current losses but limit the use of the
isometric drawing — The representation of an object in
transformer to lower frequencies.
isometric projection in which the lines parallel to the
iron-vane movement — An AC electric measuring edges of the object are drawn to true length.
instrument that depends upon a soft‑iron vane or movable
isometric projection — A three-dimensional projection in
core operating with a coil to produce an indication of AC
which the three faces of an object are equally inclined
current flow.
to the surface of the drawing, and all of the edges are
irrelevant questions — A question that has no relationship equally foreshortened.
with the subject matter being tested. Serves only to
iso-octane — A hydrocarbon (C8H18) that has a very high
disrupt the orderly learning process.
critical pressure and temperature. It is used as a reference
irreversible controls — Hydraulically-controlled surfaces for measuring the anti‑detonation characteristics of a fuel.
on an aircraft that do not provide aerodynamic feedback
isopleth — A line connecting points of constant or equal value.
to the cockpit controls.
isopropyl alcohol — Fluid that prevents the formation of
isobar — A line of equal or constant barometric pressure.
ice on the blades during flight. Used in anti‑icing systems
isobar — A line on a meteorological chart that connects for propeller blades.
points on the Earth’s surface having equal barometric
isostatic forging — A similar process to isothermal forging.
pressure.
isotach — A line of equal or constant wind speed.
isobaric metering valve — A metering valve in a cabin
pressurization system that maintains a constant cabin isotherm — A line on a meteorological chart that denotes
altitude. locations having the same temperature.
isobaric range — That range of cabin pressurization in isothermal forging — A hot forging method that uses
which the cabin maintains a constant pressure, or cabin super alloy production. Materials and dies are heated
altitude, as the flight altitude changes. to the same temperature usually in a vacuum or highly
controlled atmosphere to prevent oxidation. One such
isogonic lines — Lines
process utilizes an alloy in powder form, which when
on charts that connect
compressed, results in closer, near-net-shape than older
points of equal
methods. This results in the production of hot section
magnetic variation.
parts with less waste during final machining.
isogonic lines — Lines on
isothermal layers — A layer in the atmosphere where the
an aeronautical chart
temperature is the same from the bottom of the layer to
connecting points of
the top of the layer.
equal magnetic declination (angle between magnetic North
and true North). This angle is known as compass variation. isotopes — An atom that has the same atomic number as
a chemical element, but a different atomic mass and
different physical properties.

179

10001930-002_AviationDictionary_2012_BOOK.indb 179 3/27/2012 9:38:14 AM

 J • jettison

J Jet B — A wide-cut blend of hydrocarbon fuels for use in

turbine engines. Used primarily in the military as JP-4 fuel.
jack pads — Structural locations capable of supporting the jet blast — Jet engine exhaust (thrust stream turbulence).
weight of an aircraft when being jacked from the ground.
jet efflux — The gas flowing from the exhaust nozzle.
jacket — A metal blanket or shroud used to insulate a
portion of a turbine engine. jet engine — A reaction engine that derives its thrust from the
acceleration of an air mass through an orifice. There are
jacks — The hydraulic or mechanical devices used to lift an four common types: rocket, ramjet, pulsejet, and turbojet.
aircraft off of the ground for testing or servicing.
jet fuel control (JFC) — The fuel metering system for a
jackscrew — A threaded, hardened steel rod that can be turbine engine. Measures the operating conditions of the
rotated to lift an object or to apply a force. engine and meters into the burners the correct amount of
jagged edge — An irregularly shaped edge on a piece of fuel for the condition.
metal, wood, or plastic material. jet nozzle — A specially designed device shaped to produce
jam acceleration — The rapid movement of the power a jet stream.
control lever of a gas turbine engine. Done when jet nozzle area — The area in square feet of the opening
measuring the RPM acceleration rate. through which the engine exhaust gases pass to the
jam nut — A thin check-nut screwed down against a regular atmosphere.
nut to lock it in place. jet propulsion — The propulsion produced when a
jamming — Electronic or mechanical interference that can relatively small mass of air is given a large amount of
disrupt the display of aircraft on radar or the transmission/ acceleration
reception of radio communications/navigation. jet pump — A pump that operates by producing a low
J-block — A precision block ground to an accuracy of pressure through a venturi. Seen in oil scavenge systems
approximately 0.00001”, used as a reference in precision as oil pumps and fuel systems as vapor eliminators.
machining operations. jet route — A route designed to serve aircraft operations
Jeppesen Information Services — A subscription service, from 18,000 feet MSL up to and including flight level 450.
for pilots, which provides revisions for several flight The routes are referred to as “J” routes with numbering to
information publications including the Jeppesen AIM, identify the designated route; e.g., J105.
Jeppesen FARs for Pilots, the Jeppesen Airport Directory, jet silencer — A device used to reduce and modify the
JeppGuide, and the GPS/LORAN Coordinate Directory lower frequency sound waves emitting from an engine’s
jerry can — A specially designed five gallon container used exhaust nozzle, and thus reducing the noise factor.
for carrying fuel. jet streak — A portion of the jet stream where wind speeds
jet — 1. A calibrated, restricted orifice in the fuel passage are greater than in regions up- or downstream. Jet streaks
of a carburetor used to control the amount of fuel that are several hundred to 1,000 miles long.
can flow under a given pressure. The size of the hole jet stream — A narrow band of high speed winds (speeds
(jet) determines the amount of flow through the jet. 2. A exceed 60 knots). Normally found near the tropopause.
forceful stream of fluid discharged from a small nozzle.
3. An aircraft powered by a turbojet engine. 4. The hot, jet stream axis — The line of maximum winds (>60 knots)
high velocity gas stream issuing from the tailpipe of a gas on a constant pressure chart.
turbine engine. jet stream cirrus — Associated with an extratropical
Jet A-1 — A kerosene‑type turbine engine fuel similar to cyclone, these anticyclonically curved bands of cirrus
the military JP-8 fuel with additives to make it usable at clouds are usually located just downstream of the upper
very low temperatures of approximately -58°F. trough.
Jet A — A kerosene‑type turbine engine fuel similar to jet stream front — High-level frontal zone marked by a
the military JP-5. It has a very low vapor pressure and a sloping layer below the jet core.
relatively high flash point. jet thrust — The thrust produced by a jet.
Jet Assist Takeoff (JATO) — An auxiliary means of Jetcal analyzer — A trade name for an electronic test
assisting a heavily loaded aircraft to takeoff, particularly apparatus for checking the calibration of the EGT system,
on a short runway. The JATO consists of small rockets the RPM system, and the accuracy of their associated
attached to the aircraft and provides the required instruments.
additional thrust needed for takeoff.
jettison — To cast off or drop from an aircraft in flight.

180

10001930-002_AviationDictionary_2012_BOOK.indb 180 3/27/2012 9:38:14 AM

 jettisoning of external stores • jury strut

jettisoning of external stores — Airborne release of jumbo jets — The name given to wide-body airplanes such
external stores; e.g., tiptanks, ordnance. as the Boeing 747, 757, 767, 777, McDonald Douglas
DC‑10, Lockheed L‑1011, A‑300 Airbus, etc.
jewel bearing — A cup-type bearing surface that rides on
a hardened steel pivot used extensively in many types of jump seat — A compact portable seat positioned slightly
indicating instruments. behind the pilot’s and copilot’s seats in an airplane where
a flight engineer sits to monitor certain engine‑operating
jeweler’s rouge — A very fine ferric oxide abrasive used
instruments and operate some of the auxiliary controls.
for polishing hard metal surfaces.
jumper — A temporary electrical lead wire used to bypass
jig — The framework or alignment structure used in the
a circuit for purposes of troubleshooting.
construction or repair of an aircraft to hold all the parts in
proper alignment while they are fastened together. junction — The point at which two conductors or circuits
join.
jigsaw — An electric or pneumatically operated saw tool
that uses a variety of narrow blades to cut small curves in junction box — A metal or fiberglass box for holding
wood, metal, or plastic. the electrical terminal strips to which wire bundles are
attached.
Jo‑bolts — An internally
threaded three‑piece Junction Field Effect Transistor (JFET) — A
rivet. semiconductor device that uses voltage to control
conductivity instead of current as in the normal transistor.
joggle — A small offset in
sheet metal formed to junction transistor — A transistor consisting of a single
allow one part to overlap another. crystal of P- or N-type germanium between two electrodes
of opposite types. The center layer is the base and forms
Johnson bar — A brake control found on some early
junctions with the emitter and collector.
airplanes. A Johnson bar consisted of a long bar mounted
between the seats in the cockpit that, when pulled jury strut — A small strut extending from approximately
rearward, applied both main wheel brakes and, when the mid‑point of a wing strut to the spar of the wing. Its
pulled diagonally rearward, applied one of the brakes. purpose is to stabilize the main strut against vibrations.
joint use restricted area — See restricted area.
jointer — An electrically powered woodworking machine
used to smooth the edges of wood.
joule — The international system unit of energy equal to the
work done when a current of 1 ampere is passed through
a resistance of 1 ohm for 1 second.
joule rating — A turbine engine’s ignition system.
journal — The polished surface of a crankshaft on which
the bearings ride.
joystick — A slang term used for the control stick that
controls an airplanes ailerons and elevator. Moving the
joystick fore and aft moves the elevators, and moving the
joystick side to side moves the ailerons.
JP-4 — A gas turbine engine kerosene‑type fuel made up
of approximately 65% gasoline and 35% distillates. Also
referred to as Jet B.
JP-5 — A highly refined gas turbine kerosene‑type engine
fuel. Also referred to as Jet A.
JP-7 — A gas turbine engine kerosene‑type fuel with
additives for use at extremely high altitudes.
judgment — Process of recognizing and analyzing
information, evaluating alternative actions, and making
a timely decision on action to take.

181

10001930-002_AviationDictionary_2012_BOOK.indb 181 3/27/2012 9:38:14 AM

 K • kirksite

K keyway — A slot or groove machined into a hole or a shaft

onto which a key is fitted.
K — The abbreviated use for kilo or one thousand. An item kHz — Abbreviation for kilohertz (1,000 CPS).
that weighs 3 Kg (kilograms) weighs 3,000 grams.
kickback — The reverse rotation of a reciprocating engine
K index — A stability index used to determine the due to premature ignition during starting.
percentage probability of the occurrence of an airmass
thunderstorm. Kidde — A manufacturer of fire detection systems.
K monel — A high‑strength, non‑magnetic, heat‑treatable, kilo (K) — A metric term used to indicate one thousand.
corrosion­ resistant alloy made up of nickel, copper, and Kilo is also used as the prefix for kilogram, kilometer,
aluminum. and kilohertz.
katabatic — Any wind blowing down slope.
 kilogram (kg) — One thousand grams. 1 kg = 1,000 grams.
katabatic wind — Any wind blowing down slope. kilohertz — A frequency of 1,000 cycles per second.
K-band — A radar wavelength. kilomega — An outdated term for one thousand million
(i.e., a billion or 1,000,000,000). Giga is now used.
K-chart — A sheet metal fabrication chart providing the
multiplier to use when determining the setback for bends kilovolt — 1,000 volts.
of other than 90°. kilovolt amperes reactive (KVAR) — A measure of
keel — A longitudinal member or ridge along the center reactive power.
bottom of a seaplane float or hull. kindling point — That temperature at which combustion
keeper — A soft iron bar or plate placed across the poles of can take place for a particular fuel/oxygen combination.
a magnet when the magnet is not being used in order to kindling temperature — The temperature required for a
keep the magnet from losing any of its magnetism. material to burn when combined with oxygen.
Kelvin bridge — A resistance-measuring instrument used kinds of operations list — A list found in the pilot’s
for accurate measurements of low resistances. operating handbook (POH) of an aircraft that includes
Kelvin (K) — The absolute temperature scale with minus all equipment originally installed in the aircraft at the
273°C as absolute zero. Used in many engine performance time of certification. It also includes notations on which
calculations. equipment must be operational for various types of flight
including day and night VFR.
Kennelly-Heaviside layer — An ionized layer in the upper
atmosphere that reflects radio waves to Earth. Also kinematic viscosity — The ratio of absolute viscosity and
referred to as E-layer or ionosphere. density, ex­pressed in units of centistokes.
kerf — The slot or groove left by a cutting tool as it cuts kinesthetic learners — People who prefer to be doing
through a material. something and primarily absorb information through
actual hands-on experience. Kinesthetic learners
kerosene — A thin, colorless, flammable hydrocarbon ascertain more from performing a preflight inspection
material distilled from crude oil and used as a base for than from studying a checklist.
turbine engine fuel and as a solvent for cleaning parts.
kinetic energy — Energy due to motion, defined as one half
Kett saw — A metal cutting, hand-held, power-operated mass times velocity squared.
tool. The head can be turned to any desired angle for
cutting sheet stock aluminum. Uses various sizes of kink — A sharp twist or bend in a piece of wire, sheet metal,
blades. or a piece of tubing.
Kevlar® — Trademark of DuPont. A strong, lightweight Kirchhoff ‘s current law — “The algebraic sum of the
aramid fiber used as a reinforcement fiber. currents enter­ing and leaving any junction of conductors
is equal to zero.” Simply stated, this means that all of the
keyhole saw — A small U-shaped hand saw with a stiff, current that arrives at a point must leave that point.
narrow blade used to cut a larger hole from a small drilled
hole. Kirchhoff’s voltage law — The law of electrical circuits
that states the sum of voltage that drops around a series
keying — The process of modulating a continuous carrier circuit is equal to the applied voltage.
wave (cw) with a key circuit to provide interruptions
in the carrier in the form of dots and dashes for code kirksite — An alloy of aluminum and zinc.
transmission.

182

10001930-002_AviationDictionary_2012_BOOK.indb 182 3/27/2012 9:38:14 AM

 kite • Kreuger flap

kite — A framework covered with paper, cloth, metal, or Kreuger flap — A leading edge wing flap hinged at the
other material, intended to be flown at the end of a rope bottom side of an airfoil. When it is actuated, the leading
or cable, and having as its only support the force of the edge bends downward, increasing the overall wing
wind moving past its surfaces. camber and allowing the wing to develop additional lift
at lower airspeeds.
Klyston tube — An electron tube in which modulation is
accomplished by varying the velocity of the electrons
flowing through the tube.
knife edge — A sharp‑edged piece of steel or other hard
material used as a balance point or fulcrum for precision
balance of a control surface or a propeller.
knife edge filter — A piece of metal shaped like a cylinder
whose surface is cut with incoming and outgoing sharp
cut grooves. When inserted in an oil passageway,
contaminants remain in the incoming groove and clean
oil squeezes between the knife edge and the casing and
through the outgoing groove to the oil jet.
knife edge tip — Thin metal rims on a shrouded‑tip turbine
blade. These sealing tips establish their own clearance to
the shroud ring by contact loading and wear.
knife switch — A switch that uses a blade that fits between
two spring-loaded contacts to complete a circuit. When
the blade is rotated out of the slot between the contacts,
the circuit is opened.
knock — A loud knocking or banging noise made inside
a reciprocating engine cylinder during the compression
stroke. The knock is an explosion rather than a smooth
burning process and is caused by the almost instantaneous
release of heat energy from fuel in an aircraft engine
caused by the fuel air mixture reaching its critical
pressure and temperature.
knot — 1. One nautical mile per hour, or 1.1508 statute
miles per hour. 2. A round, hard section of a tree branch
embedded in a board and that weakens the overall
strength of the board.
known traffic — With respect to ATC clearances, aircraft
whose altitude, position and intentions are known to ATC.
knuckle pin — The hardened steel pin that holds an
articulating rod in the master rod of a radial engine.
knurl — A series of small ridges on the surface of a material
to aid in gripping.
Kollsman window — Registered trade name for the
altimeter setting window of a Kollsman altimeter.
Sometimes erroneously used to describe the altimeter
setting window of any altimeter.
Koroseal — Plastic lacing used for support and anti-chafing
protection of wires and lines.
Kraft paper — Strong brown paper such as the material of
which grocery sacks are made.

183

10001930-002_AviationDictionary_2012_BOOK.indb 183 3/27/2012 9:38:15 AM

 L • landing direction indicator

L laminated — Composed of thin layers of material firmly

bonded or united together.
labyrinth air seal — The thin sheet metal rims on turbine laminated core — The core of a coil, transformer, or
blades, either rotating or stationary, that control air other electrical device consisting of a stack of thin, soft
leakage from the gas path to the inner portions of the iron sheets insulated from each other by a film oxide
engine. Same as knife edge air seal. or varnish. Laminated cores are used to minimize eddy
labyrinth oil seal — A main bearing oil seal. It is currents.
configured with thread-­type grooves that allow gas path laminated plastic material — A reinforced plastic resin
air to leak inward to the bearing sump and keep oil mist made up of layers of material such as cloth, paper, or
from escaping. Unlike the carbon seal, which rides on wood bonded with plastic resin to form complex shapes
a surface, the labyrinth oil seal has a small clearance or to produce a material with high strength for its weight.
between its sealing lands and the rotating shaft.
laminated structure — An element or part of an aircraft
lacing cord — A strong cotton, linen, or synthetic fiber cord made up of layers of material bonded together to form
used to rib stitch fabric covering to an aircraft structure. complex shapes or to produce a material with high
Also referred to as rib‑stitching cord. strength for its weight.
lack of common experience — In communication, a laminated wood — Layers of wood bonded together to
difficulty that arises because words have different make a stronger material.
meanings for the source and the receiver of information
due to their differing backgrounds. lampblack — The black soot from incompletely burned
carbonaceous materials used for making generator
lacquer — The pigments dissolved in a volatile base brushes. Lampblack is used as a pigment when mixed
(solvents, plasticizers, and thinners) in preparation for with rubber for making tires.
spraying as a liquid. Cures to a durable surface when the
solvent evaporates. land and hold short operations (LAHSO) — Operations
that include simultaneous takeoffs and landings and/or
lag — 1. A delay in time. 2. To fall behind. simultaneous landings when a landing aircraft is able
lagging current — An occurrence in an AC inductive and is instructed by the controller to hold-short of the
reactance circuit whereby changes in the voltage occur intersecting runway/taxiway or designated hold-short
before changes in the current. Current, therefore, lags the point. Pilots are expected to promptly inform the
voltage. controller if the hold short clearance cannot be accepted.
lagging material — An insulating material wrapped around land breeze — A coastal breeze blowing from land to sea,
aircraft plumbing to prevent the unwanted loss of heat to caused by temperature difference when the sea surface
the outside air. is warmer than the adjacent land. Therefore, it usually
blows at night and alternates with a sea breeze, which
LAHSO — An acronym for “Land and Hold Short blows in the opposite direction by day.
Operation.” These operations include landing and
holding short of an intersecting runway, a taxiway, a land plane — An airplane designed to operate from the
predetermined point, or an approach/departure flightpath. surface of land using wheeled landing gear rather than
pontoons or skis for landing on water or snow.
LAHSO-dry — Land and hold short operations on runways
that are dry. lander — A space vehicle designed for landing on a celestial
body.
LAHSO-wet — Land and hold short operations on runways
that are wet (but not contaminated). landing area — Any locality either on land, water, or
structures, including airports/heliports and intermediate
laminar — Arranged in or consisting of thin layers. landing fields, used or intended to be used, for the
laminar flow — The nonturbulent flow of air or viscous landing and takeoff of aircraft whether or not facilities
fluid over a surface. are provided for the shelter, servicing, or for receiving or
discharging passengers or cargo.
laminate — A structure made by bonding together two or
more layers of material with resin. It contains no core landing area [ICAO] — That part of the movement area
material. intended for the landing and takeoff of aircraft.
laminate ply — In composites, one fabric-resin or landing direction indicator — A device that visually
fiber-resin layer that is bonded to adjacent layers in the indicates the direction in which landings and takeoffs
curing process. should be made.

184

10001930-002_AviationDictionary_2012_BOOK.indb 184 3/27/2012 9:38:15 AM

 landing distance available • large scale integration

landing distance available — The length of runway position from which a normal approach to the runway of
declared available and suitable for the ground run of an intended landing can be made and adequate visual
aeroplane landing. reference to required visual cues is maintained.
landing flaps — A secondary control surface that increases landing roll — The distance from the point of touchdown
the overall wing area or changes the camber of the wing. to the point where the aircraft can be brought to a stop or
The increased wing area permits a lower landing speed. exit the runway.
Increased camber increases the lift and allows lower
landing sequence — The order in which aircraft are
landing speeds and shorter landing distances.
positioned for landing.
landing gear — The wheels, floats, skis, and all of the
landing weight — The weight of the aircraft at touchdown.
attachments that support an airplane when it is resting on
Often limited by the manufacturer to less than takeoff
a landing surface.
weight for structural reasons.
landing gear door warning system — A group of
landing wires — The streamlined wires attached to the
components that warn of an unsafe landing gear door
upper wing above the fuselage and extending to near
condition by the use of a horn, indicators, or red warning
the outboard end of the lower wing in a biplane. These
lights. Used on aircraft with retractable landing gear.
wires brace the wings against the forces that affect the
landing gear extended speed — The maximum speed at wings during landing. These forces are opposite those
which an aircraft can be safely flown with the landing encountered during flight.
gear extended.
lap belt — A seat belt or safety belt that crosses a person’s
landing gear operating speed — The maximum speed lap while seated in an aircraft.
at which the landing gear can be safely extended or
lap joint — A joint in a sheet metal structure where the
retracted.
edge of one sheet overlaps the other. Welding, riveting,
landing gear position indicating system — A group of or bolting fastens the lap joints together.
components that shows the position of the landing gear
lap winding — A method of manufacturing the armature
though the use of lights or instruments. Used on aircraft
of a DC gener­ator by connecting the ends of each coil
with retractable landing gear.
wound on the armature to the next adjacent commutator
landing gear warning system — A group of components segment with the coils lapping over each other.
incorporated on all retractable gear aircraft to warn of
lapping — To rub two surfaces together with a very fine
an unsafe landing gear condition. The pilot is warned of
abrasive be­tween them in order to produce an extremely
an unsafe condition by a warning light and aural device.
close fit.
The horn blows and the light comes on when one or
more throttles are retarded and the landing gear is in any lapping compound — An abrasive paste used to polish
position other than down and locked. surfaces.
landing lights — The high‑intensity lights located on laps — The surface defects in sheet metal caused by the
the wing or fuselage used to illuminate the runway for folding over of fins or sharp corners into the surface of
landing and taking off at night. These lights also make the material. Occurs during the rolling process.
an aircraft more visible to other aircraft during the day.
lapse rate — The rate of decrease of an atmospheric
landing minimums — The minimum visibility prescribed variable with altitude; commonly refers to a decrease of
for landing a civil aircraft while using an instrument temperature or pressure with altitude.
approach procedure. The minimum applies with other
lapse rate — The rate of decrease of an atmospheric variable
limitations set forth in FAR 91 with respect to the
with height; commonly refers to decrease of temperature
Minimum Descent Altitude (MDA) or Decision Height
with height.
(DH) prescribed in the instrument approach procedures
as follows: large aircraft — Aircraft of more than 12,500 pounds,
maximum certificated takeoff weight.
a. Straight-in landing minimums – A statement of MDA
and visibility, or DH and visibility, required for large calorie (Cal.) — A unit of heat energy. It is the amount
straight-in landing on a specified runway, or of heat energy necessary to raise the temperature of 1 kg
of water 1°C.
b. Circling minimums – A statement of MDA and
visibility required for the circle-to-land maneuver. large scale integration — A method of fabricating
integrated circuit (IC) chips to place multiple transistors
NOTE: Descent below the established MDA or DH is not
or logic circuits on one small IC. Large scale integration
authorized during an approach unless the aircraft is in a
was an early version that placed hundreds of logic circuits

185

10001930-002_AviationDictionary_2012_BOOK.indb 185 3/27/2012 9:38:15 AM

 laser • LCR electrical circuit

on one chip. Very large scale integration (VLSI) places lateral axis — An imaginary straight line drawn
thousands of logic circuits on a chip and most recently, perpendicularly (laterally) across the fuselage and
millions are placed on a single chip. through the center of gravity. Pitch movement occurs
around the lateral axis, and is controlled by the elevator.
laser — A device that emits coherent light (light that vibrates
in phase) used in many applications, from CD players lateral navigation (LNAV) — A function of area navigation
to powerful metal cutting devices. Acronym for Light (RNAV) equipment that calculates, displays, and provides
Amplification by Stimulated Emission of Radiation. lateral guidance to a profile or path.
laser beam welding — The use of laser beam heat for lateral separation — The lateral spacing of aircraft at the
welding engine parts. Currently used to weld titanium same altitude by requiring operation on different routes
fan blades, which could not be welded by conventional or in different geographical locations.
methods.
lateral stability — The stability about the longitudinal
laser memory — A method of storing billions of bits of axis of an aircraft. Rolling stability or the ability of an
digital informa­tion on a disk such as a CD or DVD. airplane to return to level flight due to a disturbance that
causes one of the wings to drop.
laser printer — A printer that prints a high quality copy of
the information being processed by a computer. lateral vibration — An unwanted lateral or side-to-side
movement in a helicopter. The cause of lateral vibration
last assigned altitude — The last altitude/flight level
is normally an unbalanced main rotor.
assigned by ATC and acknowledged by the pilot.
lathe — A wood or metal‑working tool in which the material
last chance filter — The final filter located just before the
is turned about its longitudinal axis and cutting tools are fed
spray nozzle of a turbine lubrication system. Used to
into its outer circumference in order to change its shape.
prevent foreign matter from clogging the spray nozzle.
latitude — Measurement north or south of the equator in
latch — A fastening device used to hold a door closed.
degrees, minutes, and seconds. Lines of latitude are also
latching relay — An electrically operated relay that, once referred to as parallels.
energized, holds the contacts in the energized position
launch — The release of an aircraft or rocket for flight.
by a mechanical latch and can only be released by some
mechanical means. launching pad — A specially designed platform from
which rockets can be fired to launch them.
late timing — On a reciprocating engine, the condition
where the timing is late (retarded). That is, the ignition law of conservation of energy — The law that states
occurs very near top dead center (TDC) on the that the internal energy of an isolated system remains
compression stroke or even after TDC. Late timing is constant; only forms of energy can be changed.
an inefficient fuel condition and the causes the engine to
lay of a control cable — The twist of the strands of a wire
develop less than optimum power.
cable.
latent heat — The amount of heat required to change the
layer — 1. A single thickness. 2. In reference to sky cover,
state of a material without changing its temperature (eg.,
clouds or other obscuring phenomena whose bases
The amount of heat absorbed or released during a change
are approximately at the same level. The layer can be
of state from ice to water.)
continuous or composed of de­tached elements.
latent heat of condensation — The amount of heat given
layout — A drawing, pattern, or format of a piece of sheet
off when a substance changes from a vapor to a liquid
metal in which the locations for all of the bends and
without changing its temperature.
drilled holes are indicated.
latent heat of evaporation — The amount of heat absorbed
lay-up — In composites, reinforcing material that is placed
by a sub­stance when it changes from a liquid to a vapor
in position in the mold.
without changing its temperature.
L-band radar — An airborne radar.
latent heat of fusion — The amount of heat that must be
removed from a substance to change it from a liquid to a LC circuit — A circuit network containing inductance and
solid without changing its temperature. capacitance.
latent heat of vaporization — The amount of heat that LCR electrical circuit — An AC circuit that has inductance
must be absorbed by a liquid to change it into a vapor (L), capacitance (C), and resistance (R). The total
without changing its temperature. opposition to the flow of current in an LCR circuit is
the vector sum of resistance and the difference between
lateral — The span of an airplane from wingtip to wingtip.
inductive and capacitive reactances.

186

10001930-002_AviationDictionary_2012_BOOK.indb 186 3/27/2012 9:38:15 AM

 L/Dmax • lee wave region

L/Dmax — The maximum ratio between total lift (L) and An amount of a liquid or gas that leaks into or out of
total drag (D). This point provides the best glide speed. something.
Any deviation from the best glide speed increases drag
leakage current — The amount of current that flows from
and reduces the distance of the glide.
the battery terminals to the battery case through any
lead — A heavy, pliant, silvery metallic element with a moisture or contamination on top of the battery.
symbol of Pb and an atomic weight of 82.
leakage flux — The magnetic flux that does not follow a
lead and lag — In rotorcraft, the fore (lead) and aft (lag) direct path between the poles of a magnet and which does
movement of the rotor blade in the plane of rotation. not provide any useful work.
lead of screw thread — The distance a nut will move lean blow out — A condition in jet engine fuel combustion
forward on a screw if it is turned one revolution. during which the fuel supply is decreased to maintain or
reduce engine speed. During this condition the burning
lead-acid battery — A commonly used secondary cell
can be so slow that the flame is carried out of the
having lead as its negative plate and lead peroxide as
combustion chamber and extinguished.
its positive plate. Sulfuric acid and water serve as the
electrolyte. lean flame out — A condition of turbine engine operation in
which the fire goes out in the engine because the fuel-air
leading current — An AC electrical circuit in which the
mixture is too lean to support combustion.
current that flows in the circuit has more capacitive
reactance than it has induc­tive reactance. lean mixture — A fuel‑air mixture in which there is an
excess amount of air in the mixture.
leading edge — The foremost edge of an airfoil section.
learning — A change in behavior as a result of experience.
leading edge flap — A portion of the leading edge of
an airplane wing that folds downward to increase the learning plateau — A learning phenomenon where
camber, lift, and drag of the wing. The leading‑edge flaps progress appears to cease or slow down for a time before
are extended for takeoffs and landings to increase the once again increasing.
amount of aerodynamic lift that is produced at any given
learning style — The concept that how a person learns is
airspeed.
dependent on that person’s background and personality,
leading edge mean aerodynamic chord (LEMAC) — as well as the instructional methods used.
The leading edge of the mean aerodynamic chord often
least significant bit — A bit in a binary number that has
used as a location or reference for many aerodynamic
the lowest value. It is the bit on the far right of a binary
measurements in aircraft operations and designs.
number.
lead-lag hinge — A hinge at the root of a helicopter rotor
least significant digit — A digit in a decimal number that is
blade with its axis perpendicular to the plane of rotation.
the least meaningful for accuracy. It is the digit on the far
Also referred to as the alpha, drag, or hunting hinge.
right of a decimal number.
lead-off question — A question used by an instructor to
Leclanche cell battery — A name for a common carbon‑zinc
open up an area for discussion. The purpose is to get the
cell flashlight battery.
discussion started.
lecture method — An educational presentation usually
leaf brake — A bending
delivered by an instructor to a group of students with the
tool used to form
use of instructional aids and training devices. Lectures are
straight bends in sheet
useful for the presentation of new material, summarizing
metal. The material is
ideas, and showing relationships between theory and
clamped in the tool,
practice.
and a heavy leaf folds
the metal back over a lee side — The downwind side of a mountain range,
radius block to form building, island, etc.
the desired bend. Also
lee wave — Any stationary wave disturbance caused by a
referred to as a cornice brake.
barrier in a fluid flow. In the atmosphere when sufficient
leaf spring assembly — A series of flat springs hinged at moisture is present, this wave will be evidenced by
one end and arched in the center. When a load is applied lenticular clouds to the lee of mountain barriers. Also
to the center of the arch it is absorbed as the spring referred to as a mountain wave or standing wave.
alternately straightens out and returns to its arched shape.
lee wave region — The upper layer of a two-layer lee-wave
leakage — 1. The breakdown of the dielectric strength system where smooth wave flow dominates and
of an insulator that allows current to pass through it. 2. microscale turbulence occasionally occurs.

187

10001930-002_AviationDictionary_2012_BOOK.indb 187 3/27/2012 9:38:15 AM

 lee wave system • lift-drag ratio

lee wave system — A system marked by two distinct layers. level — 1. The horizontal condition of a body: A flat
The upper layer is the lee wave region, which begins just horizontal surface of an object is level when no part of
above mountain to level, and the lower layer is the lower the object is higher than another. 2. A spirit or bubble
turbulent zone. level: An indicating device that has a curved glass tube
filled with a slightly colored liquid, except for a small air
left brain — A concept that each hemisphere of the brain
bubble. The tube is mounted in a housing so when it is
processes information differently. People with left-brain
place in a parallel position to the ground the bubble will
dominance are more verbal, analytical, and objective.
move to the center of the tube indicating a level condition.
left-hand rule — 1. The left-hand generator rule: The
leveling lugs — The points on an aircraft on which a level
fingers of the left hand are arranged in such a way that
can be placed for leveling the aircraft.
the thumb, first finger, and second finger point 90°
to each other. If the thumb points in the direction of leveling means — A method of checking an aircraft for level
movement of the conductor, the first finger will point in flight attitude as specified by the aircraft manufacturer.
the direction of the lines of flux (north to south), and the This can be longitudinal, lateral, and/or both.
second finger will point in the direction of the induced
leveling scale — A scale built into the aircraft for checking
voltage (back voltage, from positive to negative). 2.
the leveling of the aircraft in conjunction with a plumb
The direction of magnetic flux: If the fingers of the left
bob.
hand encircle a conductor in the direction of the lines of
magnetic flux, the thumb will point in the direction of lever — 1. A device such as a bar used for prying. 2. A flat
electron flow. 3. The polarity of an electromagnet: If the bar pivoting on a fulcrum.
coil of an electromag­net is grasped in such a way that the
Leyden jar — A primitive capacitor. In effect, an apparatus
fingers encircle the coil in the same way the electrons
for storing an electric charge on the inside foil lining of
are flowing, the thumb will point to the north pole of the
a glass jar.
electromagnet that is formed by the coil.
L-filter — An inductor-input filter consisting of an inductor
left-hand thread — A thread that winds in a counterclockwise
and a capacitor used to smooth the ripple from the output
direction. All left‑hand threads are designated LH.
of a rectifier.
leg — 1. One side of a formed angle. 2. One portion of a
licensed empty weight — The empty weight that consists
trip made with dead reckoning navigation (the distance
of the airframe, engine(s), unusable fuel, and undrainable
between turn points.) 3. The portion of a trip between
oil, plus standard and optional equipment as specified in
stops.
the equipment list.
legs of a right triangle — The sides of a right triangle
life-limited part — A part with a specified number of
joined by the right angle (90°).
operating hours or operating cycles before it must be
LEMAC — The leading edge of the mean aerodynamic removed for overhaul.
chord. Often used as a reference location for aerodynamic
life-support systems — The oxygen and pressurization
meas­urements in aircraft operations and designs.
systems in an aircraft that make it possible for the
lenticular cloud — A cloud shaped like a lens that forms occupants to function at high altitudes.
on the downwind side of a mountain. It usually indicates
lift — One of the four main forces acting on an aircraft.
severe air turbulence and should be avoided. They can
On a fixed-wing aircraft, an upward force created by the
extend the entire length of the mountain range producing
effect of airflow as it passes over and under the wing.
the wave and are called wave clouds or lennies by glider
pilots. lift fan — A turbofan engine with an exhaust duct that can
be pointed down to provide upward thrust for vertical or
Lenz’s law — The law of induced current that says the
short takeoff. Used in VSTOL (Vertical/Short Takeoff
current induced in a conductor will produce a magnetic
and Land) aircraft.
field that opposes the field producing the original current.
lift wires — The biplane wing support wires installed
lesson plan — An organized outline for a single instructional
between the wings of a biplane to hold the wings in
period. It is a necessary guide for the instructor in that it
alignment against the forces of lift. Lift wires extend
tells what to do, in what order to do it, and what procedure
from the inboard end of the lower wing to the interplane
to use in teaching the material of a lesson.
struts on the upper wing.
letter of authorization (LOA) — A letter from the FAA
lift-drag ratio — The efficiency of an airfoil section. It is
authorizing use of a Minimum Equipment List (MEL) for
the ratio of the coefficient of lift to the coefficient of drag
a specific airplane. The letter and the MEL together are
for any given angle of attack.
considered a supplemental type certificate.

188

10001930-002_AviationDictionary_2012_BOOK.indb 188 3/27/2012 9:38:15 AM

 lifted index • linear accelerometer

lifted index — The common approach to the evaluation lighter-than-air aircraft — An aircraft that can rise and
of potential instability requirement for thunderstorm remain suspended by using contained gas weighing less
formation. It is the difference between the observed 500 than the air that is displaced by the gas.
mb temperature and the temperature the parcel of air
lightning — An immense discharge of static electricity in
would have if lifted from the boundary layer to the 500
response to the build-up of electrical potential between
mb level.
cloud and ground, between clouds, within a single cloud,
lifting body — A wingless aircraft developed by NASA or between a cloud and the surrounding air.
where lift is created by the shape of the craft itself.
light-up — The point at which combustion occurs in a
light — The electromagnetic radiations of a frequency turbine engine as indicated by an exhaust temperature
range visible to the human eye. rise on the cockpit indicator.
light aircraft — An aircraft having a total gross weight of lime grease — A grease made up of oil and calcium
12,500 lbs. or less. See also light plane. hydroxide. It does not emulsify in water and is highly
resistant to washout in wet environments.
light emitting diode (LED) — A semiconductor diode that
emits light when current flows through it. limit load — The maximum load, expressed as multiples of
positive and negative G (force of gravity), that an aircraft
light ends — The products of petroleum that boil off first in
can sustain before structural damage becomes possible.
the process of fractional distillation.
The load limit varies from aircraft to aircraft.
light gun — A handheld directional light signaling device
limit switch — A switch designed to stop an actuator at the
that emits a brilliant narrow beam of white, green, or
limit of its movement.
red light as selected by the tower controller. The color
and type of light transmitted can be used to approve limiter — A stage in a frequency modulated receiver that
or disapprove anticipated pilot actions where radio limits the amplitude of the signal and thus removes static.
communication is not available. The light gun is used for
limits — The bounds of travel or size allowed for a
controlling traffic operating in the vicinity of the airport
component.
and on the airport movement area.
limits of size — The applicable maximum and minimum
light plane — An aircraft having a total gross weight of
dimensions of a part.
12,500 lbs. or less. Light plane is also used as a colloquial
term to mean a small, single‑engine airplane. Lindberg fire detection system — A
continuous‑element‑type fire detector consisting of a
light sport aircraft — An aircraft, other than a helicopter
stainless steel tube containing a discrete element that
or powered-lift that, since its original certificate, has
has been processed to absorb gas in proportion to the
continued to meet the following:
operating temperature. As the temperature rises, gas is
1. A maximum takeoff weight of not more than 660 released, causing the pressure in the stain­less steel tube
pounds (300 kilograms) for lighter-than-air aircraft; to increase to the operating temperature set point. This
1,320 pounds (600 kilograms) for aircraft not intended closes a switch that actuates the warning light and bell.
for operation on water; or 1,430 pounds (650
line loss — The voltage loss in a conductor. The amount of
kilograms) for an aircraft intended for operation on
loss is related to its length.
water.
line maintenance — The inspection and repairs
2. A maximum airspeed in level light, with maximum
accomplished on the flight line as opposed to shop
continuous power (VH), of not more than 120 knots
maintenance.
CAS under standard atmospheric conditions at sea
level. line of sight radio reception — The clear path between the
transmit­ting and receiving antennas of high-frequency
light year — The distance light travels in one year. Unit of
radio signals.
measurement in astronomy equal to 5.88 X 1012 miles.
line voltage — The main power line voltage that operates
light-activated silicon control rectifier — In electronics,
a system.
a semiconductor device that conducts when exposed to
light. line voltage regulator — The device used to stabilize
the line voltage by sensing and regulating the voltage
lighted airport — An airport where runway and obstruction
demands supplied to a piece of electrical or electronic
lighting is available.
equipment.
lightening hole — A hole cut in a structural part to decrease
linear accelerometer — A device that measures acceleration
weight. Strength is often maintained by flanging the area
of a body in a straight line.
around the hole.

189

10001930-002_AviationDictionary_2012_BOOK.indb 189 3/27/2012 9:38:15 AM

 linear actuator • litmus

linear actuator — An actuator that changes hydraulic or liquid crystal — A liquid whose reflectivity varies
pneumatic pressure into linear motion. according to the voltage applied to it.
linear amplification — In electronics, an amplifier in liquid crystal display — A constantly activated display that
which the change in output is proportional to the change consists of segments of a liquid crystal. Uses very low
in input. current levels, making it more suitable for displays than
light emitting diodes (LED’s).
linear control — In electronics, a control device in which
the change in output is proportional to the amount the liquid lock — A condition that occurs in reciprocating
control’s adjustment is changed. engines that have the cylinders below the crankcase.
Oil leaks past the piston rings and fills the cylinder. The
linear integrated circuit — In electronics, an integrated
engine cannot be rotated without damage. Also referred
circuit (IC) in which the change in output is proportional
to as a hydraulic lock.
to the change in input.
liquid nitrogen — Nitrogen that has been changed into its
linear movement — A movement or progression in which
liquid state by lowering its temperature to -195°C (78°
the output or result is directly proportional to the input.
Kelvin) or lower.
linear operation — The operation in which the output of
liquid oxygen (LOX) — Oxygen that has been changed
a device is directly proportional to its input. If the input
into its liquid state by lowering its temperature to -113°C
increases by 10 percent, the output will also be increased
(160° Kelvin) or lower.
by 10 percent.
liquid-cooled — A device or machine that is cooled by the
linear resistance curve — The characteristic illustrated
use of liquid.
by a load when any increase or decrease in the voltage
across the load results in a proportional change in the liquid-cooled engine — A reciprocating engine that uses a
current through the load. mixture of water and ethylene glycol to remove excess
heat. This mixture flows around the cylinders in jackets
linen — A fabric made from flax that was a favorite covering
and absorbs the heat created by the combustion in the
material for truss‑type airplanes. In the United States, it
cylinders. This heat is released to the outside air through
has been almost totally replaced by grade‑A cotton and
a radiator.
synthetic fiber.
listening — Hearing your students talk and listening to
lines of flux — The lines of magnetic force connecting the
what they are saying are two different things. Instructors
poles of a magnet.
can use a variety of techniques or tools to become
link — 1. A short connecting rod used for transmitting better listeners, including do not interrupt, do not
power and/or force. 2. On the Internet, an identifier judge, think before answering, be close enough to hear,
indicating connection with another similarly identified watch nonverbal behavior, be aware of biases, look
element. Links are usually identified by a different color for underlying feelings, concentrate, avoid rehearsing
of text, underlining, or button and can be accessed merely answers while listening, do not insist on the last word.
by clicking on them with a mouse. The mouse pointer
liter — A metric unit of volume (1.0567 qt.) used for
also will usually change from an arrow to a hand when it
gaseous or liquid measurement.
hovers over a link.
lithium — An alkaline‑metal element with a symbol of Li
link rod — An articulated rod that connects the pistons
and an atomic number of 3. The lightest metallic element
in a radial engine to the master rod. There is one less
known.
articulated rod than there are cylinders in each row of
cylinders in a radial engine since one piston is attached lithium cell — One of a family of chemical cell types
to the master rod. incorporating lithium in one pole.
linseed oil — A solvent used in some aircraft finishes. Also lithium grease — A water‑resistant, low operating
used to coat the inside of steel tubing to prevent rusting. temperature grease made of lithium salts and fatty acids.
Linseed oil is obtained from flaxseed.
lithometeor — In meteorology, dry particles suspended in
liquid — A fluid that assumes the shape of the container in the atmosphere such as dust, smoke, and haze.
which it is held.
lithosphere — The Earth’s most outer area consisting of
liquid air — A slightly bluish, transparent liquid that has the Earth’s crust and the upper mantle. The lithosphere
been changed into a liquid by lowering its temperature extends downward toward the center of the Earth
to -312°F (-191º C, 81º Kelvin). It is used chiefly as a approximately 50 to 60 miles.
refrigerant.
litmus — A water‑soluble powder that turns red in acid
solutions and blue in alkaline solutions.

190

10001930-002_AviationDictionary_2012_BOOK.indb 190 3/27/2012 9:38:15 AM

 litmus paper • locked-rotor current

litmus paper — An indicator paper that changes color when pertinent known field conditions, airport taxi routes and
it comes in contact with an acid or an alkali. It turns red traffic patterns, and authorized instrument approach
when wet with an acid, and blue when wet with an alkali. procedures. This information is advisory in nature and
does not constitute an ATC clearance.
live center — A lathe component with a sharp‑pointed
center that fits into the headstock of a lathe and turns with local Mach number — In aerodynamics, the speed of air
it. Used to locate the exact center of the headstock. flow (Mach number) at a specified location. Because of
the aerodynamic shape of an aircraft, the speed of airflow
load — An energy-absorbing or energy-using device of any
at any point can be greater than the air speed of the
sort connected to a current.
aircraft as a whole.
load bank — A heavy-duty resistor used to discharge a
local oscillator — The internal oscillator section of a
storage battery.
superhetrodyne circuit.
load cell — An electronic weighing system component that
local traffic — Aircraft operating in the traffic pattern or
contains the strain gauges. It is placed between an aircraft
within sight of the tower, or aircraft known to be departing
jack pad and the jack to measure the weight of the aircraft
or arriving from flight in local practice areas, or aircraft
load.
executing practice instrument approaches at the airport.
load chart — A chart used for weight and balance purposes
localizer — The component of an ILS that provides course
that specifies the location and distribution of weights. It
guidance to the runway.
aids the pilot in determining the loaded center of gravity
condition. localizer course [ICAO] — The locus of points, in any
given horizontal plane, at which the DDM (difference in
load, electrical — Any apparatus that uses electrical power
depth of modulation) is zero.
to perform a function such as operating a motor.
localizer offset — An angular offset of the localizer from
load factor — The ratio of the load supported by the
the runway extended centerline in a direction away
airplane’s wings to the actual weight of the aircraft and
from the no transgression zone (NTZ) that increases the
its contents. Also referred to as G-loading.
normal operating zone (NOZ) width. An offset requires a
load manifest — An itemized list of weights and moments 50 foot increase in DH and is not authorized for CAT II
of a particular load taken on a specific flight. Used by and CAT III approaches.
FAR Part 121 and 135 operators.
localizer performance with vertical guidance (LPV)
loading graph — A method of computing the loaded weight
— An instrument approach that takes advantage of WAAS
and center of gravity of an aircraft.
to provide electronic lateral and vertical guidance.
loading schedule — A document showing where cargo
localizer type directional aid — A NAVAID used for
should be stowed and in what weights at specified
nonprecision instrument approaches with utility and
locations.
accuracy comparable to a localizer but that is not a part
loadmeter — A current measuring instrument calibrated in of a complete ILS and is not aligned with the runway.
terms of the percentage of the total rated current of the
localizer usable distance — The maximum distance from
power source.
the localizer transmitter at a specified altitude, as verified
lobes — The eccentric portions of a cam or camshaft. by flight inspection, at which reliable course information
is continuously received.
LOC mode — The operating position of an automatic pilot
when it is receiving its signals from the localizer portion locator — An L/MF NDB used as an aid to final approach.
of an instrument landing system. NOTE: A locator usually has an average radius of rated
coverage of between 18.5 and 46.3 km (10 and 25 NM)
local action — The formation of tiny chemical cells in one
or both of the poles of a chemical cell (battery) due to lock tabs — A washer with tabs that are bent to prevent a
impurities in the material. Local action can result in the nut from loosening.
exhausting of the service capacity of a cell or corrosion
locked-rotor current — The amount of current flowing
of the pole pieces.
through the windings of an electric motor when the motor
local airport advisory (LAA) — A service provided is prevented from turning. This is the highest current
by flight service stations or the military at airports not draw of the motor since once the motor starts rotating,
serviced by an operating control tower. This service counter electromotive force (CEMF) is generated in the
consists of providing information to arriving and windings that opposes voltage and, in turn, current flow
departing aircraft concerning wind direction and speed, through the windings.
favored runway, altimeter setting, pertinent known traffic,

191

10001930-002_AviationDictionary_2012_BOOK.indb 191 3/27/2012 9:38:15 AM

 lockout debooster • longitudinal axis

lockout debooster — A hydraulic component that decreases be made at various points. Boxes show information, a
the pressure applied to aircraft brakes. Its lockout function diamond shaped figure is a logical decision point, and a
shuts off all flow of fluid to the brake in the event of a parallelogram is a point where data is either put into or
rupture of the brake line below the debooster. taken out of the program.
lockring — A horseshoe‑shaped ring that snaps into a logic functions — Statements of logic conditions used in
groove on a shaft in order to hold the shaft in position. digital computers. Usually associated with logic gates
such as AND, OR, NOT, NAND, NOR, and exclusive
lockstitch — A modified seine knot used to lock the stitches
OR. See also AND, OR, NOT, NAND, NOR, and
when hand sewing aircraft fabric. The baseball stitch is
exclusive OR.
used for sewing and it is locked with the seine knot every
eight to ten stitches to prevent loosening. logic gate — See logic functions.
locktab — A mechanical lock used to prevent a nut from logic one — In logic functions, the ON, YES, or TRUE
coming loose. Its appearance is similar to a washer but choices that correspond to a binary “1.”
with notches cut from the periphery. When a locktab is
logic state — The state or condition (logic one or zero) of a
placed under a nut on the shaft of a bolt, one or more of
digital electronic conductor.
the external locking tabs are bent up against the flats of
the nut to keep it from backing off and becoming loose. logic zero — In logic functions, the OFF, NO, or FALSE
choices that correspond to a binary “0.”
lockwire — A stainless steel, brass, or galvanized steel wire
used to exert a pulling motion on the head of screws or logical one — A YES or a TRUE condition in digital
bolts to prevent them from loosening. Also referred to as electronics. It is produced by a closed switch or the
safetywire. presence of a voltage.
lockwiring — A method of tying two or more screws or logical zero — A NO or a FALSE condition in digital
bolts together by twisting lockwire between them in such electronics. It is produced by an open switch or the
a way that tension is held on the head of each fastener in absence of a voltage.
the direction of tightening.
long duct turbofan — A design that ducts the cold stream
lodestone — A natural rock having magnetic characteristics. to the rear of the engine and to the atmosphere. The cold
and hot streams mix on some engines.
log — A journal containing a record of activities. Pilots keep
a log of their flight time, and ground crews keep logs on long range navigation (LORAN) — An electronic
the mechanical operating com­ponents of the aircraft, navigational system by which lines of position are
airframe, engine, propeller, and rotor to show the amount determined by measuring the difference in the time of
of time in service, and to record all the maintenance that reception of synchronized pulse signals from fixed
has been completed on each device. transmitters
logarithm — The exponent that indicates the power to long waves — In meteorology, the wave-like structure in
which a number is raised to produce a given number. For the contour and westerly wind patterns in the mid- and
52 = 25, the logarithm of 25 to the base 5 is 2. upper troposphere. Marked by long, (5,000 miles) slow
moving wave troughs located frequently along the east
logarithmic or audio taper potentiometer — A volume
coasts of both Asia and North America.
control poten­tiometer whose resistance decreases
(volume increases) logarithmically as the control shaft is longeron — The main longitudinal strength-carrying
rotated in a clockwise direction. member of an aircraft fuselage or engine nacelle.
logbooks, mechanical — The journals containing records longitude — Measurement east or west of the Prime
of the total operating time, repairs, alterations or Meridian in degrees, minutes, and seconds. The Prime
inspections performed, and all AD notes complied with. Meridian is 0 degrees longitude and runs through
A mechanical logbook should be kept for the airframe, Greenwich, England. Lines of longitude are also referred
for each engine, and for each propeller. to as meridians.
logic — Valid reasoning through facts and actuality. longitudinal — Of or pertaining to length.
logic circuit — A circuit designed to operate according to longitudinal axis — The axis of an airplane that extends
the fundamen­tal laws of logic. through the fuselage from the nose to the tail, passing
through the center of gravity. Longitudinal axis is also
logic flowchart — A flowchart that resembles a pert
referred to as the roll axis, which is controlled by the
chart, which graphically shows the flow of information
movement of the ailerons.
through a computer program, and the decisions that must

192

10001930-002_AviationDictionary_2012_BOOK.indb 192 3/27/2012 9:38:16 AM

 longitudinal separation • low IFR (LIFR)

longitudinal separation — The longitudinal spacing LORAN — An electronic navigational system by which
of aircraft at the same altitude by a minimum distance hyperbolic lines of position are determined by measuring
expressed in units of time or miles. the difference in the time of reception of synchronized
pulse signals from two fixed transmitters. Loran A
longitudinal stability — Stability about the lateral axis. A
operates in the 1750-1950 kHz frequency band. Loran C
desirable characteristic of an airplane whereby it tends to
and D operate in the 100-110 kHz frequency band.
return to its trimmed angle of attack after displacement.
lost communications — Loss of the ability to communicate
longitudinal wave — A wave in which the particles vibrate
by radio. Aircraft are sometimes referred to as NORDO
in the same direction as the wave as a whole is moving..
(No Radio). Standard pilot procedures are specified in
long-range communication system (LRCS) — A system FAR 91. Radar controllers issue procedures for pilots to
that uses satellite relay, data link, high frequency, or follow in the event of lost communications during a radar
another approved communication system that extends approach when weather reports indicate that an aircraft
beyond line of sight. will likely encounter IFR weather conditions during the
approach.
long‑range navigation (LORAN) — A radio navigation
system that utilizes the master and slave stations louver — An opening with fixed or movable slanted slats.
transmitting timed pulses. The time difference in Also spelled louvre.
reception of pulses from several stations estab­lishes a
low — In meteorology, an area of low barometric pressure,
hyperbolic line of position, which can be identified on
with its attend­ant system of winds. Also referred to as a
a loran chart. A fix in position is obtained by utilizing
cyclone.
signals from two or more stations.
low altitude airway structure — The network of airways
long-range navigation system (LRNS) — An electronic
serving aircraft operations up to but not including 18,000
navigation unit that is approved for use under instrument
feet MSL.
flight rules as a primary means of navigation, and has
at least one source of navigational input, such as inertial low altitude airway structure / federal airways (USA) —
navigation system, global positioning system, Omega/ The network of airways serving aircraft operations up to
very low frequency, or Loran C. but not including 18,000 feet MSL.
long-term memory — The portion of the brain that stores low altitude alert, check your altitude immediately — A
information which has been determined to be of sufficient safety alert issued by ATC to aircraft under their control
value to be retained. In order for it to be retained in if ATC is aware the aircraft is at an altitude which, in
long-term memory, it must have been processed or coded the controller’s judgment, places the aircraft in unsafe
in the working memory. proximity to terrain/obstructions.
long-wire antenna — A radio energy antenna with a length low altitude alert system — An automated function of
greater than one‑half the wavelength of the frequency of the TPX-42 that alerts the controller when a Mode C
the energy being transmitted or received. transponder-equipped aircraft on an IFR flight plan
is below a predetermined minimum safe altitude. If
loom — A tubular flexible insulating material used for wire
requested by the pilot, LAAS monitoring is also available
protection.
to VFR Mode C transponder-equipped aircraft.
loop — 1. A control circuit consisting of a sensor, a
low approach — An approach over an airport or runway
controller, an actuator, a controller unit, and a follow‑up
following an instrument approach or a VFR approach
or feedback to the sensor. Also, any closed electronic
including the go-around maneuver where the pilot
circuit including a feedback signal that is com­pared with
intentionally does not make contact with the runway.
the reference signal to maintain a desired condition. 2.
A flight maneuver executed in such a manner that the low blower — The lower speed setting of a two­-speed
airplane follows a closed 360º circle in a vertical plane. internal supercharger.
loop antenna — A highly directional sensitive antenna low bypass turbofan — An engine with a one-to-one
wound in the form of a coil used to find the direction bypass ratio. Approximately the same air mass flows
between the loop and the station transmitting the received across the fan as across the core engine.
signal.
low frequency (LF) — The frequency band between 30 and
loopstick antenna — An antenna with a large number of 300 kHz.
turns of wire wound on a powdered iron (ferrite) rod to
low IFR (LIFR) — Weather characterized by ceilings
increase the radio signal the coil receives. Loopsticks are
lower than 500 feet AGL and/or visibility less than one
particularly useful in small portable radio receivers.
statute mile.

193

10001930-002_AviationDictionary_2012_BOOK.indb 193 3/27/2012 9:38:16 AM

 low pitch, high RPM setting • lye

low pitch, high RPM setting — The setting of a a carbon brush‑type distributor. The primary current
controllable‑pitch propeller that allows the engine to is directed through the distributor to a coil for each
produce its highest RPM with the propeller at its lowest individual spark plug. These coils have a primary and a
pitch. secondary winding that generate the high voltage at the
spark plug.
low pressure turbine — The turbine rotor that drives the
low pressure compressor in a dual or triple spool axial low-voltage ignition system — A main ignition system
flow gas turbine engine. used on turbine engines with a voltage output in the range
of approximately 1,000 to 5,000 volts delivered to the
lower turbulent zone — The portion of the lee wave
igniter plug.
system, starting at ground level extending to just above
the mountaintop, and marked by turbulence. low-wing airplane — An airplane having one main
supporting aerodynamic surface flush with the bottom of
low-frequency radio waves — Radio waves of frequency
the fuselage.
lower than the bottom of the commercial AM broadcast
radio band. lubber line — The reference line on a magnetic compass
or directional gyro that represents the heading of a ship
low-lead 100‑octane aviation gasoline (100 LL) —
or aircraft.
Gasoline that contains a maximum of 2 ml. of tetraethyl
lead per gallon. Normal 100‑octane avgas is allowed to lubricant — A natural or artificial substance used to reduce
contain 4.6 ml. of tetraethyl lead per gallon. friction, heat, and wear between moving parts. It also can
be used to prevent corrosion on metallic surfaces.
low-level wind shear — Wind shear below 2,000 feet AGL
along the final approach path or along the takeoff and lubricating — The process of applying a lubricant.
initial climb out path.
Lucite — A transparent, thermoplastic resin used for
low-level wind shear alert system (LLWAS) — A system windshields and side win­dows of small aircraft. A
installed at many large airports that continually monitors trademark of the DuPont company.
surface winds at remote sites on the airport. A computer
lug — A projection from a structural member used as an
evaluates the wind differences from the remote sites to
attachment point.
determine if a wind shear problem exists.
luminance — The intensity of light emitted or scattered
low-pass filter — A filter circuit designed to pass
from a surface area in a given direction.
low‑frequency signals and attenuate high‑frequency
signals. luminescence — The emission of light from essentially
nonthermal sources such as phosphorescence.
low-pressure compressor — The front section of a dual
compressor gas turbine engine Also referred to as the N1 luminous paint — A paint that glows in the dark. Used for
compressor or low-speed compressor. marking aircraft instrument dials and pointers.
low-pressure compressor gas turbine engine — The front lye — An alkaline solution consisting of potassium
section of a dual compressor driven by the last stages hydroxide or sodium hydroxide.
of the turbine. Also referred to as the N1 compressor or
low-speed compressor.
low-pressure oxygen system — A gaseous oxygen system
formerly used in military aircraft in which the oxygen is
stored under pressures of approximately 450 PSI.
low-tension ignition system — A magneto system used for
reciprocating engine airplanes that fly at high altitudes.
It consists of a rotating magnet, a cam, breaker points,
a condenser, a coil with only the primary winding, and
a carbon brush‑type distributor. The primary current
is directed through the distributor to a coil for each
individual spark plug. These coils have a primary and a
secondary winding that generate the high voltage at the
spark plug.
low-tension magneto — An ignition system used for
reciprocating en­gine airplanes that fly at high altitudes.
It consists of a rotating magnet, a cam, breaker points,
condenser, a coil with only the primary winding, and

194

10001930-002_AviationDictionary_2012_BOOK.indb 194 3/27/2012 9:38:16 AM

 M • magnetic brake

M for measuring the difference between pitot pres­sure and

static pressure, and includes an aneroid that modifies the
mach — The ratio of the aircraft’s true airspeed to the speed output from this differential pressure bellows to correct
of sound. for the changes in altitude.
mach cone — The cone-shaped shock wave produced by an mackerel sky — A meteorological condition of clouds
object exceeding the speed of sound. that resemble the scales on a mackerel fish. The clouds
consist of rows of altocumulus or cirrocumulus clouds.
mach number — The ratio of the speed of an airplane to
the speed of sound in the same atmospheric conditions; macroscale — Spatial scales of 1,000 NM or more.
e.g., MACH.82, MACH 1.6. magamp — A contraction of magnetic amplified. An
mach technique [ICAO] — Describes a control technique amplifier system using saturable reactors to control
used by air traffic control whereby turbojet aircraft an output to obtain amplification. See also magnetic
operating successively along suitable routes are cleared amplifier.
to maintain appropriate MACH numbers for a relevant magnesium — A silver-white, malleable, ductile metallic
portion of the enroute phase of flight. The principle element with a symbol of Mg and an atomic number of
objective is to achieve improved utilization of the 12. Used to produce light alloys for aircraft construction.
airspace and to ensure that separation between successive
aircraft does not decrease below the established minima. Magnesyn system — An AC remote indicating system in
which a per­manent magnet is used as the rotor. Based
mach tuck — A condition that can occur when operating upon the synchronous-motor principle, in which the
a swept-wing airplane in the transonic speed range. A angular position of the rotor of one motor at the measuring
shock wave could form in the root portion of the wing and source is duplicated by the rotor of the indicator motor.
cause the air behind it to separate. This shock-induced Used in fuel-quantity or fuel-flow measuring systems,
separation causes the center of pressure to move aft. position-indicating systems, etc.
This, combined with the increasing amount of nose down
force at higher speeds to maintain level flight, causes the magnet — A device or material that has the property of
nose to “tuck.” If not corrected, the airplane could enter a attracting or repelling other magnetic materials. Lines
steep, sometimes unrecoverable dive. of magnetic flux link its external poles, and a conductor
cutting across the flux will have a voltage induced into it.
machine bolt — The common name for a hex head bolt
with uniform threads. magnet keeper — A soft iron bar placed across the north
and south poles of a U-shaped magnet. The iron bar
machine language — A language used in a computer produces a closed path through which magnetic lines of
system made up of zeros and ones. A special program force pass.
called a compiler converts a programming language into
machine language that can be used by the computer. magnet wire — A small‑diameter, varnish-insulated
copper wire used in coil windings for electromagnets,
machine screw — A screw fastener with uniform threads transformers, motors, and generators.
that can be screwed into a tapped hole or into a nut. The
head of a machine screw can be round, flat, truss, oval, magnetic amplifier — An electronic control device that
or a fillister‑type. uses a saturable reactor. The condition of saturation is
controlled by the input signal to modulate the flow of a
machine-sewn fabric seams — Machine-sewn aircraft much larger current in the output circuit. It is essentially
fabric seams. The most common types of machine-sewn a multi-coil transformer that controls the amount of load
fabric seams include the French fell, folded fell, and plain current allowed to flow in the load winding by a small
overlap. amount of current in the magnetic core. Changing the
machining — The process of forming the surface by cutting amount of DC flowing in the magnetic core changes
away material by turning, planing, shaping, and milling. the permeability of the core. This, in turn, changes the
Normally accomplished with machine ­operated tools amount of inductive reactance that opposes the AC
such as lathes, milling machines, shapers, and planers. flowing in the load winding.
machinist — A skilled person in the operation of magnetic bearing — The magnetic course to go direct to
metal‑working machine tools such as lathes, shapers, an NDB station.
planers, and milling machines. magnetic brake — 1. A friction brake controlled by
machmeter — A direct-reading indicator installed in an electromagnetic solenoid. The brake can be either
the instrument panel of high‑speed aircraft that gives actuated or released by electromagnetic action (usually
the pilot an indication of his flight Mach number. The on or off). 2. A brake that uses magnetism to oppose
internal mechanism of a machmeter in­cludes a bellows rotation of a disc or drum without any physical contact

195

10001930-002_AviationDictionary_2012_BOOK.indb 195 3/27/2012 9:38:16 AM

 magnetic bubble memory • magnetic pickup RPM system

to create the slowing force. Often used in motor driven interacts with those of the rotating magnet and the cup
devices and in effect reverses the rotational forces on then is displaced axially by the rotation.
the motor until the motor comes to a stop. If the reverse
magnetic drain plug — Similar to a chip detector, except
forces were not removed when the motor stops, the motor
some types cannot be powered to show contamination on
would start to turn the opposite direction.
a warning light in the cockpit. The drain plug consists
magnetic bubble memory — The memory stored in of two small permanent magnets built into it to attract
the form of bubbles or circular areas on a thin film of and hold any ferrous metal particles that can be in the
magnetic media. Used on early digital computers as lubricating oil system. Ferrous metal chips on the drain
non-volatile memory, but no longer widely used. plug indicate the possibility of internal engine failure.
Usually located in the lower portion of a sump in the
magnetic chuck — A metal machining tool that consists of
scavenge oil subsystem.
a special work surface that uses electromagnetism to hold
the material being machined. magnetic field — The space around a magnet or conductor
where magnetic flux is found.
magnetic circuit — Any complete path of magnetic lines
of flux that leaves the north magnet pole of an electrical magnetic flux — The invisible lines of magnetic force that
machine such as a motor or generator and enters the exist between the poles of a magnet, and which follow
magnetic south pole. the path of least resistance. Traditionally, they are given
the direction from north pole to south pole. When an
magnetic circuit breaker — A circuit breaker that opens
electrical conductor cuts across the lines of magnetic
a circuit when­ever there is an excess of current flow in
flux, a voltage is produced in the conductor. One line of
the circuit. It works on the principle of electromagnetism.
magnetic force is called one maxwell.
When rated current flow is exceeded, the magnetic field
develops enough strength to open a set of contacts and magnetic flux density — The unit of field intensity is the
deenergize the circuit. gauss. An individual line of force, called a maxwell, in an
area of one square centimeter produces a field intensity
magnetic compass error — Acceleration error, magnetic
of one gauss.
dip, and turning error. Acceleration error is inherent in
magnetic compasses, caused by the force of acceleration magnetic heading — The angle between the longitudinal
acting on the dip compensating weight when the aircraft axis of an aircraft and magnetic north.
accelerates or decelerates on an easterly or westerly
magnetic hysteresis — The tendency of a material to retain
heading. In compasses compensated for flight in the
magnetism after the magnetizing influence has been
Northern Hemisphere, when the aircraft accelerates on
removed. Hysteresis loops are graphs that indicate the
an easterly or westerly heading, the compass gives the
magnetic properties of different materials.
indication that the aircraft is turning to the North. When
the aircraft decelerates on either of these headings, the magnetic north — True north direction corrected for
compass gives the indication that the aircraft is turning variation error.
to the South. Magnetic dip is an error as the result of
magnetic north pole — The point on the Earth’s surface in
the north end of the compass trying to dip toward the
the Northern Hemisphere where isolines of the Earth’s
magnetic poles in the North and South Hemispheres.
magnetic field converge. Compasses align with the
This is compensated for by adding weights on the south
lines of magnetic flux that connect the north and south
end of the bar magnet in the Northern Hemisphere, and
magnetic poles, with the north-facing pointer directed
the north end in the Southern Hemisphere. Turning error
toward the magnetic north pole. The pole’s location is
is caused by the dip compensating weight. It shows up
not co-located with the north axis of rotation of the Earth
mostly on turns to or from north or south headings and
known as true north.
causes the compass to lead or lag the actual turn.
magnetic particle inspection — A nondestructive inspection
magnetic course — The path of an airplane as measured
for ferrous metal parts in which the part is magnetized,
from magnetic north.
producing north and south poles across any discontinuity,
magnetic deviation — A compass error caused by localized either on the surface or subsurface. Iron oxide, sometimes
magnetic fields in the airplane attracting the floating mixed with a fluorescent dye, is attracted and held over
magnets in the magnetic compass and deflecting it away the discontinuity. The discontinuity shows up as a line of
from magnetic north. iron oxide. If using fluorescent dye, an ultraviolet light (a
black light) shined on the part shows the discontinuity as
magnetic drag cup — The aluminum or copper cup
an incandescent line.
surrounding the rotating magnet in a simple mechanical
tachometer. Eddy currents are generated in this cup by magnetic pickup RPM system — A newer fan speed
the rotating magnetic field, resulting in eddy currents and indicating system that uses a magnetic pickup in the
attendant magnetic fields. This resultant magnetic field fan case. Blade motion produces eddy currents that are

196

10001930-002_AviationDictionary_2012_BOOK.indb 196 3/27/2012 9:38:16 AM

 magnetic poles • major axis of an ellipse

measured and interpreted electronically and displayed as magnetomotive force (MMF) — The magnetizing force in
RPM on a cockpit indicator. a magnetic field. Measured in gilberts or ampere‑turns.
magnetic poles — A suspended magnet swinging freely magnetosphere — The magnetic field surrounding a
will align itself with the Earth’s magnetic poles. One end celestial object (Earth , Moon, stars, etc.). Charged
is labeled “N,” meaning north‑seeking. The opposite end particles are trapped within the magnetosphere.
of the magnet is labeled “S,” meaning south‑seeking.
magnetron — A vacuum tube that generates power
magnetic saturation — A magnet’s saturated condition in at microwave frequencies. The flow of electrons is
which all of the magnetic domains are lined up in the controlled by an externally applied magnetic field.
same direction, and any increase in the magnetic field is
magnitude — A condition of size, quantity, or number.
not possible.
main bus — A common voltage tie point for electrical
magnetic shunt — A piece of soft iron shunted across
circuits.
the air gap of a magnet used in an electrical measuring
instrument. The position of the magnetic shunt can main fuel system — The fuel distribution system used for
be changed to calibrate the instrument by varying the all normal engine operating conditions.
amount of magnetic flux that crosses the air gap.
main rotor — The rotor that supplies the principal lift to a
magnetic variation — The angular difference between the rotorcraft.
geographic north pole and the magnetic north pole. The
main wheels — The wheels of an aircraft landing gear that
exact value of variation depends on the position on the
support the major part of the aircraft weight.
Earth where the measurement is taken.
maintain — 1. Concerning altitude/flight level, the term
magnetic wave — The component of a radio wave
means to remain at the altitude/flight level specified.
perpendicular to the antenna.
The phrase “climb and” or “descend and” normally
magnetic yoke — The mechanical support that completes precedes “maintain” and the altitude assignment; e.g.,
the mag­netic circuit between the poles of a generator. “descend and maintain 5,000.” 2. Concerning other ATC
Also used to describe any ferrous material within the instructions, the term is used in its literal sense; e.g.,
magnetic field of a magnet. This material serves as a low maintain VFR.
impedance “path of least resistance” route for magnetic
maintenance — The inspection, overhaul, repair,
lines of flux.
preservation, and replacement of parts, excluding
magnetic-drag tachometer — A simple mechanical preventive maintenance.
tachometer that contains an aluminum or copper drag cup
maintenance manual — A manual produced by the
surrounding a rotating magnet. The magnet is connected
manufacturer of an aircraft, aircraft engine, or component,
to the equipment whose RPM is to be measured and the
which details the approved methods of maintenance.
drag cup is attached to the pointer in the tachometer
instrument. Eddy currents are generated in this cup by maintenance planning friction level — The friction
the rotating magnetic field, resulting in eddy currents and level specified in AC 150/5320-12, Measurement,
attendant magnetic fields. This resultant magnetic field Construction, and Maintenance of Skid Resistant Airport
interacts with those of the rotating magnet and the cup is Pavement Surfaces that represents the friction value
then displaced axially by the rotation. below which the runway pavement surface remains
acceptable for any category or class of aircraft operations
magnetism — The ability to attract certain materials
but that is beginning to show signs of deterioration.
containing iron and to influence moving electrons.
This value will vary depending on the particular friction
magneto — A self‑contained, permanent‑magnet AC measurement equipment used.
generator with a set of current interrupter contacts and a
maintenance release — A return to service approval of an
step‑up transformer. It is used to supply the high voltage
aircraft by an authorized A&P technician or IA. Logged
required for ignition in an aircraft reciprocating engine.
in the appropriate maintenance record.
magneto safety check — An operational check on an
major alteration — An alteration not listed in the aircraft,
aircraft reciprocat­ing engine in which the magneto switch
aircraft engine, or propeller specification, and one which
is placed in the OFF position with the engine idling to
might appreciably affect weight, balance, structural
ascertain that the switch actually does ground out both
strength, performance, powerplant operation, flight
magnetos.
characteristics, or other qualities affecting airworthi­ness.
magnetometer — An instrument used to measure the
major axis of an ellipse — The longer axis passing through
intensity of a magnetic field. Also used detect the
one focus of an ellipse. See also ellipse.
presence of a metallic object.

197

10001930-002_AviationDictionary_2012_BOOK.indb 197 3/27/2012 9:38:16 AM

 major diameter • Marconi antenna

major diameter — The diameter of a bolt or a screw to the rod with a rounded end inserted into a piece of metal
tip of the threads. tubing in order to keep the tubing from flattening while
it is being bent.
major overhaul — The complete disassembly, cleaning,
inspection, repair, and reassembly of an aircraft, engine, maneuverability — The ability of an aircraft to change
or other aircraft component in accordance with the directions along a flight path and withstand the stresses
manufacturer’s specifications, and which will return the imposed upon it.
device to a serviceable condition. maneuvering — In aviation, to move through a specific
major repair — A repair that, if improperly done, might series of changes in direction, speed and position for a
appreciably affect weight, balance, structural strength, specific purpose. Often used in regards to positioning an
performance, powerplant operation, flight characteristics, aircraft in the landing pattern.
or other qualities affecting airworthiness. FAR 43, manganese — A non‑magnetic chemical element of grayish
Appendix A provides guidance on what constitutes major white with a symbol of Mn and an atomic number of 25.
repairs and alterations. Used in the manufacturing of iron, aluminum, and copper
major structural damage — Damage to a structure that alloys.
requires a major repair in order to return it to proper manganese dioxide — A chemical compound used in
working or operating condition. carbon­-zinc batteries to absorb the hydrogen gas that
make short approach — Used by ATC to inform a pilot would otherwise insulate the carbon rod when electrons
to alter his traffic pattern so as to make a short final flow from the zinc can to the carbon.
approach. Manganin — An alloy of copper, manganese, and nickel.
make-and-break ignition — One of the earliest forms of manifest — A list of passengers and cargo carried on any
electrical ignitions for internal combustion engines. It one flight.
produced an arc when two contacts carrying low-voltage
current within the cylinder were separated. manifold — A chamber having several outlets through
which a liquid or gas is distributed or gathered.
male electrical connector — The pin contact that completes
manifold absolute pressure (MAP) — The absolute
a circuit by sliding inside a socket (the female connector).
pressure, measured in inches of mercury, existing in the
male fitting — A fitting designed to be placed, screwed, or intake manifold of an engine. This is the pressure that
bolted into another unit. forces the fuel-air mixture into the cylinders.
malfunction — The failure of a part of a component to manifold pressure — The absolute pressure, measured
function; a deviation in the operation of a unit from its in inches of mercury, existing in the intake manifold of
intended purpose or design. an engine. This is the pressure that forces the fuel-air
mixture into the cylinder.
malleability — The measure of a material’s ability to
be stretched or shaped by beating it with a hammer or manometer — An instrument consisting of a glass tube
passing through rollers without breaking. filled with a liquid for measuring the pressure of gases or
vapors either above or below atmospheric pressure.
malleable — The ability to be stretched or shaped by
beating with a hammer or passing through rollers without manual depressurization valve — A back‑up valve used
breaking. to control cabin pressurization by manually controlling
the outflow of air from the cabin if the automatic system
mallet — A hammer with a heavy wood, plastic, rubber, or malfunctions.
leather head.
manufactured rivet head — The preformed head of an
mammatus — Bulges or pouches that appear under the aircraft rivet when it is manufactured at the factory. Also
anvil of a mature cumulonimbus cloud. referred to as a shop head.
mandatory altitude — An altitude depicted on an manufacturer — In aviation, a person or a company
instrument Approach Procedure Chart requiring the who manufactures aircraft, aircraft engines, or aircraft
aircraft to maintain altitude at the depicted value. components.
mandatory altitude — An altitude depicted on an manufacturing — The process of taking raw materials and
instrument Approach Procedure Chart requiring the changing them into finished and usable products.
aircraft to maintain altitude at the depicted value.
Marconi antenna — A non-directional, quarter-wave
mandrel — 1. Lathe: A tapered shaft that fits into a hole antenna utilizing a ground plane that serves as a
used to support and center a device or piece of material quarter‑wave reflector. Used for transmitting and receiving
so that it can be machined. 2. Tube bending: A long steel radio communications in the higher frequency bands.

198

10001930-002_AviationDictionary_2012_BOOK.indb 198 3/27/2012 9:38:16 AM

 marginal VFR (MVFR) • maximum authorized altitude (MAA)

marginal VFR (MVFR) — Weather characterized by mast bumping — In rotorcraft, the action of the rotor head
ceilings 1,000 to 3,000 feet AGL and/or visibility three striking the mast, occurring on underslung rotors only.
to five statute miles.
master cylinder — A combination cylinder, piston, and
marine grommet — A plastic or metal reinforcement reservoir used in an aircraft brake system. Fluid is stored
ring designed with a special shield used to keep water when the brakes are not applied and is then forced into
spray caused by takeoff and landings from entering the the system for braking.
structure. It is normally attached to the underside of
master minimum equipment list (MMEL) — A master
wings and control surfaces of fabric-covered aircraft and
list developed by the Federal Aviation Administration for
used to reinforce drain holes that are cut into the fabric.
an aircraft by make and model delineating the specific
marker beacon (MB) — An electronic navigation facility equipment allowed to be inoperative during various
transmitting a 75 MHz vertical fan or boneshaped types of flight operations. The MMEL is the basis for the
radiation pattern. Marker beacons are identified by development of an MEL.
their modulation frequency and keying code, and when
master rod — The only connecting rod in
received by compatible airborne equipment, indicate to
a radial engine attached directly to the
the pilot, both aurally and visually, that he is passing over
crankshaft. All of the other rods connect to
the facility.
the master rod rather than the crankshaft.
married needles — A term used regarding an engine‑rotor
master switch — A single switch designed
tachometer when the hands are superimposed. One hand
to control electric power to all circuits in
indicates engine RPM and the other hand indicates the
a system.
main rotor RPM.
mat — In composites, typically used in the mold making
Marvel balancer — A universal balancer commonly used
process. Chopped fibers are held together with a binder.
throughout the helicopter industry.
When the resin matrix is applied, the binder melts.
masking material — Aluminum foil or special paper used Typically used with polyester resin systems.
during painting to cover areas of an aircraft surface that
matched gears — Two gears used in a set and only replaced
are not to be sprayed or on which a finish is not to be
in a set.
applied.
matching transformer — An electronic device used to
masking tape — Paper tape that has a sticky surface on one
connect a load and a source of electrical power that differ
side and generally comes in rolls of varying widths. Used
in their impedance. It consists of a transformer with a
for masking areas during painting.
primary winding that matches the impedance of the
Maslow’s hierarchy of human needs — A listing by source and a secondary winding that matches the load.
Abraham Maslow of needs from the most basic to the
mathematics — That branch of science dealing with
most fulfilling. These range from physical through safety,
numbers and their operation.
social, and ego to self-fulfillment.
mating surfaces — Two surfaces that come together to
Masonite — A type of fiberboard.
form a seal.
mass — A measure of the amount of material or matter
matrix — In composite construction, the material that
contained in a body. It is the property of a body that
bonds the fibers together, and distributes the stress to the
causes the force of gravity to give a body weight.
fibers. Typically in advanced composites, the matrix is a
mass flow rate — The result of a fluid’s density and its resin.
linear velocity.
matter — Any substance that has weight and occupies space.
mass production — The production of objects in very large
mature stage — In meteorology, the most intense stage of
quantities in a relatively short time period by the use of
a thunderstorm. Begins when the precipitation-induced
complex, and often computerized, equipment.
downdraft reaches the ground. Usually lasts about 20
massive-electrode spark plug — Spark plugs using two, minutes.
three, or four, large nickel-alloy ground electrodes.
maximum allowable zero-fuel weight — The maximum
mass-type fuel flowmeter — A fuel-flow measurement weight authorized for an aircraft excluding its fuel load.
system used with turbine engines that indicates the mass
maximum authorized altitude (MAA) — A published
flow rather than the volume flow.
altitude representing the maximum usable altitude or
mast — In rotorcraft, the component that supports the main flight level for an airspace structure or route segment.
rotor. It is the highest altitude on a Federal airway, jet route,

199

10001930-002_AviationDictionary_2012_BOOK.indb 199 3/27/2012 9:38:16 AM

 maximum except takeoff power (METO) • medium-scale integration

area navigation low or high route, or other direct route mechanical advantage — The increase in force or speed
for which an MEA is designated in FAR 95 at which gained by using such devices as levers, pulleys, gears, or
adequate reception of navigation aid signals is assured. hydraulic cylinders.
maximum except takeoff power (METO) — The mechanical blockage thrust reverser — A thrust reverser
maximum con­tinuous power an engine is allowed to usually of the post exit-type (clamshell) used to reverse
develop without any time restrictions. the hot exhaust stream of a gas turbine engine to help
slow the airplane during landings.
maximum landing weight — The maximum authorized
weight of the aircraft for landing. mechanical bond — The joining of two or more parts or
pieces by mechanical methods such as bolts, rivets, or
maximum range — The maximum distance an aircraft can
pins.
travel by flying at the most economical speed and altitude
during all stages of flight. mechanical efficiency — The ratio of the brake horsepower
delivered to the output shaft of an engine to its indicated
maximum takeoff power — The maximum power an
horsepower.
engine is allowed to develop for a limited period of time,
usually about one minute. mechanical energy — Energy that expresses itself in
mechanical movement or the physical production of
maximum takeoff weight — The maximum design weight
work.
of any aircraft for takeoff.
mechanical linkage — A direct connection between a
maximum weight — The maximum allowable weight for
control and a unit. No remote actuator.
an aircraft under any conditions.
mechanical mixture — A mixture of two or more elements
maxwell — A unit of magnetic flux. One magnetic line of
or compounds that can be identified by microscopic
force.
ex­amination.
may — As related to aircraft maintenance, means that such
mechanical properties — Those properties that involve a
an item is allowed, but not required.
relationship between strain and stress.
mayday — The international radiotelephony distress signal.
mechanical turbulence — The turbulence that results
When repeated three times, it indicates imminent and
when airflow is slowed by surface friction.
grave danger and that immediate assistance is requested.
median — In mathematics, the number in an ordered set of
mean — The average of a number of factors. Often used to
values below and above which there is an equal number
indicate the mid-point between two extremes.
of values. In the list 1,2,3,7,15,16, and 23, the median
mean aerodynamic chord (MAC) — The chord of is seven since there are three numbers smaller and three
an imaginary rectangular airfoil having the same numbers greater than seven. Note that this differs from
aerodynamic characteristics as that of the actual wing. the mathematical mean.
mean sea level (MSL) — The reference used for measur­ing medical certificate — Short for FAA Airman Medical
altitude above sea level. Mean sea level is the average Certificate. Obtained by passing a physical examination
height of the surface of the sea. administered by a doctor who is an FAA-authorized
Aviation Medical Examiner (AME).
mean solar day — The average time it takes the Earth to
rotate about its axis in one day. medium bypass turbofan — Engines with 2:1 or 3:1
bypass ratios, which is the ratio of the amount of air the
measured ceiling — In weather, a classification where
fan moves (or bypasses) in relation to the core engine.
the height of the ceiling has been determined (by one of
Also referred to as moderate bypass.
several measures) as opposed to estimated.
medium frequency (MF) — The band of electromagnetic
measuring circuit — Any combination of resistors,
radiation frequencies that lie between 300 kHz and 3
batteries, and meters that make it possible to measure
MHz.
electrical values.
medium-frequency radio transmission — An outgoing
mechanic — In aviation, a person certificated by the FAA
signal from a transmitter broadcasting an electromagnetic
as an Airframe and Powerplant (A & P) mechanic.
radiation frequency between 300 kHz and 3 MHz.
(Mechanics can be certified as either a Powerplant and/or
Airframe mechanic.) Aviation Maintenance Technician medium-scale integration — A method of fabricating
(AMT) has become the preferred term. integrated circuit (IC) chips to place multiple transistors or
logic circuits on one small IC. Medium-scale integration
places 10 to 100 circuits on one integrated circuit.

200

10001930-002_AviationDictionary_2012_BOOK.indb 200 3/27/2012 9:38:16 AM

 megahertz (MHz) • mesosphere

megahertz (MHz) — 1,000,000 cycles per second. mercury cell — A primary cell using zinc for the negative
electrode, mercuric oxide for the positive electrode, and
megger — A high‑voltage, high‑range ohmmeter that has a
potassium hydroxide as the electrolyte.
built‑in (often hand‑turned) generator for producing the
voltage needed to measure insulation resistance and the mercury clutch — A centrifugal clutch in which mercury is
resistance between a com­ponent and electrical ground. used to engage the clutch.
Also referred to as a megohmmeter.
mercury oxide cell — A chemical cell using powdered
megohmmeter — High‑resistance measuring instrument mercuric oxide and powdered zinc as its pole pieces. The
incorporating a high‑voltage DC generator in the electrolyte is a liquid solution of potassium hydroxide.
instrument case. Not only does this measure high
mercury switch — A switch that makes and breaks the
resistance, it does it with a high enough voltage to cause
circuit by way of mercury in a glass tube bridging the
insulation breakdown if it has been weakened. Also
contacts as the tube is rocked back and forth.
referred to as a megger.
mercury thermometer — A thermometer consisting of a
melt — A change in the physical state of a material when
glass tube with an extremely small inside diameter to
it goes from a solid to a liquid as a result of absorbing
which is attached a small reservoir containing mercury.
sufficient heat to produce the change.
A temperature scale marked alongside the tube is used to
melting — The change of state of a solid to a liquid, as ice indicate the temperature when the mercury expands up
to water. the tube due to a rise in temperature.
melting point — A temperature at which a solid becomes mercury trap — A container in the pick‑up tube of a
a liquid. vacuum cleaner used to retrieve spilled mercury. The
mercury is sucked up by the cleaner and deposited in
member — Any portion of the aircraft structure essential the bottle that prevents it from being sprayed out by the
to the whole. discharge of the cleaner.
memory effect — A reduction in the service capacity of mercury vapor lamp — A lamp that glows from the
nickel-cadmium cells that occurs when cells on standby excitation of mercury vapor atoms by an electric arc.
service are regularly recharged after being discharged to
only a small fraction of their full service capacity. mercury-vapor rectifier — A rectifier tube containing
mercury, which vaporizes during operation and increases
meniscus — The curved upper surface of a column of liquid the current‑carrying capacity of the tube.
in a tube. If the liquid wets the tube, the curve will be
concave; if the liquid does not wet the tube, the curve mesh — The engagement of the teeth of gears.
will be convex. mesh rating — A U.S. sieve number and filtration rating
mensuration — The act or process of measuring. common to fuel filters. Similar to a micron rating, e.g. a
74 micron filter carries an equivalent U.S. sieve number
Mercator projection — A map projection where parallel of 200 and has 200 openings per linear inch.
meridians and lines of latitude are straight lines at right
angles to the meridians. The distance between lines of mesopause — The outer extent of the mesosphere, slightly
latitude increases as they move farther away from the more than 280,000 feet MSL, the boundary between the
equator. mesosphere and thermosphere.

mercerize — See mercerizing. mesoscale — Spatial scales from 1 to 1,000 nautical miles.

mercerizing — The process of dipping cotton yarn or fabric mesoscale convective complex (MCC) — The nearly
into a hot solution of caustic soda. It gives the material circular clusters of thunderstorms 300 NM or more in
greater strength and luster and is stronger and more diameter. MCC develops primarily between the Rockies
pliable than untreated fabric. and the Appalachians during the warmer part of the year.

mercury — A heavy, silver-colored, toxic, liquid, metallic mesoscale convective systems (MCS) — A large cluster of
chemical element with a symbol of Hg and an atomic thunderstorms with horizontal dimensions on the order
number of 80. Mercury remains in a liquid state under of 100 miles. MCSs are sometimes organized in a long
standard conditions of pressure and temperature. Mercury line of thunderstorms (e.g., a squall line) or as a random
is approximately 13 times as heavy as water. grouping of thunderstorms. Individual thunderstorms
within the MCS may be severe.
mercury barometer — A closed glass tube partially filled
with mercury, used to determine the pressure exerted by mesosphere — A layer of the atmosphere between the top
the atmosphere. The standard atmospheric pressure at sea of the strato­sphere or the ionosphere and the exosphere
level will hold the mercury in the tube to a height of 760 (about 250-600 miles above the Earth).
mm or 29.92”.

201

10001930-002_AviationDictionary_2012_BOOK.indb 201 3/27/2012 9:38:17 AM

 metal • meter list display interval

metal — A chemical possessing most of the following metallic pigment — Extremely tiny flakes of metal
characteristics: usually rather heavy, with a bright and suspended in paint to produce a sheen.
shining surface, malleable, ductile, and a good electrical
metallic ring test — A test for delaminations in a bonded
conductor.
structure in which a coin or similar object is used to tap
metal chip detector (MCD) — An electrical device on the surface. If the bond is good, a metallic ringing
for warning the aircrew of ferrous particles in the oil. sound will be produced, however, if it is delaminated, a
Consists of two magnets separated by a narrow gap or dull thud will be heard.
insulator. The detector is found in the bottom of the oil
metallizing — 1. To replace the fabric covering on an
sump. When ferrous particles from the oil are attracted
aircraft structure with sheet metal. 2. A method of metal
to the magnets and bridge the gap, a circuit is completed
overlay or metal bonding to repair worn parts
and a warning lamp illuminates in the cockpit.
metallurgy — The science and technology dealing with
metal fatigue — A method of work hardening or cold
metals and their use.
working of a metal that results from flexing or vibration
and which increases the brittleness of the material to its metal-matrix composites (MMC) — In composites, fibers
breaking point. bonded together with a metal as the bonding material.
metal foil — A very thin sheet of metal such as aluminum foil. metalworking tools — Machines and tools used in the
construction and repair of sheet metal structures.
metal oxide rectifier — An electronic device that enables
one-way flow of current through the flow of electrons metamerism index — A measurement used for scientific
from the base material to an oxide layer, but not from the color match­ing. It indicates the way a pigment will look
oxide layer to the base material. under varying light conditions.
metal oxide semiconductor capacitor — An electronic METAR — The international weather reporting code that
device that utilizes metal oxide as a dielectric to create will be introduced in the U.S., after June 1, 1996.
capacitance.
metastable compound — A chemical compound that has
metal oxide semiconductor field effect transistor only a slight margin of stability.
(MOSFET) — A semiconductor whose gate is insulated
meteor — A small particle of matter in the solar system
from the channel. The MOSFET was originally called
visible only as it burns due to the high temperature
the insulated-gate FET (IGFET). The MOSFET has an
caused by friction as the meteor falls through the Earth’s
extremely large input impedance. Because the insulating
atmosphere.
oxide layer is extremely thin, the MOSFET is susceptible
to destruction by electrostatic charges. Special precautions meteorological impact statement — An unscheduled
are necessary when handling or transporting MOS devices. planning forecast describing conditions expected to
begin within 4 to 12 hours that can impact the flow of air
metal sheath — A close-fitting metal cover.
traffic in a specific center’s (ARTCC) area.
metal spinning — A process of metal forming in which
meteorological visibility — A measure of horizontal
sheet metal is clamped into a lathe along with the male
visibility in a given direction near the Earth’s surface,
die. A shaping tool is used to force the spinning metal
based on sighting of objects in the daytime or unfocused
against the die.
lights of moderate intensity at night.
metal spraying — A method of covering or repairing a
meteorology — The study of weather and atmospheric
material with a coating of metal. The metal to be used
phenomena.
for the coating is melted and sprayed out with hot,
high‑velocity compressed air. meter — 1. A device used to measure, indicate, or record.
2. The basic unit of length measurement in the metric
metal-film resistor — A resistor in which an oxide of metal
system equal to approximately 39.37”.
is deposited as a film onto a base material. The type of
metal and the thickness determine the resistance of the meter fix time/slot time — A calculated time to depart the
device. meter fix in order to cross the vertex at the ACLT. This
time reflects descent speed adjustment and any applicable
metallic — Having the nature of metal or containing metal.
time that must be absorbed prior to crossing the meter fix.
metallic ion concentration cell corrosion — Corrosion
meter list display interval — A dynamic parameter that
that results from a concentration of metallic ions in the
controls the number of minutes prior to the flight plan
electrolyte. The area of high concentration of metallic
calculated time of arrival at the meter fix for each
ions is the cathode.
aircraft, at which time the TCLT is frozen and becomes
an ACLT; i.e., the VTA is updated and consequently the

202

10001930-002_AviationDictionary_2012_BOOK.indb 202 3/27/2012 9:38:17 AM

 metering • microcircuit

TCLT modified as appropriate until frozen at which time is equal to 1.0139 mechanical horsepower in the system
updating is suspended and an ACLT is assigned. When of measurement used in the United States.
frozen, the flight entry is inserted into the arrival sector’s
metric prefixes — A system of prefixes that indicate
meter list for display on the sector PVD/MDM. MLDI is
multiples and submultiples of ten. Some of the more
used if filed true airspeed is less than or equal to freeze
common prefixes used are:
speed parameters (FSPD).
Tera 1012
metering — A method of time-regulating arrival traffic flow
Giga 109
into a terminal area so as not to exceed a predetermined
Mega 106
terminal acceptance rate.
Kilo 103
metering airports — Airports adapted for metering and for milli 10-3
which optimum flight paths are defined. A maximum of micro 10-6
15 airports can be adapted. nano 10-9
pico 10-12
metering device — -A device used to measure or control
the amount of fluid flow. mho — A unit of electrical conductance; the reciprocal of ohm.
metering fix — A fix along an established route from over mica — A transparent silicate mineral. It is used as an
which aircraft will be metered prior to entering terminal electrical insulator in capacitors and as an insulator for
airspace. Normally, this fix should be established at electric irons and heaters.
a distance from the airport that will facilitate a profile
Micarta — A phenolic‑type thermosetting resin
descent 10,000 feet above airport elevation (AAE) or
impregnated cloth. It is used as an electrical insulator and
above.
for the manufacturing of control pulleys.
metering jet — The calibrated orifice in a fluid-flow system
mice — Small sheet metal, wedge‑shaped tabs inserted
used to control the amount of flow for a given pressure
into the tail pipe of some older turbine engines to reduce
drop across the jet.
the nozzle opening and increase thrust. Used to “trim” a
metering pin — A flow control device such as a tapered pin turbine engine. Also referred to as tail pipe inserts.
in an oleo shock absorber used to progressively restrict
micro — One millionth (0.000001) of a unit.
the passage of fluid from one chamber into the other,
cushioning the landing im­pact. The shape or contour of microammeter — An electrical current measuring
the metering pin determines the amount of fluid that can instrument capable of measuring current flow in
flow with the pin in any position other than full in or full millionths of an ampere.
out.
microballoons — Microscopic‑size phenolic or glass
metering valve — A valve used to control the flow of a spheres used to add body with very little weight to a resin
fluid. when used as a filler or potting compound.
meter-kilogram — The amount of work produced when microbarograph — An instrument used in meteorology to
one kilogram of force acts through a distance of one measure very small changes in pressure.
meter.
microbes — Microscopic forms of animal life. They exist
methanol wood alcohol — A liquid alcohol produced by in water and feed on hydrocarbon aircraft fuel. Microbes
the distillation of wood pulp. form a water‑entrapping scum on the bottom of jet
aircraft fuel tanks.
methyl bromide — A fire extinguishing agent (CH3Br).
More effective than C02 from a standpoint of weight, but microbiological corrosion — The deterioration of
more toxic than CO2. It will seriously corrode aluminum materials caused directly or indirectly by bacteria,
alloy, zinc, and magnesium. Methyl bromide cannot be algae, molds, or fungi, either alone or in combination.
used in areas where harmful concentrations can enter Microbiological corrosion is significant to aviation when
personnel compartments. linked to corrosion of airframe components, particularly
in fuel tanks and related systems.
methylene chloride — A liquid solvent (CH2CL2) used as
the active agent in many paint strippers. microburst — A small downburst with outbursts of
damaging winds extending 2.5 miles or less. In spite of
methyl-ethyl-ketone (MEK) — A low-­cost solvent similar
its small horizontal scale, an intense microburst could
to acetone. Used as a cleaning agent to prepare a surface
induce wind speeds as high as 150 knots.
for painting and as a stripper for certain finishes. Should
be used only in well-ventilated areas. microcircuit — An extremely small electronic component
that has a large number of circuit elements combined into
metric horsepower — A measurement of power in the
a single unit.
metric system of measurement. One metric horsepower
203

10001930-002_AviationDictionary_2012_BOOK.indb 203 3/27/2012 9:38:17 AM

 microelectronics • mid-span weight

microelectronics — The branch of electronics that deals microphone — A device for converting sound waves to
with integrated circuits and other small electronic electric signals.
devices.
microprocessor — A small central processing unit (CPU)
micro-en route automated radar tracking system for a microcomputer.
(M-EARTS) — An automated radar and radar
microscale — Spatial scales of 1 n.m. or less.
beacon tracking system capable of employing both
short-range (ASR) and long-range (ARSR) radars. microscope — An optical instrument used to magnify extremely
This microcomputer driven system provides improved small objects so they can be seen by the human eye.
tracking, continuous data recording, and use of full
microsecond — One millionth (0.000001) of a second.
digital radar displays.
microshaver — An adjustable metal‑cutting tool used for
microfarad (µF ) — One millionth (0.000001) of a farad.
shaving the heads of countersunk rivets so they are flush
microfiche — Sheets of film that store reduced-size printed with the surface.
and graphic information. One sheet of microfiche can
microshaving — A process in sheet metalwork in which
stores between 24 and 288 individual frames or pages of
the head of the countersunk rivet is shaved to absolute
material on a single 4” x 6” sheet of photographic film.
smoothness with the surface of the skin.
The microfiche film is read on a reader that enlarges the
image and can often make a printed copy of the desired microswitch — An electrical switch used to open or close a
page(s), if needed. circuit with an extremely small movement of the actuator.
microfilm — Reproduction of printed material on 35 mm or microwave landing system — A precision instrument
16 mm photographic film; used to store vast quantities of approach system operating in the microwave spectrum
written material in a small space. The microfilm is read that normally consists of the following components:
on a reader that enlarges the image and can make a full
a. Azimuth Station.
size printed copy of the desired page(s), if needed.
b. Elevation Station.
microinch — One millionth (0.000001) of an inch.
c. Precision Distance Measuring Equipment.
micrometer — One millionth (0.000001) of a meter. A
micrometer is also referred to as a micron. microwaves — Electromagnetic radiation with a wavelength
between infrared and short-wave radio wavelengths
micrometer caliper — A precision measuring device
(frequency higher than 1 gigahertz and a wavelength
having a single movable jaw, advanced by a screw. One
shorter than 30 centimeters).
revolution of the screw advances the jaw 0.025”.
mid RVR — The RVR (runway visual range ) readout
micrometer setting torque wrench — A hand‑operated
values obtained from RVR equipment located midfield
torque wrench in which a preset torque is adjusted with
of the runway.
a micrometer‑type scale. When torque is reached, the
handle of the wrench breaks over, indicating the torque middle compass locator — A low power, low or medium
to the operator. frequency (L/MF) radio beacon installed at the site of the
middle marker of an instrument landing system (ILS).
micro-microfarad — A unit of capacitance equal to one
millionth of a millionth of a farad. Also referred to as middle marker — A marker beacon that defines a point
picofarad. along the glide slope of an ILS normally located at or
near the point of decision height (ILS Category I). It
micron — 1. One millionth (0.000001) of a meter, or one
is keyed to transmit alternate dots and dashes, with the
thousandth (0.001) of a millimeter (0.000001 meter
alternate dots and dashes keyed at the rate of 95 dot/dash
or 1 x 106 meter). Also referred to as a micrometer. 2.
combinations per minute on a 1300 Hz tone, which is
The pressure measurement in a column of mercury:
received aurally and visually by compatible airborne
One micron of pressure is equal to 0.001 millimeter
equipment.
of mercury (1 x 106 meter of mercury) at 0°C. 3. One
micron is normally used to denote the effectiveness of mid-flap — The middle flap on a triple‑slotted segmented
a filter. flap.
micronic filter — A disposable element filter used in mid-span shrouds — The lugs on fan blades that contact
hydraulic or pneumatic systems that filters particles as each other to provide a circular support ring. Mid-span
small as one micron. shrouds provide strength and reduce vibration.
microorganism — An organism of microscopic size, mid-span weight — A weight placed in the mid‑span area
normally bacteria or fungus. of a helicop­ter rotor blade to add inertia to the blade.

204

10001930-002_AviationDictionary_2012_BOOK.indb 204 3/27/2012 9:38:17 AM

 mid-wing airplane • minimum enroute IFR altitude

mid-wing airplane — An airplane having its main mill file — A single‑cut file, tapered slightly in thickness
aerodynamic surface located in the center of the fuselage. and in width for about one‑third of its length.
migrate — To move from one place to another. During an milli — One one‑thousandth (0.001) of a unit.
inspection, a technician might discover a fastener has
milliameter — An electrical current measuring device
moved or migrated from its intended location to another
calibrated to read in milliamperes. 1000 milliamperes =
location due to vibration or jostling.
1 ampere.
migration — See migrate.
milliampere — One‑thousandth (0.001) of an ampere.
mil — Commonly used to represent one one‑thousandth
millibar — A unit of barometric pressure equal to
(0.001) of an inch.
approximately 0.75 millimeters of mercury. Standard sea
mild steel — Steel that contains between 0.05 and 0.25% level atmospheric pressure is equal to 1,013.2 millibars.
carbon.
milling machine — A metal‑working machine tool with a
mildew — A gray colored parasitic fungus growth that movable table that feeds the work into a rotating milling
forms on organic matter. cutter.
mildewcide — An additive to dope or sealers used when millivolt — One‑thousandth (0.001) of a volt.
covering organic materials to inhibit the growth of
MILSPEC — A term used to identify military specifications.
mildew.
mineral-based hydraulic fluid — A petroleum‑based
mile (mi) — One statute mile. Equal to 5,280 ft.
hydraulic fluid consisting essentially of kerosene and
mileage break point — On IFR charts, points other additives to inhibit corrosion and minimize foaming. It is
than intersections or navaids where the mileage is dyed red and is identified as MIL‑H‑5606.
broken down for reasons such as reception distance.
miniature screw — A screw less than 0.06” in diameter,
The distances between navaids is in a box. A number
having a slotted head and threaded for assembly with a
without an outlined box indicates mileage between any
preformed internal thread.
combination of intersections, navaids, or mileage break
points. All distances are in Nautical Miles. minicomputer — A small digital computer.
miles-in-trail — A specified distance between aircraft, minidisk — A mass storage medium used in digital
normally, in the same stratum associated with the same computers. Most common is the 3-1/2-inch diskette, also
destination or route of flight. known as a floppy. Older computers used 8-inch and
5-1/4-inch minidisks. Most modern personal computers
military authority assumes responsibility for separation
use CD ROM disks as well as 3-1/2-inch diskettes.
of aircraft (MARSA) — A condition whereby the
military services involved assume responsibility for minima — Weather condition requirements established
separation between participating military aircraft in the for a particular operation or type of operation; e.g., IFR
ATC system. It is used only for required IFR operations takeoff or landing, alternate airport for IFR flight plans,
that are specified in letters of agreement or other VFR flight, etc. See minimums.
appropriate FAA or military documents.
minimum crossing altitude — The lowest altitude at certain
military operations area (MOA) — Airspace established fixes at which an aircraft must cross when proceeding in
outside of a Class A airspace area to separate or segregate the direction of a higher minimum enroute IFR altitude
certain nonhazardous military activities from IFR traffic (MEA).
and to identify for VFR traffic where these activities are
minimum descent altitude — The lowest altitude,
conducted.
expressed in feet above mean sea level, to which descent
Military Standards (MS) — The standards used for aircraft is authorized on final approach or during circle-to-land
hardware in order to maintain a high degree of quality maneuvering in execution of a standard instrument
standards in the manufacturing, repair, and maintenance approach procedure where no electronic glide slope is
of aircraft. Originated by the U.S. military services. provided.
military training route (MTR) — Airspace of defined minimum enroute altitude (MEA) — Typically the lowest
vertical and lateral dimensions established for the published altitude between radio fixes that guarantees
conduct of military flight training at airspeeds in excess adequate navigation signal reception and obstruction
of 250 knots IAS. clearance (2,000 feet in mountainous areas and 1,000 feet
elsewhere).
mill bit — A tool used with a router to remove metal and
honeycomb core for repairs to bonded structure. minimum enroute IFR altitude — The lowest published
altitude between radio fixes that assures acceptable

205

10001930-002_AviationDictionary_2012_BOOK.indb 205 3/27/2012 9:38:17 AM

 minimum equipment list (MEL) • minimum safe altitude (MSA)

navigational signal coverage and meets obstacle clearance minimum navigation performance specification — A
requirements between those fixes. The MEA prescribed set of standards that require aircraft to have a minimum
for a Federal airway or segment thereof, area navigation navigation performance capability in order to operate in
low or high route, or other direct route applies to the MNPS designated airspace. In addition, aircraft must be
entire width of the airway, segment, or route between the certified by their State of Registry for MNPS operation.
radio fixes defining the airway, segment, or route.
minimum navigation performance specification (MNPS)
minimum equipment list (MEL) — A list developed airspace — Designated airspace in which MNPS
for larger aircraft that outlines equipment that can be procedures are applied between MNPS certified and
inoperative for various types of flight including IFR and equipped aircraft. Under certain conditions, non-MNPS
icing conditions. This list is based on the MMEL (master aircraft can operate in MNPSA. However, standard
minimum equipment list) developed by the FAA and oceanic separation minima is provided between the
must be approved by the FAA for use. It is specific to an non-MNPS aircraft and other traffic. Currently, the only
individual aircraft make and model. designated MNPSA is described as follows:
minimum friction level — The friction level specified a. Between FL 285 and FL 420;
in AC 150/5320-12, Measurement, Construction,
b. Between latitudes 27º N and the North Pole;
and Maintenance of Skid Resistant Airport Pavement
Surfaces, that represents the minimum recommended c. In the east, the eastern boundaries of the CTA’s Santa
wet pavement surface friction value for any turbojet Maria Oceanic, Shanwick Oceanic, and Reykjavik;
aircraft engaged in LAHSO. This value will vary with
d. In the west, the western boundaries of CTA’s Reykjavik
the particular friction measurement equipment used.
and Gander Oceanic and New York Oceanic excluding
minimum fuel — 1. The minimum fuel specified for weight the area west of 60º W and south of 38º 30’ N.
and balance purposes when computing an adverse loaded
minimum obstruction clearance altitude (MOCA) — The
center of gravity. It is the quantity of fuel necessary for
lowest published altitude in effect between radio fixes on
one half hour of operation at rated maximum continuous
VOR airways, off-airway routes, or route segments that
power. 2. Indicates that an aircraft’s fuel supply has
meets obstacle clearance requirements for the entire route
reached a state where, upon reaching the destination, it
segment and that assures acceptable navigational signal
can accept little or no delay. This is not an emergency
coverage only within 25 statute (22 nautical) miles of a VOR.
situation but merely indicates an emergency situation is
possible should any undue delay occur. minimum off-route altitude (MORA) — On Jeppesen
Enroute charts, provides clearance from known
minimum holding altitude — The lowest altitude
obstructions within 10 NM of the route centerline.
prescribed for a holding pattern that assures navigational
signal coverage, communications, and meets obstacle minimum reception altitude — The lowest altitude at
clearance requirements. which an intersection can be determined.
minimum IFR altitudes — Minimum altitudes for IFR minimum safe altitude (MSA) — 1. The minimum altitude
operations as prescribed in FAR 91. These altitudes are specified in FAR 91 for various aircraft operations. 2.
published on aeronautical charts and prescribed in FAR Altitudes depicted on approach charts that provide at
95 for airways and routes, and in FAR 97 for standard least 1,000 feet of obstacle clearance for emergency use
instrument approach procedures. If no applicable within a specified distance from the navigation facility
minimum altitude is prescribed in FAR 95 or FAR 97, the upon which a procedure is predicated. These altitudes will
following minimum IFR altitude applies: be identified as Minimum Sector Altitudes or Emergency
Safe Altitudes and are established as follows:
a. In designated mountainous areas, 2,000 feet above
the highest obstacle within a horizontal distance of 4 minimum sector altitudes – Altitudes depicted on
nautical miles from the course to be flown; or approach charts that provide at least 1,000 feet of obstacle
clearance within a 25-mile radius of the navigation
b. Other than mountainous areas, 1,000 feet above the
facility upon which the procedure is predicated. Sectors
highest obstacle within a horizontal distance of 4
depicted on approach charts must be at least 90 degrees
nautical miles from the course to be flown; or
in scope. These altitudes are for emergency use only and
c. As otherwise authorized by the Administrator or do not necessarily assure acceptable navigational signal
assigned by ATC. coverage.
minimum level flight speed — The speed below which a Emergency Safe Altitudes – Altitudes depicted on
gyroplane, the propeller of which is producing maximum approach charts that provide at least 1,000 feet of obstacle
thrust, loses altitude. clearance in nonmountainous areas and 2,000 feet of
obstacle clearance in designated mountainous areas

206

10001930-002_AviationDictionary_2012_BOOK.indb 206 3/27/2012 9:38:17 AM

 minimum safe altitude warning • missed approach procedure [ICAO]

within a 100-mile radius of the navigation facility upon are present in a semiconductor. The more abundant charge
which the procedure is predicated and normally used carriers are called majority carriers; the less abundant
only in military procedures. These altitudes are identified are called minority carriers. In N-type semiconductor
on published procedures as “Emergency Safe Altitudes.” material, electrons are the majority carriers and holes are
the minority carriers. In P-type semiconductor material,
minimum safe altitude warning — A function of the
the reverse is true. Current leakage in a reverse-bias
ARTS III computer that aids the controller by alerting
direction is flow of the minority carriers.
him when a tracked Mode C equipped aircraft is below or
is predicted by the computer to go below a predetermined minuend — The number from which the subtrahend is
minimum safe altitude. subtracted.
minimum sector altitude [ICAO] — The lowest altitude minus — A negative value. Minus values are indicated by
that can be used under emergency conditions to provide using a short dash in front of the value (-4). A minus sign
a minimum clearance of 300 m (1,000 feet) above all is used in electricity to indicate a negative condition.
obstacles located in an area contained within a sector of
minute — 1. Measurement: An angular measurement equal
a circle of 46 km (25 NM) radius centered on a radio aid
to 1/60 of a degree in a 360° circle (21,600 minutes of
to navigation.
angle in a circle.) 2. Time: A unit of time that is equal to
minimum sink airspeed — In gliders, the airspeed, as 1/60 of an hour or 60 seconds.
determined by the performance polar, at which the glider
minutes-in-trail — A specified interval between aircraft
will achieve the lowest sink rate. That is, the glider
expressed in time. This method would more likely be
will lose the least amount of altitude per unit of time at
utilized regardless of altitude.
minimum sink airspeed.
mirror image — An object that is an exact duplicate of the
minimum vectoring altitude (MVA) — The lowest MSL
original but reversed as if the object were viewed through
altitude at which an IFR aircraft will be vectored by a
a mirror.
radar controller, except as otherwise authorized for radar
approaches, departures, and missed approaches. The misalignment — A condition that exists when two mating
altitude meets IFR obstacle clearance criteria. It may be surfaces do not meet or match as they should.
lower than the published MEA along an airway or J-route
miscible — The ability of a material to combine or mix with
segment. It may be utilized for radar vectoring only upon
another material.
the controller’s determination that an adequate radar
return is being received from the aircraft being controlled. misfire — The failure of an explosive charge, as in the
Charts depicting minimum vectoring altitudes are misfire of a rocket or an engine.
normally available only to the controllers and not to pilots.
misfiring — The interruption of even firing of a reciprocating
minimum-flow stop — Refers to a fuel control design engine’s cylinders.
that prevents the power lever from shutting off fuel. A
missed approach — 1. A maneuver conducted by a pilot
separate shutoff is provided in this case.
when an instrument approach cannot be completed to
minimums — Weather condition requirements established a landing. The route of flight and altitude are shown on
for a particular operation or type of operation; e.g., IFR instrument approach procedure charts. A pilot executing
takeoff or landing, alternate airport for IFR flight plans, a missed approach prior to the Missed Approach Point
VFR flight, etc. (MAP) must continue along the final approach to the
MAP. The pilot can climb immediately to the altitude
minor alteration — Any alteration not considered to be a
specified in the missed approach procedure. 2. A term
major alteration.
used by the pilot to inform ATC that he is executing
minor axis of an ellipse — A straight line that passes the missed approach. 3. At locations where ATC radar
through the center of the ellipse and is perpendicular to service is provided, the pilot should conform to radar
the major axis. vectors when provided by ATC in lieu of the published
missed approach procedure.
minor fastener diameter — The diameter of a threaded
fastener measured at the thread root. missed approach point — A point prescribed in each
instrument approach procedure at which a missed
minor repair — Any repair not considered a major repair or
approach procedure shall be executed if the required
preventive maintenance. FAR 43, Appendix A provides
visual reference does not exist.
guidance on what constitutes a major repair or alteration
and preventive maintenance.. missed approach procedure [ICAO] — The procedure to
be followed if the approach cannot be continued.
minority carriers — A term used in reference to
semiconductor electronic devices. Both electrons and holes

207

10001930-002_AviationDictionary_2012_BOOK.indb 207 3/27/2012 9:38:17 AM

 missed approach segment • modular structure

missed approach segment — See segments of an mobile charges — Electrons in a semiconductor material
instrument approach procedure. that drift within the material from one electrically charged
region to another.
mist — Tiny droplets of water suspended in the air.
mobile test stand — An engine run‑in stand that is portable
mist coat — A very light spray coat of thinner or other
and can be used at multiple locations.
volatile solvent with little or no color in it.
Mobius loop — A continuous loop with one surface and
miter — A cut to the edges of a board or surface in such a
one edge. Made by twisting one end of a long, thin strip
way that they will match or fit together.
one half turn and attaching this end to the other end of the
miter box — A device used to guide a hand saw at the proper strip. This creates a loop with one edge and one surface.
angle to cut wood or metal in order to form a miter joint.
mock-up — A full-size reproduction of a part or assembly
miter square — A small square used for marking the ends used to determine whether or not all of the components
of wood or metal for other than right angle cuts. will fit as they are designed. It is also used for instruction
when the real object is impractical to use.
mixed exhaust — On a turbofan, a design that allows the
primary and secondary airstreams to mix prior to leaving mode — 1. The manner of doing some operation. 2. The
the engine. A sound attenuation feature of more modern letter or number assigned to a specific pulse spacing
engines. Same as forced exhaust mixer. of radio signals transmitted or received by ground
interrogator or airborne transponder components of the
mixed icing — A combination of clear and rime icing. See
Air Traffic Control Radar Beacon System (ATCRBS).
also clear ice and rime ice.
Mode A (military Mode 3) and Mode C (altitude
mixer — 1. A system of bellcranks that prevents the cyclic reporting) are used in air traffic control.
inputs from changing the collective inputs on a helicopter
mode C intruder alert — A function of certain air traffic
control system. 2. A circuit in which two frequencies are
control automated systems designed to alert radar
combined to produce sum and difference frequencies.
controllers to existing or pending situations between
mixing ratio — The ratio of the mass of water vapor to the a tracked target (known IFR or VFR aircraft) and an
mass of dry air. untracked target (unknown IFR or VFR aircraft) that
requires immediate attention/action.
mixture — A combination of matter composed of two or
more com­ponents that retain their own properties. mode (SSR mode) [ICAO] — The letter or number assigned
to a specific pulse spacing of the interrogation signals
mixture control — The primary carburetor control for
transmitted by an interrogator. There are 4 modes, A, B,
adjusting the fuel-air mixture ratio. It can be either a
C and D corresponding to four different interrogation
manual or automatic control, or it can be a combination
pulse spacings.
of both. In the case of the combination, the pilot adjusts
for a particular ratio and the automatic control maintains model — A copy of a real object, which can be life-size,
that ratio by compensating for temperature and pressure smaller, or larger than the original.
variations of the atmosphere.
model number — A manufacturer’s designation of a
MLS categories — 1. MLS Category I — An MLS particular piece of equipment.
approach procedure that provides for an approach to a
modem — A modulator‑demodulator device used to
height above touchdown of not less than 200 feet and a
connect two computers and allow them to communicate.
runway visual range of not less than 1,800 feet. 2. MLS
Category II — Undefined until data gathering/ analysis modification — The change in the design or configuration
completion. 3. MLS Category III — Undefined until data of an original unit.
gathering/ analysis completion.
modify — 1. To change something such as an alteration or
MMM (manufacturers maintenance manual) — A redesign of an original unit. 2. To change a schedule from
manual developed by the aircraft manufacturer that the original date or time.
includes information prepared for the AMT or technician
modular maintenance — A maintenance procedure that
who performs work on units, components, and systems
allows replacement of major assemblies, called modules,
while they are installed on the airplane. It is normally
in a minimum amount of time and expense. The removed
supplied by the manufacturer and approved by the FAA as
module is returned to a repair facility, bench tested, and
part of the original process of certification. It will contain
repaired as needed.
the required instructions for continued airworthiness that
must accompany each aircraft when it leaves the factory. modular structure — Standardized units built up as
modules.

208

10001930-002_AviationDictionary_2012_BOOK.indb 208 3/27/2012 9:38:17 AM

 modulate • monoplane

modulate — To change. This normally refers to a radio molybdenum — A metallic element similar to chromium
carrier wave being modulated to transmit audio with a symbol of Mo and an atomic number of 42. Used
information. as an alloying agent in most aircraft alloys.
modulated anti-skid system — An anti‑skid brake system moment — The product of the weight of an object in
that senses the rate of deceleration of the wheels. The pounds and the distance from the center of gravity of the
system maintains just enough pressure in the brakes object to the datum or fulcrum (the point about which a
to hold the tire in a slip condition, yet not allow a skid lever rotates) in inches. Moment is used in weight and
to develop. It does this by modulating, or continually balance computations and is expressed in pound‑inches.
changing, the pressure in the brake system. The formula used is: Moment = distance x force.
modulated continuous wave — A radio code transmission moment index — The moment divided by a constant such
that consists of a carrier wave modulated with a series of as 200, 1,000, or 10,000. Its use is to simplify weight and
short and long bursts. balance computations by eliminating large and unwieldy
numbers.
modulated light — Light that is modulated by audio
frequency AC voltage. Such light can be received by a momentum — The tendency of a body to continue in
photo electric cell and fed into an amplifier to recreate the motion after being placed in motion.
original audio qualities.
moment-weight number — An identification number or
modulation — The changing of frequency or amplitude by letter indicating a measurement of both weight and center
superimpos­ing an audio frequency on a carrier frequency. of gravity and used on rotating airfoils for balancing
purposes.
modulator — That portion of a transmitter circuit that
modulates the carrier wave. Monel — A nickel-copper alloy that is extremely resistant
to corrosion.
modulus — The ratio of a stress load applied to the
deformation of a material. monitor — (When used with communication transfer) listen
on a specific frequency and stand by for instructions. Under
moisture — An all-inclusive term denoting water in any or
normal circumstances do not establish communications.
all of its three states.
monitor alert (MA) — A function of the ETMS that
moisture absorption — The pickup of water vapor from air
provides traffic management personnel with a tool for
by a material, in reference to vapor withdrawn from the
predicting potential capacity problems in individual
air only, as distinguished from water absorption, which
operational sectors. The MA is an indication that traffic
is the gain in weight due to the absorption of water by
management personnel need to analyze a particular sector
immersion.
for actual activity and to determine the required action(s),
moisture separator — A device used in a pneumatic system if any, needed to control the demand.
to separate moisture from the air.
monitor alert parameter (MAP) — The number
moisture‑proof — The property of an object that resists designated for use in monitor alert processing by the
absorption of moisture. ETMS (enhanced traffic management system). The MAP
is designated for each operational sector for increments
mold — The hollow form used to give shape to a laminate
of 15 minutes.
part while curing.
monkey wrench — A slang name for an adjustable wrench
mold line — In metal layout, a line used in the develop­ment
that has one fixed jaw and one movable jaw.
of the pattern used for forming a piece of sheet metal. It is
that part of the formed part that remains flat and is formed monocoque — A stressed‑skin type of construction in
by the intersection of the flat surfaces of two sides of a which the stiffness of the skin provides a large measure
sheet metal part. of the strength of the structure. No truss or substructure
is required.
mold line dimension — The distance from the edge of
metal to a mold point or between mold points. monolithic casting — A casting formed as a single piece.
mold release agent — A material applied to the surface of monomer — A chemical compound that can be polymerized.
a mold that prevents the molded product from sticking to (Polymerization is a chemical reaction in which two or
the mold. Also referred to as a parting agent. more molecules are combined to form a larger molecule
that contains repeating structural units.)
molecule — The smallest particle of an element or
compound that retains all the properties of the substance. monoplane — An airplane with one main supporting wing
Composed of one or more atoms. sometimes divided into two parts by the fuselage.

209

10001930-002_AviationDictionary_2012_BOOK.indb 209 3/27/2012 9:38:18 AM

 monopropellant • multicell thunderstorm

monopropellant — A rocket engine propellant in which the mountain breeze — Occurring on a larger scale than
fuel and the oxidizer are both part of a single substance. downslope winds, it blows down the valley with a return
flow, or anti-mountain wind, above the mountaintops.
monorail — A single rail used to carry cars or objects.
mountain wave — An atmospheric gravity wave that forms
monospar wing — A fundamental wing design that
in the lee of a mountain barrier. See lee wave.
incorporates only one main longitudinal member in its
construction. mountain wave turbulence (MWT) — Turbulence
produced in conjunction with the mountain lee wave.
monostable — The condition of a device that has one stable
condi­tion. When disturbed from this, it will attempt to mounting lug — A lug used to secure an accessory, cylinder,
return to its original state. etc.
monostable multivibrator — An electronic circuit that mounting pad — A provision made on the accessory section
tries to maintain a condition of on or off. When it is of an aircraft engine for attaching such accessories as
disturbed from this position, it will automatically return magnetos, generators or alternators, and fluid pumps.
to its stable condition.
movement — The moving parts of a device that move in a
monsoon — A wind that blows in the summer from the defined manner, i.e., the inner workings of a watch.
sea to a continental interior, bringing copious rain, and
movement area — The runways, taxiways, and other areas
in winter blows from the interior to the sea, resulting in
of an airport/heliport utilized for taxiing/hover taxiing,
sustained dry weather.
air taxiing, takeoff, and landing of aircraft, exclusive
Morse code — A system of dots and dashes used for of loading ramps and parking areas. At those airports/
transmitting messages by audible or visual signals. Used heliports with a tower, specific approval for entry onto
in aviation to identify radio navigation facilities. the movement area must be obtained from ATC.
most significant bit — A bit in a binary number that has movement area [ICAO] — That part of an aerodrome to
the highest value. It is the bit on the far left of a binary be used for the takeoff, landing and taxiing of aircraft,
number. consisting of the maneuvering area and the apron(s).
most significant digit — A digit in a decimal number that moving target indicator — An electronic device that
is the most meaningful. It is the digit on the far left of a permits radar scope presentation only from targets in
decimal number. motion. A partial remedy for ground clutter.
mothball — To preserve and store surplus airplanes, parts, moving-coil meter — A d’Arsonval meter movement.
or equipment for future use. Most commonly used meter movement in DC measuring
instruments. A movable coil on which a pointer is
mothballed — Parts, machinery, or equipment that has
mounted rotates in the field of a permanent magnet. The
been preserved and placed in storage.
amount of current in the coil determines the strength of the
mother board — The primary printed circuit board in an coil’s electromagnetic field and the amount the pointer is
electronic device into which all other components are deflected by the magnetic field of the permanent magnet.
connected.
moving-iron meter movement — A d’Arsonval meter
motion — The act of changing place or position. movement where the coil is fixed and the magnet (iron)
is free to move.
motivation — A need or desire that causes a person to
act. Motivation can be positive or negative, tangible or muff — A shroud placed around a section of the exhaust
intangible, subtle or obvious. pipe. The shroud is open at the ends to permit air to flow
into the space between the exhaust pipe and the wall of
motor bypass — A device in a hydraulic system that
the shroud and be heated. This heated air can be used for
prevents a hydraulic motor from receiving excessive
carburetor heat or cockpit and cabin heat.
fluid. The fluid bypasses the motor.
mule — An auxiliary hydraulic power supply that can supply
motor over — The process of rotating the engine with the
fluid under pressure to the aircraft hydraulic system when
starter for reasons other than for starting.
the engines are not running. The mule is normally used to
motoring — Rotating a turbine engine with the starter for test the landing gear and flight control systems.
reasons other than starting.
multicell thunderstorm — A group of thunderstorm cells
motorization — The adding of an electric motor to at various stages of development. The proximity of the
equipment normally operated manually or by mechanical cells allows interaction that prolongs the lifetime of the
means other than electric motors. group beyond that of a single cell.

210

10001930-002_AviationDictionary_2012_BOOK.indb 210 3/27/2012 9:38:18 AM

 multicom • Mylar capacitor

multicom — A mobile service not open to public muriatic acid — Commercial hydrochloric acid (HCl).
correspondence used to provide communications
mushroom head — A flared
essential to conduct the activities being performed by or
head that forms on a pounding
directed from private aircraft. tool such as a punch or chisel
multi-engine — An aircraft having more than one engine. when it is hammered. This is
a dangerous condition, and it
multimedia — A combination of more than one instructional must be ground away.
medium. This format can include audio, text, graphics,
animations, and video. Recently, multimedia implies a mutual inductance — The inductance of a voltage in one
computer-based presentation. coil due to the magnetic field produced by an adjacent
coil. Inductive coupling is accomplished through the
multimeter — A piece of electrical test equipment consisting mutual inductance of two adjacent coils.
of one meter movement and several shunts, multipliers,
and other circuit elements to allow the meter to be used Mylar — A polyester film.
as a voltmeter, ohmmeter, milliammeter, and ammeter. Mylar capacitor — A capacitor that uses Mylar film as a
Rectifiers make it usable for AC and well as DC. dielectric.
multiple runways — The utilization of a dedicated arrival
runway(s) for departures and a dedicated departure
runway(s) for arrivals when feasible to reduce delays and
enhance capacity.
multiple-choice — A test item consisting of a question or
statement followed by a list of alternative answers.
multiple-disk brake — An aircraft brake in which a series
of discs, keyed to the wheel, mesh and rotate between a
series of stationary discs keyed to the axle. The brakes
are applied by hydraulically clamping the discs together.
multiple-spar (multi-spar) wing — An airplane wing
structure that uses several spanwise structural members
to give the wing its strength.
multiplex communications — A method of two‑way
communication in which two sites can transmit and
receive on the same frequency and at the same time.
multiplicand — Any number to be multiplied by another.
multiplier — A number by which another number is
multiplied. The factor by which something is multiplied
or extended.
multiplier resistor — The resistor in series with a voltmeter
movement used to multiply or extend the range of the
meter.
multiplier tube — An electron tube designed to amplify
or multiply very weak electron currents by means of
secondary emission.
multi-spar wing — A fundamental wing design that
incorporates more than one spanwise structural member
for support.
multivibrator — An oscillator that produces its output
by having two transistors or vacuum tubes alternately
conduct current. When one conducts, the other is shut off.
Conduction alternates between the two.
Mumetal — A nickel alloy of iron, nickel, chromium,
molybdenum, and copper. Used in transformer cores and for
shielding electronic devices from external magnetic fields.

211

10001930-002_AviationDictionary_2012_BOOK.indb 211 3/27/2012 9:38:18 AM

 N • navigate

N National Flight Data Digest — A daily (except weekends

and Federal holidays) publication of flight information
N3 — The speed of high pressure compressor in a appropriate to aeronautical charts, aeronautical
triple-spool turbine engine. publications, Notices to Airmen, or other media serving
the purpose of providing operational flight data essential
nacelle — The streamlined enclosure on the wing or to safe and efficient aircraft operations.
fuselage of an aircraft that houses the engine.
national route program (NRP) — The NRP is a set of
NAND gate — A “not and” logic device, which will not rules and procedures designed to increase the flexibility
have a voltage at its output only when a voltage appears of user flightplanning within published guidelines.
at all of the inputs. Opposite to an “and” gate.
national search and rescue plan — An interagency agreement
nano — One billionth (0.000000001) of a unit. that provides for the effective utilization of all available
nanovoltmeter — A sensitive voltmeter that measures facilities in all types of search and rescue missions.
voltages as low as one nanovolt. natural aging — The aging of solution, heat‑treated
nap — The short fiber ends that protrude from the surface aluminum alloy material. It is allowed to harden at room
of a fabric. When the fabric is doped, these fibers become temperature following heat treatment.
stiff and must be sanded off. natural numbers — Positive integers such as 1, 2, 8, and
naphtha — A volatile and flammable hydrocarbon liquid 9. Negative numbers, zero and fractions are NOT natural
used chiefly as a solvent or cleaning agent. numbers.
narrowing grinding — The removable part of the valve naturally aspirated engine — A reciprocating aircraft
seat’s top edge in the cylinder of a reciprocating engine. engine that is not supercharged, but whose induction air
is forced into the cylinders by atmospheric pressure only.
NAS drawings and specifications — Dimensional and
material stand­ards for aircraft fasteners developed by nautical mile — A measure of distance used primarily in
the National Aircraft Stand­ards (NAS) Committee. All navigation. It is equal to 6,076 feet and is one minute of
drawings and specifications are prefixed by NAS. latitude at the equator.
NAS stage A — The enroute ATC system’s radar, computers nautical twilight — The periods before sunrise and after
and computer programs, controller plan view displays sunset when the sun is not more than 12º below the horizon.
(PVDs/Radar Scopes), input/output devices, and the NAVAID — Any visual or electronic device, airborne or
related communications equipment that are integrated to on the surface, that provides point-to-point guidance
form the heart of the automated IFR air traffic control information, or position data, to aircraft in flight.
system. This equipment performs Flight Data Processing NAVAIDs include VORs, ILSs, and DMEs.
(FDP) and Radar Data Processing (RDP). It interfaces
with automated terminal systems and is used in the NAVAID classes — VOR, VORTAC, and TACAN aids
control of enroute IFR aircraft. are classed according to their operational use. The three
classes of NAVAIDs are:
National Airspace System — The common network of
United States airspace, air navigation facilities, equipment a. T – Terminal
and services, airports or landing areas, aeronautical charts, b. L – Low altitude
information and services, rules, regulations and procedures,
technical information, and manpower and material. Included c. H – High altitude
are system components shared jointly with the military. NOTE: The normal service range for T, L, and H class
National Beacon Code Allocation Plan (NBCAP) aids is found in the AIM. Certain operational requirements
airspace — Airspace over United States territory located make it necessary to use some of these aids at greater
within the North American continent between Canada and service ranges than specified. Extended range is made
Mexico, including adjacent territorial waters outward to possible through flight inspection determinations. Some
about boundaries of oceanic control areas (CTA)/Flight aids also have lesser service range due to location, terrain,
Information Regions (FIR). frequency protection, etc. Restrictions to service range
are listed in the Airport/Facility Directory.
National Flight Data Center — A facility in Washington
D.C., established by FAA to operate a central aeronautical navigable airspace — Airspace at and above the minimum
information service for the collection, validation, and flight altitudes prescribed in the FARs including airspace
dissemination of aeronautical data in support of the activities needed for safe takeoff and landing.
of government, industry, and the aviation community. The navigate — To move between sites on the Internet. Often
information is published in the National Flight Data Digest. done by means of links or connections between sites.

212

10001930-002_AviationDictionary_2012_BOOK.indb 212 3/27/2012 9:38:18 AM

 navigation lights • negative resistance

navigation lights — Lights on an aircraft consisting of a negative acceleration — Deceleration; slowing down.
red light on the left wing, a green light on the right wing,
negative angle of
and a white light on the tail. FARs require that these
attack — A flight
lights be displayed in flight during the hours of darkness.
condition where
navigational aid (NAVAID) — Any visual or electronic the angle of attack
device, airborne or on the surface, that provides formed between the relative wind and the chord line
point-to-point guidance information, or position data, of the airfoil is formed with the relative wind being the
to aircraft in flight. NAVAIDs include VORs, ILSs, and top leg in relation to the chord line and the so-called top
DMEs. surface of the aircraft. An aircraft in inverted, level flight
would have a negative angle of attack.
NBCAP (National Beacon Code Allocation Plan)
airspace — Airspace over United States territory located negative battery terminal — The terminal of a battery
within the North American continent between Canada and from which the electrons leave and enter the circuit.
Mexico, including adjacent territorial waters outward to
negative buoyancy — The tendency of an object, when
about boundaries of oceanic control areas (CTA)/Flight
placed in a fluid, to sink because it is heavier than the
Information Regions (FIR).
fluid it displaces.
N-channel field effect transistor (FET) — A device with a
negative condition — One in which there is an excess of
conducting channel of N-type material that is on a P-type
electrons.
substrate. It can conduct in either direction, thus it can
pass AC. One end of the channel is called a “drain” and negative contact — Used by pilots to inform ATC one of two
the other a “source.” These are brought out to pins for things. Either that previously issued traffic is not in sight
connection into an external circuit. A third connection is or that they were unable to contact ATC on a particular
to the “gate.” The gate can be P-type material. When the frequency. The first instance might be followed by the
gate is made negative in respect to the channel, a depletion pilot’s request for the controller to provide assistance in
area is formed that reduces the channel current and allows avoiding the traffic.
control of it. The input impedance of any FET is very high.
negative dihedral — A downward inclination of a wing or
neck — 1. A portion of a fastener’s body near the head that other surface. It is the downward angle that is formed
performs a definite function such as preventing rotation, between the wings and the lateral axis of the airplane.
etc. 2. A reduced diameter of a portion of a fastener’s
negative electrical charge — An unbalanced electrical
shank required for design or manufacturing reasons.
condition caused by an atom having more electrons than
needle and ball indicator — A flight instrument consisting protons.
of a rate gyro that indicates the rate of yaw and a curved
negative electrical condition — A condition in which there
glass clinometer that indicates the relationship between
are more negative charges than there are positive charges.
gravity and centrifugal force. It indicates the relationship
between angle of bank and rate of yaw. Also referred to negative electrical resistance — A decrease in current
as a turn and slip indicator. through a device when there is an increase in voltage.
needle bearings — An anti‑friction bearing made of negative feedback — Information or a signal that is fed
hardened steel. The bearing consists of a series of small back into a circuit or device that tends to cause a decrease
diameter rollers that ride between two hardened and in the output.
polished steel races. One race is pressed into the housing,
negative ion — An atom that has more electrons than
and the other race is pressed onto the rotating shaft.
protons spinning around its nucleus.
needle valve — A tapered
negative moment — In aircraft weight and balance
end fluid control needle
calculations, a moment resulting from an arm being
valve that fits into a seat
forward of the datum.
or recess to control or
restrict a flow of fluid negative pressure — Pressure that is less than atmospheric
through an orifice. pressure.
negative — 1. A condition negative pressure relief valve — A valve in an aircraft
in which there is an pressurization system that prevents the outside air pressure
excess of electrons. 2. from becoming greater than the pressure inside the cabin
An accepted name for
negative resistance — A condition in which the normal
the terminal of a battery
direct relationship between voltage and current is
or power source from which the electrons flow. 3. During
reversed.
communications, this indicates: “No,” “Permission not
granted,” or “That is not correct.”
213

10001930-002_AviationDictionary_2012_BOOK.indb 213 3/27/2012 9:38:18 AM

 negative stagger • nibbler

negative stagger — The placement of the wings of a biplane neutral plane — An

in which the leading edge of the lower wing is ahead of imaginary line drawn
the leading edge of the upper wing. perpendicular to the
resultant flux in a
negative static stability — A condition in which an object
generator. For arcless
disturbed from a condition of rest will tend to move
com­mutation, the neutral
further away from its condition of rest.
plane should lie directly over the plane of the brushes.
negative temperature coefficient — A condition where
a conductor or device decreases in resistance as the neutral position — The position of the rotating magnet of a
temperature increases. magneto between the pole shoes. In the neutral position,
no lines of flux flow in the magneto frame.
negative thrust — The thrust produced when a propeller is
moved into the beta range. neutral stability — A system is characterized by neutral
stability if, when displaced, it accelerates neither toward
negative torque system (NTS) — A system in a turboprop nor away from its original position. The atmosphere
engine that prevents the engine from being overdriven by displays neutral stability when lapse rate is equal to the
the propeller. The NTS increases the blade angle when dry adiabatic lapse rate.
the propellers try to overdrive the engine.
neutral static stability — The condition of an object in
negative transfer of learning — Students interpret new which, when once disturbed from a condition of rest, it
things in terms of what they already know. Some degree has neither the tendency to return to a condition of rest
of transfer is involved in all learning. Previous learning nor to depart further from it. It continues in equilibrium
interferes with students’ understanding of the current task. in the direction of disturbance.
negative vacuum relief valve — A relief valve used on neutralize — To make balanced or inert by combining
pressurized aircraft that opens when outside air pressure equal positive and negative quantities.
is greater than cabin pressure.
neutron — An uncharged particle in the nucleus of an atom.
negative value — A value less than zero. Its mass is essentially equal to that of a proton.
neon — A gaseous element with a symbol of Ne and an never exceed speed — The speed beyond which an aircraft
atomic number of 10. should never be operated.
neon bulb — A bulb that glows when neon vapor atoms are newton — The unit of force in the meter-kilogram-second
excited by an electric arc. system equal to the force required to impart an
neoprene — An oil-resistant synthetic rubber made by acceleration of one meter per second squared to a mass
polymerizing chloroprene. Used in items such as seals of one kilogram.
and locknuts. Newton’s first law of motion — The law of physics that
net thrust (Fn) — The effective thrust developed by a jet describes inertia. “A body at rest tends to remain at
engine during flight, taking into consideration the initial rest and a body in motion tends to continue to move at
momentum of the air mass prior to entering the engine. constant speed, along a straight line, unless it is acted
upon by an external force.”
neutral — 1. The condition in which a gear, lever, or other
mechanism is not engaged. 2. An electrical condition that Newton’s second law — The law of physics that states:
is neither positive nor negative. “The acceleration produced in a mass by the addition of
a given force is directly proportional to the force, and
neutral axis — An imaginary line through the length of a
inversely proportional to the mass.”
loaded beam where the forces of compression and tension
are neutral. Newton’s second law of motion — “The greater the force
acting on an object, the greater the acceleration. And the
neutral conductor — The conductor of a 3-phase circuit
greater the mass, the less the object will accelerate.”
or a single-phase three wire circuit that is of a ground
potential. The potential between the neutral and each of Newton’s third law — The law of physics that states: “For
the other conductors is equal in magnitude and phase. every action, there is an equal and opposite reaction.”
neutral flame — A flame used in oxyacetylene welding Newton’s third law of motion — The law of physics that
that is neither carburizing nor oxidizing and that uses the describes action and reaction. “For every action, there is
correct ratio of acetylene gas and oxygen. an equal and opposite reaction.”
neutral line — In sheet metal bending, the line near nibble — To take small bites or quantity.
the middle of the sheet that is unaffected by either
compression on the inside of the curve, or by stretching nibbler — A sheet metal cutting tool that cuts the metal by
on the outside of the curve. a series of small nibbles or bites.

214

10001930-002_AviationDictionary_2012_BOOK.indb 214 3/27/2012 9:38:18 AM

 nichrome • nonabrasive scraper

nichrome — An alloy of nickel and chromium. It is used for no gyro approach — A radar approach/vector provided in
making precision wire‑wound resistors. case of a malfunctioning gyro-compass or directional gyro.
Instead of providing the pilot with headings to be flown,
nick — A sharp‑sided gouge or depression with a V-shaped
the controller observes the radar track and issues control
bottom that is generally the result of careless handling.
instructions “turn right/left” or “stop turn” as appropriate.
nickel — A silver-white, hard, malleable, metallic chemical
no gyro vector — See no gyro approach.
element with a symbol of Ni and an atomic number of
28. Used for plating because of its high resistance to no procedure turn (NOPT) — No procedure turn is
oxidation. required nor authorized.
nickel silver — A metal alloy of copper, zinc, and nickel. no transgression zone (NTZ) — The NTZ is a 2,000 foot
wide zone, located equidistant between parallel runway
nickel-cadmium battery (Nicad) — A battery made up of
final approach courses in which flight is not allowed.
alkaline secondary cells. The positive plates are nickel
hydroxide, the negative plates are cadmium hydroxide, noble — Chemically inert or inactive, especially toward
and potassium hydroxide is used as the electrolyte. oxygen.
night — The time between the end of evening civil twilight noble gas — An inert gas such as neon, argon, krypton, and
and the beginning of morning civil twilight, as published xenon.
in the American Air Almanac, converted to local time.
nocturnal inversion — A surface-based stable layer that
night [ICAO] — The hours between the end of evening occurs due to nighttime radiational cooling.
civil twilight and the beginning of morning civil twilight
nodal system — A vibration dampening system used by
or such other period between sunset and sunrise as can be
Bell Helicopter to reduce main rotor vibration.
specified by the appropriate authority.
noise — 1. A general term for any loud or unusual sound
NOTE: Civil twilight ends in the evening when the center
that is annoying or excessive. 2. Undesired signals within
of the sun’s disk is 6 degrees below the horizon and
an electronic circuit.
begins in the morning when the center of the sun’s disk is
6 degrees below the horizon. noise suppressor — A device installed in the tailpipe of a
turbojet engine to slow the mixing of the exhaust gases
nimbostratus — A dark gray cloud layer that produces rain
with the surrounding air, thus decreasing the intensity of
or snow.
the sound.
NimonicÒ alloy — A nickel-chromium alloy used for
no-load current — The electrical current draw of a device
sheet-metal fabrications in gas-turbine engines.
when the device is not under load.
nipple pipe fitting — A short piece of pipe fitting threaded
Nomex® — Trademark of DuPont. A nylon paper treated
on both ends.
material that is made into a honeycomb core material.
nitrate — A salt or ester of nitric acid (HNO3). Used in
nominal rating — The stated value of a quantity or
some dopes to protect fabric-covered aircraft.
component, which might not be the actual value
nitrate dope — A finish for aircraft fabric, consisting of a measured.
film base of cellulose fibers dissolved in nitric acid with
nominal resistance of a thermistor — The true resistance
the necessary plas­ticizers, solvents, and thinners.
of a thermis­tor at a particular reference temperature. Most
nitric acid — A colorless or yellowish flowing, suffocating, manufacturers use 20°C as the reference temperature.
caustic, corrosive, water‑soluble liquid (HN03) with
nominal size — The designation used for the purpose of
powerful oxidizing properties.
general identification.
nitriding — A case hardening in which a steel part is
nominal value — A stated value that has a tolerance that
heated in an atmosphere of ammonia (NH3.) The
would allow the actual value to be somewhat different.
ammonia breaks down, freeing the nitrogen to combine
with aluminum in the steel to form an extremely hard nomograph-viscosity index — An ASTM-produced chart
abrasive‑resistant aluminum nitride surface. Cylinder used to plot the viscosity change of turbine oils with
walls and crankshaft journals can be nitrided. temperature change.
nitrite — A salt or ester of nitrous acid (HNO2). nonabrasive — Material that will not scratch or scar when
rubbed on another surface.
nitrogen — A colorless, tasteless, odorless, gaseous element
forming nearly 4/5 of the Earth’s atmosphere. nonabrasive scraper — A scraper that has no abrasive
materials attached to it.

215

10001930-002_AviationDictionary_2012_BOOK.indb 215 3/27/2012 9:38:18 AM

 non-airworthiness item • nonradar

non-airworthiness item — An inspection item that if noninductive winding — A winding consisting of two
broken or inoperative does not affect the airworthiness parts wound in such a way that the magnetic field from
of the aircraft. one cancels the other. The result is no inductive load.
nonapproach control tower — Authorizes aircraft to land noninductlve load — An electrical load with no inductance.
or takeoff at the airport controlled by the tower, or to The entire load is due to resistance and capacitance.
transit the airport Class D airspace. The primary function
nonlinear output — Any output not directly proportional
of a nonapproach control tower is the sequencing of
to the input.
aircraft in the traffic pattern and on the landing area.
Nonapproach control towers also separate aircraft nonlinear scale — The scale of an indicating instrument
operating under instrument flight rules clearances from in which the numbers are spread out at one end and are
approach controls and centers. They provide ground bunched up at the other.
control services to aircraft, vehicles, personnel, and
nonlinear system — Nonuniform in length, width, or output.
equipment on the airport movement area.
nonmagnetic — Metal that does not have the properties of
non-aqueous developer — In dye-penetrant inspections,
a magnet and/or that cannot be magnetized or attracted
a material that causes a crack to show up. Non-aqueous
by a magnet.
developer is not water based and is less corrosive to the part.
nonmovement areas — Taxiways and apron (ramp) areas
non-atomizing spray — The application of a material to a
not under the control of air traffic.
surface by a spray gun in which the material is fed in a
solid stream rather than in tiny droplets. non-owner liability coverage — An insurance policy
against claims arising from bodily injury or damage
non-atomizing spray gun — A spray gun that propels a
caused to others or their property while using an aircraft
solid stream from the spray nozzle.
that one does not own.
noncommon route/portion — That segment of a North
nonporous — Any material that does not allow a liquid to
American Route between the inland navigation facility
pass through it.
and a designated North American terminal.
nonprecision approach (NPA) — An instrument approach
noncomposite separation — Separation in accordance with
based on a navigation system which provides course
minima other than the composite separation minimum
deviation information, but no glidepath deviation
specified for the area concerned.
information.VOR, NDB, and LNAV are nonprecision
nondestructive inspection (NDI) — An inspection of approaches. Vertical Descent Angle (VDA) on some
aircraft parts, units, components, etc., that doesn’t alter nonprecision approaches may provide a Vertical Descent
or destroy the physical or material properties and/or Angle as an aid in flying a stabilized approach, without
integrity of the part. It is used to determine the continued requiring its use in order to fly the procedure. This does
serviceability. Also referred to as nondestructive testing. not make the approach an APV (Approach With Vertical
Guidance), since it still must be flown to an MDA and has
nondestructive testing (NDT) — See nondestructive
not been evaluated with a glidepath.
inspection (NDI).
nonprecision approach procedure — A standard
nondimensional number — A number that does not have a
instrument approach procedure in which no electronic
dimensional value such as a Mach speed.
glideslope is provided; e.g., VOR, TACAN, NDB, LOC,
nondirectional antenna — An antenna that has the ability ASR, LDA, or SDF approaches.
to receive or transmit equal signals in all directions.
nonradar — Precedes other terms and generally means
nondirectional beacon — An L/MF or UHF radio beacon without the use of radar, such as:
transmitting nondirectional signals whereby the pilot of
a. Nonradar Approach – Used to describe instrument
an aircraft equipped with direction finding equipment can
approaches for which course guidance on final
determine his bearing to or from the radio beacon and “home”
approach is not provided by ground based precision or
on or track to or from the station. When the radio beacon is
surveillance radar. Radar vectors to the final approach
installed in conjunction with the Instrument Landing System
course may or may not be provided by ATC. Examples
marker, it is normally called a Compass Locator.
of nonradar approaches are VOR, NDB, TACAN, and
nonferrous metal — A metal that contains no iron. ILS/MLS approaches.
nonflexible control cable — A grouping of seven or 19 b. Nonradar Approach Control – An ATC facility providing
strands of solid wire preformed into a helical or spiral approach control service without the use of radar.
shape. Can be used for straight runs where it does not
c. Nonradar Arrival – An aircraft arriving at an airport
pass over any pulleys.
without radar service, or at an airport served by a radar

216

10001930-002_AviationDictionary_2012_BOOK.indb 216 3/27/2012 9:38:18 AM

 nonradar separation [ICAO] • normally open relay

facility and radar contact has not been established or Radar controllers issue procedures for pilots to follow in
has been terminated due to a lack of radar service to the event of lost communications during a radar approach
the airport. when weather reports indicate that an aircraft will likely
encounter IFR weather conditions during the approach.
d. Nonradar Route – A flight path or route over which
the pilot is performing his own navigation. The pilot norm reference testing (NRT) — System of testing where
can be receiving radar separation, radar monitoring, or students are rank ordered in accomplishment of objectives.
other ATC services while on a nonradar route.
normal category airplane — An airplane certificated for
e. Nonradar Separation – The spacing of aircraft in nonacrobatic operation.
accordance with established minima without the use of
normal heptane — A liquid hydrocarbon material (C7H17)
radar; e.g., vertical, lateral, or longitudinal separation.
having a low critical pressure and temperature and whose
nonradar separation [ICAO] — The separation used when detonation characteristics are used in determining the
aircraft position information is derived from sources octane rating of aviation gasoline.
other than radar.
normal operating speed — The velocity ob­tained in level
nonrepairable — Something that cannot be repaired and flight at design altitude of the airplane at no more than
which, therefore, renders the part nonserviceable. 70% of normal rated engine power.
nonrepairable damage — Damage that requires the aircraft normal operating zone (NOZ) — The NOZ is the operating
or aircraft component to be replaced. zone within which aircraft flight remains during normal
independent simultaneous parallel ILS approaches.
nonrigid airship — An engine-driven, lighter‑than‑air
aircraft such as a blimp that uses gas pressure to maintain normal rated power — The highest power at which an
the shape of the craft. engine can be operated continuously without damage.
nonscheduled airline — An airline that does not operate normal refraction — The refraction of a radar beam as
according to a regularly published schedule. it passes through the atmosphere due to changes in air
density with height. Usually, because the atmosphere’s
nonservo brakes — Brakes that do not use the momentum
density decreases rapidly with height, the radar beam will
of the aircraft to assist in the application of the brakes.
be deflected downward.
nonskid brakes — A feature found in high performance
normal shock wave — A
aircraft braking systems that provides wheel antiskid
shock wave formed ahead
protection. A skid control generator unit measures
of an airfoil approaching
the wheel rotational speed. As the wheel rotates, the
the speed of sound. It is
generator develops a voltage and current signal. The
perpendicular to the path
signal strength indicates the wheel rotational speed. This
of the airfoil.
signal is fed to the skid control box though the harness.
The box interprets the signal and if the wheel is slowing normalizing — A heat treatment in which a metal is heated
too quickly, it signals a solenoid in the skid control valve to its critical temperature and allowed to cool slowly in
to release the brake pressure until the wheel begins to still air. Normalizing relieves stresses in the metal.
speed up allowing the wheel to continue to rotate without
normally aspirated engine — An engine that does not
skidding.
compensate for decreases in atmospheric pressure
nonstandard fastener — A fastener that differs in size, through turbocharging or other means.
length, material, or finish from established and published
normally closed relay — A relay switch consisting of a coil
standards.
or solenoid, an iron core, and movable contacts controlled
nonstructural — The portion of an aircraft that does not by a spring. Normally closed relay contacts are held
carry any aerodynamic loads. closed by the spring. When current flows through the
solenoid, the contacts are opened by the magnetic pull of
nontautening dope — A special formulation of aircraft
the electromagnetic coil.
dope used on heat‑shrunk polyester fabric. It provides
the necessary fill for the fabric, but produces a minimum normally open relay — A relay switch consisting of
of shrinkage. a coil or solenoid, an iron core, and movable contacts
controlled by a spring. Normally open relay contacts are
NOR gate — A “not or” logic device that will produce a
held open by the spring. When current flows through the
voltage at its output only when there is no voltage on any
solenoid, the contacts are closed by the magnetic pull of
input.
the electromagnetic coil.
NORDO (No Radio). — Loss of the ability to communicate
by radio. Standard pilot procedures are specified in FAR 91.

217

10001930-002_AviationDictionary_2012_BOOK.indb 217 3/27/2012 9:38:19 AM

 norm-referenced testing (NRT) • nozzle, fuel

norm-referenced testing (NRT) — System of testing NOT gate — A logic device having one input and one
where students are ranked against the performance of output. There will be no voltage on the output when a
other students. voltage appears at the input.
North American route — A numerically coded route NOTAM [ICAO] — A notice, containing information
preplanned over existing airway and route systems to and concerning the establishment, condition or change in
from specific coastal fixes serving the North Atlantic. any aeronautical facility, service, procedure or hazard,
North American Routes consist of the following: the timely knowledge of which is essential to personnel
concerned with flight operations.
a. Common Route/Portion – That segment of a North
American Route between the inland navigation facility I Distribution. Distribution by means of
and the coastal fix. telecommunication.
b. Non-Common Route/Portion – That segment of a II Distribution. Distribution by mean other than
North American Route between the inland navigation telecommunications.
facility and a designated North American terminal.
NOTAM(D) — A (distant) NOTAM that is disseminated
c. Inland Navigation Facility – A navigation aid on a for all navigational facilities which are part of the U.S.
North American Route at which the common route airspace system, all public use airports, seaplane bases,
and/or the noncommon route begins or ends. and heliports listed in the A/FD.
d. Coastal Fix – A navigation aid or intersection where NOTAM(L) — A (local) NOTAM that is distributed locally
an aircraft transitions between the domestic route only and is not attached to an hourly weather report.
structure and the oceanic route structure.
notes — Specific instructions on an aircraft drawing.
north mark — A beacon data block sent by the host
notice to airmen (NOTAM) — A notice containing
computer to be displayed by the ARTS on a 360 degree
information (not known sufficiently in advance to
bearing at a locally selected radar azimuth and distance.
publicize by other means) concerning the establishment,
The North Mark is used to ensure correct range/azimuth
condition, or change in any component (facility, service,
orientation during periods of CENRAP.
or procedure of, or hazard in the National Airspace
north pacific — An organized route system between the System) the timely knowledge of which is essential to
Alaskan west coast and Japan. personnel concerned with flight operations.
north pole — The north-seeking pole of a magnet. a. NOTAM(D) – A NOTAM given (in addition to local
dissemination) distant dissemination beyond the area
northerly turning error — In the Northern Hemisphere, a
of responsibility of the Flight Service Station. These
weight is placed on the south-facing end of the compass
NOTAMs will be stored and available until cancelled.
needle to compensate for dip (See dip). When a turn is
made toward the north from a westerly or easterly heading b. NOTAM(L) – A NOTAM given local dissemination
the dip weight causes the compass to overshoot the actual by voice and other means, such as telautograph and
heading. When turning toward the south, the heading telephone, to satisfy local user requirements.
is undershot. The effects are reversed in the Southern
c. FDC NOTAM – A NOTAM regulatory in nature,
Hemisphere if the compass is compensated with a weight
transmitted by USNOF and given system wide
on the north-facing end of the compass needle.
dissemination.
nose cone — A conical‑shaped dome usually attached to
Notices To Airmen Publication (NOTAM) — A publication
the front portion of a fuselage to house the radar antenna
issued every 28 days, designed primarily for the pilot,
or other electronic equipment. A nose cone can also be
which contains current NOTAM information considered
described as the front cover of propellers, intakes for jet
essential to the safety of flight as well as supplemental
engines, etc., for streamlining and directing the airflow.
data to other aeronautical publications. The contraction
nose gear — The forward gear on an aircraft equipped with NTAP is used in NOTAM text.
tricycle landing gear.
nozzle — The tapered end of a duct.
nose heavy — A condition that exists on an aircraft in which
nozzle blades — Any of the blades of a nozzle diaphragm.
the center of gravity is ahead of the forward limit.
nozzle diaphragm — A ring of stationary blades in a turbine
nose rib — A false, or partial, wing rib extending back from
engine ahead of the turbine wheel. Used to direct the flow
the leading edge only to the main spar. Its purpose is to
of hot gases into the turbine for maximum efficiency.
add smoothness to the leading edge of a wing.
nozzle, fuel — The pressure‑atomizing unit that receives
nose section — The forward section of an aircraft.
fuel under high pressure from the fuel manifold and

218

10001930-002_AviationDictionary_2012_BOOK.indb 218 3/27/2012 9:38:19 AM

 NPN transistor • nylon

delivers it to the combustor in a highly atomized, equations that describe the physics of the atmosphere;
precisely patterned spray. used exten­sively in weather services throughout the world.
NPN transistor — A three‑element semiconductor made numerous targets vicinity (location) — A traffic advisory
up of a sandwich of P-type silicon or germanium between issued by ATC to advise pilots that targets on the radar
two pieces of N-type material. scope are too numerous to issue individually.
N-strut — Struts of a biplane near the wing tips shaped in nut — An internally threaded collar used to screw onto
the form of the letter N. bolts or screws to form a complete fastening device.
N-type semiconductor material — A semiconductor nutation — The wobbling of the axis of a spinning body
material that has been doped (an impurity added) that such as the Earth, or a gyroscope.
leaves the outer ring of the valence shells with electrons
nutplate — A nut that can be riveted to the inside of a
that are readily given up.
structure. Bolts and screws can be screwed into the
N-type silicon — Silicon that has been doped with an nutplate without a wrench to hold the nut in place.
impurity having five valence electrons.
nylon — A tough, lightweight, elastic polyamide material
nuclear energy — Energy released as a result of either used especially in fabrics and plastics.
nuclear fission, nuclear fusion, or radioactive decay.
Nuclear fusion is not yet commercially feasible.
nuclear fission — The splitting of an atomic nucleus
resulting in the release of energy.
nuclear fusion — The union of atomic nuclei of certain
light elements to form heavier nuclei resulting in the
release of energy.
nuclei — Plural of nucleus.
nucleonics — The branch of science that deals with atomic
nuclei and nuclear energy.
nucleus — 1. The center or core around which other parts
are grouped. 2. The center or core of an atom consisting
of positively charged protons and uncharged neutrons.
nucleus of an atom — In chemistry, the central portion of
an atom.
null — An indicated low or zero point in a radio signal.
null balance — An electrical circuit in which two voltages
have can­celled each other out.
null detector — An electrical instrument that determines
values by adjusting a known quantity until it is identical
with the quantity to be measured. Often utilizes a
Wheatstone bridge.
numbers — A symbol used to assign a value of quantity or
placement in a sequence.
numerator — The part of a fraction that illustrates a portion
of something that makes up a whole. In decimals, the
numerator is the number to the right of the decimal point.
In a fraction, it is the number above the line and signifies
the number of parts of the denominator used.
numerical control — Allows more precise control of
operations than analog control. Also referred to as digital
control.
numerical weather prediction — Meteorological
forecasting using digital computers to solve mathematical

219

10001930-002_AviationDictionary_2012_BOOK.indb 219 3/27/2012 9:38:19 AM

 O • obstruction clearance limit (OCL) (ICAO)

O to enter the area using the provisions of FAAO 7110.65,

Para 3-1-5, VECHILES/ EQUIPMENT/PERSONNEL
objectivity — Characteristic of a measuring instrument ON RUNWAYS. The runway OFZ and, when applicable,
when it is free of any personal bias by the person grading the inner-approach OFZ, and the inner-transitional OFZ,
the test. comprise the OFZ.
oblique angle — An angle other than a right angle. A view a. Runway OFZ – The runway OFZ is a defined volume
on a mechanical drawing at other than normal front, rear, of airspace centered above the runway. The runway
top, bottom, and side angles. OFZ is the airspace above a surface whose elevation
at any point is the same as the elevation of the nearest
oblique photography — An aerial photograph taken with point on the runway centerline. The runway OFZ
a camera pointed at an angle other than straight down. extends 200 feet beyond each end of the runway. The
oblique shock wave — A shock wave attached to the bow width is as follows:
and tail of an aircraft flying at a speed greater than the 1). For runways serving large airplanes, the greater of:
speed of sound. The sides of the oblique shock wave
form the Mach cone. (a) 400 feet, or
oblique triangle — A three‑sided, closed figure that does (b) 180 feet, plus the wingspan of the most
not contain a right angle. demanding airplane, plus 20 feet per 1,000 feet
of airport elevation.
oblong shape — An object that is longer than it is broad. An
elongated circle or square. 2). For runways serving only small airplanes:
obscuration — Denotes sky hidden by surface‑based (a) 300 feet for precision instrument runways.
obscur­ing phenomena and vertical visibility restricted (b) 250 feet for other runways serving small
overhead. airplanes with approach speeds of 50 knots,
observation aircraft — Military aircraft that fly behind or more.
enemy lines and observe the movement of troops or (c) 120 feet for other runways serving small
supplies. airplanes with approach speeds of less than
obsolete — Something no longer in use or in practice. 50 knots.
obstacle — Something that impedes progress or b. Inner-approach OFZ – The inner-approach OFZ is a
achievement. In avation, an object or terrain at a fixed defined volume of airspace centered on the approach
geographical location (or which is expected to be at a area. The inner-approach OFZ applies only to runways
fixed location) within a prescribed area with reference to with an approach lighting system. The inner-approach
which vertical clearance is or must be provided during OFZ begins 200 feet from the runway threshold at the
flight operation. same elevation as the runway threshold and extends
200 feet beyond the last light unit in the approach
obstacle clearance altitude (height) OCA(H) (ICAO) lighting system. The width of the inner-approach OFZ
— The lowest altitude (OCA), or alternatively the is the same as the runway OFZ and rises at a slope of
lowest height above the elevation of the relevant runway 50 (horizontal) to 1 (vertical) from the beginning.
threshold or above the aerodrome elevation as applicable
(OCH), used in establishing compliance with the c. Inner-transitional OFZ – The inner transitional surface
appropriate obstacle clearance criteria. OFZ is a defined volume of airspace along the sides of
the runway and inner-approach OFZ and applies only
obstacle clearance surface (OCS) — An inclined or level to precision instrument runways. The inner-transitional
surface associated with a defined area for obstruction surface OFZ slopes 3 (horizontal) to 1 (vertical) out
evaluation. from the edges of the runway OFZ and inner-approach
obstacle departure procedure (ODP) — A departure OFZ to a height of 150 feet above the established
procedure that simply provides obstacle clearance and airport elevation.
does not include ATC related climb requirements. obstruction — Any object/obstacle exceeding the
obstacle free zone (OFZ) — A three dimensional volume obstruction standards specified by FAR 77, Subpart C.
of airspace that protects for the transition of aircraft obstruction clearance limit (OCL) (ICAO) — The height
to and from the runway. The OFZ clearing standard above aerodrome elevation below which the minimum
precludes taxiing and parked airplanes and object prescribed vertical clearance cannot be maintained either
penetrations, except for frangible NAVAID locations that on approach or in the event of a missed approach.
are fixed by function. Additionally, vehicles, equipment,
and personnel may be authorized by air traffic control

220

10001930-002_AviationDictionary_2012_BOOK.indb 220 3/27/2012 9:38:19 AM

 obstruction light • Ohm’s law

obstruction light — A light, or one of a group of lights, usually odd harmonics — The odd multiples of a frequency.
red or white, mounted on a surface structure or natural
oersted — A magnetomotive force of 1 gilbert per square
terrain to warn pilots of the presence of a flight hazard.
centimeter or 79.577 ampere-turns per meter.
obtuse angle — An angle greater than 90°. Also referred to
off course — A term used to describe a situation where an
as an open angle.
aircraft has reported a position fix or is observed on radar
obtuse triangle — A triangle that contains an angle greater at a point not on the ATC-approved route of flight.
than 90°.
off-idle mixture — The fuel-air mixture ratio of an aircraft
occluded front — The surface front after a cold front engine in the transition period between idle RPM
overtakes a warm front. utilizing the idle jets and higher power settings using the
main metering system.
occlusion process — The process by which a cold front
overtakes the warm front in a wave cyclone, pushing the off-route vector — A vector by ATC which takes an aircraft
warm sector air aloft. off a previously assigned route. Altitudes assigned by
ATC during such vectors provide required obstacle
oceanic airspace — Airspace over the oceans of the world,
clearance.
considered international airspace, where oceanic separation
and procedures per the International Civil Aviation offset parallel runways — Staggered runways having
Organization are applied. Responsibility for the provisions parallel centerlines.
of air traffic control service in this airspace is delegated
offset rivet set — A rivet
to various countries, based generally upon geographic
set used in a hand-held
proximity and the availability of the required resources.
pneumatic riveting gun
oceanic display and planning system — An automated digital in which the head is
display system that provides flight data processing, conflict offset from the center
probe, and situation display for oceanic air traffic control. line of the shank. Offset rivet sets are used in locations
where a straight set cannot be used.
oceanic navigational error report — A report filed when
an aircraft exiting oceanic airspace has been observed by offset screwdriver — A screwdriver in which the blades
radar to be off course. ONER reporting parameters and are oriented at 90° to the shank. An offset screwdriver is
procedures are contained in FAAO 7110.82, Monitoring used to turn screws when there is not enough clearance
of Navigational Performance In Oceanic Areas. in line with the screw to allow a regular screwdriver to
be used.
oceanic published route — A route established in
international airspace and charted or described in flight offshore control airspace area — That portion of airspace
information publications, such as Route Charts, DOD between the U.S. 12 NM limit and the oceanic CTA/FIR
[and Jeppesen] Enroute Charts, Chart Supplements, boundary within which air traffic control is exercised.
NOTAMs, and Track Messages. These areas are established to provide air traffic control
services. Offshore/Control Airspace Areas can be
oceanic transition route — An ATS route established for
classsified as either Class A airspace or Class E airspace.
the purpose of transitioning aircraft to/from an organized
track system. off-the-shelf item — Any standard item, part, or program
that can be used in place of a custom part.
O-condition — A temper designation. The soft or annealed
temper condition of a wrought metal product. ohm (Ώ) — The unit of electrical opposition equal to the
resis­tance of a circuit in which an electromotive force of
octagon — An eight-sided figure with each side having the
one volt will maintain a current of one ampere.
same length.
ohmmeter — An electrical measuring instrument used to
octahedron — A solid design or figure with eight plane
measure resis­tance in a circuit. An ohmmeter measures
surfaces.
resistance by calculating the amount of current that flows
octal number system — In digital electronics, the number when a known voltage is applied across an unknown
system based on eight units (0-7). resistance.
octane rating — The rating system of aviation gasoline Ohm’s law — The law that establishes the relationship
with regard to its antidetonating qualities. Fuel with between current, voltage, and resistance in an electrical
an octane rating of 87 is made up of a mixture of 87% circuit. The current in a circuit is directly proportional to
isooctane and 13% heptane. the voltage causing it and inversely proportional to the
resistance of the circuit.
octave — Musical interval of eight tones or notes. The
interval between two frequencies having a ratio of 2 to 1.

221

10001930-002_AviationDictionary_2012_BOOK.indb 221 3/27/2012 9:38:19 AM

 ohms-per-volt • Omega navigation system

ohms-per-volt — The measure of a voltmeter’s sensitivity. oil scraper ring — A piston ring located at the bottom or
It is found by dividing the number one by the amount of skirt end of a piston used to wipe the oil either toward or
current needed to deflect the meter pointer full scale. away from the oil control ring depending on the design
of the engine.
oil canning — A condition of the sheet metal skin of an
aircraft that is slightly bulged or stretched between rows oil screen — A fine mesh screen in the engine lubrication
of rivets. This bulge will pop back and forth in the same system used to stop and hold impurities, preventing their
way the bottom of an oil can pops back and forth. passage through the engine and causing damage.
oil circuit breaker — A circuit breaker used in high oil seal — A device used to prevent engine oil from leaking
amperage circuits such as municipal power plants and past a moving shaft.
distribution grids. Oil is used to quench the arcs that form
oil separator — A device used to separate oil from the
when connecting and disconnecting such circuits.
discharge air of a wet-type air pump.
oil control ring — The piston ring below the compression
oil slinger — A rotating device used as a centrifugal impeller
rings used to control the amount of oil between the piston
to direct oil flow, usually away from a bearing sump and
and the cylinder wall of an aircraft reciprocating engine.
toward a scavenge pump.
It is usually a multi‑piece ring and normally fits into a
groove with holes to drain part of the oil back to the oil sump — A container built into the lower part of an
inside of the piston. aircraft engine that holds the supply of lubricating oil.
oil cooler — 1. A heat exchanger used to cool the oil. 2. A oil tank pressurizing valve — A check valve used to trap
radiator used to maintain normal operating temperature oil vapors in the expansion space above the oil surface to
of lubricat­ing oil. Some coolers utilize air as a cooling provide a pressurization effect of approximately 3 to 5
agent; others use fuel. PSI within the oil tank.
oil dilution — The process of thinning engine oil by adding oil temperature indicator — Indicates oil temperature
fuel to it at shutdown to make starting easier in cold of the inlet oil to the engine. System usually is of the
weather. ratiometer type. Normal temperature is a good signal to
the pilot that the engine is warmed up for takeoff.
oil film — A light coating of oil sufficient to prevent metal‑
to‑metal con­tact or to protect metal parts from corrosion. oil temperature regulator — A control device that
maintains the oil temperature within the desired operating
oil filter — A device for removing impurities and foreign
range by either passing the oil through the core of the
matter from the lubricating oil used in an aircraft engine.
cooler or around the jacket of the cooler.
oil hardening — A process of hardening steel using oil as
oil wiper ring — The bottom ring on a piston used to
a quenching agent. When red hot steel is immersed in
direct oil up between the piston and the cylinder wall for
a bath of oil, the steel cools more slowly than by other
lubrication and sealing.
methods and gives the steel a more uniform hardness.
oil-cooled transformer — Transformers that use oil to cool
oil inlet — The fitting on an aircraft engine through which
the coils during the transforming of very high voltages in
the lubricating oil enters the oil system.
municipal power grids.
oil jet — A small nozzle opening that directs a stream of oil
Oilite bushing — A friction bushing made of a bronze
onto an area to be lubricated such as bearings, gears, etc.
material impregnated with oil. Friction of the moving
oil outlet — The fitting on an aircraft engine from which the parts generates enough heat to bring the oil to the surface
lubricating oil leaves the engine to return to the external and provide the needed lubrication.
reservoir.
oleo strut — An aircraft landing gear shock strut that
oil pan — The removable part of the crankcase where absorbs the initial landing impact by the transfer of oil
engine lubricating oil is collected by gravity and stored. from one chamber to another through a restricting orifice.
Oil in the pan is forced through passages in the engine by Taxi shocks are absorbed with compressed air or by a
a pressure pump. spring.
oil passages — Channels or holes in an engine through Omega — An RNAV system designed for long-range
which lubricat­ing oil flows to lubricate, seal, or cool the navigation based upon ground-based electronic
engine. navigational aid signals.
oil pressure indicator — An instrument that indicates the Omega navigation system — An RNAV system designed
pressure of the oil in the engine lubricating system. for long-range navigation based upon ground-based
electronic naviga­tional aid signals.

222

10001930-002_AviationDictionary_2012_BOOK.indb 222 3/27/2012 9:38:19 AM

 omni • operate

omni — Variable Omni Range (VOR). A navigation system one-shot rivet gun — A rivet gun that hits the rivet with
that uses phase comparison of two navigational signals a single hard blow for each pull of the trigger. It is used
transmitted from ground stations. The signals are in phase for rivets that are subject to becoming brittle if driven
when they are received at a location directly magnetic by ordinary rivet guns that deliver a continuous series of
north of the station. An instrument tells the pilot when blows as long as the trigger is held.
the needle is off center from the pre‑selected radial. If the
one-to-one vibration — In rotorcraft, a low frequency
aircraft gets away from the pre-selected radial, the needle
vibration having one beat per revolution of the rotor. This
moves out of center to show the pilot which direction
vibration can be lateral, vertical, or horizontal.
to turn in order to bring the aircraft back to the selected
radial. on-speed — The condition in which the actual engine speed
is equal to the desired engine speed as set on the propeller
omni bearing selector (OBS) — On a VOR indicator, the
control by the pilot.
course selector. The knob a pilot uses to select the radial
from the VOR station along which to fly. The OBS shifts on-speed condition — A condition of a propeller governor
the phase of the course deviation indicator reference system that maintains the selected RPM by metering to
signal so the needle will center when the aircraft is on the or draining from the propeller piston the exact quantity
selected radial. of oil necessary to maintain the proper blade angle for
that RPM.
omni station — The ground station of a VOR.
open angle — The angle through which metal has been bent
omnidirectional microphone — A non-directional
that is greater than 90º. Produces a “V” with less than 90°
microphone that picks up sounds equally from all
between the sides.
directions.
open circuit — An incomplete electrical circuit. Does not
omnidirectional radio antenna — A non-directional radio
provide a continuous path for electrons to flow.
anten­na that transmits or receives signals equally well in
all horizontal directions. open wiring — A wire, wire group, or wire bundle not
enclosed in conduit.
omnirange navigation equipment (VOR) — A phase
com­parison type of electronic navigation equipment that open-assembly time — The assigned time between the
provides a directional reference (measured from magnetic time when an adhesive is spread on to two surfaces to
north) between the airplane and the ground station. be joined and the time the surfaces are clamped together.
on course — 1. Used to indicate that an aircraft is established open-center selector valve — A hydraulic selector valve
on the route centerline. 2. Used by ATC to advise a pilot used in open‑center hydraulic systems that allows fluid
making a radar approach that his aircraft is lined up on to flow from the pump to the reservoir when the selector
the final approach course. valve is placed in neutral (when none of the actuating
cylinders are receiving fluid under pressure).
on-condition maintenance — A maintenance concept
whereby some components of the engine remain in service open-circuit voltage — The measured voltage of a battery
as long as they appear airworthy at each inspection. The or generator when there is no load or flow of electrons in
replace-on-condition concept is opposed to the concept the circuit.
of replacing a component after a “life-limited” time
open-end wrench — A solid, nonadjustable wrench with
interval. In the case of engines themselves, this means no
open parallel jaws on one or both ends.
TBO (time between overhaul) is required.
open-tip turbine blades — A blade with no shroud attached
on-course indication — An indication on an instrument,
at the tip. This blade can withstand higher speed‑induced
which provides the pilot a visual means of determining
tip loading than the shrouded tip blade. Also referred to
that the aircraft is located on the centerline of a given
as an open perimeter tip.
navigational track, or an indication on a radar scope that
an aircraft is on a given track. operant conditioning — Behavior initiated voluntarily by
the individual, such as turning on a fuel pump, reading
one hundred and eighty degree ambiguity — An error
a checklist, or initiating a go-around. Operant behavior
inherent in radio direction finding systems, in which the
is the target of learning and the most important to a
system is unable to determine whether the bearing to the
flight instructor. It generally consists of three phases:
station is as indicated or 180º different than indicated, for
cues are provided to initiate the behavior, the behavior
example, whether the station is in front of or behind the
is performed, and consequences associated with that
aircraft.
performance are received.
one-minute weather — The most recent one minute
operate — With respect to aircraft, means use, cause to
updated weather broadcast received by a pilot from an
use or authorize to use aircraft, for the purpose (except
uncontrolled airport ASOS/AWOS.

223

10001930-002_AviationDictionary_2012_BOOK.indb 223 3/27/2012 9:38:19 AM

 operate • optional equipment

as provided in FAR 91.13) of air navigation including their piloting skills under stressful conditions. The
the piloting of aircraft, with or without the right of legal operational pitfalls are as follows: mind set, scud running,
control (as owner, lessee, or otherwise). continuing VFR into IMC, operating without adequate
fuel reserves, flying outside the envelope, neglect of
operate — To use, cause to be used, or authorize the use of
flight planning, preflight inspections and checklists,
an aircraft for the purpose of air navigation.
getting behind the aircraft, peer pressure, get-there-itis,
operating center of gravity range — The distance between duck-under syndrome, and descent below minimum
the for­ward and rearward center of gravity limits as enroute altitude.
specified in the Aircraft Specifications or Type Certificate
Operations Limitations Manual — Approved information
Data Sheets.
that must be carried in an airplane, including the speeds,
operating pressures — The hydraulic or pneumatic engine operating limits, and any other information vital
pressures to which an object or system is subjected in to the pilot. Also referred to as a flight manual.
normal operation.
opposed-type engine — A reciprocating engine with the
operating relay time — The measured time from when a cylinders arranged in two horizontal rows, one on either
relay control switch is closed until the relay contacts are side of the crankshaft. The cylinders are slightly staggered,
completely closed. with the cylinders in one bank slightly ahead of those in
the other bank. Staggering the cylinders allows each piston
operating time — The time measured from when an engine,
to be connected to a separate throw of the crankshaft. Also
component, or unit begins to operate until the operating
referred to as a horizontally‑opposed engine.
unit com­pletes its operation or movement.
opposite direction aircraft — Aircraft are operating in
operating weight — The empty weight of the aircraft along
opposite directions when:
with items carried in the aircraft during flight such as
crew, water, food, etc. a. They are following the same track in reciprocal
directions; or
operation raincheck — A program designed to familiarize
pilots with the ATC system, its functions, responsibilities b. Their tracks are parallel and the aircraft are flying in
and benefits. Visiting facilities such as control towers, reciprocal directions; or
approach control, or air route traffic control centers can
c. Their tracks intersect at an angle of more than 135°.
expand an aviation professional’s knowledge of ATC
services. opposite side — The leg of a right triangle opposite the
reference angle.
operation takeoff — A program that educates pilots on
how best to utilize the FSS modernization efforts and optical coupler — An optoelectronic device that connects
services that are available in automated flight service circuits together with no physical electrical connection.
stations (AFSS), as stated in FAA Order 7230.17. One Usually consists of a light emitting diode (LED) on
can interact with weather briefers at a local flight service the input side connected optically to a light-sensitive
station and learn tips and techniques to get the most out electronic device on the output side to reconstruct the
of the services they provide. electronic input.
operational — A phase of flight wherein an aircraft optical micrometer — A precision measuring device
commander of a State-operated aircraft assumes used to measure the depth of scratches or fissures in the
responsibility to separate his aircraft from all other aircraft. surface of a material by measuring the change in focus
of a complex lens. The lens is focused on an undamaged
operational amplifier — A DC amplifier with a high input
surface of the material that is used as a reference, and
impedance and a low output impedance. Most basic type
then it is focused at the base of the damage. The amount
of integrated circuits. Also referred to as an op-amp.
of change in the lens focus is converted into a measure of
operational checks — The inspection of a unit done the depth of the damage.
to determine if it is operating properly within the
optical pyrometer — A temperature measuring instrument
manufacturer’s specifications.
used to indicate the temperature of molten metal inside
operational control — With respect to a flight, means a furnace.
the exercise of authority over initiating, conducting or
option approach — An approach requested and conducted
terminating a flight.
by a pilot that will result in either a touch-and-go, missed
operational pitfalls — The desire to complete a flight approach, low approach, stop-and-go, or full stop landing.
as planned, please passengers, meet schedules, and
optional equipment — Aircraft equipment approved for
demonstrate that they have the right stuff can all have an
installa­tion in an aircraft, but which is not required for
adverse effect on safety by causing pilots to overestimate
airworthiness.

224

10001930-002_AviationDictionary_2012_BOOK.indb 224 3/27/2012 9:38:19 AM

 OR gate • out

OR gate — A logic device that will have a voltage on its ornithopter — An aircraft designed to produce lift by the
output any time a voltage appears at any one or more of flapping of its wings.
its inputs.
OROCA (off--route obstruction clearance altitude) —
oral quizzing — The most common means of evaluating a An offroute altitude that provides obstruction clearance
student’s knowledge. Proper oral quizzing during a lesson with a 1,000 foot buffer in nonmountainous terrain areas
promotes active student participation, identifies points and a 2,000 foot buffer in designated mountainous areas
that need more emphasis, and reveals the effectiveness of within the United States. This altitude may not provide
training procedures. signal coverage from groundbased navigational aids, air
traffic control radar, or communications coverage.
orange peel — A defect in a painted surface that resembles
the skin of an orange. It can be caused by errors in paint orographic — Relating to mountains. In weather, refers to
viscosity, air pressure, spray gun settings, or an improper phenomena caused by mountains, i.e., orographic clouds.
distance be­tween the spray gun and the surface.
orographic lifting — The lifting of an airmass when it
orbital electron — An electron spinning around the nucleus encounters a barrier, for example, mountains or a hill.
of an atom; different from free electrons, which are able
oronasal oxygen mask — An oxygen mask covering only
to move from one atom to another.
the mouth and the nose of the wearer.
ordinate — A line parallel to the Y‑axis of a graph. A
orphaned airplane — Slang, for an aircraft that is
specified distance from the X-axis, used to fix a point.
frequently non-airworthy and spends a lot of time in the
organic brake linings — Organic material reinforced with hangar. In the military or commercial aviation, these
brass wool and attached to solid metal backings. Used for aircraft are frequently robbed of parts to keep other
single‑disk brakes. aircraft airworthy, thus prolonging the status of the
hangar queen. Also referred to as a hangar queen.
organic fabric — A woven material made of natural origin
fibers such as cotton or linen. Used in the manufacturing orthographic projection — In mechanical drawing,
of aircraft fabric covering materials. six different views of an object are possible through
orthographic projection: front, rear, top, bottom, left side,
organic fibers — Fibers of natural origin such as cotton or
and right side. Each view is drawn as if the object were
linen. Used in the manufacture of aircraft fabric covering
placed in a box and only one side of the box opened to
materials.
reveal one view (either front, rear, top, bottom, left side,
organic lining — The friction material used in spot‑type, or right side) of the object.
single disk brakes. It is a composition material in which
oscillate — To swing back and forth with a consistent force
brass‑ or copper‑wool or particles of brass are embedded
or rhythm.
to control the coefficient of friction.
oscillator — 1. An electronic device that converts DC
organized track system — 1. A movable system of oceanic
into AC. 2. An electronic circuit that produces AC with
tracks that traverses the North Atlantic between Europe
frequencies deter­mined by the inductance and capacitance
and North America the physical position of which is
in the circuit.
determined twice daily taking the best advantage of the
winds aloft. 2. A series of fixed and charted ATS (Air oscillograph — A device for mechanically or
Traffic Services) routes; i.e., CEP, NOPAC; or flexible photographically producing a graphical representation of
and described by NOTAM; i.e., NAT Track Message an electric signal.
orientation — In composites, the alignment of the fibers oscilloscope — An electrical measuring instrument with
(0º, 45º, 90º) to the baseline set by the manufacturer for a which repeating voltage and current changes can be
particular component. observed on a cathode-ray tube similar to a small
television tube.
orifice — A small hole of a specific size that meters or
controls the flow of a fluid. Otto cycle — A constant‑volume cycle of events used to
explain the energy transformation that takes place in a
orifice check valve — A component in a hydraulic or
reciprocating engine. In this type of engine, four strokes
pneumatic system that allows unrestricted flow in one
are required to complete the required series of events
direction and restricted flow in the opposite direction.
or operating cycle of each cylinder. Two complete
original skin — The skin or metal covering originally used revolutions of the crankshaft (720°) are required for the
in the manufacturing of an airplane. four strokes and the spark plug in each cylinder fires once
for every two revolutions of the crankshaft.
O‑ring — A sealing device used in a pneumatic or hydraulic
system that has a circular cross section and is made in the out — The conversation is ended and no response is expected.
form of a ring.

225

10001930-002_AviationDictionary_2012_BOOK.indb 225 3/27/2012 9:38:20 AM

 out of ground effect (OGE) hover • over

out of ground effect (OGE) hover — In rotorcraft, outer liner — The annular and can‑annular combustion
hovering greater than one rotor diameter distance above liner outer shell as opposed to its inner shell. Formerly
the surface. Because induced drag is greater while used to refer to the outer case of a can-type combustion
hovering out of ground effect, it takes more power to chamber.
achieve a hover out of ground effect.
outer marker — A marker beacon at or near the glide
out of phase — A condition in which two cyclic waves such slope intercept altitude of an ILS approach. It is keyed
as voltage and current do not pass through the same point to transmit two dashes per second on a 400 Hz tone,
at the same time. which is received aurally and visually by compatible
airborne equipment. The OM is normally located four to
out time — In composites, the time a pre-preg is exposed
seven miles from the runway threshold on the extended
to ambient temperature, namely, the total amount of
centerline of the runway.
time the pre-preg is out of the freezer. This can include
shipping time as well as the time it takes to cut off a small outflow boundary — The remnant of a gust front that
piece from the roll. continues to exist long after the thunderstorms that
created it dissipates.
outer area — Airspace surrounding a Class C airspace
area, extending out to a radius of 20 NM ATC provides outflow valve — The valve in a pressurized aircraft cabin
radar vectoring and sequencing for all IFR aircraft and that main­tains the desired pressure level inside the cabin
participating VFR aircraft. by controlling the amount of air allowed to flow out of
the cabin.
outer area (associated with class C airspace) —
Nonregulatory airspace surrounding designated Class C outlook briefing — A general overview forecast of the
airspace airports wherein ATC provides radar vectoring weather for a period 6 to 12 hours in advance.
and sequencing on a full-time basis for all IFR and
out-of-rig — A condition of aircraft flight control rigging
participating VFR aircraft. The service provided in the
in which the controls are not properly adjusted, thus
outer area is called Class C service and includes: IFR/
preventing the aircraft from being flown without the aid
IFR-standard IFR separation; IFR/VFR-traffic advisories
of the pilot touching the controls.
and conflict resolution; and VFR/VFR-traffic advisories
and, as appropriate, safety alerts. The normal radius out-of-round — Eccentrically shaped because of damage
will be 20 nautical miles, with some variations based on or wear.
site-specific requirements. The outer area extends outward
out-of-track — A condition of a helicopter rotor or the
from the primary Class C airspace airport and extends from
propeller of an airplane in which the tips of the blades do
the lower limits of radar/radio coverage up to the ceiling
not follow the same path in their rotation.
of the approach control’s delegated airspace excluding the
Class C charted area and other airspace as appropriate. out-of-trim — A condition in an aircraft in which
straight-and-level, hands-off flying is impossible due to
outer compass locator — A low power, low or medium
an aerodynamic load caused by an improperly adjusted
frequency (L/MF) radio beacon installed at the site of the
trim device.
outer marker of an instrument landing system (ILS). It
can be used for navigation at distances of approximately output — The power or energy a device delivers or
15 miles or as authorized in the approach procedure. produces.
outer fix — 1. A general term used within ATC to describe output transformer — A transformer used to match
fixes in the terminal area, other than the final approach the high impedance of an electronic circuit to the low
fix. Aircraft are normally cleared to these fixes by an Air impedance of the output device, usually a speaker.
Route Traffic Control Center or an Approach Control
outside air temperature (OAT) — The measured
Facility. Aircraft are normally cleared from these fixes
or indicated air temperature (IAT) corrected for
to the final approach fix or final approach course. 2. An
compression and friction heating. Also referred to as true
adapted fix along the converted route of flight, prior to
air temperature.
the meter fix, for which crossing times are calculated and
displayed in the metering position list. outside caliper — A measuring device having two movable
legs. Used to determine the distance across an object. Once
outer fix time — A calculated time to depart the outer fix in
the distance has been established, the actual dimension
order to cross the vertex at the ACLT. The time reflects
can be made using a steel scale or a vernier caliper.
descent speed adjustments and any applicable delay time
that must be absorbed prior to crossing the meter fix. outside skin — The outer surface of an aircraft.
outer flame — The enveloping, almost transparent flame over — My transmission is ended; I expect a response.
that surrounds the bluish-white inner flame or cone in
oxyacetylene welding.

226

10001930-002_AviationDictionary_2012_BOOK.indb 226 3/27/2012 9:38:20 AM

 overall efficiency • oversize

overall efficiency — In turbine engines, the product of overhead question — In the guided discussion method, a
multiplying propulsive efficiency and thermal efficiency. question directed to the entire group to stimulate thought
and discussion. An overhead question can be used by an
overbalance — The adding of counterbalancing weight to
instructor as the lead-off question.
the extent that the trailing edge of a control sur­face is
above the horizontal position when performing a static overhead valve — A valve located in the upper part of an
balance test. In a balanced condition, the control surface aircraft reciprocating engine cylinder head.
would rest in the neutral position.
overheat warning system — A system that warns of an
overboost — A condition in which the manifold pressure overheat condition that could lead to a fire.
of a reciprocating engine has exceeded the maximum
overinflation valve — A relief valve that opens to relieve
specified by the manufacturer. Can cause damage to
excessive air pressure. Used in some of the larger aircraft
internal engine components.
wheels that mount tubeless tires.
overcompounded motor — A compound-wound motor
overlapping — To lap over or extend beyond.
with more series windings than parallel windings. Tends
to try to speed up under increased loads. overload — To apply a load in excess of that for which a
device or structure is designed.
overcontrol — Any movement of a control device in excess
of that needed for a given condition. overlying center — The ARTCC facility that is responsible
for arrival/departure operations at a specific terminal.
overcurrent protection device — An electronic device that
protects a circuit against abnormally high currents. overrunning — In meteorology, when a warm, moist, stable
airmass moves over a warm front or a stationary front.
overhang — In meteorology, the anvil of a thunderstorm,
under which hail can occur and a turbulent wake can overrunning clutch — Generally, a pawl and ratchet
create severe turbulence. arrangement used on various types of starters. It permits
the starter to drive the engine but not allow the engine to
overhaul — To restore an aircraft, engine, or component to
drive the starter. The ratchet on the engine side will slip
a condition of airworthiness.
around within the pawls if normal disengagement does
overhead cam — The cam of an aircraft reciprocating not occur.
engine located above the cylinder head. The overhead
overseas air commerce — The carriage by aircraft of persons
cam operates the valves directly without the aid of
or property for compensation or hire, or the carriage of
pushrods.
mail by aircraft, or the operation or navigation of aircraft
overhead maneuver — A series of predetermined in the conduct or furtherance of a business or vocation, in
maneuvers prescribed for aircraft (often in formation) commerce between a place in any State of the United States,
for entry into the visual flight rules (VFR) traffic pattern or the District of Columbia, and any place in a territory or
and to proceed to a landing. An overhead maneuver is not possession of the United States; or between a place in a
an instrument flight rules (IFR) approach procedure. An territory or possession of the United States, and a place in
aircraft executing an overhead maneuver is considered any other territory or possession of the United States.
VFR and the IFR flight plan is cancelled when the aircraft
overseas air transportation — The carriage by aircraft of
reaches the “initial point” on the initial approach portion of
persons or property as a common carrier for compensation
the maneuver. The pattern usually specifies the following:
or hire, or the carriage of mail by aircraft, in commerce:
a. The radio contact required of the pilot.
a. Between a place in a State or the District of Columbia
b. The speed to be maintained. and a place in a possession of the United States; or
c. An initial approach 3 to 5 miles in length. b. Between a place in a possession of the United States and a
place in another possession of the United States; whether
d. An elliptical pattern consisting of two 180 degree turns.
that commerce moves wholly by aircraft or partly by
e. A break point at which the first 180 degree turn is aircraft and partly by other forms of transportation.
started.
overshoot — Overshoot is caused by rapid increase in
f. The direction of turns. throttle, which causes the controller to overshoot the
requirement for the engine boost, resulting in overboost.
g. Altitude (at least 500 feet above the conventional
pattern). overshooting tops — In thunderstorms, very strong
updrafts that penetrate the otherwise smooth top of the
h. A “Roll-out” on final approach not less than 1/4 mile
anvil cloud.
from the landing threshold and not less than 300 feet
above the ground. oversize — A question with many possible correct answers.

227

10001930-002_AviationDictionary_2012_BOOK.indb 227 3/27/2012 9:38:20 AM

 oversized stud • ozonosphere

oversized stud — A stud having a greater diameter than oxidizing flame can be recognized by its sharp‑pointed
standard for the portion that is pressed or threaded into inner cone and a hissing noise made by the torch.
the stud boss. The external diameter and thread pitch are
oxyacetylene — Gas welding that uses oxygen and
the same as original standard stud.
acetylene.
overspeed — 1. A condition in which an engine has produced
oxy-gas welding — Gas welding that uses oxygen and a gas
more RPM than the manufacturer recommends. 2. The
such as acetylene.
condition in which the actual engine speed is higher than
the desired engine speed as set on the propeller control. oxygen — One of the basic elements with a symbol of
O and an atomic weight of 8. In the free gas state, it is
overspeed condition — A condition of the propeller
always O2 because two atoms of oxygen must combine to
operating system in which the propeller is operating
form one molecule of oxygen gas. Oxygen is a colorless,
above the RPM for which the governor control is set.
odorless, tasteless, gaseous chemical element that makes
This causes the propeller blades to be at a lower angle
up about 21% of the Earth’s atmosphere. It will not burn
than that required for the desired speed.
but supports combustion and is essential to life processes.
overspeed governor — A speed-limiting device. Governors
oxygen bottle — Special, high‑strength steel cylinder used
regulate speed through the fuel control.
to store gaseous oxygen under pressure.
overspeeding — Exceeding the maximum RPM limits of
oxygen cell corrosion — Corrosion that results from a
the engine. Adjusting pitch stops in the prop governor
deficiency of oxygen in the electrolyte.
allow RPM limits to be set.
oxygen concentration cell corrosion — Corrosion that
overtemperature — 1. A condition in which a device
forms between the lap joints of metal where moisture
has reached a temperature above that approved by the
gets trapped.
manufacturer. 2. Any exhaust temperature that exceeds
the maximum allowable for a given operating condition oxygen manifold — A device for connecting several
or time limit. oxygen masks into one oxygen supply or several oxygen
sources into a master manifold.
overtemperature warning system — A warning system
that warns the pilot of an overheat condition. If the oxygen mask — A small face mask with special attachments
temperature rises above a set value in any one section for breathing oxygen.
of the overheat sensing circuit, the sensing device
oxygen plumbing — Tubing and fittings used in the oxygen
turns on a cockpit light indicating the location of the
system to connect the various components.
overtemperature.
oxyhydrogen — Gas welding that uses oxygen and
over-the-top — Above the layer of clouds or other obscuring
hydrogen.
phenomena forming the ceiling.
ozone — A variety of oxygen that contains three atoms
overview — A concise presentation of the objective and key
of oxygen per molecule rather than the usual two. The
ideas, supplemented with appropriate visual aids, to give
major portion of ozone in the atmosphere is formed by
students a clear picture of what is to come.
the interaction of oxygen with the sun’s rays near the
overvoltage protector — An electrical circuit protection top of the ozone layer. It is also produced by electrical
device used to protect components from damage caused discharges (lightning storms). Ozone is important to
by high voltage surges. If the voltage is excessive, the living organisms because it filters out most of the sun’s
overvoltage protector opens and protects the component. ultraviolet radiation.
oxidation — A chemical action in which a metallic element ozone hole — The region of the ozone layer that has a lower
is combined with oxygen. Electrons are removed from than normal concentration of O3.
the metal in this process.
ozone layer — A layer of O3 found in the lower stratosphere.
oxide — A chemical combination in which oxygen is Characterized by a relatively high concentration of ozone,
combined with another element. this layer is responsible for the increase of temperature in
the stratosphere.
oxide film — A layer, coating, or metallic oxide on the
surface of a material. ozonosphere — The stratum of the Earth’s atmosphere that
has a high concentration of ozone and absorbs ultraviolet
oxidized — 1. Combined with oxygen. 2. A substance that
radiation from the sun. The ozonosphere is approximately
causes another to combine with oxygen.
20 to 30 miles above the Earth.
oxidizing flame — An oxyacetylene welding flame in which
there is an excess of oxygen passing through the torch. An

228

10001930-002_AviationDictionary_2012_BOOK.indb 228 3/27/2012 9:38:20 AM

 P • parallel MLS approaches

P pan-pan-pan — The international radio-telephony urgency

signal. When repeated three times, indicates uncertainty
P factor — A tendency for an aircraft to yaw to the left or alert followed by the nature of the urgency.
due to the descending propeller blade on the right pants — Streamlined airplane wheel covers.
producing more thrust than the ascending blade on the
left. This occurs when the aircraft’s longitudinal axis is paper electrical capacitor — An electrical component that
in a climbing attitude in relation to the relative wind. uses two strips of metal foil for its plates and strips of
The P factor would be to the right if the aircraft had a waxed paper as its dielectric.
counter-clockwise rotating propeller. parabola — A plane curve equally distant from a fixed
P time — Proposed Departure Time. The time a scheduled point and a fixed line.
flight will depart the gate (scheduled operators) or the parabolic light reflector — A light
actual runway off time for nonscheduled operators. For reflector, such as a light bulb, with
EDCT purposes, the ATCSCC adjusts the “P” time for a curved or parabolic surface.
scheduled operators to reflect the runway off times.
parabolic microphone — A
pack carburizing — A heat treatment method for sensitive, highly directional
case‑hardening steel parts in which the parts are packed microphone mounted at the focal
in the carburizing compound, placed into a drum, and point of a parabolic dish capable
heated to a temperature of about 1500º F. of picking up sound from long
package — A complete assembly unit. distances.
packing — The hydraulic seal that prevents fluids from parachute — A device used or intended to be used to retard
leaking between two surfaces that move in relation to the fall of a body or object through the air.
each other. parachute — A large cloth device shaped like an umbrella
packing ring — An O‑ring used to confine liquids or gases, used to retard the fall of a body or object through the air.
preventing their passing between a fixed body and a par-al-ketone — A heavy, waxy grease used to protect
movable shaft. control cables and hardware fittings from corrosion on
paint — An aircraft finish that consists of pigments seaplanes.
suspended in a solvent-type vehicle. The paint protects parallax — Apparent displacement of an object if first
and improves the ap­pearance of the aircraft. viewed from one position and then from another.
paint drier — Any substance added to paint to improve its parallax — The apparent change in relationship of two
drying properties. objects when viewed from different locations not in line
paint stripper — A chemical material that softens the paint with the objects.
film and loosens its bond to the metal, thus enabling the parallel — 1. Lines that run in the same direction and will
paint to be easily wiped or washed away. never meet or cross because the distance between them is
pal nut — A thin, pressed‑steel check nut screwed down constant. 2. Having more than one path for electron flow
over an ordinary nut to prevent it from coming loose or between the two sides of the electron source.
backing off. parallel access — In computers, a term used to describe a
palladium — A metallic element with a symbol of Pd and method of accessing data simultaneously, or all data at
an atomic number of 46. the same time.
pan — A hollow depression or shallow metal object used parallel circuits — Two or more complete circuits
to hold oil. connected to the same two power terminals.
pancake landing — An aircraft landing procedure in which parallel ILS approaches — Approaches to parallel
the aircraft is on an even plane with the runway. As the runways by IFR aircraft that, when established inbound
aircraft reduces speed and lift, it drops to the ground in a toward the airport on the adjacent final approach courses,
flat or prone attitude. are radar separated by at least 2 miles.
panel — Any separate or distinct portion of an aircraft parallel lines — Two or more lines extending in the same
surface. direction and at the same distance apart at all points.
pan-head screw — A machine screw or sheet metal screw parallel MLS approaches — See parallel ILS approaches.
that has a large, slightly domed head.

229

10001930-002_AviationDictionary_2012_BOOK.indb 229 3/27/2012 9:38:20 AM

 parallel of latitude • parting film

parallel of latitude — Any of the imaginary lines on Parco lubrizing — Anti-friction coatings that contain
the surface of the Earth parallel to the equator and solvent-based suspensions of solid lubricants instead of
representing degrees of latitude on the Earth’s surface. a coloring pigment.
parallel offset route — A parallel track to the left or right Parkerizing — A method of treating metal parts by
of the designated or established airway/route. Normally immersing them in a solution of phosphoric acid and
associated with Area Navigation (RNAV) operations. manganese dioxide. Used to protect the surface from
rusting.
parallel operation — In computers, an operation that
moves information simultaneously over several lines as Parker-Kalon (PK) screws — Self‑tapping sheet metal
opposed to serially, which moves information one bit at a screws. PK screws are made of hardened steel, and have
time over a single line. Also used to describe an operation sharp, coarse threads that combine drilling, tapping and
using more than one processor simultaneously. fastening.
parallel resonant electrical circuit — A circuit made up parking brake — A mechanical or hydraulic brake system
of an inductor and a capacitor connected in parallel. used to prevent an aircraft from moving from its parked
If a circuit is resonant, the inductive reactance and the position.
capacitive reactance are equal at a particular frequency.
Also referred to as a tank circuit part number — An identification number assigned to a
particular part or assembly by the manufacturer.
parallel runways — Two or more runways at the same
airport whose centerlines are parallel. In addition to part power trim check — The act of trimming the engine with
runway number, parallel runways are designated as L the power lever against a trim stop or rig pin, then checking
(left) and R (right) or, if three parallel runways exist, L the EPR or N1 speed against a trim curve for ambient
(left), C (center), and R (right). conditions. If the correct values are not present, adjust­ment
of the fuel control, referred to as trimming, is required.
paralleling — Controlling the output of more than one
generator in order to share a load equally. This involves partial obscuration — Denotes that 1/8th or more of the
matching the voltage outputs, the frequency (of AC sky, but not all of the sky, is hidden by surface-based
generators) and the phase relationship of the AC current (excluding precipitation) phenom­ena in the atmosphere.
(of AC generators). partial panel — Controlling the airplane without the benefit
paralleling generators — An operational procedure of all instrumentation due to failure of one or more
in which the output voltages of multi‑engine aircraft instruments in flight. Pilots are required to demonstrate
electrical system generators are adjusted to share the basic attitude instrument flying on partial panel and are
electrical load equally. This involves matching the also required to fly a partial panel instrument approach
voltage outputs, the frequency (of AC generators) and the during the practical test for the instrument rating.
phase relationship of the AC current (of AC generators). partial pressure — The gases that make up the atmosphere
paramagnetic material — A material that becomes each exert a partial pressure. When all of the partial
magnetic when placed in a strong magnetic field and pressures are added together, they equal the total
retains some level of magnetic property as long as the atmospheric pressure.
strong magnetic field is present. However, when the
partial-panel flight — Instrument flight without
strong magnetic field is removed, the material loses its
vacuum-powered gyroscopic instruments. Remaining
magnetic properties.
instruments would be the altimeter, airspeed indicator,
parameter — A quantity or constant whose value varies turn coordinator, vertical speed indicator, and magnetic
with the circumstances of its application. compass.
parasite drag — That part of total drag created by the form particle — A small piece of any substance or matter.
or shape of airplane parts.
particulates — Very small liquid or solid particles in the
parasite drag — Drag caused by the friction of the air atmosphere. When suspended in the atmosphere, they are
flowing over a body. Parasite drag increases as airspeed called aerosols.
increases.
parting agent — In composites, a lubricant used to prevent
parasol wing airplane — An airplane having one main the part from sticking to the mold.
supporting surface mounted above the fuselage on
cabane struts. parting film — In composites, a layer of thin plastic to
prevent bagging materials from sticking to the part. It
parcel — A volume of air, small enough to contain uniform can be perforated to vent excess resin. It is removed after
distribution of its meteorological properties, but large cure. Can be used instead of peel ply.
enough to remain relatively self‑contained and re­spond
to all meteorological processes.
230

10001930-002_AviationDictionary_2012_BOOK.indb 230 3/27/2012 9:38:20 AM

 parts manufacturing approval (PMA) • pentagrid converter

parts manufacturing approval (PMA) — Approval P-channel field effect transistor (FET) — Similar to an
by the Federal Aviation Administration to design and N-channel FET but with the types of material reversed.
manufacture aircraft replacement parts for sale directly Control is achieved by the application of positive voltage
to the public. to the gate.
pascal — A metric unit of pressure. Equals one newton per peak alternating current — The greatest amount of
square meter. current that flows in one alternation of alternating current.
The greatest amount of deviation from the zero line of
Pascal’s law — A basic law of fluid power that states that
deviation as measured on an oscilloscope.
pressure in an enclosed container is transmitted equally,
undiminished to all points of the container, and acts at peak inverse voltage — The maximum voltage that can be
right angles to the enclosing walls. applied safely to an electron tube in the direction opposite
to normal current flow.
passenger mile — An airline statistic used to track
utilization of aircraft. One passenger mile is equal to one peak value — The maximum value of AC or voltage
passenger traveling one mile. Five passengers traveling measured from the zero reference line.
100 miles would equal 500 passenger miles.
peak wind — The maximum wind speed since the last
passivating — A treatment of corrosion‑resistant steels hourly observation.
after welding. The purpose is to remove iron from the
peak-to-peak voltage — Absolute value of the difference
surface and expose more chromium, allowing a chrome
between the maximum positive and maximum negative
rich oxide film to form and protect the surface from
values of an AC waveform.
corrosion.
pedestal grinder — A grinder mounted on a pedestal and
passive electrical circuit — An electrical circuit that does
stands on the floor of the shop.
not contain any source of electrical energy such as a
battery or generator. Such circuits would include only peel ply — In composites, a layer of fabric used in
passive electronic components. One example would be a manufacturing to vent excess resin up into the bleeder
filter (consisting of inductors and capacitors) in a receiver material. It prevents bagging materials from sticking to
circuit that is powered only by the received signal. the part, and it leaves a very finely etched surface for
painting. It is removed after cure.
passive electrical component — An electrical component,
such as resistor, capacitor or inductor, that produces no peel strength — In composites, the amount of strength it
gain in the circuit. takes a part to resist the stress applied from peeling apart
of two plies.
passive satellite — A passive satellite reflects received
radio signals back to Earth without amplification. peen — To round over or flatten the end of a shaft or rivet
by light hammer blows.
passive sonar — A device for detecting the presence of an
object by the sound it emits in water. Sonar stands for peened surface — A marked surface as from an impact
sound navigation ranging. with a blunt instrument. Caused by careless handling or
concentrated load suffi­cient to permanently deform the
passive video — Refers to segments of video that are
metal surface.
simply watched by the students.
pencil compass — A drawing instrument that uses a pencil
patch — A small piece of material used for strengthening,
to draw circles or arcs.
reinforcing, or covering a hole or weak spot in a structure.
pendular action — In rotorcraft, the lateral or longitudinal
pattern — 1. A model, guide, or plan used to form or make
oscillation of the fuselage due to it being suspended from
things. 2. The flight pattern an aircraft must follow when
the rotor system.
approaching the airport for landing and when leaving the
airport after taking off. Aircraft operating from the airport pendulum — A body suspended from a fixed point but that
must follow the same flight pattern in order to reduce the is free to swing back and forth or oscillate.
danger of an in‑flight collision.
pendulum valves — Gravity-operated air valves over
pawl — A pivoted stop in a mechanical device that allows the discharge ports of a pneumatic gyro horizon’s rotor
motion one way but prevents it in the opposite direction. housing. When the gyro tilts, the pendulum valves change
It is commonly used in a ratchet mechanism. the airflow from the housing and cause a precessive force
that erects the gyro.
payload — That part of the useful load of an aircraft that is
over and above the load necessary for the operation of the pentagrid converter — A five-grid electron tube that
vehicle. The term used for passengers, baggage, and cargo. serves as a mixer, local oscillator, and first detector in a
superheterodyne radio receiver.

231

10001930-002_AviationDictionary_2012_BOOK.indb 231 3/27/2012 9:38:20 AM

 pentode • personal checklists

pentode — A five-element vacuum tube or electron tube peripheral equipment — Devices that provide support
containing five electrodes: cathode, plate, control grid, for primary units of equipment. In computers, peripheral
suppressor grid, and screen grid. equipment would include hard disk drives, floppy drives,
modems, and CD ROM drives.
perceptions — The basis of all learning. Perceptions
result when a person gives meaning to external stimuli periphery — The outside of a circular or curved figure.
or sensations. Meanings, which are derived from
Permalloy — An alloy of iron and nickel used in the
perceptions, are influenced by an individual’s experience
manufacture of permanent magnets.
and many other factors.
permamold crankcase — An engine crankcase that has
percussive welding — A resistance welding process in
been pres­sure molded in a permanent mold. It is thinner
which an electrical arc and pressure are simultaneously
and denser than a sand‑cast crankcase.
applied across the materials being welded.
permanent ballast — A weight that has been permanently
perfect dielectric — A dielectric that has no conductivity. A
installed in an aircraft to bring its center of gravity into
perfect dielectric is an insulator that returns all of the used
allowable limits
energy to establish an electric field when the electrical
field is removed. permanent echo — Radar signals reflected from fixed
objects on the Earth’s surface; e.g., buildings, towers,
perforate — To create a hole in a material such as paper.
terrain. Permanent echoes are distinguished from
perforated parting film or release film — In composites, a “ground clutter” by being definable locations rather than
thin layer of plastic film used to prevent bagging materials large areas. Under certain conditions they can be used to
from sticking to the part. The perforations allow some check radar alignment.
resin to flow through small holes in the plastic. Used in
permanent magnet — A ferrous metal or alloy of ferrous
the same way as peel ply.
metals usually containing nickel and cobalt, in which
performance chart — A chart detailing the aircraft the magnetic domains are aligned, and tend to remain
performance that can be expected under specific aligned. Lines of magnetic flux join the poles of the
conditions. permanent magnet so that an electrical current can be
generated when these lines of flux are cut by a conductor.
performance envelope — A range of flight conditions and
performance for which an aircraft has been designed and permanent magnet speaker — A speaker that uses a small
tested for. Flying an aircraft outside these parameters is permanent magnet to provide the magnetic field for the
done so at the risk of unknown consequences. voice coil.
performance number — The anti-detonation rating of a permanent mold — A mold that can be used repeatedly to
fuel that has a higher critical pressure and temperature produce molded parts. Usually constructed of metal or
than isooctane. Isooctane is used as the reference. ceramic materials.
performance-based objectives — A statement of purpose permanent set — A mechanical deformity caused by
for a lesson or instructional period that includes three excessive stress placed on a material.
elements: a description of the skill or behavior desired of the
permeability — The ability of a material to accept and
student, a set of conditions under which the measurement
concentrate lines of magnetic flux.
will be taken, and a set of criteria describing the standard
used to measure accomplishment of the objective. Perminvar — Special alloy used for permanent magnets.
period — The time required for one cycle of AC. persistence — In cathode-ray tubes (CRTs), the length of
time the phosphorescent glow remains after the electron
period oscillation — The amount of time needed to
beam has moved on.
complete one cycle of an oscillation.
persistence forecast — A weather prediction based on
periodic event — Any regularly repeated event.
the assumption that future weather will be the same as
periodic inspection — Any regularly repeated inspection. current weather.
An annual or 100-hour inspection of an aircraft is a
person — An individual, firm, partnership, corporation,
periodic inspection.
company, association, joint-stock association, or
periodic table of chemical elements — A table of chemical governmental entity. It includes a trustee, receiver,
elements arranged in the order of their atomic numbers. assignee, or similar representative of any of them.
periodic vibration — A vibration that has a regularly personal checklists — To help students determine if they are
recurring resonance. prepared for a particular flight, encourage them to create
personal checklists that state their limitations based on

232

10001930-002_AviationDictionary_2012_BOOK.indb 232 3/27/2012 9:38:20 AM

 personal computer-based aviation training devices (PCATDs) • phosphoric acid etchant

such factors as experience, currency, and comfort level in phase shift — The difference in time between similar points
certain flight conditions. of an output and an input electrical wave form.
personal computer-based aviation training devices phenol-formeldehyde resin — A thermosetting plastic
(PCATDs) — A computer based flight simulator that has resin reinforced with cloth or paper to make molded
been authorized by the FAA to be used for a small portion plastic objects.
of the instrument time required for instrument ratings.
phenolic material — A thermosetting resin or plastic made
Uses cathode ray tube computer monitor for display.
by condensation of a phenol with an aldehyde and used
personality — A set of personal traits and characteristics of for molding and insulating.
an individual.
phenolic plastic — Plastic thermosetting
perspective — The technique of representing the spatial phenolic‑formaldehyde resin material, reinforced with
relationship of objects as they appear to the eye. cloth or paper.
petroleum — A substance containing chemical energy phenolic resin — A thermosetting resin produced by the
and used as a fuel for most of engines. It is a natural condensation of an aromatic alcohol with an aldehyde,
hydrocarbon product that was at one time plant or animal particularly of phenol with formaldehyde.
life, but was buried under billions of tons of Earth. It is
Phillips-head screw — A recessed-head screw designed to
obtained as a liquid from deep wells or from oil shale.
be driven with a cross‑pointed screwdriver whose point
petroleum-zinc-dust compound — A material used inside has two distinct tapers and a blunt point. The Reed and
an aluminum terminal lug when swaging the lug onto Prince is another cross-point driver but it has straight
aluminum wire. The zinc dust abrades the oxides from the sides, only one taper, and tapers to a point.
aluminum, and the petrolatum prevents its reformation.
phonetic alphabet — Standard words (lexicon) and
pH — A measure of acidity and alkalinity of a solution on combinations of words used for each of the letters in the
a 14 point scale where a value of 7 represents neutrality. alphabet during radio transmission. Examples of standard
1 indicates maximum acidity and 14 indicates maximum phonetic alphabet now in use are:
alkalinity. ALFA INDIA UNIFORM
BRAVO LIMA VICTOR
phantom line — CHARLIE NOVEMBER WHISKEY
Thin lines made DELTA OSCAR X-RAY
up of alternating ECHO PAPA YANKEE
long dashes and FOXTROT ROMEO ZULU
two short dashes. GOLF SIERRA
Used to show an HOTEL TANGO
alternate position
or a missing part phosgene — A colorless gas with an unpleasant odor
in a mechanical produced when Refrigerant-12 is passed through an open
drawing. flame. Causes severe respiratory irritation.

phase — 1. The time difference between an event in the phosphate ester-base hydraulic fluid — A synthetic,
voltage waveform and the equivalent event in the fire‑resistant hydraulic fluid used in high-pressure
current waveform in an AC circuit. 2. A section or hydraulic systems of modern jet aircraft. It is identified
a distinguishable part of a maintenance program or by the specifications MIL-H-8446.
inspection. phosphate film — A dense, insoluble, inorganic film
phase angle — The number of degrees of generator rotation deposited on the surface of a metal treated with a
between the time the voltage passes through zero and the conversion coating.
time the current passes through zero in the same direction. phosphor coating — A coating for the numerals and
phase change — A change of state. pointers on instrument dials. The coating glows when
excited with ultraviolet light rays.
phase inverter — An electronic device that changes the
phase of a signal by 180º. phosphorescent paint — A paint that absorbs energy from
natural light or from ultraviolet light and which continues
phase lock — A method of modulating the phase, condition, to glow after the natural light is removed.
or state of one electronic oscillating device so it will
exactly follow that of another oscillating device. phosphoric acid etchant — That constituent of a conversion
coating that microscopically roughens the surface of the
phase modulation — A method of modulating the carrier metal being treated and deposits a phosphate film.
wave of a radio signal. The phase angle is changed
relative to voltage changes of the input signal.

233

10001930-002_AviationDictionary_2012_BOOK.indb 233 3/27/2012 9:38:20 AM

 phosphorus • pie chart

phosphorus — A chemical element with a sign of P and an of attack remains constant, and the pilot often corrects for
atomic number of 15. phugoid oscillations without even being aware of them.
photo cell — An electronic device that becomes conductive physical needs — Needs that encompass the necessities for
or produces a voltage when struck by light. survival, which include food, rest, exercise, and protection
from the elements. Until these requirements are satisfied,
photo reconnaissance — Military activity that requires
students cannot fully concentrate on learning.
locating individual photo targets and navigating to the
targets at a preplanned angle and altitude. The activity physical organism — A perception factor that describes a
normally requires a lateral route width of 16NM and person’s ability to sense the world around them.
altitude range of 1,500 feet to 10,000 feet AGL.
physical properties — Those properties of a body that can
photocathodes — An electrode within an electron tube that be deter­mined by methods other than chemical, including
releases electrons after it has been exposed to light. weight, strength, and hardness.
photochemistry — That branch of chemistry having to do physical tables — Tables that list the physical properties
with the effects of light on chemical reactions. and charac­teristics of materials.
photoconductive cell — A photoelectric cell that changes physics — A natural science that deals with matter and
its resistance according to the amount of light exposure. energy and their interaction in the various fields of
Photoconductive cells are used in photographic light mechanics.
meters.
pi (π) — A mathematical constant representing the ratio
photodiode — A semiconductor diode that can conduct in between the circumference and diameter of a circle with
its reverse direction when light is shown on its junction. a value of approximately 3.1415927. Represented by the
Greek letter π.
photoelectric characteristics — The changes (positive or
negative) produced in the electrical characteristics of a pi filter — A network consisting of two capacitors and an
material when exposed to light. inductor net arranged in the form of the Greek letter pi
(π). It is essentially a capacitor-input filter followed by
photoelectric material — Any element that emits electrons
an L-filter.
when exposed to light. Elements such as alkaline metals,
cesium, lithium, and rubidium are photoelectric. piano hinge — A continuous metal hinge consisting of
hinge bodies attached to both fixed and movable surfaces.
photoelectricity — Electricity produced by the action of
A hard steel wire connects the two bodies and serves as
light on certain photoemissive materials.
the hinge pin.
photoemissive characteristic — The trait of a material to
pickling — 1. The treatment of a metal surface with acid to
emit electrons when exposed to light.
remove surface contamination. 2. Preparing an aircraft
photoemissivity — The tendency of a material to emit engine for longtime storage.
electrons when exposed to light.
pick-off — That portion of a device or system that removes
photon — A particle of radiant energy. a signal from a sensor.
photonegative characteristics — The characteristics of a pico — One-millionth of a millionth (0.000,000,000,001)
material increasing in resistance when exposed to light. of a unit.
photosensitive — The property of emitting electrons when picofarad (pf or μμf) — One‑millionth (0.000001) of a
struck by light. See also photoemissive. microfarad.
photothyristor — A semiconductor device that is pictorial diagram — A diagram used by maintenance
responsive to visible or infrared radiant energy. May or technicians. It can be either a line drawing, sometimes
may not include mounting hardware and/or heat sink. with shading to emphasize shapes, a picture of a part
enlarged to show detail, or a photograph of a piece of
phototransistor — A transistor that can be forward‑biased
equipment, illustrating the overall appearance of a unit,
into con­duction by applying light to its emitter‑base
its shape, relative sizes and location of components,
junction.
interconnecting wires, cables, etc.
photovoltaic cell — A solid‑state electrical component that
pictorial drawing — A drawing consisting of pictures that
produces a voltage when exposed to light.
shows an object as it appears to the eye.
phugoid oscillations — Long‑period oscillations of an
pie chart — A graph drawn in the shape of a circle and
aircraft around its lateral axis. It is a slow change in pitch
divided into pieces like a pie to convey data or proportions.
accompanied by equally slow changes in airspeed. Angle

234

10001930-002_AviationDictionary_2012_BOOK.indb 234 3/27/2012 9:38:21 AM

 piezoelectric crystal • pilot proficiency award program

piezoelectric crystal — A thin crystal that produces a and/or three times. Approved lighting systems can be
voltage when distorted. Used in strain gauges and activated by keying the mike as indicated below:
vibration detectors. Also produces vibration when a
KEY MIKE ( ) times within 5 seconds – FUNCTION:
voltage is applied. Used in ultrasonic transducers.
7 times within 5 seconds – Highest intensity available
piezoelectric effect — The property of certain crystals
that enables them to generate an electrostatic voltage 5 times within 5 seconds – Medium or lower intensity
between opposite faces when subjected to mechanical (Lower REIL or REIL-Off)
pressure. Conversely, the crystal will expand or contract
3 times within 5 seconds – Lowest intensity available
if subjected to a strong electrical potential.
(Lower REIL or REIL-Off)
piezoelectric transducer — An electrical device that
Due to the close proximity of airports using the same
enables a mechanical movement to generate an electrical
frequency, radio controlled lighting receivers can be set
signal.
at a low sensitivity requiring the aircraft to be relatively
piezoelectricity — Electricity produced when certain close to activate the system. Consequently, even when
crystalline materials such as quartz are subjected to lights are on, always key mike as directed when overflying
mechanical pressure. an airport of intended landing or just prior to entering the
final segment of an approach. This will assure the aircraft
pig iron — Crude iron, reduced from the iron ore in a blast
is close enough to activate the system and a full 15
furnace.
minutes lighting duration is available.
pigment — A powder or paste mixed with a paint finish to
pilot error — An action or decision made by the pilot that
give the desired color.
was the cause of, or contributing factor, which led to an
pigtail — A piece of wire that sticks out of a component and accident or incident. This definition also includes failure
allows the component to be installed or tied. of the pilot to make a decision or take action.
pilot — 1. A person licensed to operate an airplane, ship, or pilot hole — A small hole drilled or punched in sheet metal
balloon in flight. 2. A part that guides another part in its that is smaller than the bolt or rivet to be used. The pilot
movement. hole serves as a guide for final drilling.
pilot balloon — In weather, a small balloon that is released pilot in command — The person who: (1) Has final
and tracked in order to determine wind direction and speed. authority and responsibility for the operation and safety
of the flight; (2) Has been designated as pilot in command
pilot balloon observation — In weather, a method of
before or during the flight; and (3) Holds the appropriate
determining wind direction and speed by tracking a pilot
category, class, and type rating, if appropriate, for the
balloon. Also referred to as a pibal.
conduct of the flight.
pilot briefing — A service provided by the FSS to assist
pilot light — Electrical equipment light indicating power
pilots in flight planning. Briefing items can include
is on.
weather information, NOTAMs, military activities, flow
control information, and other items as requested. pilot proficiency award program — WINGS is the FAA
Pilot Proficiency Award Program designed to encourage
pilot chute — A small parachute attached to the canopy of
general aviation pilots to continue their training. The
the main parachute. The pilot chute pulls the main canopy
objective is to provide pilots with the opportunity to
out of the parachute pack so that it can open.
establish and participate in a personal recurrent training
pilot controlled lighting (PCL) — Radio control of lighting program. WINGS is an excellent opportunity for pilots
is available at selected airports to provide airborne to reevaluate their flight proficiency and knowledge.
control of lights by keying the aircraft’s microphone. The WINGS is open to all pilots holding a recreational
control system consists of a 3-step control responsive to certificate or higher with a current medical certificate,
7, 5, and/or 3 microphone clicks. The 3-step and 2-step when required. After pilots log three hours of dual
lighting facilities can be altered in intensity. All lighting is instruction under the program and attend at least one FAA
illuminated for a period of 15 minutes (except for 1-step sanctioned safety seminar, they are eligible to receive and
and 2-step REILs which can be turned off by keying the wear a distinctive set of WINGS. They will also receive
mike 5 or 3 times, respectively). a certificate of completion. Each twelve-month interval
after earning the first set of WINGS, the pilot will be
Suggested use is to always initially key the mike 7 times;
eligible for more WINGS. CFIs can substitute completion
this assures that all controlled lights are turned on to the
of a flight instructor refresher clinic or renewal program
maximum available intensity. If desired, adjustment can
for the safety seminar. In addition, they can satisfy the
then be made, where the capability is provided, to a lower
flying portion of the first three phases by providing the
intensity (or the REIL turned off) by keying the mike 5

235

10001930-002_AviationDictionary_2012_BOOK.indb 235 3/27/2012 9:38:21 AM

 pilot weather report (PIREP) • piston insulator

instruction for three WINGS candidates ― a minimum pinch-off voltage — In electronics, the reverse bias that
of nine hours of instruction. must be applied to an FET to reduce source-drain current
to a specific value.
pilot weather report (PIREP) — A report, generated
by pilots, concerning meteorological phenomena pinhole — A tiny defect in a finish caused by a bubble in
encountered in flight. the paint film.
pilotage — Navigation by visual reference to landmarks. pinion — A small cogwheel whose teeth fit into a larger
gear.
pilot-in-command — The person who has final authority
and responsibility for the operation and safety of the pinion gear — A small gear on a
flight; has been designated as pilot in command before shaft driven by either a sector
or during the flight; and holds the appropriate category, gear or a toothed rack.
class, and type rating, if appropriate, for the conduct of
pinked edge — The edge of a
the flight.
fabric material that has been
pilot-induced oscillation (PIO) — Rapid oscillations cut into a series of small V’s
caused by the pilot’s over-controlled motions. PIOs to prevent the material from
usually occur on takeoff or landings with pitch sensitive unraveling.
gliders and in severe cases can lead to loss of control or
pinked‑edge fabric — A fabric material with an edge that
damage.
has been cut into a series of small V’s to prevent the
pilot’s discretion — When used in conjunction with material from unraveling.
altitude assignments, pilot discretion means that ATC has
pinked‑edge tape — A surface tape whose edges have been
offered the pilot the option of starting climb or descent
cut into small V’s.
whenever the pilot wishes and conducting the climb or
descent at any rate. The pilot can temporarily level off pinking shears — Scissors that cut fabric in a series of
at any intermediate altitude. However, once the pilot has small V’s.
vacated an altitude, the pilot cannot return to that altitude.
pinouts — Diagrams that show the positions of and
pilot’s telephone weather answering service (PATWAS) name the functions of the connections to the pins of an
— A recorded, continuous telephone briefing, forecast electronic device.
for the local area within a 50 nautical mile radius of the
pint — A measure unit of volume equal to 1/2 quart, l/8
station. No longer provided by Flight Service Stations,
gallon, 28.875 cubic inches, or approximately 4.73 x
has been replaced by the Telephone Information Briefing
10-4 cubic meter.
Service (TIBS), an automated service.
pipe threads — The tapered threads on a hollow pipe or a
pin — A straight cylindrical or tapered fastener designed to
piece of round stock. The taper provides the seal.
perform an attaching or locating function.
piston — 1. A cylindrical member that moves back and
pin contacts — Electrical connector contacts, called male
forth within a steel cylinder. 2. In a reciprocating engine,
contacts, in the form of a set of metal pins in one-half
a cylindrical member that moves back and forth in the
of a connector. These pins fit into sockets, called female
cylinder. Alternately compresses the fuel-air mixture and
contacts, in the other half of a connector.
is pushed by the expanding gases to transfer mechanical
PIN diode — A junction diode with a region of intrinsic power to the crankshaft of the engine.
semiconductor between layers of n-silicon and p-silicon.
piston displacement — The total volume swept by the
pin holes — In composites, small holes caused by the mold piston of an engine in one stroke (one half revolution)
used. of the crankshaft. The total displacement of an engine
would be equal to piston displacement multiplied by the
pin jack — A female receptacle that will accept and hold a
number of pistons.
small metal pin attached to the end of a wire or a test lead.
Pin jacks are used on test equipment such as multimeters. piston engine — A reciprocating engine.
pin punch — A long punch with straight sides. Used to piston fuel pump — Sometimes used as a main fuel pump
remove bolts and rivets from tight-fitting holes. See also in place of the more typical spur gear pump. This pump
punch. is capable of delivering fuel at higher pressures than
other types and can also vary its output per revolution. A
pin spanner — A semi‑circular wrench with pins that fit
variable displacement-type pump.
into holes around the edge of a circular nut.
piston insulator — Composition insulators between the
hydraulic actuating pistons and the pressure plate. Used to

236

10001930-002_AviationDictionary_2012_BOOK.indb 236 3/27/2012 9:38:21 AM

 piston pin • plan view

prevent heat transferring from the pressure plate into the pitot static system — The pressure system for airspeed
piston where it would likely damage the seals and the fluid. indicators, altimeters, and vertical speed indicators. It
consists of the pitot tube and a static port, along with all
piston pin — The hardened steel pin that attaches the small
of the necessary tubing and moisture traps.
end of a connecting rod into a piston.
pitot tube — An open‑ended tube that faces directly into
piston pin boss — The enlarged area on the interior of a piston
the relative airstream of an aircraft and picks up the ram,
that provides additional bearing area for the wrist pin.
or pitot, pressure to be used in an airspeed indicator.
piston pump — A pump in a fluid power system used to
pitot-static tube — A combination tube with the pick‑up
move fluid and apply pressure to the system.
for the pitot pressure as well as openings that pick up
piston ring grooves — The grooves in the circumference of undisturbed, or static, air pressure.
a piston into which the piston rings fit.
pitting — The formation of small pockets on the surface
piston rings — Rings made of a special gray cast iron that of a metal.
fit into grooves in the periphery of a piston. Piston rings
pitting corrosion — A metal corrosion in which small,
form a seal between the piston and the cylinder wall.
localized pits filled with the corrosive salts form on the
piston skirt — The lower portion of a piston. surface of the metal.
piston‑type pump — A hydraulic fluid pressure pump in pivot trunnion — A bearing surface on the top of the
which fluid is moved by pistons that move up and down landing gear on which the gear rides when folding into
in the cylinders of the pump. the aircraft.
pitch — 1. The rotation of an airplane about its lateral axis. placard — Small statement or pictorial sign permanently
2. The distance between the centers of adjacent rivets fixed in the cockpit and visible to the pilot. Placards are
in the same row. 3. On threaded fasteners, the distance used for operating limitations (e.g., weight or speeds) or
measured between corresponding points on two adjacent to indicate the position of an operating lever (e.g., landing
threads. gear retracted or down and locked).
pitch angle — In rotorcraft, the angle between the chord plain bearing — A simple bearing used to support an
line of the rotor blade and the reference plane of the main aircraft engine crankshaft or camshaft and only designed
rotor hub or the rotor plane of rotation. to take loads that are perpendicular to its face.
pitch attitude — The angle of the longitudinal axis relative plain flap — A wing flap in which a portion of the trailing
to the horizon. Pitch attitude serves as a visual reference edge of the wing folds down to increase the camber of the
for the pilot to maintain or change airspeed. wing without increasing the wing area.
pitch axis — The lateral axis of an aircraft or the axis about plain nut — A simple hex nut that has no provisions for
which an aircraft pitches in a nose-up or nose-down locking.
attitude.
plain overlap seam — A seam used for machine sewing
pitch, bolt threads — The distance from any point on of aircraft fabric in which the edge of one piece of fabric
the thread of a screw to the corresponding point on an laps over the edge of the other and one or more rows of
adjacent thread. stitches hold the pieces together.
pitch of a propeller — Zero‑thrust pitch. The distance a plain rib — A rib used to give an airfoil its shape. Also
propeller would have to advance in one revolution to give referred to as a former rib.
no thrust. Also referred to as experimental mean pitch.
plain washer — A flat washer used to provide a smooth
pitch of screw thread — The distance from the center of bearing surface for a nut or to shim between a surface
one thread to the center of the next thread. and a nut.
pitch ratio of propeller — The ratio of the pitch to the plain weave — A weaving pattern in which the warp and
diameter. fill fibers alternate; that is, the repeat pattern is warp/fill/
warp/fill.
pitch setting — The propeller blade setting as determined
by the blade angle measured in a manner, and at a radius, plan position indicator (PPI) scope — A radar indicator
specified by the instruction manual for the propeller. scope displaying range and azimuth of targets in polar
coordinates.
pitot pressure — Ram or impact pressure used in the
measurement of airspeed. plan view — The view from the top of an object.

237

10001930-002_AviationDictionary_2012_BOOK.indb 237 3/27/2012 9:38:21 AM

 plane of rotation • plenum chamber

plane of rotation — The plane in which a propeller or plastic — Any of the thermoplastic or thermosetting
a helicopter rotor rotates. It is perpendicular to the polymers used in modem aircraft construction.
crankshaft or the rotor shaft.
plastic range — The stress range of a material in which,
plane of symmetry — A vertical plane that passes through though the material does not fail when subjected to force,
the lon­gitudinal axis of an aircraft and divides the aircraft the material does not completely return to its original
into two symmetri­cal sides. shape but is deformed.
planetary gears — A reduction gearing arrangement Plastic Wood — A registered trade name for a filler
in which the propeller shaft is attached to an adapter consisting of wood fibers and a resin that sets as
holding several small planetary gears. These gears run plasticizing solvents evaporate.
between a sun gear and a ring gear, either of which can be
plasticizer — A chemical used in a lacquer finish to give
driven by the crankshaft, while the other is fixed into the
film its flexibility and resilience.
nose section. Planetary gears reduce the propeller speed
without reversing the direction of rotation. plate — 1. The electrode in a vacuum tube that serves as the
anode receiv­ing the electrons from the cathode. 2. The
planform — The outline of a wing as viewed from above.
active element in a storage battery. 3. Metal of a thickness
The shape seen when looking at a top view of a blueprint
greater than 1/4”. Metal thinner than ¼” is referred to as
or plan.
sheet metal.
plans display — A display available in URET CCLD
plate current — In a vacuum tube, the current that flows
(User Request Evaluation Tool Core Capability Limited
between the plate and the cathode.
Deployment ) that provides detailed flight plan and
predicted conflict information in textual format for plate glass — A rolled sheet of glass that is ground and
requested Current Plans and all Trial Plans. polished to provide an undistorted view.
Plante cell — A secondary cell in which the pole pieces are plate power supply — A high-voltage supply of positive
formed of sheets of lead and lead dioxide. The electrolyte direct current for use in vacuum tubes.
is a dilute solution of sulfuric acid.
plate resistance — In an electron tube, the ratio of a change
plaque — The base for plates of nickel‑cadmium (Nicad) in plate voltage to a change in plate current given a
batteries. Plaque is covered by nickel, formed under heat constant grid voltage.
and pressure onto a fine mesh nickel screen.
plate saturation — The condition in an electron tube when
plasma — A gas that is sufficiently ionized so as to affect the plate will no longer attract electrons as fast as they are
its electrical properties and behavior. Plasmas are used in emitted by the cathode.
low temperature forms for the construction of integrated
plating — A process in which one metal is used to
circuits and for providing light in fluorescent lights. In
cover another using a process of electrical deposition.
high temperature applications, they are used for cutting
Specifically, chromium and cad­mium are useful metals
and welding metals and for propulsion for interplanetary
for covering steel.
probes.
platinum — A hard, gray metallic element with a symbol of
plasma arc welding — A very localized, high temperature
Pt and an atomic number of 78. Platinum has an extremely
form of welding that minimizes distortion of the metal
high melting point and is used for the electrodes of
being welded. See also plasma.
fine-wire spark plugs.
plasma coating — The process of applying a thin coating
platinum spark plug — A fine‑wire electrode spark plug
of highly wear-resistant material on the surface of turbine
that can operate at very high temperatures.
engine parts. The process is accomplished by spraying
material under high pressure and high heat onto the play — The relative movement between parts. Play is
surface of the blades. the amount of movement that occurs in a cockpit flight
control before the associated flight surface to move.
plasma engine — An engine used in outer space that uses
plasma technology for propulsion. P-lead — The primary lead of an aircraft magneto.
Connected to the ignition switch.
plasma generator — A device that uses electricity,
magnetism, and low pressures to generate ionized plasma plenum — An enlargement of a duct or an enclosing space
gases. Also, a device that uses plasma gases to generate in an aircraft engine induction system or air conditioning
electricity. system. Used to smooth out the pulsations in the flow of
the air.
plasma torch — A device that utilizes hot, high velocity,
ionized gases in the cutting and welding of metals. plenum chamber — An enclosed volume of air in which
the air is held at a slightly higher pressure than that of the
surrounding air.
238

10001930-002_AviationDictionary_2012_BOOK.indb 238 3/27/2012 9:38:21 AM

 Plexiglas • polar front model

Plexiglas — A transparent acrylic plastic material used for pneumatic starter — Starting motor operated by air
aircraft windshields and side windows. pressure.
pliers — Small, pincher-like hand tools used for holding pneumatic system — The power system in an aircraft used
small objects or for bending and cutting wire. for operating landing gear, brakes, wing flaps, etc. with
compressed air as the operating fluid.
plies — Sheets of material that are laminated together.
pneumatic‑mechanical fuel control — A fuel control that
plumb — A weight attached to a line or string and used to
utilizes pneumatic and mechanical forces to operate its
indicate vertical direction. Anything that lines up with the
fuel schedul­ing mechanisms.
plumb line is said to be plumb or in plumb.
pneumatics — The system of fluid power that transmits
plumb bob — A weight attached to a line or string and used
force by the use of a compressible fluid.
to establish a location directly below the point to which
the line is attached. PNP transistor — The three‑element semi­conductor device
made up of a sandwich of N-type silicon or germanium
plumb line — The straight line of a string to which a plumb
between two pieces of P‑type material.
bob is attached and hung. Anything that lines up with the
plumb line is said to be plumb or in plumb. pod — An enclosure housing a complete engine assembly.
plumbing — Tubing and fittings or connectors used for pogonip — A dense winter fog containing frozen particles.
transmitting fluid within a structure or piece of equipment. Forms in deep mountain valleys.
plumbing connection — Threaded connections that join point out — An action taken by a controller to transfer the
sections of tubing, or which are used to connect the radar identification of an aircraft to another controller
tubing to a component. if the aircraft will or can enter the airspace or protected
airspace of another controller and radio communications
plunger — A part of a machine that works with a relatively
will not be transferred. Also referred to as radar point out.
rapid downward motion.
pointer — A thin strip of movable metal moved over a
plutonium — A radioactive metallic element with the
calibrated scale by an analog instrument mechanism.
symbol Pu and an atomic number of 94.
Also referred to as hands or needles.
ply — In composites, one layer of reinforcement in a
point-to-point wiring — An antiquated method of building
laminate.
electronic units. Electronic components were mounted
ply rating — A load rating for aircraft tires that relates to directly on the chassis and interconnected by means of
the strength of cotton plies. For example, a 20-ply rating wires that were integral parts of the components’ leads or
nylon tire has the same load rating as a tire with 20 cotton by means of insulated hook up wire.
plies.
polar airmass — An airmass with characteristics developed
plywood — Layers of wood glued together so that the grain over high latitudes, especially within the sub polar highs.
in each layer is placed 45° or 90° to the others. Con­tinental polar air (cP) has cold surface temperatures,
low moisture content, and, especially in its source regions,
PN Junction — In semiconductor devices, a PN junction
has great stability in the lower layers. It is shallow in
is fabricated from a single slice of semiconductor with
com­parison with Arctic air. Maritime polar (mP) initially
one side doped as P-type and the other side doped as
possesses similar properties to those of continental polar
N-type. In operation, the migration of electrons to the P
air, but in passing over warmer water it becomes un­stable
side and the holes to the N side creates a depletion area
with a higher moisture content. See also tropical airmass.
that resists further migration of ions. The flow of current
is then controlled by the types of voltage applied to the polar easterlies — Surface winds generated by polar highs
ends of the device. north of 60º N latitude.
pneudraulic — A combination of air and hydraulic pressure. polar front — The semi-permanent, semi-continuous front
separating airmasses of tropical and polar origins.
pneumatic altimeter — An altimeter that measures height
above a given pressure level. Its calibration is based on polar front jet stream — One of two jet streams that
a specified lapse rate or change in pressure with height. commonly occur in the westerlies. Associated with the
polar front.
pneumatic drill motor — An air motor equipped with a
chuck to hold twist drills. polar front model — An idealized representation of events
that follow the development of a frontal low. The surface
pneumatic fire detection system — A system that uses a
component of the model describes the structure and
gas-filled continuous tube. The gas expands when heated
behavior of fronts and airmasses in the lower atmosphere.
and acts on a diaphragm to close an electrical circuit and
show a warning light in the cockpit.
239

10001930-002_AviationDictionary_2012_BOOK.indb 239 3/27/2012 9:38:21 AM

 polar track structure • pores

The upper air part of the model deals with the associated and moisture‑resistant charac­teristics. It is used for
development of troughs, ridges, and jet streams. plastic sheeting and containers.
polar track structure — A system of organized routes Poly-Fiber® — A fabric woven from polyester fibers.
between Iceland and Alaska that overlie Canadian MNPS
polymer paint — A fast drying, water‑based paint that
Airspace.
contains vinyl or acrylic resins. When the water in the paint
polarity — The property of an electrical device having two evaporates, it leaves a waterproof film of the plastic resin.
different types of electrical charges: positive (deficiency
polymerization — The process of joining two or more
of electrons) or nega­tive (excess of electrons).
chemicals with molecules of similar structure, forming
polarization — A degradation in chemical cell performance, a more complex molecule with different physical
particularly in the case of Leclanche cells, caused by gas properties. In this chemical reaction, the material
formation and the resulting insulation of portions of the essentially jells.
pole area.
polymid — A translucent plastic material commonly
polarized capacitor — A capacitor that can only be hooked referred to as nylon.
up to direct current of the proper polarity. Electrolytic
polyphase alternating current — Three‑phase AC
capacitors are normally polarized, and are labeled for
electricity produced by more than one set of generator
proper polarity connection.
windings.
polarized light — Light that has all the light waves in the
polyphase electric motor — An induction motor that
same plane.
operates on two-phase or three-phase AC.
polarized receptacle — A receptacle that has its sockets
polystyrene — A transparent plastic used to make cell cases
arranged so that the plug can only be inserted one way.
for some nickel‑cadmium batteries.
This is done either through the shape of the plug/socket
in two prong receptacles or by the arrangement of three polyurethane enamel — A two‑component, chemically
or more prongs. cured enamel finishing system noted for its hard, flexible,
high-gloss finish.
pole — The designation given to the ends of a magnet.
polyvinyl chloride (PVC) — 1. A thermoplastic resin used
pole shoes — The field assembly part of an electric
in the manufacture of transparent tubing for electrical
generator or motor.
insulation and fluid lines that are not subject to any
poles of a magnet — The north and south poles of a magnet pressure. 2. A popular, low-cost, wire insulating material.
where magnetic lines of flux leave the south pole and
pontoon — A float attached to the landing gear of a land
reenter at the north pole.
airplane to allow it to operate from water.
polishing — The process of producing a smooth surface by
poor judgment chain — A series of mistakes that can lead
rubbing it with fine abrasive wheels, belts, or compounds.
to an accident or incident. Two basic principles generally
polyacrylonitrile (PAN) — The base material used in associated with the creation of a poor judgment chain are:
manufacturing some types of carbon fibers. (1) one bad decision often leads to another; and (2) as
a string of bad decisions grows, it reduces the number
polyconic projection — A map projection where the
of subsequent alternatives for continued safe flight.
parallels of latitude are arcs of a circle centered on the
Aeronautical decision making is intended to break the
north or south pole and the meridians are straight lines
poor judgment chain before it can cause an accident or
radiating from the poles as in the spokes of a wheel.
incident.
polyester fiber — A synthetic fiber noted for its mechanical
pop-open nozzle — The afterburner nozzle that pops full
strength, chemical stability, and long life. It is used to
open at idle for the purpose of efficient engine operation
make woven fabric for covering aircraft structures.
at very low thrust.
polyester resin — A synthetic resin, usually reinforced with
poppet valve — A circular‑headed, T-shaped valve. Used to
fiberglass cloth or mat, and used to form complex shapes
seal the combustion chamber of a reciprocating engine,
for aircraft structures.
and at the proper time, either admit the fuel-air mixture
polyethylene — A lightweight, thermoplastic resin material into the cylinder or conduct the burned exhaust gases out
with good chemical resistance. Polyethylene resins are of the cylinder.
used for making containers for liquids and sheets of
porcelain — A hard, smooth surfaced ceramic material.
protective covering material.
pores — Small holes or openings on the surface of metals.
polyethylene plastic material — A lightweight,
thermoplastic resin material that has very good chemical-

240

10001930-002_AviationDictionary_2012_BOOK.indb 240 3/27/2012 9:38:21 AM

 porosity • potassium

porosity — The condition of a material having small pores positive electrical charge — An electrical condition caused
or small cavities throughout the material. by a deficiency of electrons.
porous chrome — A plating of hard chromium on bearing positive feedback — In electronics, a signal fed from the
surfaces. The surface of the plating consists of tiny cracks output section back into the amplifier to reinforce the
in which lubricant can adhere to reduce sliding friction. input signal.
porous chrome plating — An electrolytically deposited positive ion — An atom that has fewer electrons than
coating of chromium on the walls of aircraft engine protons.
cylinders. The surface contains thousands of tiny cracks
positive logic — The logic used in binary computers. The
that hold oil to provide for cylinder wall lubrication.
more positive signal is considered to be equal to a one and
porous salt — The residue normally left on the surface of a the less positive or more negative signal is considered to
metal that has been attacked by corrosion. be equal to a zero.
porpoising — Hunting, or oscillating, around the lateral positive static stability — The condition of stability of an
axis of the aircraft normally caused by an incorrectly aircraft that causes it, when disturbed from a condition of
functioning automatic pilot. straight and level flight, to tend to return to straight and
level flight.
port side — The left‑hand side of an aircraft or ship as one
faces the nose of the aircraft or bow. positive temperature coefficient — A ratio that shows an
increase in length, resistance, capacitance, etc. with an
position error — The error in an airspeed indicator caused
increase in temperature.
by the static source not being exposed to absolutely still air.
positive terminal — The terminal of a battery or power
position lights — Lights on an aircraft consisting of a red
source where electrons enter the source after they have
light on the left wing, a green light on the right wing, and
passed through the exter­nal source.
a white light on the tail. FARs require that these lights be
displayed in flight during the hours of darkness. positive transfer of learning — Since students interpret
new things in terms of what they already know, some
position report — A report over a known location as
degree of transfer is involved in all learning. During
transmitted by an aircraft to ATC.
a learning experience, knowledge or skills they have
position symbol — A computer-generated indication shown gained in the past can aid students.
on a radar display to indicate the mode of tracking
positive vorticity — In weather, the vertical component
positive — Symbol: +. A condition of electrical pressure of vorticity (i.e., a measure of how rapidly the air is
caused by a deficiency of electrons. spinning) leading to cyclonic flow. It is associated with
upward air motions.
positive acceleration — An increase in the rate of change
of velocity. positive‑displacement pump — A fluid pump that moves
a specific amount of fluid each time it rotates. Examples
positive angle of attack
of positive-­displacement pumps include gear pumps,
— A flight con­dition
gerotor pumps, and vane pumps.
where the angle
of attack formed positron — The positive counterpart of an electron, which
between the relative wind and the chord line of the airfoil has the same mass and spin characteristics as an electron,
is formed with the relative wind being the bottom leg in but with a positive electrical charge.
relation to the chord line and the so-called top surface of
post exit thrust reverser — A thrust reverser used to
the aircraft.
reverse the hot exhaust stream of a gas turbine engine to
positive buoyancy — The tendency of an object, when help slow the airplane during landings.
placed in a fluid, to ascend or float because it is lighter
postcure — During the curing cycle of a manufactured
than the fluid it displaces.
composite component, the postcure is an additional
positive control — Control of all air traffic, within elevated temperature soak to improve the mechanical
designated airspace, by air traffic control. properties.
positive control area — An obsolete term that designated pot life — The usable life of a resin. The time before it
what is now referred to as Class A Airspace. begins to thicken after the catalyst and accelerator have
been added.
positive course guidance (PCG) — A continuous display
of navigational data that enables an aircraft to be flown potassium — A metallic element with a symbol of K and an
along a specific course line, e.g., radar vector, RNAV, atomic number of 19.
ground-based NAVAID.

241

10001930-002_AviationDictionary_2012_BOOK.indb 241 3/27/2012 9:38:21 AM

 potential • power (P)

potential — The electrical pressure or voltage caused by produce superalloys for high heat, high strength turbine
dis­similar metals in an acid solution or an electrolyte. components and for bearing material (sintered bearings).
potential barrier — The difference in forward bias potential powdered‑iron core — A molded, magnetic powdered
between the N side and the P side of a semiconductor. iron mixed with a binder. Used in magnetic applications
This is the amount of forward voltage necessary to begin when high permeability and low eddy current losses are
current flow through a device. The nominal amount of the desired.
potential barrier is 0.3 volts for a germanium device and
power amplifier — An electronic device designed to
0.7 volts for a silicon device. OK, but fails to mention the
create an increase in power (voltage times amperage) as
effect of temperature.
opposed to an amplifier designed to create an increase in
potential difference — The difference in voltage that voltage.
exists between two terminals or two points of differing
power brake control valve — A pressure regulator
potential.
between the aircraft hydraulic system and the brake
potential drop — A drop in voltage in an electrical circuit cylinders. The amount of pressure applied to the brakes
caused by the resistance of current flow through a is directly proportional to the force the pilot puts on the
resistance. brake pedals.
potential energy — The energy possessed by an object power control system — A control system in which the
because of its position, configuration, or chemical normal movement of the controls is assisted by the use of
arrangement of its constituents. hydraulic or pneumatic actuators to reduce the amount of
force the pilot must apply.
potential instability — A layer of air that is not only
potentially unstable, it is conditionally unstable, and power density — In radar, the amount of radar energy per
has a high moisture content. Potential instability is one cross-sectional area.
of the two basic requirements for the formation of a
power enrichment system — A carburetor subsystem for a
thunderstorm; the other is initial lift.
reciprocat­ing engine that increases the fuel mixture when
potentiometer — 1. A variable resistor having both ends the engine is operating at full power.
and its wiper in the circuit. Used as a voltage divider.
power factor — The ratio of the resistance of an electrical
2. An instrument used for measuring differences in
circuit to the circuit impedance measured by a wattmeter.
electrical potential by balancing the unknown voltage
against a known variable voltage. power frequency — Frequency of AC electricity used for
heat and light. Commercial power frequency in the U.S.
potentiometer ohmmeter — An ohmmeter circuit in which
is 60 Hz, and the aircraft power frequency is 400 Hz.
resistance is measured by placing a known voltage across
a standard resistor; then the circuit is opened and the power lever — The cockpit lever that connects to the fuel
unknown resistor is placed in series. The voltage drop control unit for scheduling fuel flow to the combustor.
across the standard resistor is read and displaced on the Also referred to as power control lever or throttle.
meter as ohms.
power lever angle (PLA) — A protractor on the fuel control
pot-life — In composites, the length of time that the resin, showing movement of the power lever in degrees.
mixed with catalyst, will be in a workable state.
power loading — The ratio of an aircraft’s maximum gross
potted circuit connector — An electrical circuit connector weight to the brake horsepower produced by the engines.
protected by encapsulating it with an insulating potting
power overlap — The time in which two or more cylinders
compound.
of an engine are simultaneously on the power stroke. The
potting compound — 1. A resin having filler capability, more cylinders an engine can have on the power stroke at
used to fill cells when making minor repairs to damaged one time, the greater the power overlap and the smoother
honeycomb panels. 2. A non‑hardening, rubber-like the operation.
material used to moisture proof and protect the wires in
power (P) — 1. The time-rate of doing work. Force times
certain electrical plugs.
distance, divided by time. Power can be expressed
pound — A measure of mass equal to approximately 0.454 kg. in terms of foot‑pounds of work per minute, or in
horsepower (HP). One HP is 33,000 ft.‑lbs. of work
pour point — 1. The lowest temperature at which a fluid
per minute. 2. The basic unit of electrical power is the
will pour without disturbance. 2. The lowest temperature
watt, and 746 watts of electrical power is equal to one
at which oil will gravity flow.
mechanical horsepower. In electrical problems, power is
powder metallurgy — A development that makes use of the product of voltage (E) times current (I) (P = E X I).
powdered metals rather than ingots. A process used to Power in watts delivered to a circuit varies directly with

242

10001930-002_AviationDictionary_2012_BOOK.indb 242 3/27/2012 9:38:22 AM

 power pump • precipitation static

the square of the applied voltage and inversely with the Pratt truss — A truss
circuit resistance. structure in which
power pump — A hydraulic pump driven by the aircraft the verti­cal members
engine or by an electric motor. carry only com­pressive
loads, and the diagonal
power recovery turbine (PRT) — A power recovery members carry only tensile loads. A Pratt truss is used for
device used on the Wright R-3350 engine. The exhaust most fabric-covered wings.
gases spin a series of small turbines that are clutched to
the crankshaft by fluid-coupling devices. preamplifier — An electronic circuit component that
amplifies an extremely weak input signal to a value
power section — That portion of a radial engine on which strong enough to be used in other amplifiers.
the cylinders are mounted.
prearranged coordination — A standardized procedure
power stroke — The movement of the piston of an aircraft that permits an air traffic controller to enter the airspace
reciprocating engine when the piston is forced down assigned to another air traffic controller without verbal
by the expanding gases. This is the only time work is coordination. The procedures are defined in a facility
accomplished by the engine. directive that ensures standard separation between aircraft.
power supply — The part of an electronic circuit that precession — One of the characteristics of a gyroscope that
supplies the filament and plate voltages for the operation causes an applied force to be felt, not at the point of application,
of the circuit. but 90° from that point in the direction of rotation.
power transformer — An electrical power supply precious metal — Highly valued metal because of scarcity.
transformer that changes voltage to that needed for the Examples of precious metals are gold, silver, and
operating unit. platinum.
power turbine — A turbine rotor connected to an output precipitable water — The amount of liquid precipitation
shaft but not connected to the compressor. Also referred that would result if all water vapor were condensed.
to as free power turbine.
precipitate — To condense out of, or to separate from, a
powered parachute — A powered aircraft comprised of a mixture.
flexible or semi-rigid wing connected to a fuselage so that
the wing is not in position for flight until the aircraft is in precipitation — Any or all forms of water particles (rain,
motion. The fuselage of a powered parachute contains the sleet, hail, or snow), that fall from the atmosphere and
aircraft engine, a seat for each occupant, and is attached reach the surface.
to the aircraft’s landing gear. precipitation attenuation — In radar meteorology, any
powered-lift — A heavier-than-air aircraft capable of process that reduces intensity of radar signals from
vertical takeoff, vertical landing, and low speed flight precipitation.
that depends principally on engine-driven lift devices or precipitation fog — Fog that develops when rain saturates
engine thrust for lift during these flight regimes and on the air near the ground.
non-rotating airfoil(s) for lift during horizontal flight.
precipitation hardening — Hardening caused by the
powerplant — The complete installation in an aircraft precipitation of a constituent from a supersaturated solid
of the engine, propeller, and all of the accessories and solution. A process of reheating an alloy and allowing
controls needed for its proper operation. it to cool slowly. Allows crystalline structure to harden
powerplant technician — A person who holds a certificate uniformly.
from the FAA authorizing him or her to perform precipitation heat treatment — A step in the heat‑treating
maintenance or inspection on the powerplant, including process of aluminum in which the metal, after having
the propeller, of certificated aircraft. been heated to its critical temperature and quenched, is
practical test standards (PTS) — An FAA published list of raised to an elevated temperature and held for a period
standards that must be met for the issuance of a particular of time. This process artificially ages the metal and
pilot certificate or rating. FAA inspectors and designated increases its strength.
pilot examiners use these standards when conducting precipitation static — The static heard on communication
pilot practical tests and flight instructors should use the gear when electricity is discharged from radio antennas
PTS while preparing applicants for practical tests. or other objects on the aircraft as it flies through clouds
practice instrument approach — An instrument approach containing ice particles.
procedure conducted by a VFR or an IFR aircraft for the
purpose of pilot training or proficiency demonstrations.

243

10001930-002_AviationDictionary_2012_BOOK.indb 243 3/27/2012 9:38:22 AM

 precipitation-induced downdraft • pre-flight pilot briefing

precipitation-induced downdraft — Downdrafts present preferential routes — Preferential routes (PDRs, PARs, and
inside of a thunderstorm that are induced by rainfall and PDARs) are adapted in ARTCC computers to accomplish
are much stronger than downdrafts that exist outside of inter/intra-facility controller coordination and to assure that
the thunderstorm. flight data is posted at the proper control positions. Locations
having a need for these specific inbound and outbound routes
precision approach (PA) — An instrument approach
normally publish such routes in local facility bulletins, and
based on a navigation system that provides course and
their use by pilots minimizes flight plan route amendments.
glidepath deviation information meeting the precision
When the workload or traffic situation permits, controllers
standards of ICAO Annex 10. PAR, ILS, and MLS are
normally provide radar vectors or assign requested routes to
precision approaches.
minimize circuitous routing. Preferential routes are usually
precision approach procedure — A standard instrument confined to one ARTCC’s area and are referred to by the
approach procedure in which an electronic glide slope/ following names or acronyms:
glide path is provided; e.g., ILS/MLS and PAR..
a. Preferential Departure Route (PDR) – A specific
precision approach procedure — A standard instrument departure route from an airport or terminal area to an
approach procedure in which an electronic glideslope/ enroute point where there is no further need for flow
glidepath is provided; e.g., ILS, MLS, PAR. control. It can be included in an Instrument Departure
Procedure (DP) or a Preferred IFR Route.
precision approach radar (PAR) — A radar system that
uses two separate antenna. One is used to determine the b. Preferential Arrival Route (PAR) – A specific arrival
aircraft’s horizontal position relative to the extended route from an appropriate enroute point to an airport
centerline of the runway, and the other to determine or terminal area. It can be included in a Standard
the aircraft’s vertical position relative to the glideslope Terminal Arrival (STAR) or a Preferred IFR Route.
leading to the runway. A ground controller directs the The abbreviation “PAR” is used primarily within
pilot of the aircraft horizontally and vertically to maintain the ARTCC and should not be confused with the
position on centerline and on glideslope. abbreviation for Precision Approach Radar.
precision measuring instruments — Instruments capable c. Preferential Departure and Arrival Route (PDAR)
of making exact measurements. – A route between two terminals that are within or
immediately adjacent to one ARTCC’s area. PDARs
precision runway monitor (PRM) — Provides air traffic
are not synonymous with Preferred IFR Routes but
controllers with high precision secondary surveillance
can be listed as such as they do accomplish essentially
data for aircraft on final approach to parallel runways that
the same purpose.
have extended centerlines separated by less than 4,300
feet. High resolution color monitoring displays (FMA) are preferred IFR routes — Routes established between busier
required to present surveillance track data to controllers airports to increase system efficiency and capacity. They
along with detailed maps depicting approaches and no normally extend through one or more ARTCC areas and
transgression zone. are designed to achieve balanced traffic flows among high
density terminals. IFR clearances are issued on the basis
precision switch — A snap-action switch that actuates
of these routes except when severe weather avoidance
at the point when a mechanism reaches a very definite
procedures or other factors dictate otherwise. Preferred
position. These switches typically have a plunger that
IFR Routes are listed in the Enroute Section. If a flight
requires an extremely small movement to trip and close
is planned to or from an area having such routes, but
the contacts. When the plunger is released, a spring snaps
the departure or arrival point is not listed in the Enroute
the contacts open.
Section, pilots can use that part of a Preferred IFR Route
predeparture clearance (PDC) — An automated Clearance that is appropriate for the departure or arrival point that is
Delivery system relaying ATC departure clearances from listed. Preferred IFR Routes are correlated with DPs and
the FAA to the user network computer for subsequent STARs and can be defined by airways, jet routes, direct
delivery to the cockpit via ACARS (Airline/Aviation routes between NAVAIDs, Waypoints, NAVAID radials/
VHF data link) where aircraft are appropriately equipped, DME, or any combinations thereof.
or to gate printers for pilot pickup.
preflight inspection — An aircraft inspection done prior
predrilling — The process of drilling a hole that is slightly to takeoff to deter­mine that all systems are functioning
smaller than required to enable reaming the hole to the properly for the intended flight.
proper size later.
pre-flight pilot briefing — A service provided by the FSS to
pre-exit thrust reverser — A thrust reverser system assist pilots in flight planning. Briefing items can include
installed forward of the exhaust nozzle. weather information, NOTAMs, military activities, flow
control information, and other items as requested. Also
referred to as a pilot briefing.

244

10001930-002_AviationDictionary_2012_BOOK.indb 244 3/27/2012 9:38:22 AM

 preform • pressure port

preform — In composites, a preshaped fibrous reinforcement press-to-test light — A light that is tested by pressing the
of mat or cloth formed to the desired shape on a mandrel light fixture to complete the circuit to ground. If the light
or mock-up before being placed in a mold press. illuminates, the bulb is good.
preformed control cable — Steel aircraft control cable pressure — Force per unit area.
whose in­dividual strands were formed into a spiral before
pressure altimeter — A barometric instrument that indicates
the cable was woven. This relieves the bending stresses
altitude. When set to standard sea level pressure of 29.92
within the cable and prevents the strands from spreading
inches of mercury, it indicates pressure altitude. When
out when the cable is cut.
set to the local altimeter setting, it indicates indicated
preignition — Ignition occurring in the cylinder before the altitude from which true altitude can be calculated.
time of nor­mal ignition. Preignition is often caused by
pressure altitude — The height above the standard pressure
a local hot spot in the combustion chamber igniting the
level of 29.92 in. Hg. It is obtained by setting 29.92 in the
fuel‑air mixture.
barometric pressure window and reading the altimeter.
pre-installation checks — Checks made on a unit before
pressure capsule — The portion of a structure subjected to
installation.
pressurization. Usually consists of the cabin and cockpit.
pre-oiling — A procedure that ensures oil has reached all
pressure carburetor — A fuel metering system that senses
critical lubrication points before an engine is started.
the relationship between impact air pressure and venturi
Methods of pre-oiling include accumulators that maintain
pressure to provide a metering force for the fuel.
oil pressure in the system when the engine is not operating
and operating the oil pump by itself before starting. pressure casting — A method of casting metal parts by
forcing molten metal into permanent molds.
preparation — The first step of the teaching process,
consisting of determining the scope of the lesson, the pressure controller — That portion of a turbocharger
objectives, and the goals to be attained. This portion also control system that maintains the desired manifold
includes making certain all necessary supplies are on pressure.
hand. In using the telling and doing technique of flight
pressure demand oxygen system — A demand oxygen
instruction, this step is accomplished prior to the flight
system that supplies 100% oxygen at sufficient pressure
lesson.
above the altitude where normal breathing is adequate.
pre-preg — In composites, reinforcing material that is Also referred to as a pressure breathing system.
pre-impregnated with resin/catalyst mixture. The resin
pressure fed gun — A paint spray gun in which the material
system is in the B-stage and requires refrigerated storage.
is fed to the gun by air pressure on the pot or cup holding
When heated, the resins begin to glow and will complete
the material.
the cure when the temperature is elevated to its cure
temperature for the proper amount of time. pressure gauge snubber — A unit installed in the pressure
gauge line that stabilizes pressures and allows the needle
prerotation — In a gyroplane, it is the spinning of the rotor
of the pressure gauge to give a steady reading.
to a sufficient r.p.m. prior to flight.
pressure gradient — The rate of change of pressure per
presentation — The second step of the teaching process,
unit distance at a fixed time.
consisting of the delivery of the knowledge and skills that
make up the lesson. The delivery would be by either the pressure gradient force — The force that arises because of
lecture method or demonstration-performance method. the pressure of a pressure gradient.
In the telling and doing method of flight instruction, this
pressure jump — In weather, a sudden change in pressure
is where the instructor both talks about and performs the
reading.
procedure.
pressure line — Tubing that carries hydraulic fluid under
press brake — A sheet metal bending tool in which the
pressure from the pump to the selector valve or the
sheet is placed on the bed with the sight line directly
control valve.
under the edge of the clamping bar with the correct bend
radius die. The clamping bar is brought down to hold the pressure plate — A heavy, stationary disc in a multiple disc
sheet firmly in place and a bending leaf is raised until it brake. It is provided with a wear surface on one side only,
bends the metal to the proper angle. and the pistons press against its backside to force the disk
stack over against the back plate.
press fit — A tight interference fit between machine parts.
Re­quires one part to be pressed into the other. pressure port — The opening in a device through which
pressure is introduced.

245

10001930-002_AviationDictionary_2012_BOOK.indb 245 3/27/2012 9:38:22 AM

 pressure pot • preventive maintenance

pressure pot — A container holding pressure‑demand oxygen regulator — An oxygen

the material to be sprayed. An regulator capable of furnishing 100% oxygen under
agitator keeps the material in pressure to force the oxygen into the lungs of the user.
motion, and a regulator maintains
pressurization — A means of increasing the partial
the proper air pressure on the
pressure of oxygen in the cabin of an airplane flying
material to feed it to the gun.
at high altitude. Accomplished by increasing the air
pressure ratio — One pressure pressure in the cabin to that of an altitude which requires
divided by another, used to describe certain engine no sup­plemental oxygen.
functions. See also compressor pressure ratio; engine
pressurization controller — A controller that maintains
pressure ratio.
the pressure in an aircraft cabin at a selected pressure.
pressure ratio controller — In turbocharged engines,
pressurized aircraft — Any aircraft in which the cabin
controls the max­imum turbocharger compressor
area is sealed off and pressurized with air from a cabin
discharge pressure (34 + or - .5 in. Hg to critical altitude
supercharger. The cabin can be pressurized to a pressure
of 18,000 ft.).
that compares with a maximum altitude of approximately
pressure reducing valve — A device that reduces the 8,000 ft.
pressure of a liquid or gas from a high value to a fixed
pressurized ignition system — An ignition system that
lower value.
is pressurized with compressed air (usually from the
pressure regulator — In a hydraulic system, a device that turbocharger system) to keep high voltage from arcing
maintains a constant output pressure from a constant between electrodes due to low air density at high altitudes.
displacement pump by bypassing a portion of the fluid
pressurizing and dump valve — A valve used with a dual
back to the inlet side of the pump.
line duplex fuel manifold and duplex nozzle system. The
pressure relief valve — In a hydraulic system, a pressure pressurizing valve opens at higher fuel flows to deliver
control valve that bypasses fluid back to the return fuel to the secondary manifold. At engine shutdown, the
manifold or reservoir in the event the pressure rises dump portion opens to drain fuel overboard from the
above a predetermined level. manifolds. Also referred to as a pressurizing and drain
valve.
pressure seal — A seal installed in a pressure bulkhead to
permit a cable to pass through it. prestretching — A means of preventing an aircraft control
cable from stretch­ing during use by applying a load to the
pressure sensing switch — An electrical switch that will
cable equal to 60% of its breaking strength for a specified
open or close when a predetermined pressure is reached
period of time before installing it in the airplane.
in a system.
pretest — A test used to determine whether a student has
pressure, static — The pressure measured in a duct
the necessary qualifications to begin a course of study.
containing air, a gas or a liquid in which no velocity
Also used to determine the level of knowledge a student
(ram) pressure is allowed to enter the measuring device.
has in relation to the material that will be presented in
Symbol Ps.
the course.
pressure tank — See accumulator.
pretrack — A method used by some manufacturers to
pressure, total — Static pressure plus ram pressure. Total preset the track of a rotor blade prior to installation. The
pressure can be measured by use of a specially shaped blade is tested at the factory and marked with appropriate
probe that stops a small portion of the gas or liquid settings so it can be adjusted properly during installation.
flowing in a duct thereby changing velocity (ram) energy
prevailing visibility — In the U.S., the greatest horizontal
to pressure energy. Symbol Pt.
visibility equaled or exceeded throughout half of the
pressure transducer — A mechanical‑to‑electrical device horizon circle; it need not be a continuous half.
in which an electrical signal is generated proportional to
prevailing westerlies — The dominant west‑to‑east motion
the pressure being sensed. The electrical signal is then
of the atmosphere, centered over middle latitudes of both
transmitted to an instru­ment on the instrument panel.
hemispheres.
pressure transmitter — A mechanical-to-electrical device
prevailing wind — Direction from which the wind blows
in which an electrical signal is generated proportional to
most frequently.
the pressure being sensed. The electrical signal is then
transmitted to an instru­ment on the instrument panel. preventive maintenance — Simple or minor preservative
operations and the replacement of small standard parts
pressure vessel — A pressurized portion of an aircraft that
not involving complex assembly operation as listed in
is sealed and pressurized in flight.
Appendix A of FAR Part 43.

246

10001930-002_AviationDictionary_2012_BOOK.indb 246 3/27/2012 9:38:22 AM

 prick punch • PRM (Precision Runway Monitoring)

prick punch — A tool used to place reference marks on primary/support concept — A method for teaching
metal. attitude instrument flying, which divides the panel
into pitch instruments, bank instruments, and power
primacy — A principle of learning where the first experience
instruments. For a given maneuver, there are specific
of something often creates a strong, almost unshakable
instruments used to control the airplane and obtain the
impression. The importance to an instructor is that the
desired performance.
first time something is demonstrated, it must be shown
correctly since that experience is the one most likely to prime coats — The first coats of an aircraft finish. Used to
be remembered by the student. bond the topcoats to the base material.
primary air — That portion of the compressor output air primer — 1. A material applied to a metal before applying
used for actual combustion of fuel. Sometimes this term the topcoats. Used to bond the topcoats to the base
is used to refer to the amount of air flowing through the material. 2. A small hand-operated pump used to spray
basic engine portion of a turbofan engine. raw gasoline into an engine cylinder to provide fuel for
starting.
primary airstream — The air that passes through the core
of the engine. primer fuel system — A low output system for engine starting.
Used primarily where the main fuel system uses vaporizing
primary cell — An electrical device that generates electron tube nozzles. Also referred to as a starting fuel system.
flow by converting some of its substance into ions that
free electrons. Some of the material is destroyed in the primer surfacer — See prime coats.
process. Primary cells are not rechargeable. priming a pump — The act of replacing air in a pump with
primary circuit — The main circuit in a magneto ignition the liquid to be pumped.
system. It consists of turns of wire in which the primary Principal Maintenance Inspector (PMI) — An FAA
current flows. employee that is the assigned primary contact between
primary controls — Movable surfaces that cause an the FAA and an airline, repair station, maintenance
aircraft to rotate about its three primary axes. The school, etc.
primary controls of an airplane are the ailerons, elevators, principal view — The view in an orthographic drawing that
and rudder. shows the most detail of the object.
primary current — The alternating or pulsating current principles of learning — Concepts that provide insight into
that flows in the primary winding of a transformer. effective learning and can provide a foundation for basic
Induces a current in the secondary winding. instructional techniques. These principles are derived
primary cycle — The most intense portion of a lee wave, from the work of E. L. Thorndike, who first proposed the
located immediately down wind of the mountain. principles of effect, exercise, and readiness. Three later
principles were added: primacy, recency, and intensity.
primary exhaust nozzle — On a turbofan, the hot exhaust
nozzle. On an afterburner, the inner exhaust nozzle. print — A copy of a formal engineering drawing.
primary fuel — In a duplex fuel nozzle, the fuel that print tolerance — A notation on an aircraft drawing that
initially flows on starting; usually from the center orifice. describes the tolerance allowed on a particular finished part.
Also referred to as pilot fuel.
printed circuit board (PCB) — Modern replacement for
primary instruments — Those instruments that provide the electronic component chassis. Consists of a plastic,
the most essential information during a given flight fiberglass, or other insulating board with bonded copper
condition. strips for component interconnection. The components
are generally soldered directly on the board.
primary radar — A radar system using only a transmitter,
receiver, antenna, and cathode-ray tube display to indicate priority valve — A pressure‑actuated hydraulic valve that
radar traffic. No transponder signal is added. Indication allows certain actuations before others. One use of this
on display is referred to as a primary return. type of valve is to assure that the gear doors will be
opened before the landing gear extends.
primary structure — The portions of the airplane that
would seriously endanger the safety of the airplane if PRM (Precision Runway Monitoring) — A system that
they failed. An aircraft’s primary structure includes the permits simultaneous independent ILS approaches. An
wing structure, controls, engine mounts, etc. instrument landing system (ILS) approach conducted
to parallel runways whose extended centerlines are
primary winding — The winding in a magneto coil through
which the current induced by the rotating magnet flows. separated by less than 4,300 feet requires the the parallel
The breaker points are in series with the primary winding. runways to have a PRM System.

247

10001930-002_AviationDictionary_2012_BOOK.indb 247 3/27/2012 9:38:22 AM

 probe • projection

probe — A sensing device that extends into the air stream program — A list of events or procedures. In computers, a
or gas stream for measuring pressure, velocity, or program is a series of instructions that tell the computer
temperature. In the case of pressure, it is used to measure exactly how it is to receive, store, process, and deliver
total pressure data for the user.
procedure turn inbound — That point of a procedure turn program flowchart — A chart (such as Pert or Gnatt) that
maneuver where course reversal has been completed and shows the steps to be taken in the execution of a program.
an aircraft is established inbound on the intermediate
programmable calculator — An electronic calculator that
approach segment or final approach course. A report of
can be programmed by the user. Programming is usually
“procedure turn inbound” is normally used by ATC as a
stored in its memory.
position report for separation purposes.
programmable indicator data processor — The PIDP is
procedure turn (PT) — A maneuver in which a turn is
a modification to the AN/TPX-42 interrogator system
made away from a designated track followed by a turn
currently installed in fixed RAPCONs. The PIDP detects,
in the opposite direction to permit the aircraft to intercept
tracks, and predicts secondary radar aircraft targets.
and proceed along the reciprocal of the designated track.
These are displayed by means of computer-generated
NOTE 1: Procedure turns are designated “left” or “right” symbols and alphanumeric characters depicting flight
according to the direction of the initial turn. identification, aircraft altitude, ground speed, and
flight plan data. Although primary radar targets are
NOTE 2: Procedure turns can be designated as being made
not tracked, they are displayed coincident with the
either in level flight or while descending, according to the
secondary radar targets as well as with the other symbols
circumstances of each individual approach procedure.
and alphanumerics. The system has the capability of
procedures — Step-by-step instructions of how to interfacing with ARTCCs.
accomplish something.
programmable read-only memory (PROM) — An
process annealing — Heating a ferrous alloy to a integrated circuit memory device for a digital computer.
temperature close to, but below, the lower limit of the Programmable read‑only memory can be modified
transformation range and then cooling in order to soften once by the user. This is called “burning” the PROM.
the alloy for further cold working. Thereafter, the PROM acts the same as read-only memory
(ROM). A computer with erasable programmable
process control record — In composites, a record of the
read-only memory (EPROM) or electrically erasable
materials and processes used in making the repair.
programmable read-only memory (EEPROM) can be
Production Certificate — A certificate issued by the FAA modified more than once.
to allow the production of a type‑certificated aircraft,
progress report — A report over a known location as
aircraft engine, or component.
transmitted by an aircraft to ATC.
professional — Characterized by or conforming to the
progressive inspection — An inspection identical in scope
technical or ethical standards of a profession. Exhibiting
and detail to an annual inspection, but which allows
a courteous, conscientious, and generally businesslike
the workload to be divided into smaller portions and
manner in the workplace.
performed in shorter time periods. This allows the aircraft
profile descent — An uninterrupted descent (except to remain airworthy and in service during the extensive
where level flight is required for speed adjustment; e.g., (sometimes up to a year long) inspection period.
250 knots at 10,000 feet MSL) from cruising altitude/
progressive taxi — Precise taxi instructions given to a
level to interception of a glide slope or to a minimum
pilot unfamiliar with the airport or issued in stages as the
altitude specified for the initial or intermediate approach
aircraft proceeds along the taxi route.
segment of a nonprecision instrument approach. The
profile descent normally terminates at the approach gate prohibited area — A prohibited area is airspace designated
or where the glide slope or other appropriate minimum under part 73 within which no person can operate an
altitude is intercepted. aircraft without the permission of the using agency.
profile drag — 1. That portion of an aircraft’s drag prohibited area [ICAO] — An airspace of defined
caused by the air flowing over the surface of the craft. dimensions, above the land areas or territorial waters of
2. In rotorcraft, drag incurred from frictional or parasitic a State, within which the flight of aircraft is prohibited.
resistance of the blades passing through the air. It does not
projection — A defense mechanism used by students to
change significantly with the angle of attack of the airfoil
relegate blame for their own shortcomings, mistakes,
section, but it increases moderately as airspeed increases.
and transgressions to others, or to attribute their motives,
prognostic chart (contracted prog) — A chart of expected desires, characteristics, and impulses to other people.
or forecast conditions.

248

10001930-002_AviationDictionary_2012_BOOK.indb 248 3/27/2012 9:38:22 AM

 prony brake • prop‑fan

prony brake — A device used to measure the usable power propeller cuff — An airfoil shaped attachment made of thin
output of an engine on a test stand. It consists largely of sheets of metal, plastic, or composite material. Propeller
a hinged collar, or brake, that can be clamped to a drum cuffs are mounted on the blade shanks and primarily used
splined to the propeller shaft. The collar and drum form a to increase the flow of cooling air to the engine nacelle.
friction brake that can be adjusted by a wheel. An arm of
propeller diameter — Twice the distance from the center
known length is attached to the collar and ter­minates at a of the propeller hub to the blade tip.
point that bears on a scale. As the propeller shaft rotates,
the force is measured on the scale. This force multiplied propeller efficiency — Ratio of thrust horsepower to
by the lever arm indicates the torque produced by the brake horse­power. On the average, thrust horsepower
rotating shaft. constitutes approximately 80% of the brake horsepower.
The other 20% is lost in friction and slippage.
proof load — 1. A load applied to a structure that does not
cause per­manent deformation. 2. A testing measure to propeller hub — The central portion of a propeller to
insure the structure will be airworthy. which the blades are attached and by which the propeller
is attached to the engine.
proof pressure test — A series of tests to show that a
pressure capsule will withstand the pressure exerted upon propeller pitch — The acute angle between the chord of
it in service. a propeller and a plane perpendicular to the axis of its
rotation.
prop blast — The colloquial term for the rush of air
generated by a propeller. propeller protractor — A tool
used to measure the blade
propeller — A device for propelling an aircraft that, angle of a propeller. It is made
when rotated, produces by its action on the air, a thrust of aluminum alloy with three
approximately perpendicular to its plane of rotation. It square sides at 90º angles. A
includes the control components normally supplied by its bubble spirit level mounted
manufacturer. on one corner or the front
of the frame swings out to
propeller anti-icer — A system within an airplane that
indicate when the protractor
meters a flow of alcohol and glycerine along the leading
is level. A movable ring is
edge of the propeller blades to prevent the formation of
located inside the frame and used to set the zero reference
ice on the blades.
angle for the blade angle measurement.
propeller blade — The part of a propeller that forms the
propeller slip — A condition of propeller aerodynamics
airfoil and converts the torque of the engine into thrust.
that equals the difference between the geometric and the
propeller blade angle — The acute angle between the effective pitch.
chord of a propeller blade and the plane of rotation.
propeller spider — The foundation unit of a controllable
propeller blade pitch — The distance a propeller will pitch propeller. It attaches to the propeller shaft, and
advance if there isn’t any slip. the propeller blades ride on bearings on the spider. The
propeller blade tipping — The thin sheet brass or stainless spider is enclosed in the propeller hub.
steel covering along the leading edge and around the propeller synchronization — In multi engine aircraft,
tip of a wooden propeller that protects the blade from adjusting the propeller controls in order to operate the
erosion. propellers in unison, eliminating the uncomfortable
propeller boot — A propeller cuff that fits around the base noise associated with two propellers operating at
of the propeller blade and causes increased airflow into slightly different rates. This can be done manually or
the engine air inlet for cooling. automatically depending on the installed equipment.

propeller boss — The thick, central portion of a fixed‑pitch propeller thrust — The component of the total air force on
propeller hub. the propeller parallel to the direction of flight.

propeller brake — A friction brake used on turbopropeller propeller tipping — The thin sheet brass or stainless steel
engines to prevent the propeller windmilling in flight covering along the leading edge and around the tip of a
after it has been feathered. wooden propeller that protects the blade from erosion.
propeller butt — The blade shank or base of the propeller prop‑fan — An advanced technology propeller, designed to
blade that fits into the propeller hub. operate at supersonic tip speeds, Mach 0.8 airspeeds and
20,000 to 35,000 ft. altitude. Referred to as unducted fans,
propeller critical range — An operational range where the concept has fallen from favor due to excessive noise.
engine speed will cause harmonic vibration in the
propeller. Engines are usually placarded against operation
in this speed range.
249

10001930-002_AviationDictionary_2012_BOOK.indb 249 3/27/2012 9:38:22 AM

 propjet • pulse counter

propjet — An aircraft having a jet engine in which psychrometer — An instrument for determining the
the energy of the jet operates a turbine that drives the relative humidity of the air by measuring both the wet
propeller. and dry-bulb temperatures.
proportional control — A mechanical control system that P-type semiconductor material — A semiconductor
creates an output proportional to input, as opposed to a material that has been doped (an impurity added) so that
control (such as a switch) that is either off or on. it leaves the outer ring of the valence shells with holes
(absence of electrons) that readily accept electrons.
proposed boundary crossing time (PBCT) — Each center
has a PBCT parameter for each internal airport. Proposed P-type silicon — Silicon doped by an impurity having three
internal flight plans are transmitted to the adjacent valence electrons.
center if the flight time along the proposed route from
public aircraft — An aircraft used only in the service of
the departure airport to the center boundary is less than
a government or political subdivision. This does not
or equal to the value of PBCT or if airport adaptation
include any government-­owned aircraft engaged in
specifies transmission regardless of PBCT.
carrying persons or property for commer­cial purposes.
proposed departure time — The time a scheduled flight
published route — A route for which an IFR altitude has
will depart the gate (scheduled operators) or the actual
been established and published; i.e., Federal Airways,
runway off time for nonscheduled operators. For EDCT
Jet Routes, Area Navigation Routes, Specified Direct
(expect departure clearance time) purposes, the ATCSCC
Routes.
(Air Traffic Control System Command Center ) adjusts
the “P” time for scheduled operators to reflect the runway puckers — In composites, local areas on pre-preg material
off times. where the material has blistered and pulled away from
the separator film or release paper.
proprietary reducers — Thinners or solvents for paints
for­mulated according to and distributed under a trade pucks — The brake linings used on disc brakes.
name of a chemical manufacturer.
pull test — A fabric‑strength test in which a one-inch
propulsive efficiency — In gas turbine engines, external sample strip is pulled until it breaks. The strength of the
efficiency of an engine expressed as a percentage. fabric is determined by the force required to break the
strip.
propwash — The force of air blown rearward by the
propeller. pulley — A simple machine in the form of a wheel grooved
to accom­modate a cable. It is used to guide cables and
protected airspace — The airspace on either side of an
change direction.
oceanic route/track that is equal to one-half the lateral
separation minimum except where reduction of protected pull-through rivet — A blind mechanically expanded rivet
airspace has been authorized. in which the hollow shank is upset by pulling a tapered
mandrel through it.
proton — The positively charged particles in the nucleus
of an atom. pull-up resistor — A resistor used to limit the current
through a two-state device when the device is in its low
prototype — The first functional unit built as an example of
resistance state and to develop a potential difference
a new design or type.
when a two‑state device is in its high resistance state.
prototype device — A working model of a design used to
pulsate — To expand and contract rhythmically, yet not
test its concept.
change direction.
protractor — A device for measuring angles in degrees.
pulsating direct current — DC that has been chopped
protruding head rivet — An aircraft rivet in which the by a vibrator or chopper and that changes from zero
head protrudes above the surface of the metal. Examples to maximum and then back to zero. This produces the
include universal-head, round-head, and flat-head rivets. changing current required for use in a transformer.
Prussian blue — A compound used in checking the contact pulsation — A beat or rhythmic throb.
of a valve with a valve seat. A thin coating of Prussian
pulse — A rhythmic throb in the voltage of an electrical
blue is applied to the valve and the valve is pressed
circuit.
against the seat. Prussian blue is transferred to the seat
where in order to determine if the contact is uniform. pulse amplifier — A wide-band electrical amplifier used to
increase the voltage of alternating current.
psychomotor domain — A grouping of levels of learning
associated with physical skill levels that range from pulse counter — A device that measures pulses of electrical
perception through set, guided response, mechanism, energy that it receives in a specific interval of time.
complex overt response, and adaptation to origination.

250

10001930-002_AviationDictionary_2012_BOOK.indb 250 3/27/2012 9:38:23 AM

 pulse generator • pyrometer

pulse generator — An electronic circuit designed to push-pull amplifier — An electronic amplifier that has
produce sharp pulses of voltage. two output circuits whose output voltages are equal but
180° out of phase with each other. Also referred to as a
pulse-echo — An ultrasonic non‑destructive inspection
balanced amplifier.
used to detect the presence of internal damage or faults in
a construction material. push-pull rod — A rigid control rod used to move a
component by alternately pushing it and pulling it.
pulse-echo method of ultrasonic inspection — A method
of detecting metal thickness or internal damage by puzzle — A question with so many parts that it is difficult
introducing a pulse of ultrasonic energy into a part and to figure out what is being asked, let alone the answer.
timing its travel through the material and back to the
pylon — The structure that holds a turbine engine pod to the
point of injection.
wing or fuselage of the aircraft.
pultrusion — In composites, a manufacturing process that
pyrometer — A temperature measuring instrument used
pulls the resin impregnated fibers through a shaping die
to indicate temperatures that are higher than can be
to form a shape. The curing process also is done while it
measured with a mercury thermometer.
is in the die.
pumice — An extremely fine natural abrasive powder used
for polishing metal surfaces.
pump — A mechanical device used to move a fluid. A pump
is not a pressure producing machine as pressure can be
produced only when a flow of fluid is restricted.
pump cavitation — The formation of partial vacuums in a
liquid caused by a moving pump rotor. Pump cavitation
creates turbulence in the pump cavity, reducing pump
efficiency.
punch — 1. A short, tapered steel rod used for driving pins,
bolts, or rivets from holes. 2. A device used to cut holes
in paper, thin metal, or gasket material by shearing the
material between close‑fitting male and female dies.
punch test — A test of the strength of aircraft fabric while
it is on the airplane. A pointed, spring-loaded plunger is
pushed into the fabric, and the amount of force required
to penetrate the fabric indicates its strength.
puncture — A hole pierced in a material.
purge — To cleanse a system by flushing.
push fit — An interference fit in which the parts can be
as­sembled by hand-pushing them together rather than
having to drive or press them.
push rod — The component in a reciprocating engine that
transmits the movement of the cam to the rocker arm to
open the valves.
push to-test light — A light fixture for an indicator light
that can be pressed to complete a circuit. Illumination of
the light indicates the bulb is in operating condition.
push-button electrical switch — An electrical switch
actuated on or off by a push button. Each time the button
is pressed, it opens or closes the circuit.
pusher propeller — A propeller that fits onto an engine
whose shaft points to the rear of the aircraft. The thrust
pushes the aircraft through the air rather than pulling it.

251

10001930-002_AviationDictionary_2012_BOOK.indb 251 3/27/2012 9:38:23 AM

 Q • queuing

Q quantum — A quantity or amount.

quantum theory — A branch of physical theory involving
Q factor — The performance measurement of an inductance the transference or transformation of energy in an atomic
coil. It is the ratio of the inductive reactance to the or molecular scale based on the concept of the subdivision
resistance of a coil. of radiant energy into finite quanta.
Q factor of a coil — The performance measurement of an quart — A liquid measurement of volume equal to 1/4
inductance coil. It is the ratio of the inductive reactance gallon, 2 pints, or 57.75 cubic inches.
to the resistance of a coil.
quarter-sawed wood — Lumber cut at 45° across the
Q‑band radar — Radar operating in a frequency range annual rings.
of 36 to 46 gigaherz (wave length of approximately 7
millimeters). Used primarily in Very Large Array (VLA) quarter-turn cowl fastener — A quick‑release cowling
intergalactic research. fastener that requires only 1/4 turn to either fasten or
release. Examples: Dzus or Camloc fasteners.
QEC unit — A completed assembly of a basic engine
and the necessary components for a particular airframe quarter-wave antenna — The length of a radio antenna
installation. A quick engine change (QEC) unit consists that is one quarter of the wavelength of the frequency for
of an engine with all of the accessories and propeller which the antenna is used.
already installed. Minimizes the time it takes to replace quartz — A mineral found in nature in the form of a
an engine. Also referred to as a quick engine change six-sided crystal.
assembly (QECA) or a QEC kit.
quartz crystal — A thin slice of quartz used in electronic
QFE — Height above airport elevation (or runway threshold devices to control frequency. A quartz crystal vibrates
elevation) based on local station pressure. when an electrical pulse is applied. The frequency is
QNE — Altimeter setting 29.92 inches of mercury, 1013.2 dependent on the size, shape, and thickness of the crystal.
hectopascals or 1013.2 millibars. quartz glass — Glass constructed of pure quartz.
QNH — The barometric pressure as reported by a particular quartz lamp — A lamp constructed with quartz glass.
station. Quartz glass does not absorb ultraviolet rays as regular
Q-springs — A system that provides artificially produced glass does.
feedback of the control surface movement to the pilot. quartz oscillator — An electronic frequency generator that
Necessary because large, high‑speed aircraft normally uses a quartz crystal to control frequency.
utilize hydraulically actuated controls that provide no
natural feedback to the pilot. quartz‑iodine lamp — Lamps with a tungsten filament in
a nitrogen-argon gaseous medium to which bromine has
quad-clamp — A quick-attach-detach clamp used to attach been added, enclosed in an envelope of quartz. These
accessories to their gearbox mounting pads. lamps have an operating life two to three times that of
quadrant — 1. The location of an aircraft’s pivoting engine standard incandescent lamps and do not blacken with
control levers. Some aircraft use push‑pull knobs in the age. Now referred to as tungsten-halogen “quartz” lamps.
instrument panel. 2. A quarter part of a circle, centered quasi-stationary front — A stationary or nearly stationary
on a NAVAID, oriented clockwise from magnetic north front. Conven­tionally, a front that is moving at a speed
as follows: NE quadrant 000-089, SE quadrant 090-179, of less than 5 knots is generally considered to be
SW quadrant 180-269, NW quadrant 270-359. 3. In quasi-stationary. Commonly referred to as a stationary
mathematics, one of four equal segments defined by front.
the intersection of the two main axes of the rectangular
coordinate system. quench hardening — A ferrous alloy hardened by
austenitizing and then cooling rapidly enough so that
quadrantal error — In navigation, the angular error in a some or all of the austenite transforms to martensite.
measured bearing due to the presence of metal structures
and engines in the vicinity of the direction-finding quenching — The rapid cooling of a metal as part of the
antenna. heat-treating process. The metal is removed from the
furnace and submerged in a liquid such as water, oil, or
quality control (QC) — A management and inspection brine.
func­tion that controls quality, standards, and performance
in the manufacturing and repair of aircraft, aircraft queuing — The placement, integration, and segregation of
engines, and components. departure aircraft in designated movement areas of an
airport by departure fix, EDCT, and/or restriction.
quantity — An amount or portion. The total amount of a
particular thing.

252

10001930-002_AviationDictionary_2012_BOOK.indb 252 3/27/2012 9:38:23 AM

 quick engine change assembly (QECA) • quotient

quick engine change assembly (QECA) — An assembly

made up of an engine, propeller, all accessories, along
with all of the necessary cowling and engine mounts.
Used to minimize downtime when an engine change is
required. Also referred to as a QEC unit or QEC kit.
quick look — A feature of NAS Stage A and ARTS that
provides the controller the capability to display full data
blocks of tracked aircraft from other control positions.
quick-break fuse — A fuse that contains a spring that pulls
the fuse link apart earlier and more quickly than a normal
fuse.
quick-break switch — A switch that has spring loaded
contacts that snap open and closed. This helps prevent
arcing during the opening and closing of the circuit.
quick-disconnect coupling — A fluid coupling that
incorporates a check valve to prevent fluid loss upon
connecting or disconnecting.
quicksilver — Mercury. A heavy, silver-colored, toxic,
liquid, metallic chemical element with a symbol of
Hg and an atomic number of 80. Mercury remains in a
liquid state under standard conditions of pressure and
temperature. Mercury is approximately 13 times as heavy
as water.
quill shaft — A hardened steel shaft with a hollow cross
section and splines on each end. Torsional flexing of the
shaft is used to ab­sorb torsional vibrations.
quota flow control — A flow control procedure by which
the Central Flow Control Function (CFCF) restricts
traffic to the ARTC Center area having an impacted
airport, thereby avoiding sector/area saturation.
quotient — The number resulting from the division of one
number by another.

253

10001930-002_AviationDictionary_2012_BOOK.indb 253 3/27/2012 9:38:23 AM

 R • radar monitoring

R radar approach — An instrument approach procedure

that utilizes Precision Approach Radar (PAR) or Airport
rabbet — A groove cut into the edge or face of a board so Surveillance Radar (ASR).
that another board or panel can be fitted into it. Allows a radar approach control facility — A terminal ATC facility
T- or L-shaped assembly to be constructed. that uses radar and nonradar capabilities to provide
rabbet plane — A woodworking tool used to create rabbets approach control services to aircraft arriving, departing,
in a surface. or transiting airspace controlled by the facility.

race — A grooved, hardened, and polished steel surface on a. Provides radar ATC services to aircraft operating in the
which a bearing is supported. vicinity of one or more civil and/or military airports in
a terminal area. The facility can provide services of
racetrack procedure (ICAO) — A procedure designed to a ground controlled approach (GCA); i.e., ASR and
enable the aircraft to reduce altitude during the initial PAR approaches. A radar approach control facility can
approach segment and/or establish the aircraft inbound be operated by FAA, USAF, US Army, USN, USMC,
when the entry into a reversal procedure is not practical. or jointly by FAA and a military service.
rack — A straight piece of metal that has teeth cut into one side. b. Specific facility nomenclatures are used for
rack and pinion — A set of gears arranged in such a way administrative purposes only and are related to the
that a rotary motion of the pinion gear is changed into physical location of the facility and the operating
service generally as follows:
linear motion of the rack.
1. Army Radar Approach Control (ARAC) (Army).
rack and pinion actuator — A rotary actuator in which the
fluid acts on the rack of gear teeth cut on a piston. As the 2. Radar Air Traffic Control Facility (RATCF) (Navy/
piston moves it rotates a mating pinion gear. FAA).
radar — A device that, by measuring the time interval 3. Radar Approach Control (RAPCON) (Air Force/
between transmission and reception of radio pulses and FAA).
correlating the angular orientation of the radiated antenna
4. Terminal Radar Approach Control (TRACON)
beam or beams in azimuth and/or elevation, provides
(FAA).
information on range, azimuth, and/or elevation of
objects in the path of the transmitted pulses. 5. Air Traffic Control Tower (ATCT) (FAA). (Only
those towers delegated approach control authority.)
a. Primary Radar – A radar system in which a minute
portion of a radio pulse transmitted from a site is radar beacon transponder — An electronic device that
reflected by an object and then received back at that receives an interrogation or transmission from ground
site for processing and display at an air traffic control radar and responds with a coded transmission that
facility. appears on the traffic controller’s radar scope.
b. Secondary Radar/Radar Beacon (Air Traffic Control radar beam — A narrow beam of electromagnetic radiation
Radar Beacon System (ATCRBS)) – A radar system in used in radar units to determine distance, height, size,
which the object to be detected is fitted with cooperative and composition of desired target items.
equipment in the form of a radio receiver/transmitter radar contact — Term used by ATC to advise a pilot that
(transponder). Radar pulses transmitted from the the aircraft is identified on radar.
searching transmitter/receiver (interrogator) site are
received in the cooperative equipment and used to radar echo — The returning radar signal that is reflected
trigger a distinctive transmission from the transponder. from an object.
This reply transmission, rather than a reflected signal, radar identified aircraft — An aircraft, the position of
is then received back at the transmitter/receiver site for which has been correlated with an observed target or
processing and display at an air traffic control facility. symbol on the radar display.
radar advisory — Information or advice provided to pilots radar monitoring — The radar flight-following of aircraft,
based on radar observations. whose primary navigation is being performed by the pilot,
radar altimeter — Aircraft equipment that makes use of the to observe and note deviations from its authorized flight
reflection of radio waves from the ground to determine path, airway, or route. When being applied specifically
the height of the aircraft above the surface. to radar monitoring of instrument approaches; i.e., with
precision approach radar (PAR) or radar monitoring of
radar altitude — Distance from the ground determined by simultaneous ILS/MLS approaches, it includes advice
radar altimeter, which makes use of the reflection of radio and instructions whenever an aircraft nears or exceeds
waves from the ground. the prescribed PAR safety limit or simultaneous ILS/
MLS no transgression zone.
254

10001930-002_AviationDictionary_2012_BOOK.indb 254 3/27/2012 9:38:23 AM

 radar navigational guidance • radar weather echo intensity levels

radar navigational guidance — Vectoring aircraft to a. An aircraft cancels its IFR flight plan, except within
provide course guidance. Class B airspace, Class C airspace, a TRSA, or where
Basic Radar service is provided.
radar point out — An action taken by a controller to transfer
the radar identification of an aircraft to another controller b. An aircraft conducting an instrument, visual, or contact
if the aircraft will or may enter the airspace or protected approach has landed or has been instructed to change
airspace of another controller and radio communications to advisory frequency.
will not be transferred.
c. An arriving VFR aircraft, receiving radar service to a
radar required — A term displayed on charts and approach tower-controlled airport within Class B airspace, Class
plates and included in FDC Notams to alert pilots that C airspace, a TRSA, or where sequencing service
segments of either an instrument approach procedure or is provided, has landed; or to all other airports, is
a route are not navigable because of either the absence instructed to change to tower or advisory frequency.
or unusability of a NAVAID. The pilot can expect to be
d. An aircraft completes a radar approach.
provided radar navigational guidance while transiting
segments labeled with this term. radar summary chart — A weather product derived from
the national radar network that graphically displays a
radar route — A flight path or route over which an
summary of radar weather reports.
aircraft is vectored. Navigational guidance and altitude
assignments are provided by ATC. radar surveillance — The radar observation of a given
geographical area for the purpose of performing some
radar separation — Radar spacing of aircraft in accordance
radar function.
with established minima.
radar traffic advisories — Advisories issued to alert pilots
radar service — A term that encompasses one or more of
to known or observed radar traffic that can affect the
the following services based on the use of radar that can
intended route of flight of their aircraft.
be provided by a controller to a pilot of a radar identified
aircraft. radar traffic information service — Advisories issued
to alert pilots to observation of radar identified and
a. Radar Monitoring – The radar flight-following of
nonidentified aircraft targets on an ATC radar display that
aircraft, whose primary navigation is being performed
may be in such proximity to the position or intended route
by the pilot, to observe and note deviations from
of flight of their aircraft as to warrant their attention.
its authorized flight path, airway, or route. When
being applied specifically to radar monitoring of radar vector — A heading issued by a radar controller to
instrument approaches; i.e., with precision approach the pilot of an aircraft to provide navigational guidance.
radar (PAR) or radar monitoring of simultaneous ILS/
radar vectoring [ICAO] — Provision of navigational
MLS approaches, it includes advice and instructions
guidance to aircraft in the form of specific headings
whenever an aircraft nears or exceeds the prescribed
based on the use of radar.
PAR safety limit or simultaneous ILS/ MLS no
transgression zone. radar weather echo intensity levels — Existing radar
systems cannot detect turbulence. However, there is a
b. Radar Navigational Guidance – Vectoring aircraft to
direct correlation between the degree of turbulence and
provide course guidance.
other weather features associated with thunderstorms and
c. Radar Separation – Radar spacing of aircraft in the radar weather echo intensity. The National Weather
accordance with established minima. Service has categorized radar weather echo intensity for
precipitation into six levels. These levels are sometimes
radar service [ICAO] — Term used to indicate a service
expressed during communications as “VIP LEVEL”
provided directly by means of radar.
1 through 6 (derived from the component of the radar
a. Monitoring – The use of radar for the purpose of that produces the information - Video Integrator and
providing aircraft with information and advice relative Processor). The following list gives the “VIP LEVELS”
to significant deviations from nominal flight path. in relation to the precipitation intensity within a
thunderstorm:
b. Separation – The separation used when aircraft
Level 1. WEAK
position information is derived from radar sources.
Level 2. MODERATE
radar service terminated — Used by ATC to inform a pilot Level 3. STRONG
that he will no longer be provided any of the services that Level 4. VERY STRONG
could be received while in radar contact. Radar service is Level 5. INTENSE
automatically terminated, and the pilot is not advised in Level 6. EXTREME
the following cases:

255

10001930-002_AviationDictionary_2012_BOOK.indb 255 3/27/2012 9:38:23 AM

 radarsonde observation • radio marker beacon

radarsonde observation — An upper air observation used radiation shield — An insulation blanket made with layers
to determine winds, and other meteorological data, by of aluminum foil used around turbine engines to prevent
tracking the range, elevation, and azimuth of a radar heat radiating from the engine into the structure.
target carried aloft, usually by a balloon.
radical sign — The mathematical symbol “√ “placed before
radial — A navigational signal generated by a VOR or a quantity to show its root is to be extracted.
VORTAC. Each VOR station has 360 radials. The
radio — 1. A device used for communication. 2. Used to
radials are assigned numbers that pertain to their position
refer to a flight service station; e.g., “Seattle Radio” is
around the magnetic compass card and are considered
used to call Seattle FSS.
being drawn away from the VOR station in a particular
magnetic direction. radio altimeter (RA) — A device that measures the
height of an aircraft above the terrain by means of the
radial engine — A reciprocating aircraft engine in which
transmissions of a continuous wave, constant amplitude,
all of the cylinders are arranged radially, or spoke-like,
frequency modulated signal. The difference in the
around a small crankcase.
frequency of the reflected signals at any time is read on
radial inflow turbine — A turbine wheel that receives the RA indicator in feet above the ground.
its gases at the blade tips and guides the air inward and
radio beacon — An L/MF or UHF radio beacon transmitting
outward to the exhaust duct. It looks similar to a radial
nondirectional signals whereby the pilot of an aircraft
outflow compressor and is used extensively in APUs.
equipped with direction finding equipment can determine his
radial lead — An electrical component lead that protrudes bearing to or from the radio beacon and “home” on or track
from the outside of a component. to or from the station. When the radio beacon is installed in
conjunction with the Instrument Landing System marker, it
radial outflow compressor — An impeller-shaped device
is normally referred to as a compass locator.
that receives air at its center and slings it outward at high
velocity into a diffuser for increased pressure. radio control — Operating a unit or device by means of
radio transmissions.
radial ply tire — A tire in which layers of metal or synthetic
casing plies are constructed at right angles to the tread. radio detection and ranging (Radar) — A device that,
The plies are folded around the wire beads and back by measuring the time interval between transmission
against the tire sidewall, completely encompassing the and reception of radio pulses and correlating the angular
tire body. orientation of the radiated antenna beam or beams in
azimuth and/or elevation, provides information on range,
radial velocity — Motion toward or away from Doppler
azimuth, and/or elevation of objects in the path of the
RADAR.
transmitted pulses.
radian — A unit of angular measurement equal to the angle
radio direction finding — A method of determining the
between two radii, separated by an arc equal to the length
direction from which signals are received. When an
of the radius. Radians are used in the measurement of
aircraft is within reception range of a radio station, a
angular velocity.
directional antenna provides a means of fixing a bearing
radiant energy — Energy due to any form of electromagnetic from the station to the aircraft. The bearings from two
radiation, for instance, from the sun. or more receivers are plotted on a chart to determine the
position of the aircraft with reasonable accuracy.
radiant heat — The transfer of heat energy from a heat
source to the surrounding air. Rooms that have heated radio frequency — The electromagnetic waves that radiate
water tubing embedded in the floor use radiant heat. from the antenna of a radio transmitter. The frequency is
higher than the audible frequency range and below the
radiation — Energy radiated in the form of electromagnetic
frequency range of heat and light.
waves.
radio frequency energy — Electromagnetic energy used
radiation — The emission of energy by a medium and
for communication. Generally in the frequency range of
transferred, either through free space or another medium,
3 kilohertz to 300 gigahertz.
in the form of electromagnetic waves.
Radio Magnetic Indicator (RMI) — A movable-card
radiation fog — Fog characteristically resulting when
instrument on which the card automatically rotates to
radiational cooling of the Earth’s surface lowers the
reflect the aircraft’s magnetic heading. Two needles
air temperature near the ground to or below its initial
display the relative bearing to ADF and VOR stations.
dewpoint on calm, clear nights.
radio marker beacon — A low-powered, single-frequency
radiation sensing detector — A fire detection system that
radio transmitter used to designate specific navigational
utilizes heat‑sensitive units to complete an electrical
points. Marker beacon receivers receive the signal only
circuit when the temperature rises to a preset value.
when flying directly over the radio marker beacon.
256

10001930-002_AviationDictionary_2012_BOOK.indb 256 3/27/2012 9:38:23 AM

 radio transmitter • ramp and soak

radio transmitter — An electronic device that transmits radius dimpling — A method of preparing thin sheet metal
electromagnetic waves for the purpose of communicating in which a cone‑shaped male die is forced into the recess
with associated receiver(s). of a female die with either a hammer or a pneumatic rivet
gun. The material can be riveted with flush rivets after the
radioactivity — The property possessed by some elements
dimpling process is complete.
or isotopes of emitting electrons or alpha particles as
their atomic nuclei disintegrate. radius gauge — A precision gauge with an accurately cut
inside and outside radii, used to measure the radius of a
radio-frequency cable — A transmission line in which
bend.
the center conductor is surrounded by an insulator and
a braided outer conductor. All of this is enclosed in a radius of turn — The amount of horizontal distance an
weatherproof outer insulator. aircraft uses to complete a turn.
radio-frequency interference (RFI) — Undesired radome — The protective covering of a radar antenna. A
electromagnetic radiation that interferes with radio radome is constructed of lightweight honeycomb core
communication. Often the result of improperly filtered material electrically transparent so it will not interfere with
radio transmitters and other electronic equipment. the transmitted and received pulses of electrical energy.
radio-frequency spectrum — The range of frequencies rag wing — A common slang term for a fabric covered
used for radio communication. Commonly used bands are: airplane.
BAND FREQUENCY RANGE rain — Precipitation with water drops larger than drizzle
Very Low Frequency (VLF) 3-30 kHz and that fall in relatively straight, although not necessarily
Low Frequency (LF) 30-300 kHz vertical, paths as compared to drizzle that falls in irregular
Medium Frequency (MF) 300-3,000 kHz paths.
High Frequency (HF) 3-30 MHz
rain bands — Streaks of rain that spiral into a storm, lines
Very High Frequency (VHF) 30-300 MHz
of convergence associated with CB’s (cumulonimbus)
Ultra High Frequency (UHF) 300-3,000 MHz
clouds and shower activity.
Super High Frequency 3-30 GHz
Extremely High Frequency (EHF) 30-300 GHz rain gauge — An instrument used to measure the amount of
rain that has fallen in a given locale.
radiography — The system of nondestructive inspection
using X-rays or gamma rays to determine the condition rain shadow — The drier downwind side of a mountain.
of a part without disassembly.
rain shower — Precipitation in the form of rain from a
radiosonde — A balloon-borne instrument for measuring cumuliform cloud; characterized by sudden onset and
pressure, temperature, and humidity aloft. cessation, rapid change of intensity, and usually by rapid
change in the appearance of the sky.
radiosonde observation — a sounding made by the
instrument. If the balloon is tracked, winds can also be ram air pressure — The air pressure caused by the forward
determined. motion of an aircraft. Ram air pressure is slightly above
ambient air pressure.
radium — A radioactive element with a symbol of Ra and
an atomic number of 88. ram air temperature rise — The increase in temperature
caused by the ram compression of the air as an aircraft
radium poisoning — A poisoning associated with the
passes through the air at a high rate of speed. The rate of
handling of luminous materials used for marking the
temperature increase is proportional to the square of the
dials on some older aircraft instruments.
speed of the aircraft.
radius — 1. The distance
ram pressure rise — The pressure rise in the inlet due to
from the center of a circle
the forward speed of the aircraft.
or sphere to its outer
circumference; one half the ram ratio — The ratio of ram pressure to ambient pressure
diameter of a circle. 2. Also, in a jet engine.
the radial part of an object.
ram temperature rise — The inlet temperature rise due to
radius bar — The part of the cornice brake top leaf that has inlet ram pressure rise.
an accurately ground radius at its edge for bending sheet
ramp — The apron or paved surface around a hangar used
metal. It is used to obtain a bend radius appropriate to the
for parking aircraft.
alloy and thickness of a material.
ramp and soak — In composites, a curing process in which
radius block — A metal block around which sheet metal is
the temperature is slowly raised at a given rate to the final
bent to obtain a specific bend radius.
cure temperature and held for a specific amount of time.

257

10001930-002_AviationDictionary_2012_BOOK.indb 257 3/27/2012 9:38:23 AM

 ramp weight • rated continuous OEI (one engine inoperative) power

After that time, the temperature is slowly lowered to room rate gyro — A device used to measure the rate of an
temperature. For example, if the final cure temperature aircraft’s rotation about its vertical axis through 360°. A
for a part is 250ºF, the temperature would be ramped up rate gyro is not affected by the roll or pitch of the aircraft
to 250º at a rate of 8º per minute. Once it reaches 250º, but aligns itself with the fore and aft line.
the temperature is held there for 1 hour and 30 minutes,
rate of burning — The time required for a specific amount
and then the temperature is lowered to 80º at a rate of
of fuel‑air mixture to burn or to release its heat energy.
5º per minute. This process is typically done by using
a temperature controller found on hot patch bonding rate of climb — The rate, measured in feet per minute, at
equipment. which vertical motion occurs.
ramp weight — The total weight of the aircraft while on rate of turn — The change of heading per unit of time. For
the ramp. It differs from takeoff weight by the weight of example, 180º per minute, or 3º per second.
the fuel that will be consumed in taxiing to the point of
takeoff. rate of yaw — The rate, in degrees per second, at which an
aircraft rotates about its vertical axis.
random altitude — An altitude inappropriate for direction
of flight and/or not in accordance with FAA Order rate signal — A signal proportional to a rate of change.
7110.65, paragraph 4-5-1. rated 2 1/2-minute OEI (one engine inoperative) power
random route — Any route not established or charted/ — With respect to rotorcraft turbine engines, means
published or not otherwise available to all users. the approved brake horsepower developed under static
conditions at specified altitudes and temperatures within
range-height indicator (RHI) scope — A radar display the operating limitations established for the engine under
with height as the vertical axis and range as the horizontal FAR Part 33, and limited in use to a period of not more
axis. A vertical cross section of the cloud masses in a than 2 ½ minutes after the failure of one engine of a
particular azimuth can be determined. multiengine rotorcraft.
Rankine Temperature — The absolute temperature scale rated 2-minute OEI (one engine inoperative) power
using degrees Fahrenheit with minus 460°F as absolute — With respect to rotorcraft turbine engines, means
zero. It is used in many engine performance calculations. the approved brake horsepower developed under static
rapid decompression — The almost instantaneous loss of conditions at specified altitudes and temperatures within
cabin pressure in aircraft with a pressurized cockpit or the operating limitations established for the engine under
cabin. FAR part 33, for continued one-flight operation after the
failure of one engine in multiengine rotorcraft, limited
rapid exit taxiway (ICAO) — A taxiway connected to a to three periods of use no longer than 2 minutes each in
runway at an acute angle and designed to allow landing any one flight, and followed by mandatory inspection and
airplanes to turn off at higher speeds than are achieved prescribed maintenance action.
on other exit taxiways thereby minimizing runway
occupancy times. rated 30-minute OEI (one engine inoperative) power
— With respect to rotorcraft turbine engines, means
rarefied air — Of or pertaining to less air. Often used to the approved brake horsepower developed under static
describe the Earth’s upper atmosphere. conditions at specified altitudes and temperatures within
rasp — A coarse file with raised cutting points used for the operating limitations established for the engine under
scraping soft materials such as wood or plastic. FAR Part 33, and limited in use to a period of not more
than 30 minutes after the failure of one engine of a
ratchet — A mechanism that consists of a toothed wheel multiengine rotorcraft.
and a bar, or pawl, which allows the wheel to rotate in
one direction but prevents its backward motion. rated 30-second OEI (one engine inoperative) power
— With respect to rotorcraft turbine engines, means
ratchet coupling — A toothed wheel into which a pawl the approved brake horsepower developed under static
drops so that motion can be imparted to the wheel in only conditions at specified altitudes and temperatures within
one direction. the operating limitations established for the engine under
ratchet handle — A handle with a ratchet coupling used FAR part 33, for continued one-flight operation after the
to turn socket‑type wrenches. A ratcheting mechanism in failure of one engine in multiengine rotorcraft, limited to
the handle allows the socket to be turned in one direction three periods of use no longer than 30 seconds each in
while the handle is moved with a back‑and‑forth any one flight, and followed by mandatory inspection and
movement. By reversing the catch in the ratchet body, the prescribed maintenance action.
same back-and‑forth movement of the handle will rotate
rated continuous OEI (one engine inoperative) power
the socket in the opposite direction.
— With respect to rotorcraft turbine engines, means
the approved brake horsepower developed under static

258

10001930-002_AviationDictionary_2012_BOOK.indb 258 3/27/2012 9:38:23 AM

 rated horsepower • reaction formation

conditions at specified altitudes and temperatures within rated thrust — A manufacturer’s guaranteed thrust as
the operating limitations established for the engine under specified on the Type Certificate.
FAR Part 33, and limited in use to the time required to
rate-of-climb indicator — A rate of air pressure change
complete the flight after the failure of one engine of a
device that indicates the rate at which an airplane is
multiengine rotorcraft.
climbing or descending in feet per minute. Also referred
rated horsepower — The maximum horsepower an engine to as a vertical speed indicator.
is approved to produce under a given set of circumstances.
rate-of-temperature rise indicator — A thermocouple
rated maximum continuous augmented thrust — With fire detection system that depends on a rapid rate of
respect to turbojet engine type certification, means the temperature rise in order to operate. It will not indicate
approved jet thrust that is developed statically or in an overheat condition that has developed slowly.
flight, in standard atmosphere at a specified altitude, with
rating — A statement that, as a part of a certificate, sets
fluid injection or with the burning of fuel in a separate
forth special conditions, privileges, or limitations.
combustion chamber, within the engine operating
limitations established under Part 33 of this chapter, and ratio — The relationship between one number and another
approved for unrestricted periods of use. number expressed as a fraction. A proportion.
rated maximum continuous power — With respect to ratiometer indicator — A DC remote‑indicating system
reciprocating, turbopropeller, and turboshaft engines, whose pointer movement is determined by the ratio
means the approved brake horsepower that is developed of current-flow between two resistors or portions of a
statically or in flight, in standard atmosphere at a special variable resistor.
specified altitude, within the engine operating limitations
rationalization — A defense mechanism that students
established under Part 33, and approved for unrestricted
employ when they cannot accept the real reason for
periods of use.
their behavior. This permits them to substitute excuses
rated maximum continuous thrust — With respect to for reasons; moreover, they can make those excuses
turbojet engine type certification, means the approved jet plausible and acceptable to themselves. A subconscious
thrust that is developed statically or in flight, in standard technique for justifying actions that otherwise would be
atmosphere at a specified altitude, without fluid injection unacceptable.
and without the burning of fuel in a separate combustion
rattail file — A steel tool that has a circular cross section
chamber, within the engine operating limitations
with hardened ridged surfaces, used in smoothing,
established under Part 33 of this chapter, and approved
grinding, or boring. Also referred to as a round file.
for unrestricted periods of use.
rawhide mallet — A mallet made of rawhide wound into a
rated takeoff augmented thrust — With respect to
tight cylinder used to form sheet metal without scratching it.
turbojet engine type certification, means the approved
jet thrust that is developed statically under standard sea RC circuit — A circuit containing both resistance and
level conditions, with fluid injection or with the burning capacitance.
of fuel in a separate combustion chamber, within the
RC time constant — The time required to charge a
engine operating limitations established under Part 33 of
capacitor to 63.2% of its full‑charge state through a given
this chapter, and limited in use to periods of not over 5
resistance.
minutes for takeoff operation.
reach — The length of the shell thread of a spark plug. For
rated takeoff power — With respect to reciprocating,
18 mm spark plugs, long‑reach plugs are threaded for
turbopropeller, and turboshaft engine type certification,
13/16” and short-reach plugs for ½”.
means the approved brake horsepower that is developed
statically under standard sea level conditions, within the reactance — The opposition to the flow of AC made by an
engine operating limitations established under Part 33, induction coil or a capacitor. Reactance is expressed in
and limited in use to periods of not over 5 minutes for ohms.
takeoff operation.
reaction — A response to a stimulus or force. An event or
rated takeoff thrust — With respect to turbojet engine sequence of events caused by another action.
type certification, means the approved jet thrust that is
reaction engine — A jet engine that receives thrust only
developed statically under standard sea level conditions,
from the reaction caused by hot gases being expelled.
without fluid injection and without the burning of fuel
in a separate combustion chamber, within the engine reaction formation — A defense mechanism where
operating limitations established under Part 33 of this students protect themselves from dangerous desires by
chapter, and limited in use to periods of not over 5 not only repressing them, but by actually developing
minutes for takeoff operation. conscious attitudes and behavior patterns that are just the

259

10001930-002_AviationDictionary_2012_BOOK.indb 259 3/27/2012 9:38:24 AM

 reaction turbine • rectify

opposite. A student can develop a who-cares-what-other- receiver autonomous integrity monitoring (RAIM) —
people-think attitude to cover up feelings of loneliness A technique whereby a civil GNSS (Global Navigation
and a hunger for acceptance. Satellite System) receiver/processor determines the
integrity of the GNSS navigation signals without
reaction turbine — A stator vane and rotor blade
reference to sensors or non-DoD integrity systems other
arrangement, whereby the vanes form straight ducts
than the receiver itself. This determination is achieved
and the blades form convergent ducts. Gases leaving the
by a consistency check among redundant pseudorange
trailing edge of the blades turn the rotor. The design is
measurements.
common to turbine-type accessories such as air‑starters.
receiving controller — A controller/facility receiving
reactive current — A current in an AC circuit not in phase
control of an aircraft from another controller/ facility.
with the voltage.
receiving facility — See receiving controller.
reactive metal — A metal such as aluminum or magnesium,
which reacts with oxygen to form corrosion. recency — A principle of learning that things learned today
are remembered better than things that were learned
reactive power — The power in a reactive AC circuit
some time ago. The longer time that passes, the less that
that subtracts from the power that would be present in
will be remembered. Instructors use this principle when
a purely resistive circuit. This represents energy that is
summarizing the important points at the end of a lecture
alternately stored and released by the action of inductors
in order that the students will better remember them.
and capacitors.
reciprocal — A reverse bearing, opposite in direction by
reactor — 1. A device in an AC circuit used to add reactance
180°.
to it. 2. A small coil installed in an alternating current
circuit to furnish inductive reactance and cancel some of reciprocating engine — An engine that converts the heat
the capacitive reactance in the circuit. energy from burning fuel into the reciprocating movement
of the pistons. This movement is converted into a rotary
read back — Repeat my message back to me.
motion by the connecting rods and crankshaft.
reader — A machine that magnifies the information on
reciprocating motion — An alternating back-and-forth
microfilm or microfiche so it can be read. Some readers
motion.
can make printed paper copies.
reciprocating saw — A power-driven saw that cuts material
readiness — A principle of learning that the eagerness and
by driving a blade back and forth.
single-mindedness of a person toward learning affect the
outcome of the learning experience. recirculating fan — A fan in an aircraft cabin comfort
system that circulates the air in the cabin without taking
real number — A number that is rational or irrational, not
in any outside air.
imaginary.
reclaimed oil — Lubricating oil that has already been used
real power — The power in an AC circuit that is the product
and is restored to a useful state by removing impurities.
of the voltage and the current in phase with that voltage.
Real power equals the voltage multiplied by the current reconditioning a cell — Procedure of servicing a nicad
multiplied by the power factor. battery cell by completely discharging it and then
bringing it and all other cells in the battery back up to a
ream — To enlarge and smooth a drilled hole with a
full state of charge. Reconditioning equalizes the cells for
precision cutting tool called a reamer. A hole is reamed in
optimum performance.
preparation for work with close-tolerance parts.
reconformance — The automated process of bringing an
reamer — A sharp edged cutting tool used for enlarging
aircraft’s Current Plan Trajectory into conformance with
or tapering drilled holes in preparation for work with
its track.
close‑tolerance parts.
rectangle — A closed plane figure with four sides and four
rebreather bag — A bag connected to an oxygen mask
right angles. The opposite sides of the figure are parallel
that allows expired air to be mixed with a fixed rate of
and equal in length.
oxygen. It allows users to rebreath a portion of each
expired breath. rectifier — A device that converts alternating current into
direct current. In effect, it is an electron check valve.
rebreather oxygen mask — An oxygen mask with a
rebreather bag attached. rectifier bridge — A rectifier using four diodes arranged in
a bridge circuit.
receiver — In communication, the listener, reader, or
student who takes in a message containing information rectify — In electricity, to change alternating current into
from a source, processes it, reacts with understanding, direct current.
and changes behavior in accordance with the message.
260

10001930-002_AviationDictionary_2012_BOOK.indb 260 3/27/2012 9:38:24 AM

 recurring • Reid vapor pressure

recurring — Happening again and again at regular or Reference designators are stackable, meaning a full
frequent intervals. reference designator identifies the major assembly,
subassemblies, and the actual component.
recurring Airworthiness Directive — An Airworthiness
Directive that requires compliance at regular hourly or reference dimensions — The dimensions on an installation
calendar time periods. drawing required to illustrate the relationship between
two parts.
red brass — A copper-zinc alloy containing approximately
85% copper and 15% zinc. It is somewhat stronger than reference junction — One of the two junctions in a
commercial bronze and is hardened by cold working. thermocouple system. The reference junction is held at a
constant or stable temperature to serve as a reference for
red line — A red mark on an aircraft instrument that
the measuring junction.
indicates a maximum allowable operating condition.
reference pressure — The pressure in the outflow valve
red rust — A nonmagnetic iron oxide.
control established by cabin air pressure flowing through
red-line condition — The maximum safe condition at the cabin air filter and orifice. It is metered by the
which a unit can operate. Most aircraft instruments are reference pressure metering valve.
marked with a red line indicating the boundaries of their
refining — A petroleum extraction process in which crude
operating limits.
oil is broken down into all of its different parts.
reduce speed to (speed) — An ATC procedure used to
reflective — A reflective student considers all possibilities
request pilots to adjust aircraft speed to a specific value
or alternatives before making a decision.
for the purpose of providing desired spacing. Pilots are
expected to maintain a speed of plus or minus 10 knots or reflector — A surface that reflects light.
0.02 mach number of the specified speed.
refrigerant — A fluid used in an air conditioning system to
reduction factor — A constant (usually 100 or 1,000) by absorb heat from the cabin and carry it to a radiator where
which a moment is divided to obtain a moment index. it can be transferred to the outside air.
A moment index is used to simplify weight and balance
refrigerant 12 — Dichlorodifluoromethane, a chemical
computations.
compound used in many aircraft air conditioning systems.
reduction gear train — The gear arrangement of an Also referred to as R-12.
operating unit in which the output shaft turns slower than
regeneration — A process in an electrical circuit in which
the input shaft. An example of this is a gear arrangement
part of the output is fed back to the input to causes
in an aircraft engine that allows the engine to turn at a
amplification.
faster speed than the propeller.
regenerative braking — A method of slowing a motor
reduction gears — The gear arrangement in an aircraft
by switching the wiring effectively to make it into a
engine that allows the engine to turn at a faster speed
generator. This applies a load to the rotating mass and
than the propeller.
slows the motor.
Reed and Prince screw — A
regional checkout — A checkout that goes beyond learning
recessed-head, cross‑point screw
about a particular airplane and encompasses learning
driven by a special cross‑point
how to fly in a specific region. Before flying or giving
screw­driver whose tip has a single taper.
flight instruction in any unfamiliar environment, obtain a
reed valve — A thin, leaf-type valve located in the valve regional checkout from a qualified CFI who is experienced
plate of a reciprocating-type air conditioning compressor in that geographical area. For example, mountain
to control the inlet and outlet of the refrigerant. flying offers some breathtaking scenery and wonderful
experiences, but it also has some unique challenges and
reface — To resurface an object in order to remove
can be extremely dangerous to inexperienced pilots.
imperfections or wear marks.
registration certificate — The document in an airplane that
reference datum — An imaginary vertical plane from
contains the name and address of the person to whom the
which all horizontal distances are measured for balance
airplane is registered.
purposes.
regulated power supply — An electrical device that
reference datum — An imaginary vertical plane at or near
converts AC voltage to DC output voltage that remains
the nose of an aircraft from which all horizontal distances
constant under changing load conditions.
are measured for weight and balance calculations.
Reid vapor pressure — The amount of pressure acting
reference designator — A combination of letters and
on a liquid to hold the vapors in the liquid at a given
numbers used to identify a component or assembly.
temperature.

261

10001930-002_AviationDictionary_2012_BOOK.indb 261 3/27/2012 9:38:24 AM

 reinforce • remote communications outlet(RCO)

reinforce — To strengthen by adding extra support or when necessary to separate a departing aircraft from
material. other traffic.
reinforced shell — The outer skin of an aircraft reinforced release time [ICAO] — Time prior to which an aircraft
by a complete framework of structural members. should be given further clearance or prior to which it
should not proceed in case of radio failure.
reinforcement — In composites, material used to strengthen
the matrix. Fiber reinforced plastic is an example. Fibers reliability — Producing consistent results on multiple tests.
are used to reinforce the plastic material.
relief — The amount one plane surface is set below or above
reinforcing tape — A narrow, woven cotton or polyester another plane, usually for clearance or for economy in
tape used as reinforcement at stitching attachments. machining.
rejuvenation — The restoring of resilience to a dope film relief hole — A hole drilled in a flat sheet metal part to
by opening up the film with potent solvents and allowing allow intersecting bends to be made. The relief hole
the plasticizers in the rejuvenator to replace those that prevents the metal from buckling.
have migrated from the dope.
relief map — A map that shows land forms with contour
rejuvenator — A finishing material consisting of potent lines, shading, or color.
solvents and plasticizers used to restore resilience to
relief tube — A urinal on an aircraft that drains overboard.
weathered and cracked dope film.
The discharge area around these tubes is an area highly
relative bearing — An angular relationship between two susceptible to corrosion.
objects measured in degrees clockwise from the twelve
relief valve — A valve that limits the pressure in a system
o’clock position of the first object.
by releasing unwanted pressure at a preset value.
relative humidity — The ratio of the existing amount
reluctance — 1. The relative difficulty with which magnetic
of water vapor in the air at a given temperature to the
domains can be aligned. 2. The opposition to magnetic
maximum amount that could exist at that temperature;
flux. The opposite of permeability.
usually expressed in percent.
remainder — The result of subtracting one number from
relative motion — The motion of one object with relation
another or the amount left when one number does not
to another.
divide evenly into another.
relative movement — The movement of one object with
remanufactured engine — An engine assembled by the
relation to another.
manufacturer or his authorized agent using used parts
relative vorticity — Rotation due entirely to the flow of air that are held to the new parts’ dimensional limits. A
at the point being measured. Absolute vorticity is relative remanufactured engine is given zero time records and
vorticity plus rotation imparted by the turning of the usually the same warranty and guarantee as a new engine.
Earth (planetary vorticity).
remote communications air/ground (RCAG) facility —
relative wind — The airflow caused by the motion of the An unmanned VHF/UHF transmitter/ receiver facility
aircraft through the air. Relative wind, also called relative used to expand ARTCC air/ ground communications
airflow is opposite and parallel to the direction of flight. coverage and to facilitate direct contact between pilots and
controllers. RCAG facilities are sometimes not equipped
relaxation oscillator — An electronic oscillator that
with emergency frequencies 121.5 MHz and 243.0 MHz.
produces pulses at an interval dependent on one or more
RC time constants. remote communications outlet(RCO) — An unmanned
communications facility remotely controlled by air traffic
relay — An electrically operated remote switch with contacts
personnel. RCOs serve FSSs. RTRs (Remote Transmitter/
that are closed or opened by an electromagnetic field.
Receivers) serve terminal ATC facilities. An RCO or RTR
relay question — Used in response to a student’s question. can be UHF or VHF and will extend the communication
The question is redirected to the group in order to range of the air traffic facility. There are several classes
stimulate discussion. of RCOs and RTRs. The class is determined by the
number of transmitters or receivers. Classes A through
release film — In composites, a layer of plastic material
G are used primarily for air/ground purposes. RCO and
used in the vacuum bagging process that does not allow
RTR class O facilities are nonprotected outlets subject
resin to bleed through it. It will not bond to the part when
to undetected and prolonged outages. RCO (O’s) and
the resins cure. Perforated release film will allow some
RTR (O’s) were established for the express purpose of
resin to bleed through.
providing ground-to-ground communications between
release time — A departure time restriction issued to a pilot air traffic control specialists and pilots located at a
by ATC (either directly or through an authorized relay) satellite airport for delivering enroute clearances, issuing

262

10001930-002_AviationDictionary_2012_BOOK.indb 262 3/27/2012 9:38:24 AM

 remote control • rescue coordination center (RCC)

departure authorizations, and acknowledging instrument repulsion causes the rotor to turn because the brushes are
flight rules cancellations or departure/landing times. offset from the field poles, so that the repulsive forces are
As a secondary function, they can be used for advisory pushing on the rotor tangential to the rotation axis of the
purposes whenever the aircraft is below the coverage of rotor. The brushes can be shifted to control the speed and
the primary air/ground frequency direction of rotation.
remote control — The control of an object with radio request full route clearance — Used by pilots to request
signals from a remote location. that the entire route of flight be read verbatim in an ATC
clearance. Such request should be made to preclude
remote (slave) scope — A cathode-ray tube that duplicates
receiving an ATC clearance based on the original filed
the display of a primary radar scope.
flight plan when a filed IFR flight plan has been revised
remote transmitter/receiver — See remote by the pilot, company, or operations prior to departure.
communications outlet.
required equipment — Equipment determined by the FAA
Rene metal — A nickel chromium alloy used in the to be necessary for an aircraft to be considered airworthy.
manufacturing of gas turbine engines.
required inspection item (RII) — A designation of items of
repair — To restore an item to a condition of practical maintenance and alteration that could result in a failure,
operation or to its original condition. malfunction, or defect endangering the safe operation of
the aircraft if an inspection is not properly performed or
repairman license — A certificate issued by the FAA
if improper parts or materials are used.
to a person employed by a repair station, a certified
commercial operator, or a certified air carrier required required navigation performance (RNP) — A statement
to provide a continuous airworthiness maintenance of the navigational performance necessary for operation
program. The repairman license is valid only as long within a defined airspace. The following terms are
as the person holding the license is employed by the commonly associated with RNP:
company for which the certificate was issued.
a. Required Navigation Performance Level or Type
repeater indicator — An instrument that repeats the (RNP-X). A value, in nautical miles (NM), from the
information via a master indicator. intended horizontal position within which an aircraft
would be at least 95-percent of the total flying time.
repeating decimal — A fraction that cannot be expressed as
a definite number. The fraction 1/3 is a repeating decimal b. Required Navigation Performance (RNP) Airspace.
(0.333333333). A generic term designating airspace, route(s), leg(s),
operation(s), or procedure(s) where minimum
report — Used to instruct pilots to advise ATC of specified
required navigational performance (RNP) have been
information; e.g., “Report passing Hamilton VOR.”
established.
reporting point — A geographical location in relation to
c. Actual Navigation Performance (ANP). A measure of
the reported position of an aircraft.
the current estimated navigational performance. Also
repression — Theory of forgetting where a person is more referred to as Estimated Position Error (EPE).
likely to forget information that is unpleasant or produces
d. Estimated Position Error (EPE). A measure of the
anxiety.
current estimated navigational performance. Also
repression — A process in which a person subconsciously referred to as Actual Navigation Performance (ANP).
forgets or excludes unpleasant or anxiety producing
e. Lateral Navigation (LNAV). A function of area
information.
navigation (RNAV) equipment that calculates,
repulsion — The force that tends to cause objects to move displays, and provides lateral guidance to a profile or
away from each other. path.
repulsion motor — The repulsion motor consists of stator f. Vertical Navigation (VNAV). A function of area
(field) windings that are powered by input power and rotor navigation (RNAV) equipment that calculates,
windings that have current induced by the magnetic field displays, and provides vertical guidance to a profile
of the stator windings. The rotor windings are connected or path.
to the commutator and the brushes are connected to each
rescue coordination center (RCC) — A search and rescue
other completing a circuit through windings within the
(SAR) facility equipped and manned to coordinate and
rotor. The closed-loop circuits in the rotor are effectively
control SAR operations in an area designated by the SAR
the short-circuited secondaries of a transformer, where
plan. The U.S. Coast Guard and the U.S. Air Force have
the motor’s field windings are the primary coil. The
responsibility for the operation of RCCs.
currents induced in the rotor create a magnetic field
that repels that of the field winding (Lenz’s law). This

263

10001930-002_AviationDictionary_2012_BOOK.indb 263 3/27/2012 9:38:24 AM

 rescue co-ordination centre [ICAO] • resistor color code

rescue co-ordination centre [ICAO] — A unit responsible resin transfer molding (RTM) — In composites, a
for promoting efficient organization of search and rescue manufacturing process in which the resin/catalyst
service and for co-ordinating the conduct of search and mixture is pumped into a two-sided mold in which a
rescue operations within a search and rescue region. fabric reinforcement has been placed. The part is then
heated and cured.
reserve — To keep something back or set it apart for use in
an emergency or for a special purpose. resistance decade box — An electrical test device that
provides the capability to insert selected values of
reservoir — A place where an extra supply of something is
resistance into a circuit.
kept, for example, a tank in which fluid is stored.
resistance furnace — A high-temperature furnace heated
residual — The remainder or anything that is left over.
by passing current through various high resistance
residual charge — The remaining electrical charge left on materials.
capacitor plates after they have been discharged.
resistance (R) — The opposition to the flow of electrons
residual fuel or oil — The fuel or oil that is trapped in the offered by a device or material. Opposition by resistance
lines and, therefore, not usable. In weight and balance causes a loss of power.
computations, residual fuel and oil are considered to be
resistance thermometer — A temperature-measuring
part of an aircraft’s empty weight.
device based on the linear change in resistance of a
residual magnetic flux — The magnetism that remains material as temperature varies. This device is connected
in the core of an electromagnet after the magnetizing to a Wheatstone bridge to determine resistance and thus
current no longer flows in the coil. Also referred to as temperature.
residual magnetism.
resistance welding — The fusion of metals by clamping
residual magnetism — The magnetism that remains in the them together and passing a high amperage electrical
core of an electromagnet after the magnetizing current current through the joint. The resulting heat melts the
no longer flows in the coil. Also referred to as residual metal and the pressure causes the two pieces to fuse
magnetic flux. together. Spot and seam welding are forms of electrical
resistance welding.
residual magnetism testing inspection — An inspection
for magnetism that might be left in a ferrous part resistance wire — A wire made from a high resistance material,
following magnetic particle inspection. The test is used in wire-wound resistors and heating elements.
conducted with a magnetic indicator that discloses any
resistive circuit — In electronics, a circuit constructed
remaining magnetic field. It is important that all residual
entirely of resistive elements (no capacitive or inductive
magnetism be removed so that ferrous particles are not
components). In such a circuit, the voltage and current
attracted to it.
are in phase.
resignation — A negative self-concept is the factor that
resistive current — The current in a circuit where current
contributes most to a student’s failure to a remain receptive
is in phase with voltage.
to new experience, and which creates a tendency to reject
additional training. resistivity — The ability of a material to resist the flow of
electrons. It is the opposite of conductivity.
resin — A family of natural or synthetic fluids or semi‑solid
substances that can be changed into a solid such as plastic resistor — An electrical circuit element used to provide a
through the addition of appropriate catalyzers. voltage drop by dissipating some of the electrical energy
in the form of heat.
resin rich — In composites, an area that has an excess
amount of matrix. A resin rich laminate usually is more resistor color code
brittle and weighs more than laminates with the proper — A color code
amount of resin. marking system
used to identify the
resin ridge — In composites, a ridge of excess resin that
resistance value of
contains only resin.
carbon resistors.
resin starved — In composites, an area deficient in resin. A Measured in ohms.
resin-starved part will not exhibit the structural strength The resistor is
that a part made with the proper amount of resin. marked by either
three or four colored bands. The first colored band
resin system — In composites, a mixture of resin and
(nearest the end of the resistor) indicates the first digit.
ingredients required for the intended processing method
The second colored band indicates the second digit. The
and final product.
third colored band indicates the number of zeros to be

264

10001930-002_AviationDictionary_2012_BOOK.indb 264 3/27/2012 9:38:24 AM

 resistor power dissipation rating • retard breaker points

added to the two digits derived from the first and second be identified, but students must develop the skills to evaluate
bands. If there is a fourth colored band, it is used as an whether they have the time to use a particular resource and
indication of percentage of tolerance. the impact its use will have upon the safety of flight.
resistor power dissipation rating — The amount of power respirator — A device worn over the mouth and nose to
a resistor can safely dissipate in the form of heat under prevent the harmful inhaling of dangerous substances.
controlled conditions.
responses — Possible answers to a multiple-choice test
resistor spark plug — A shielded spark plug with a item. The correct response is often called the keyed
composition resistor installed in the barrel. The resistor response, and incorrect responses are called distractors.
limits the current stored in the capacitive effect of the
restart — The act of starting an engine after it has been
shielding. This minimizes electrode erosion and increases
operating and then shut down.
the life of the spark plug.
restricted area — Airspace designated under FAR Part
resolution — The ability to distinguish between indications
73, within which the flight of aircraft, while not wholly
on a display. One example would be the ability to
prohibited, is subject to restriction. Most restricted
distinguish between two radar returns displayed on a
areas are designated joint use and IFR/VFR operations
cathode-ray tube.
in the area can be authorized by the controlling ATC
resolution advisory — A display indication given to the facility when it is not being utilized by the using agency.
pilot by the traffic alert and collision avoidance systems Restricted areas are depicted on enroute charts. Where
(TCAS II) recommending a maneuver to increase vertical joint use is authorized, the name of the ATC controlling
separation relative to an intruding aircraft. Positive, facility is also shown.
negative, and vertical speed limit (VSL) advisories
restricted area [ICAO] — An airspace of defined
constitute the resolution advisories. A resolution advisory
dimensions, above the land areas or territorial waters of
is also classified as corrective or preventive.
a State, within which the flight of aircraft is restricted in
resonance — A frequency in any given RLC (Resistance, accordance with certain specified conditions.
Inductance, Capacitance) AC circuit at which the
restrictor — An orifice for reducing or restricting the flow
capacitive reactance is equal to the inductive reactance.
of a fluid.
resonance method of ultrasonic inspection — A method
resultant flux — The flux in a magnetic circuit of an aircraft
of detecting material thickness or indications of internal
magneto. Resultant of the flux of the rotating permanent
damage by injecting variable frequency ultrasonic energy
magnet and the flux that surrounds the primary windings
into a material. A specific frequency of energy produces
when primary current is flowing.
the greatest return in a given thickness of material. When
the equipment is calibrated for a specific thickness and this resultant lift — The vector sum of the magnitude and
thickness changes, an aural or visual indication is given. direction of all of the lift forces produced by an airfoil.
resonant circuit — An electrical circuit in which the resultant relative wind — In rotorcraft, airflow from
inductive reactance is equal to the capacitive reactance. rotation that is modified by induced flow.
They will be equal at a particular frequency called the
resume normal speed — Used by ATC to advise a pilot
resonant frequency. The circuit can be made resonant by
that previously issued speed control restrictions are
either varying the frequency until resonance occurs, or
deleted. An instruction to “resume normal speed”
holding the frequency constant and varying inductance
does not delete speed restrictions that are applicable to
or capacitance to achieve resonance.
published procedures of upcoming segments of flight,
resonant frequency — The frequency of a source of unless specifically stated by ATC. This does not relieve
vibration that is exactly the same as the natural vibration the pilot of those speed restrictions that are applicable to
frequency of a structure. FAR 91.117.
resonate — To vibrate at a certain frequency. A mechanical resume own navigation — Used by ATC to advise a pilot
system is said to resonate when its natural vibration to resume his own navigational responsibility. It is issued
frequency is the same as that of the force applied. The after completion of a radar vector or when radar contact
level of vibration of an object increases immensely as is lost while the aircraft is being radar vectored.
that frequency is reached and will be less on either side
retard — To slow or delay the progress of something.
of that frequency.
retard breaker points — An auxiliary set of breaker
resource use — An essential part of ADM training. Since
points in a magneto equipped with the Shower of Sparks
useful tools and sources of information may not always be
starting system. These points are operative only during
readily apparent, it is important to teach students how to
the starting cycle and open later than the run, or normal,
recognize appropriate resources. Resources must not only

265

10001930-002_AviationDictionary_2012_BOOK.indb 265 3/27/2012 9:38:24 AM

 retard points • reversible-pitch propeller

points. This provides a late or retarded spark. Also retrofit — To furnish something with new or modified parts
referred to as retard points. or equipment not available or considered necessary at the
time the part was manufactured.
retard points — An auxiliary set of breaker points in a
magneto equipped with the Shower of Sparks starting return flow — The upper branch of a thermal circulation.
system. These points are operative only during the starting return stroke — Lightning that is visible to the eye and
cycle and open later than the run, or normal, points. This marks the path of the positive charge of the step leader
provides a late or retarded spark. Also referred to as back into the clouds.
retard breaker points.
return to service — The completion of all applicable
retarder — A slow‑drying solvent used to prevent blushing maintenance records and forms after maintenance has
or to provide a more glossy finish by allowing the finish been performed on an aircraft that will allow the aircraft
a longer flow‑out time. to be legally flown.
retention — There are five principles that promote deep revalidate — To confirm, sanction or make something valid
learning and enhance retention of course material: again.
praise stimulates remembering, recall is promoted by
association, favorable attitudes aid retention, learning reverse bias — The polarity relationship between a
power supply and a semiconductor that does not allow
with all the senses is most effective, and meaningful
conduction of current.
repetition aids recall.
reverse idle — A power lever position where the thrust
retentivity — The ability of a material to retain its magnetic
reversers are deployed, but engine power is idle.
properties.
reverse pitch — An angle to which the propeller blade
retina — The photosensitive portion of the eye, made up
can be turned in order to provide reverse thrust from the
of cells called rods and cones, that is connected to the propeller.
optic nerve.
reverse polarity welding — In electric arc welding, reverse
retirement schedule — A list of limited life parts and the polarity occurs when the electrode is positive and the
times when they must be replaced. This list records the work is negative. The opposite polarity is called straight
part, serial number, time installed, and removal time. polarity. Straight polarity puts more heat into the work
retort — A laboratory vessel with a long tube used to distill piece, while reverse polarity minimizes the heat in the
substances by heat. work piece.

retract — To pull in or draw back. reverse question — A response to a question. Rather than
give a direct answer to the student’s query, the instructor
retractable gear — This is a pilot controllable landing gear can redirect the question to another student to provide
system, whereby the gear can be stowed alongside or the answer.
inside the structure of the airplane during flight.
reverse riveting — A process of driving aircraft rivets in
retractable landing gear — Landing gear that folds into which the manufactured head is bucked by holding it in
the aircraft structure to reduce parasite drag. a rivet set supported in a bucking bar and upsetting the
shank with a flush rivet set.
retraction test — The portion of an aircraft inspection in
which the airplane is put on jacks and the landing gear reverse‑current relay — A relay incorporated into a
cycled through its retraction and extension sequences. generator circuit to disconnect the generator from the
battery when the battery voltage is greater than generator
retread — In tire recapping, a tire that has been renewed voltage.
to serviceable condition. Tires that meet injury
limitations can be recapped. Retreading or recapping reverse-flow annular combustor — A combustor design
means reconditioning of a tire by renewing the tread, or that forms an S-shaped path in which the gases flow from
renewing the tread plus one or both sidewalls. the diffuser to the exhaust. This design shortens the entire
engine length because the liner is coaxial to the turbines
retreating blade — In rotorcraft, any blade, located in rather than in front of them as in a conventional annular
a semicircular part of the rotor disc, where the blade combustor.
direction is opposite to the direction of flight.
reversible-pitch propeller — A propeller system with a
retreating blade stall — In rotorcraft, a stall that begins pitch change mechanism that includes full reversing
at or near the tip of a blade in a helicopter because of capability. When the pilot moves the throttle controls
the high angles of attack required to compensate for to reverse, the blade angle changes to a pitch angle and
dissymmetry of lift. In a gyroplane the stall occurs at 20 produces a reverse thrust, which slows the airplane down
to 40 percent outboard from the hub. during a landing.

266

10001930-002_AviationDictionary_2012_BOOK.indb 266 3/27/2012 9:38:24 AM

 reversing mechanism • right-hand rule of electric generators

reversing mechanism — A linkage that reverses the rib stitching — The attachment of fabric to an aircraft
direction of movement between two parts. structure with rib stitching cord. A series of loops around
the structure and through the fabric are secured with
review and evaluation — The fourth and last step in the
seine knots. Also referred to as rib lacing.
teaching process, which consists of a review of all material
and an evaluation of the students. In the telling-and-doing rib stitching cord — A strong cotton, linen, or polyester
technique of flight instruction, this step consists of the fiber cord used to stitch or lace fabric to an aircraft
instructor evaluating the student’s performance while the structure.
student performs the required procedure.
ribbon direction — In composites, on a honeycomb core,
revision — In mechanical drawings, a change in dimensions, the way the honeycomb can be separated. The direction
design, or materials. of one continuous ribbon.
revision block — That portion of an aircraft drawing that ribbon parachute — A parachute that consists of strips or
contains a record of all of the revisions. Symbols are used ribbons of material instead of a solid fabric. This type of
to indicate changes and their locations. chute is used in instances where it is desirable to have less
revolutions per minute (RPM) — The number of complete opening shock, since air escapes between the ribbons.
revolutions a body makes in one minute. rich flameout — A condition of turbine engine operation in
revolved section — A detail on an aircraft drawing in which which the fire goes out in the engine because the fuel‑air
the external view shows the shape of a part’s cross section mixture is too rich to support combustion.
as though it were cut out and revolved. rich solvent — A slow-drying solvent.
Reynolds Number — A dimensionless ratio that relates ridge/ridge line — In meteorology, an elongated area of
how smoothly a fluid flows. At low velocities fluid flow relatively high atmospheric pressure; usually associated
is smooth or laminar. As the fluid flows more rapidly, it with and most clearly identified as an area of maximum
reaches a velocity, known as the critical velocity, at which anticyclonic curvature of the wind flow (isobars,
the motion changes from laminar to turbulent, with the contours, or streamlines).
formation of eddy currents and vortices that disturb the
flow. rigging — The final adjustment and alignment of an aircraft
and its flight control system that provide the proper
RF alternating current — Radio frequency (RF) is a term aerodynamic characteristics.
that refers to alternating current (AC) that, when fed into
an antenna, generates an electromagnetic field suitable rigging fixture — A template designed to measure control
for communications. These frequencies range from nine surface travel.
kilohertz (9 kHz) to thousands of gigahertz (GHz). rigging pins — The pins that can be inserted into control
rheostat — A variable resistor having only two terminals. It system components to hold the controls in their neutral
is normally used in a circuit to drop voltage by dissipating position for rigging the control cables and rods.
some of the energy as heat. right angle — A 90° angle. Formed by the perpendicular
rhetorical question — A question asked to stimulate intersection of two straight lines.
group thought. Normally answered by the instructor, it is
right brain — A concept that each hemisphere of the
more commonly used in lecturing rather than in guided
brain processes information differently. Students with
discussions.
right-brain dominance are characterized as being spatially
rhomboid — A parallelogram in which the angles are oriented, creative, intuitive, and emotional. They can be
oblique and the adjacent sides are unequal. very good with art or music and can easily put together
the big picture.
rhumb line — In navigation, a rhumb line crosses all lines
of longitude at the same angle. right-hand rule for the direction of magnetic flux — A
method of determining the relation of the flow of magnetic
rib — The structural member of an airfoil that gives it the
flux to the direction of current flow in a conductor. The
desired aerodynamic shape.
right hand is wrapped around the conductor with the
rib cap — A thin, narrow strip of material usually glued to thumb pointing in the direction of current flow (positive
wooden ribs or riveted to metal ribs to enlarge the contact to negative), and the fingers will point in the direction
surface for the attachment of skin to the wing or flight of the flow of magnetic flux from the north pole to the
control surface. south pole.
rib lacing — The attachment of fabric to an aircraft right-hand rule of electric generators — A method of
structure with rib stitching cord. A series of loops around determining the relative directions of current flow,
the structure and through the fabric are secured with magnetic flux, and motion of a conductor when the
seine knots. Also referred to as rib stitching.
267

10001930-002_AviationDictionary_2012_BOOK.indb 267 3/27/2012 9:38:25 AM

 right-hand thread • riveting burr

conductor is passing through a magnetic field. The right ripple — A small periodic variation in the voltage level of a
hand should be held with the thumb pointing vertically, direct current power supply.
the first finger pointing away, and the second finger
ripple filter — A filter consisting of capacitors or inductors,
pointing to the left (the thumb and two fingers will be
or both, that attenuates the AC component in the output
at right angles to each other). The thumb points in the
of a rectifier circuit. The ripple is the amount of AC that
direction the conductor is moving. The first finger points
remains on the DC.
in the direction of the lines of magnetic flux (north pole to
south pole), and the second finger points in the direction ripple frequency — The frequency of the ripple in DC
of current flow (positive to negative) within the conductor. voltage when rectified from an AC current. A full-wave
rectifier produces a ripple frequency of twice the input
right-hand thread — A thread that, when viewed axially,
AC frequency while a half-wave rectifier produces a
winds in a clockwise and receding direction. All threads
ripple frequency that is the same as the input frequency.
are right-hand threads unless otherwise designated.
ripsaw — A saw with course teeth used for cutting lumber
rigid airship — A dirigible that has a rigid framework
along the direction of its grain.
covered with cloth fabric and a cabin suspended
underneath the frame that houses the crew and engines risk elements — How to assess risk is a skill that students
for driving it through the air. need to learn to make effective decisions. When students
are faced with making a decision regarding a flight, ask
rigid rotor — In rotorcraft, a rotor system permitting blades
them to evaluate the status of the four risk elements: the
to feather but not flap or hunt.
pilot in command, the aircraft, the environment, and the
rigid tubing — Fluid lines made of thin wall aluminum alloy, operation.
copper, or stainless steel used in an aircraft when there is
risk elements in ADM — In aeronautical decision making
no relative movement between the ends of the tube.
the four elements considered are the pilot, aircraft,
rigidity — The state of being rigid. environment, and type of operation.
rigidity in space — The principle that a wheel with a risk management — Part of the decision making process.
heavily weighted rim spun rapidly will remain in a fixed Situational awareness, problem recognition, and good
position in the plane in which it is spinning. judgment are used to reduce risks.
rime ice — The rough textured ice that forms on a surface, rivet — A small metal pin with a specially formed head
such as the leading edge of an airplanes wing, when on one end used to fasten sheet metal parts together by
flown through supercooled fog or certain types of clouds. upsetting the shank to form a clamping head.
rime icing — The formation of a white or milky and opaque rivet cutter — A tool used to cut rivets to the required
granular deposit of ice formed by the rapid freezing of length.
supercooled water droplets as they impinge upon an
rivet gauge — The transverse pitch or distance between
exposed aircraft.
rows of rivets.
ring and tube assembly — The ring of outer combustion
rivet gun — A hand‑held pneumatic riveting hammer used
chambers on a multiple-can-type combustor engine.
to vibrate aircraft rivets against a heavy bucking bar to
ring cowl — A streamlined covering over the cylinders of form the upset head.
a radial engine.
rivet pitch — The distance between the center of rivet holes
ring gear — One of the gears in a turboprop negative in adjacent rows. Also referred to as rivet spacing.
torque signal and prop reduction gear system. When a
rivet set — A tool that fits into a rivet gun used to hammer
predetermined negative torque is applied to the reduction
against the manufactured head of a rivet so the bucking
gearbox, the ring gear moves forward against the spring
bar can form the upset head on the opposite side of the
force due to a torque reaction generated by helical splines.
skin. Also referred to as a rivet snap.
In moving forward, the ring gear pushes two operating
rods through the reduction gear nose. rivet spacing — The distance between the center of rivet
holes in adjacent rows. Also referred to as rivet pitch.
ring grooves — The grooves in the circumference of a
piston into which the piston rings fit. rivet squeezer — A heavy, tong‑like clamping machine
used to squeeze the ends of a rivet to form an upset head.
ringworms — A circular pattern of cracks in a brittle dope finish
that results from a blunt object pressing against the fabric. riveting burr — A small plain washer placed on a rivet before
the rivet is upset. Provides a larger area of contact on the
rip panel — A free floating balloon’s air dump panel that
part than would have been provided with the rivet alone.
can be opened by pulling a rip-cord. Air is dumped for
landings or in the event of an emergency.

268

10001930-002_AviationDictionary_2012_BOOK.indb 268 3/27/2012 9:38:25 AM

 Rivnut • rosin joint

Rivnut — A patented, hollow, blind rivet manufactured by the Rockwell hardness tester — A machine used to determine
B.F Goodrich Company, in which the inside of the shank is the hardness of a material by using a calibrated weight to
threaded. The upset rivet can be used as a blind nut. press either a diamond pyramid or a hardened steel ball
into the material. A dial indicator measures the depth of
RNAV approach — An instrument approach procedure
penetration and specifies it with a Rockwell number.
that relies on aircraft area navigation equipment for
navigational guidance. rods — The cells concentrated on the outside of the foveal
area of the eye that are sensitive to low light and not to color.
RNAV DP — A departure procedure developed for
RNAV-equipped aircraft whose ground track is based on roger — During communications, this indicates: I have
satellite or DME/DME navigation systems. received all of your last transmission. “Roger” should not
be used to answer a question requiring a yes or no answer.
RNAV way point (W/P) — A predetermined geographical
position used for route or instrument approach definition role model — A person whose behavior in a particular role
or progress reporting purposes that is defined relative to a is imitated by others.
VORTAC station position.
roll — The motion of an aircraft about its longitudinal axis.
road reconnaissance — Military activity requiring This motion is controlled by the ailerons.
navigation along roads, railroads, and rivers.
roll cloud — The dense and horizontal cloud band occasionally
Reconnaissance route/route segments are seldom along
found parallel to gust fronts. Also used to describe the rotor
a straight line and normally require a lateral route width
clouds associated with mountain lee waves.
of 10NM to 30NM and an altitude range of 500 feet to
10,000 feet AGL. roll pin — A pressed‑fit pin made of a roll of spring steel.
The spring force tending to unroll the pin holds it tight
robot — An automated mechanism built to do functions
in the hole.
ordinarily assigned to humans.
roll threading — Applying a thread to a bolt or screw by
robotics — The research and development of technology
rolling the piece between two grooved die plates, one of
that deals with the design, application, construction, and
which is in motion, or between rotating grooved circular
maintenance of automated mechanisms.
rolls.
rock wool — A mineral wool made by blowing a jet of
roller bearing — An antifriction bearing with hardened
steam through molten rock and used chiefly for heat and
steel rollers between two hardened steel races.
sound insulation
rollout RVR — The RVR (Runway Visual Range) readout
rocker arm — A pivoted arm, as in an aircraft reciprocating
values obtained from RVR equipment located nearest the
engine, used to transfer pushrod motion to a valve stem.
rollout end of the runway.
rocker arm boss — That portion of the cylinder head of an
root — The supporting base or structure, as in the wing
aircraft engine that provides support for the rocker arm shaft.
root, connected to the fuselage.
rocket — A device propelled by the high-velocity ejection of
root mean square (RMS) — The value of direct current
gases produced by internal ignition of solid or liquid fuels.
equivalent to an alternating current sine wave. The value
rocket assisted takeoff — An auxiliary means of assisting is 0.707 times the peak value of one alternation.
an aircraft when taking off. The system consists of
rosette weld — A weld made through a small hole in a piece
small rockets fastened to the aft structure. When a
of steel tubing to weld an inner tube to the outer tube to
heavily loaded aircraft rotates for takeoff, the jets are
prevent relative movement.
fired. The added boost provides extra thrust needed for
takeoff. Once airborne the rockets are jettisoned. Often rosin — A light yellow-colored resin. Rosin remains after
abbreviated as JATO. oil of turpentine has been distilled from the oleoresin of
pine trees.
rocket fuel — Any fuel specifically developed for rocket
engines. rosin core solder — A soft solder made chiefly of tin and
lead alloys used primarily for bonding copper, brass, and
rocket ship — Any spacecraft that uses rocket engines for
coated iron. Rosin core solder is a hollow wire filled with
propulsion.
rosin. During the soldering process the rosin serves to
rocketry — The study, theory, and development of rockets. clean corrosion from the components being soldered in
order to make a sound bond.
rocking shaft — A shaft or rod in an instrument that
oscillates or rocks upon its bearings, but does not revolve. rosin joint — A soldered electrical connection in which the
rosin, not the solder, holds the connection. Rosin joints
are not considered to be airworthy connections.

269

10001930-002_AviationDictionary_2012_BOOK.indb 269 3/27/2012 9:38:25 AM

 rotary breather • route minimum off-route altitude (route MORA)

rotary breather — A rotating set of vanes or a centrifuge rotor disc area — In rotorcraft, the area swept by the blades
device through which oil laden air from the vent of the rotor. It is a circle with its center at the hub and has
subsystem passes. Deaeration takes place and the oil a radius of one blade length.
is returned to the sump while the air exits back to the
rotor force — The force produced by the rotor in a
atmosphere.
gyroplane. It is comprised of rotor lift and rotor drag.
rotary pick‑off — A device attached to a rotating object that
rotor streaming — In meteorology, a phenomenon that
generates a signal proportional to the amount of rotation.
occurs when the air flow at mountain levels can be
rotary radial engine — An aircraft engine popular in sufficient for wave formation, but begins to decrease
World War I, in which the propeller was attached to the with altitude above the mountain. In this case, the air
crankcase and the pistons were attached to a crankshaft downstream of the mountain breaks up and becomes
mounted on the airframe. When the engine ran, the turbulent, similar to rotor, with no lee waves above.
cylinders, crankcase, and propeller all rotated and the
rotorcraft — A heavier-than-air aircraft that depends
crankshaft remained stationary.
principally for its support in flight on the lift generated
rotary solenoid — An electromagnet whose movable core by one or more rotors.
is rotated by current through the coil.
rotorcraft-load combination — The combination
rotary switch — A switch that consists of one or more of a rotorcraft and an external-load, including the
circular wafers, each with multiple contacts. A central external-load attaching means.
shaft rotates a wiper from contact to contact, switching
rotorcraft-load combinations — Class A, Class B, Class
connection from one circuit to another. When multiple
C, and Class D rotorcraft-load combinations, as follows:
wafers are stacked on the shaft, multiple circuits can be
selected simultaneously. Class A – one in which the external load cannot move
freely, cannot be jettisoned, and does not extend below
rotating wing — The rotors of a helicopter.
the landing gear.
rotation — The act of turning about an axis.
Class B – one in which the external load is jettisonable
rotational velocity — In rotorcraft, the component of and is lifted free of land or water during the rotorcraft
relative wind produced by the rotation of the rotor blades. operation.
rote learning — A basic level of learning where the student Class C – one in which the external load is jettisonable
has the ability to repeat back something learned, with no and remains in contact with land or water during the
understanding or ability to apply what was learned. rotorcraft operation.
rotor — 1. The rotating Class D – one in which the external-load is other than a
element in an alternator. Class A, B, or C and has been specifically approved by
It is excited by direct the Administrator for that operation.
current, and the
round file — A steel tool that has a circular cross section
inter­lacing fingers on the
with hardened ridged surfaces, used for smoothing,
faces of the rotor form
grinding, or boring. Also referred to as a rattail file.
the alternating north
and south poles. 2. The round head — A fastener with a semi-elliptical top surface
rotating blades of a helicopter. 3. The portion of a turbine and a flat bearing surface.
compressor that spins. 4. Either compressor or turbine.
round off — 1. To make an edge round as by filing. 2. In
A rotating disk or drum to which a series of blades is
mathematics, to change a fraction to the closest whole
attached. 5. In meteorology, a turbulent circulation under
number.
mountain-wave crests, to the lee and parallel to the
mountains creating the wave. Glider pilots use the term round-nose pliers — Pliers with round jaws. Used to form
rotor to describe any low-level turbulent flow associated loops in wire and thin strips of sheet metal.
with mountain waves.
route — A defined path, consisting of one or more courses
rotor brake — A device used to stop the rotor blades of a in a horizontal plane, which aircraft traverse over the
rotorcraft on shutdown. This can be either a hydraulic or surface of the Earth.
mechanical mechanism.
route minimum off-route altitude (route MORA) — This
rotor disc — The area within the tip path plane of a is an altitude derived by Jeppesen. The Route MORA
helicopter’s rotor. Also referred to as the disc area. altitude provides reference point clearance within 10 NM
of the route centerline (regardless of the route width) and
end fixes. Route MORA values clear all reference points

270

10001930-002_AviationDictionary_2012_BOOK.indb 270 3/27/2012 9:38:25 AM

 route segment • runway edge lights (USA)

by 1000 feet in areas where the highest reference points run-in — The period of time an aircraft engine is operated
are 5000 feet MSL or lower. Route MORA values clear all to seat the moving parts after an overhaul.
reference points by 2000 feet in areas where the highest
running fit — A fit between moving parts that allows them
reference points are 5001 feet MSL or higher. When a
to move freely.
Route MORA is shown along a route as “unknown” it is
due to incomplete or insufficient information. runout — A term frequently used interchangeable with
eccentricity but which normally refers to the amount
route segment — 1. A part of a route. Each end of that part
which the outside surface of one component moves with
is identified by: a. A continental or insular geographical
respect to the outside surface of another component. As
location; or b. A point at which a definite radio fix can be
such, it includes eccentricity, angularity and bow. The
established. 2. As used in Air Traffic Control, a part of a
amount of runout is usually expressed in terms of Total
route that can be defined by two navigational fixes, two
Indicator Reading (TIR).
NAVAIDs, or a fix and a NAVAID.
runout check — A dial indicator check for measuring the
route segment [ICAO] — A portion of a route to be flown,
plane of rotation of a rotor shaft or disc.
as defined by two consecutive significant points specified
in a flight plan. runway — A defined rectangular area on a land airport
prepared for the landing and takeoff run of aircraft along
router — An electric machine that uses a high‑speed, rotary
its length. Runways are normally numbered in relation
cutting tool. In aircraft maintenance, routers are often
to their magnetic direction rounded off to the nearest 10
used to remove damaged honeycomb core from a bonded
degrees; e.g., Runway 1 (010º), and Runway 25 (250º).
aircraft structure.
runway centerline lighting — Flush centerline lights
routine service items — The items in a progressive
spaced at 50-foot intervals beginning 75 feet from the
inspection that consists of a thorough check of the
landing threshold and extending to within 75 feet of the
aircraft, engines, appliances, components, and systems
opposite end of the runway.
normally without disassembly.
runway condition reading — Numerical decelerometer
roving — A bundle of filaments that are twisted together for
readings relayed by air traffic controllers at USAF and
weaving into fabric.
certain civil bases for use by the pilot in determining
rubber cement — An adhesive made from rubber that has runway braking action. These readings are routinely
not gone through the vulcanization process but has been relayed only to USAF and Air National Guard Aircraft.
dissolved in solvent.
runway edge lights (ICAO) — Are provided for a runway
rudder — The vertically hinged control surface used to intended for use at night or for a precision approach runway
effect horizontal changes in course or rotate an aircraft intended for use by day or night. Runway edge lights shall
about its vertical axis. The pilot operates the rudder by be fixed lights showing variable white, except that:
the movement of the foot pedals in the cockpit.
a. in the case of a displaced threshold, the lights between
rudder pedals — The foot-operated controls in an airplane the beginning of the runway and the displaced
that move the rudder. threshold shall show red in the approach direction; and
ruddervator — A pair of control surfaces on the tail of an b. a section of the lights 600m or one-third of the runway
aircraft arranged in the form of a “V.” These surfaces, length, whichever is the less, at the remote end of
when moved in the same direction vertically by the the runway from the end at which the take-off run is
control wheel, serve as elevators. When moved in the started, may show yellow.
same direction horizontally by the rudder pedals, they
runway edge lights (USA) — Lights used to outline the
serve as a rudder.
edges of runways during periods of darkness or restricted
rule — A straightedge usually with etched, calibrated, visibility conditions. The light systems are classified
dimensional markings. according to the intensity or brightness they are capable
of producing: they are the High Intensity Runway Lights
rumble — A combustor noise caused by choking and
(HIRL), Medium Intensity Runway Lights (MIRL), and
unchoking of the turbine nozzle. Caused by improper
the Low Intensity Runway Lights (RL). The HIRL and
fuel scheduling.
MIRL systems have variable intensity controls, where
run — 1. A defect in a painted surface caused by too much the RLs normally have one intensity setting.
finish being applied. The material gathers and attempts to
a. The runway edge lights are white, except on instrument
flow off the surface. 2. To set something in motion, such
runways amber replaces white on the last 2,000 feet or
as running an engine.
half of the runway length, whichever is less, to form a
caution zone for landings.

271

10001930-002_AviationDictionary_2012_BOOK.indb 271 3/27/2012 9:38:25 AM

 runway end identifier lights • runway use program

b. The lights marking the ends of the runway emit red runway overrun — In military aviation exclusively, a
light toward the runway to indicate the end of runway stabilized or paved area beyond the end of a runway, of
to a departing aircraft and emit green outward from the same width as the runway plus shoulders, centered on
the runway end to indicate the threshold to landing the extended runway centerline.
aircraft.
runway profile descent — An instrument flight rules (IFR)
runway end identifier lights — Two synchronized flashing air traffic control arrival procedure to a runway published
lights, one on each side of the runway threshold, which for pilot use in graphic and/or textual form and may
provide rapid and positive identification of the approach be associated with a STAR. Runway Profile Descents
end of a particular runway. provide routing and may depict crossing altitudes,
speed restrictions, and headings to be flown from the
runway gradient — The average slope, measured in
enroute structure to the point where the pilot will receive
percent, between two ends or points on a runway.
clearance for and execute an instrument approach
runway heading — The magnetic direction that procedure. A Runway Profile Descent can apply to more
corresponds with the runway centerline extended, not than one runway if so stated on the chart.
the painted runway number. When cleared to “fly or
runway safety area — A defined surface surrounding
maintain runway heading,” pilots are expected to fly or
the runway prepared, or suitable, for reducing the risk
maintain the heading that corresponds with the extended
of damage to airplanes in the event of an undershoot,
centerline of the departure runway. Drift correction shall
overshoot, or excursion from the runway. The dimensions
not be applied; e.g., if the actual magnetic heading of the
of the RSA vary and can be determined by using the
runway centerline of Runway 4 is 044º, a heading of 044º
criteria contained within Advisory Circular 150/5300-13,
should be flown..
Chapter 3. The design standards dictate that the RSA
runway in use/active runway/duty runway — Any shall be:
runway or runways currently being used for takeoff or
a. Cleared, graded, and have no potentially hazardous
landing. When multiple runways are used, they are all
ruts, humps, depressions, or other surface variations;
considered active runways. In the metering sense, a
selectable adapted item that specifies the landing runway b. Drained by grading or storm sewers to prevent water
configuration or direction of traffic flow. The adapted accumulation;
optimum flight plan from each transition fix to the vertex
c. Capable, under dry conditions, of supporting snow
is determined by the runway configuration for arrival
removal equipment, aircraft rescue and fire fighting
metering processing purposes.
equipment, and the occasional passage of aircraft
runway incursion — Any occurrence at an airport involving without causing structural damage to the aircraft; and,
an aircraft, vehicle, person, or object on the ground that
d. Free of objects, except for objects that need to be
creates a collision hazard or results in loss of separation
located in the runway safety area because of their
with an aircraft taking off, intending to takeoff, landing,
function. These objects shall be constructed on
or intending to land.
low impact resistant supports (frangible mounted
runway lights — Lights having a prescribed angle of structures) to the lowest practical height with the
emission used to define the lateral limits of a runway. frangible point no higher than 3 inches above grade.
Runway lights are uniformly spaced at intervals of
runway temperature — The air temperature immediately
approximately 200 feet, and the intensity can be
above a runway at approximately wing level.
controlled or preset.
runway use program — A noise abatement runway
runway markings — 1. Basic marking – Markings on
selection plan designed to enhance noise abatement
runways used for operations under visual flight rules
efforts with regard to airport communities for arriving
consisting of centerline markings and runway direction
and departing aircraft. These plans are developed into
numbers and, if required, letters. 2. Instrument marking
runway use programs and apply to all turbojet aircraft
– Markings on runways served by nonvisual navigation
12,500 pounds or heavier; turbojet aircraft less than
aids and intended for landings under instrument weather
12,500 pounds are included only if the airport proprietor
conditions, consisting of basic marking plus threshold
determines that the aircraft creates a noise problem.
markings. 3. All-weather (precision instrument) marking
Runway use programs are coordinated with FAA offices,
– Marking on runways served by nonvisual precision
and safety criteria used in these programs are developed
approach aids and on runways having special operational
by the Office of Flight Operations. Runway use programs
requirements, consisting of instrument markings plus
are administered by the Air Traffic Service as “Formal”
landing zone markings and side strips.
or “Informal” programs.

272

10001930-002_AviationDictionary_2012_BOOK.indb 272 3/27/2012 9:38:25 AM

 runway visibility value (RVV) • rust

a. Formal Runway Use Program – An approved noise

abatement program defined and acknowledged in a
Letter of Understanding between Flight Operations,
Air Traffic Service, the airport proprietor, and the
users. Once established, participation in the program is
mandatory for aircraft operators and pilots as provided
for in FAR 91.129.
b. Informal Runway Use Program – An approved noise
abatement program that does not require a Letter of
Understanding, and participation in the program is
voluntary for aircraft operators/pilots.
runway visibility value (RVV) — The visibility
determined for a particular runway by a transmissometer.
A meter provides a continuous indication of the visibility
(reported in miles or fractions of miles) for the runway.
RVV is used in lieu of prevailing visibility in determining
minimums for a particular runway.
runway visual range (RVR) — An instrumentally derived
horizontal distance a pilot should see down the runway
from the approach end; based on the sighting of high
intensity runway lights.
runway visual range (RVR) — An instrumentally derived
value, based on standard calibrations, that represents the
horizontal distance a pilot will see down the runway from
the approach end. It is based on the sighting of either high
intensity runway lights or on the visual contrast of other
targets whichever yields the greater visual range. RVR,
in contrast to prevailing or runway visibility, is based
on what a pilot in a moving aircraft should see looking
down the runway. RVR is horizontal visual range, not
slant visual range. It is based on the measurement of a
transmissometer made near the touchdown point of the
instrument runway and is reported in hundreds of feet.
RVR is used in lieu of RVV and/or prevailing visibility in
determining minimums for a particular runway.
a. Touchdown RVR – The RVR visibility readout values
obtained from RVR equipment serving the runway
touchdown zone.
b. Mid RVR – The RVR readout values obtained from
RVR equipment located midfield of the runway.
c. Rollout RVR – The RVR readout values obtained from
RVR equipment located nearest the rollout end of the
runway.
rust — A reddish brown, crusty coating of hydrated ferric
oxide that forms on iron and iron-containing materials
when the material is exposed to moist air.

273

10001930-002_AviationDictionary_2012_BOOK.indb 273 3/27/2012 9:38:25 AM

 S • sandbag

S safety glass — A glass that does not leave potentially

dangerous jagged fragments when it is broken. Some safety
saber saw — A hand‑held, electrically operated jigsaw that uses glass is laminated with a tough plastic membrane between
a short, stiff blade. It operates using reciprocating motion. layers of glass, while others consist of tempered glass.

sacrificial corrosion — A method of corrosion protection safety needs — A level of Maslow’s Hierarchy of human
in which a surface is plated with a metal less noble than needs, which includes protection against danger, threats,
itself. Any corrosion will attack the plating rather than and deprivation.
the base metal. safety program manager — An FAA employee who
saddle-mount oil tank — An externally mounted sheet designs, implements, and evaluates the Aviation Safety
metal tank with a contour, which allows the tank to mount Program within the FAA Flight Standards District Office
around the curvature of a turbine engine compressor case. (FSDO) area of responsibility.

S.A.E. — Society of Automotive Engineers. safety valve — A relief valve that opens to relieve pressure in a
container if the pressure rises above a predetermined value.
safety alert — A safety alert issued by ATC to aircraft under
their control if ATC is aware the aircraft is at an altitude safety wire — Soft wire made of galvanized low‑carbon
that, in the controller’s judgment, places the aircraft in steel, annealed stainless steel, or brass, used to prevent
unsafe proximity to terrain, obstructions, or other aircraft. nuts and bolts from vibrating loose.
The controller can discontinue the issuance of further safety wiring — A method of fastening bolts or screw‑heads
alerts if the pilot advises he is taking action to correct the together with soft wire to help prevent loosening.
situation or has the other aircraft in sight.
safetying — Installing a device in order to help prevent an
a. Terrain/Obstruction Alert – A safety alert issued by attachment from loosening.
ATC to aircraft under their control if ATC is aware
sail back — A maneuver during high wind conditions
the aircraft is at an altitude that, in the controller’s
(usually with power off) where float plane movement is
judgment, places the aircraft in unsafe proximity to
controlled by water rudders, opening and closing cabin
terrain/obstructions; e.g., “Low Altitude Alert, check
doors, etc.
your altitude immediately.”
sailplane — A high performance glider.
b. Aircraft Conflict Alert – A safety alert issued by ATC
to aircraft under their control if ATC is aware of an sal ammoniac — Ammonium chloride.
aircraft that is not under their control at an altitude salient pole — The field pole of a motor or generator that
that, in the controller’s judgment, places both aircraft extends out from the field frame toward the armature.
in unsafe proximity to each other. With the alert, ATC
will offer the pilot an alternate course of action when salt — The result of the combination of an alkali with
feasible; e.g., “Traffic Alert, advise you turn right an acid. Salts are generally porous and powdery in
heading zero niner zero or climb to eight thousand appearance and are the visible evidence of corrosion in
immediately.” a metal.

c. The issuance of a safety alert is contingent upon the samarium — A metallic element with a symbol of Sm and
capability of the controller to have an awareness of an an atomic number of 62.
unsafe condition. The course of action provided will same direction aircraft — Aircraft are operating in the
be predicated on other traffic under ATC control. Once same direction when:
the alert is issued, it is solely the pilot’s prerogative to
determine what course of action, if any, he will take. a. They are following the same track in the same
direction; or
safety belt — A belt designed specifically to fasten a person
to an object such as an aircraft seat to prevent injury or b. their tracks are parallel and the aircraft are flying in the
falling. same direction; or

safety factor — A structural design feature. Safety factor c. Their tracks intersect at an angle of less than 45
is the ratio of the maximum load a structural member is degrees.
designed to support compared to the maximum probable sand casting — A casting in which the mold is made by
load to which it will be subjected. shaping special casting sand around a pattern. The
safety gap — A specifically designed space in a high‑tension pattern is removed, and molten metal is poured into the
magneto that allows a spark to jump without damaging the mold. When the molten metal has hardened, the mold is
broken away.
magneto’s internal parts. This can occur in the event that
the spark plug lead is disconnected from the spark plug. sandbag — A heavy canvas or leather bag filled with coarse
sand. It is used as a surface to form sheet metal by the

274

10001930-002_AviationDictionary_2012_BOOK.indb 274 3/27/2012 9:38:25 AM

 sanding coat • scheduled maintenance

bumping process. A bag filled with lead shot is referred sawtooth wave — The waveform produced by a relaxation
to as a shot bag. oscillator in which the voltage rises slowly and drops rapidly.
sanding coat — A coat of surfacer or heavy bodied material say again — Used to request a repeat of the last
that is applied to a material and then sanded off to fill transmission. Usually specifies transmission or portion
small surface imperfections resulting in a smoother thereof not understood or received; e.g., “Say again all
surface for subsequent coats. after ABRAM VOR.”
sandpaper — An abrasive paper made by bonding grains of say altitude — Used by ATC to ascertain an aircraft’s
sand to the surface. specific altitude/flight level. When the aircraft is climbing
or descending, the pilot should state the indicated altitude
sandwich construction — A bonded structure in which
rounded to the nearest 100 feet.
a core of material is inserted between two face sheets
of metal or fiberglass cloth. Core materials include say heading — Used by ATC to request an aircraft heading.
metallic or plastic honeycomb and end-grain balsa wood. The pilot should state the actual heading of the aircraft.
Sandwich construction is used when high strength, light
Saybolt Seconds Universal (SSU) Viscosimeter — A
weight materials are required.
device that measures the viscosity of lubricating oils by
sandwich structure — In composites, a thick, low density, giving the time in seconds it takes for 60 cu. cm of oil to
core (Usually foam or honeycomb) between thin faces of flow through its calibrating orifice. Aviation 80 engine oil
high strength material. has an SSU viscosity of 79.2, and Aviation 100 oil has an
SSU viscosity of 103.0.
satellite — A man-made object that rotates around the
Earth. A small object that rotates around a larger object. S-band radar — Radar frequency range between 1,550 and
5,200 MHz.
saturate — A material that is thoroughly soaked, or
penetrated, to the extent that it cannot absorb any more scalar — A variable that only has magnitude such as
liquid. temperature and pressure compared to vector.
saturated adiabatic lapse rate (SALR) — The rate of scale — 1. A graduated measure. 2. An oxide of iron
decrease of temperature with height as saturated air is sometimes formed on the surfaces of hot forged fasteners.
lifted with no gain or loss of heat from outside sources.
scale effect — The change in any force coefficient such
Unlike the dry adiabatic lapse rate (DALR), the SALR
as the drag coefficient due to a change in the value of
is not a constant numerical value but varies with
Reynold’s number.
temperature, being greatest at low temperatures.
scale model — A smaller version of the original model
saturated adiabatic process — The rate at which saturated
made in the same proportions.
air cools as it ascends. It is less than the dry adiabatic
lapse rate because adiabatic cooling is offset partially scalene triangle — A three‑sided form in which all sides
by the release of latent heat. The difference is larger at and angles are unequal.
higher temperatures.
scales of circulations — The typical horizontal dimension
saturated air — Air containing the maximum amount of size and lifetime of an individual circulation. See also
water vapor it can hold at a given temperature (100% macroscale, mesoscale, and microscale.
relative humidity).
scarf joint — A joint used for the construction or repair of a
saturated vapor — The vapor state above a liquid in which wooden aircraft or component. The two parts to be joined
no further vaporization can take place without an increase are cut with a shallow taper and glued together.
in temperature.
scarf patch — A flush repair to plywood skins where the
saturated vapor pressure — The partial pressure of water slope must be shallower than 1 in 12, or about 12 times
vapor at saturation. the thickness of the plywood.
saturation — A state of equilibrium where the same amount scavenge — To remove an undesirable material from an area.
of molecules are leaving a water surface as are returning
scavenger pump — A constant displacement pump in an
and the vapor pressures are balanced.
engine that picks up oil after it has passed through the
saturation current — In electronics, the condition where the engine and returns it to the oil reservoir.
maximum amount of current able to flow in a transistor or
scheduled maintenance — The inspection and replacement
vacuum tube has been reached. The application of additional
of components that are planned in advance on a day,
current to the base or gate has no effect on the output.
month, or operating hour basis.

275

10001930-002_AviationDictionary_2012_BOOK.indb 275 3/27/2012 9:38:25 AM

 schematic diagram • seal

schematic diagram — A graphical presentation used to screw dowel — A dowel pin provided with a straight or
explain the operation of a system without showing its tapered thread for threading into a material.
mechanical details or physical layout. Also referred to as
screw pitch gauge — A gauge with a series of V‑notches
a schematic drawing.
cut along one edge. Used to check the number of threads,
schematic drawing — A graphical presentation or diagram or pitch, of a screw or bolt.
used to explain the operation of a system without showing
screwdriver — A hand tool used for turning screws.
its mechanical details or physical layout. Also referred to
as a schematic diagram. scriber — A hardened steel or carbide-tipped, pointed tool
used to scratch lines on metal for cutting.
scientific notation — In mathematics, a form of shorthand.
Numbers are displayed by using powers of ten to indicate scribing — The process of marking a line on metal with the
very large or very small numbers. For example, 4,000,000 use of a scriber.
would be written as 4 X 106 and 0.000004 would be
scroll combustor — Used widely on auxiliary power
written as 4 X 10-6.
units in conjunction with a radial inflow turbine, a scroll
Scintilla magneto — A Swiss-designed and built magneto. combustor fits around the turbine nozzle that has vane
It is the forerunner of the current Bendix magneto. openings at its inner perimeter. The vanes direct the gases
inward onto the turbine.
scoop — An air inlet that projects beyond the immediate
surface of an aircraft structure. scroll shear — A floor- or bench-mounted sheet metal
cutting tool used to cut irregular lines in a piece of sheet
scope — 1. A contraction of oscilloscope. 2. Extent and
metal without having to cut to the edge of the sheet.
detail of an inspection or repair.

scud — Small patches of low clouds that usually form
score — A deep scratch mark or line made across a piece of
below heavier overcast clouds.
material making it possible to break the material along
the line. scuffing surface — A dulling or moderate wear of a surface
resulting from a slight amount of rubbing. Usually caused
scoring — Deep scratches on the surface of a material
by improper clearance and insufficient lubrication. Parts
caused by foreign particles between moving parts.
affected are rollers, rings, and steel parts bolted together.
scraper ring — The bottom ring on a piston whose function
scupper — A recess around the filler neck of a fuel tank. It
is to scrape the lubricating oil away from the cylinder
collects any fuel spilled during the fueling operation and
wall. This prevents oil from getting into the combustion
drains it overboard rather than allowing it to enter the
chamber of the cylinder.
aircraft structure.
scratching surface — Narrow, sharp, shallow markings or
sea anchor — An apparatus towed in the water to retard a
lines resulting from the movement of a particle or sharp
ship’s drift and to keep the vessel facing into the wind.
pointed object across a surface. The most common cause
is carelessness in handling and any part can be so affected. sea breeze — A coastal breeze blowing from sea to land. It
NOTE: To distinguish it from scoring, scratching is not occurs in the daytime when the land surface is warmer
considered to be caused by engine operation. than the sea surface.
screech liner — A perforated liner within an afterburner, sea breeze front — The boundary between the cool,
designed to combat destructive vibrations that cause inflowing marine air in the sea breeze and the warmer
metal fatigue and noise emissions. air over land.
screeching — A shrill, high-pitch noise that comes from a sea lane — A designated portion of water outlined by visual
gas turbine engine caused by the instability of combustion surface markers for and intended to be used by aircraft
in the engine. designed to operate on water.
screeding tool — A tool used to smooth out or level plastic sea level — A reference height used to determine standard
resins used in bonded structure manufacturing or repair. atmospheric conditions and altitude measurements.
screen — A frame covered with a netting or mesh material used sea level engine — A reciprocating aircraft engine having
to cover an opening to prevent the entry of foreign objects. a rated takeoff power that is producible only at sea level.
screen grid — The electrode in a four-element vacuum tube sea level pressure — The atmospheric pressure at mean sea
used to minimize the interelectrode capacitance between level.
the plate and the control grid.
sea smoke — Steam fog, evaporation fog.
screen-type filter — A fluid filter with an element that
seal — A component or material used to prevent fluid
consists of a wire screen.
leakage between two surfaces.

276

10001930-002_AviationDictionary_2012_BOOK.indb 276 3/27/2012 9:38:25 AM

 sealant • Sectional Aeronautical Chart

sealant — A material used to form a seal between surfaces. and stored until needed then converted back into electrical
Sealants differ from gaskets in that they are usually liquid energy. Secondary cells do not produce electricity; they
or semi‑solid. merely store it.
sealed compartments — The compartments in an aircraft secondary coil — The secondary winding of a transformer.
structure that are sealed off and used as fuel tanks.
secondary control surfaces — Control surfaces, such as
seam welding — A method of electrical resistance welding trim tabs, servo tabs, and spring tabs, that reduce the
that forms a continuous line of weld instead of individual force required to actuate the primary controls.
spots. See also spot welding.
secondary current — The current that flows in the
seaplane — An airplane designed to land and take off from secondary winding of a transformer. Secondary current
the surface of water. is induced in the secondary winding of a coil by the
collapse of the primary coil circuit current.
search and rescue — A service that seeks missing aircraft
and assists those found to be in need of assistance. It is secondary emission — In electron tubes, the emission of
a cooperative effort using the facilities and services of electrons from a surface when struck by high‑velocity
available Federal, state and local agencies. The U.S. electrons from the cathode.
Coast Guard is responsible for coordination of search and
secondary exhaust nozzle — On a turbofan, the cold
rescue for the Maritime Region, and the U.S. Air Force is
exhaust fan nozzle. On an afterburner, the aft or outer
responsible for search and rescue for the Inland Region.
exhaust nozzle. In this instance, it is made up of moveable
Information pertinent to search and rescue should be
flaps that change the geometry of the nozzle in different
passed through any air traffic facility or be transmitted
modes of engine operation.
directly to the Rescue Coordination Center by telephone.
secondary fuel — Refers to the duplex fuel nozzle and
search and rescue facility — A facility responsible for
the fuel that flows at higher power settings from the
maintaining and operating a search and rescue (SAR)
secondary orifice. Also referred to as the main fuel.
service to render aid to persons and property in distress.
It is any SAR unit, station, NET, or other operational secondary stall — A demonstration that a flight instructor
activity that can be usefully employed during an SAR shows a student pilot. It is normally caused by poor stall
Mission; e.g., a Civil Air Patrol Wing, or a Coast Guard recovery technique, such as attempting to climb prior to
Station. attaining sufficient flying speed. A secondary stall can
occur as a result of increasing angle of attack beyond the
search engine — Software that reviews a database to find
critical angle during recovery from a preceding stall.
and display information. Used to find information on the
Internet. secondary structure — In aircraft and aerospace
applications, a structure that is not critical to flight safety.
seasoned lumber — Lumber that has been dried or had its
moisture content reduced to a specified amount. secondary voltage — The voltage in a circuit produced
across the secondary winding of a transformer.
seat — A place or space on which something sits.
secondary winding — Output winding of a transformer.
seat belt — A belt designed specifically to fasten a person
to an object such as an aircraft seat to prevent injury or second‑class lever — A lever commonly used to help in
falling. overcoming larger resistance with relatively small effort.
The second-class lever has the fulcrum at one end while
seated — A condition in which moving parts have worn
the effort is applied at the other end. The resistance is
together until they are fitted together and a minimum of
somewhere between these points. A wheelbarrow is an
leakage exists between them.
example of a second-class lever.
second in command — A pilot who is designated to be
section line — The crosshatching used in a cutaway section
second in command of an aircraft during flight time.
of an aircraft drawing to identify a type of material.
secondary — Something at a second level of importance,
Sectional Aeronautical Chart — Chart designed for visual
rank or value.
navigation of slow or medium speed aircraft. Topographic
secondary air — That portion of compressor output air information on these charts features the portrayal of relief,
used for cooling engine parts and combustion gases. and a judicious selection of visual check points for VFR
flight. Aeronautical information includes visual and radio
secondary airstream — The air that passes through the fan
aids to navigation, airports, controlled airspace, restricted
portion of a turbofan engine.
areas, obstructions, and related data. Each chart covers 6°
secondary cell — A storage cell or an electrical device in to 8° of longitude and approximately 4° of latitude. With
which electrical energy is converted into chemical energy a scale of 1:500,000 the resolution of terrain features is
very good. Also refereed to as a sectional chart.
277

10001930-002_AviationDictionary_2012_BOOK.indb 277 3/27/2012 9:38:26 AM

 sectional view • selective plating

sectional view — Drawing details obtained by cutting away ICAO

part of an object to show the shape and construction of
a. Initial Approach – That segment of an instrument
the object at the cutting line.
approach procedure between the initial approach fix
sectioning — Marking a drawing by suitable crosshatching and the intermediate approach fix or, where applicable,
or other symbols to indicate the material in the cutaway the final approach fix or point.
view of a part.
b. Intermediate Approach – That segment of an
sector — A part of a circle bounded by any two radii and the instrument approach procedure between either the
arc included between the two radii. intermediate approach fix and the final approach fix or
point, or between the end of a reversal, race track or
sector gear — A portion of a gear that appears to have been
dead reckoning track procedure and the final approach
purposely cut from a whole gear wheel. It consists of the
fix or point, as appropriate.
hub as a pivot point and a portion of the rim with the
teeth. Sector gears generally drive a smaller pinion gear c. Final Approach – That segment of an instrument
for small angular movements. approach procedure in which alignment and descent
for landing are accomplished.
sector list drop interval — A parameter number of minutes
after the meter fix time when arrival aircraft will be d. Missed Approach Procedure – The procedure to be
deleted from the arrival sector list. followed if the approach cannot be continued.
sector visibility — Meteorological visibility within a USA
specified sector of the horizon circle.
a. Initial Approach – The segment between the initial
securing strap — A strap used to secure an oil or fuel tank approach fix and the intermediate fix or the point
to the airframe or engine. where the aircraft is established on the intermediate
course or final course.
sediment — Any matter that settles to the bottom of a liquid
or container. b. Intermediate Approach – The segment be­tween the
intermediate fix or point and the final approach fix.
see and avoid — When weather conditions permit, pilots
operating IFR or VFR are required to observe and c. Final Approach – The segment between the final
maneuver to avoid other aircraft. Right-of-way rules are approach fix or point and the runway, airport or missed
contained in FAR 91. approach point.
seesaw rotor — A term used for a semi-rigid rotor. d. Missed Approach – The segment between the missed
approach point, or point of arrival at decision height,
seesaw rotor system — A rotor system using a semi-rigid
and the missed approach fix at the prescribed altitude.
rotor
seize — Equipment failure in which moving parts fuse
segment — A division or a section. A part of a figure.
or bind because of friction, pressure, or excessive
segmented circle temperature.
— An on-ground
SELCAL — A contraction of selective calling referring to
visual indicator
an automatic signaling system used in aircraft to notify a
that provides traffic
particular aircraft of an incoming call.
pattern information. It
consists of “L” shaped selected ground delays — A traffic management procedure
indicators around the periphery of a circle that indicate whereby selected flights are issued ground delays to
pattern direction on various runways. Often includes a better regulate traffic flows over a particular fix or area.
tetrahedron or wind sock in the center to indicate wind
selection-type test items — Questions where the student
direction.
chooses from two or more alternatives provided.
segmented rotor brake — A heavy-duty multiple disc True-false, matching, and multiple-choice type questions
brake used on large, high speed aircraft. Stators are keyed are examples of selection-type test items.
to the axle and contain high‑temperature lining material.
selective call system (SELCAL) — A system that
The rotors, keyed into the wheel, are made in segments
permits the selective calling of individual aircraft over
to allow for cooling and the large amounts of expansion
radiotelephone channels linking a ground station with the
encountered.
aircraft.
segments of an instrument approach procedure — An
selective plating — A process of electroplating only a
instrument approach procedure can have as many as
section of a metal part.
four separate segments depending on how the approach
procedure is structured.

278

10001930-002_AviationDictionary_2012_BOOK.indb 278 3/27/2012 9:38:26 AM

 selectivity • sender

selectivity — The ability to select or choose from among self-healing capacitor — In electronics, an electrolytic
several choices. capacitor that restores the dielectric film if it is damaged
by over-voltage.
selector switch — A multi-pole switch that takes the
place of several switches. It is used to connect a single self-induction — The generation of back voltage in a
conductor to one of several other conductors. conductor. This occurs when lines of flux created by
the AC current in the conductor alternately expand and
selector valve — A hydraulic flow control valve that directs
contract across the conductor. The moving lines of flux
hydraulic pressure to one side of an actuator and connects
create a back voltage opposite in direction to the original
the other side to the system return line.
voltage.
selenium — A chemical element in the sulfur family with
self-launch glider — A glider equipped with an engine,
a symbol of Se and an atomic number of 34. Used in
allowing it to be launched under its own power. When
photoelectric devices because it changes its conductivity
the engine is shut down, a self-launch glider displays the
with a change in temperature.
same characteristics as a non-powered glider.
selenium rectifier — A rectifier using laminated plates of
self-locking nut — A nut designed with a built‑in locking
metal, usually iron, that have been coated with selenium
device that grips the threads of a bolt when the nut is
on one side. It is designed to develop a unidirectional
tightened. This prevents the nut from loosening because
current‑carrying characteristic. The flow of electrons
of vibration. Locking devices can be fiber or non‑fiber
from the conductive metal to the selenium occurs more
depending on their intended purpose.
readily than the flow in the opposite direction.
self-tapping screw — A wood or metal screw that cuts its
self concept — A perception factor that ties together how
own threads as it is screwed into sheet metal or wood.
people feel about themselves with how well they will
receive further experiences. Selsyn system — A DC‑type of synchro remote indicator
system.
self-accelerating — The ability of a turbine engine to
produce enough power to accelerate. selvage edge — A manufactured woven edge on fabric that
runs the length of the fabric or in the warp direction. It is
self-aligning bearing — A rod end bearing consisting of a
removed for all fabrication and repair work.
ball fitted into a socket that maintains alignment between
the operating control and the unit being controlled. semi — A prefix meaning a half or part of something.
self-centering chuck — A drill motor chuck with semiautomatic operation — A device that is partially
interconnecting jaws. They move at the same time to hold automatic and partially manual in its operation.
a drill bit when loosening or tightening.
semi-cantilever — An externally braced wing.
self-concept — A perception factor that ties together how
semicircular — In the form of a half circle.
people feel about themselves with how well they will
receive further experiences. semiconductor — An insulating material treated with
certain impurities that add free electrons to act as current
self-demagnetization — The process in which a magnet
carriers, carrying the flow of current in one direction and
loses its magnetism if allowed to sit for long periods
blocking it in the other.
without a keeper bar.
semiconductor diodes — A semiconductor type of electron
self-excited generator — A generator whose field excitation
check valve. A device that allows the flow of electrons in
is taken directly from the armature rather than from an
one direction but not the opposite.
outside source. A self-excited DC generator depends
on residual magnetism. Without residual magnetism, it semi-monocoque — A stressed‑skin structure in which the
would be impossible to start a self-excited generator once skin is supported by a lightweight framework to provide
stopped. extra rigidity. Most of the larger modern aircraft are of
semi‑monocoque construction.
self-extinguishing — The ability of a material to
automatically stop burning as soon as the outside source semirigid rotor — In rotorcraft, a rotor system in which the
of the flame is removed. blades are fixed to the hub but are free to flap and feather.
self-fulfillment needs — Occupy the highest level of semispherical — In the shape of half a sphere. Dome-shaped.
Maslow’s pyramid. They include realizing one’s own
sender — In a fuel quantity system, a measuring device
potential for continued development, and for being
located in a reservoir or fuel tank. The sender consists
creative in the broadest sense. Maslow included various
of a float mounted on an arm that rides on the top of
cognitive and aesthetic goals in this echelon.
the liquid. The arm is free to float and is connected to
a variable resistor. Any change in the fluid level sends

279

10001930-002_AviationDictionary_2012_BOOK.indb 279 3/27/2012 9:38:26 AM

 sense antenna • service ceiling

a signal to an indicator on the pilot’s instrument panel serial number — A number indicating placement within a
showing the amount of fluid in the tank. series and used as a means of identification.
sense antenna — A non‑directional radio antenna that picks serial operation — In computers, operations are conducted
up a signal with equal strength from all directions. one at a time rather than several operations occurring
simultaneously (parallel operation).
sensible heat — Heat added to a substance that causes
a change in the temperature without changing the serialists — A learning style that starts with the components
substance’s physical condition. Can be felt and measured. and pieces them together to understand the whole.
Opposite of latent heat Serialists prefer to start at the beginning and examine the
material in order.
sensitive altimeter — A pneumatic altimeter in which a
pointer makes a complete revolution every thousand feet. series circuit — A circuit allowing only one path for
It also has an adjustable barometric scale allowing it to be electron flow from the source through the load back to
adjusted to the existing barometric pressure. the source.
sensitive relays — A relay that operates electromagnetically series ohmmeter — An ohmmeter circuit where resistance
with very small current. When the relay closes it controls is measured by determining the amount of current flow
a larger current to operate other devices. through the unknown resistor by placing a known voltage
in series with the meter and the unknown resistor.
sensitivity — A measure of the ability of something to be
sensitive or responsive to very small changes in external series resonant circuit — An AC circuit that has a capacitor
conditions. and an inductor connected in series. The capacitive
reactance and the inductive reactance are equal at the
sensitized paper — Chemically treated paper used for
specific frequency of the circuit.
making photographic prints of drawings.
series RLC circuit — An AC circuit where resistance,
sensor — A device used to actuate signal‑producing devices
capacitance, and inductance are arranged so that all
in response to changes in physical conditions.
current must flow through all three elements.
sensory register — That portion of the brain that receives
series wound generator — A generator where the field and
input from the five senses. The individual’s preconceived
armature are connected in series.
concept of what is important will determine how much
priority the register will give in passing the information series‑parallel circuit — A circuit consisting of groups
on to the rest of the brain for action. of parallel components connected in series with other
components.
separation — 1. Phenomenon occurring when a moving
stream of fluid flowing past a body separates from the series-wound motor — An electric motor with
surface of that body. 2. Spacing between aircraft, levels electromagnetic field coils connected in series with the
or tracks. armature. Series‑wound motors are used as starter motors
because of their high starting torque.
separation minima — The minimum longitudinal, lateral,
or vertical distances by which aircraft are spaced through serrations — A formation resembling the teeth along the
the application of air traffic control procedures. cutting edge of a saw.
separator — 1. In composites, a permeable layer that also service — A generic term that designates functions or
acts as a release film. This could be in the form of a peel assistance available from or rendered by air traffic
ply or a porous Teflon®-coated fiberglass. Often placed control. For example, Class C service would denote the
between lay-up and bleeder to facilitate the excess resin ATC services provided within a Class C airspace area.
wicking into the bleeder. It is removed from the laminate
service bulletin — Information issued by the manufacturer
after cure. 2. In batteries, a porous material that keeps
of an aircraft, aircraft engine, or component that detail
the positive and negative plates apart and prevents them
maintenance procedures to enhance safety or improve
from shorting.
performance of the product.
sequence valve — A mechanically actuated hydraulic
service capacity — A measurement of the amount of
valve causing a sequential action of certain actuators.
electrical energy that can be obtained from a chemical
Wheel-well doors, for example, must open and contact a
cell. Measured under controlled conditions and given in
sequence valve before the landing gear can extend.
ampere‑hours.
sequential logic devices — A digital memory device whose
service ceiling — The height above standard sea level
output depends not only on current input but on past
beyond which an airplane can no longer climb more than
inputs as well.
100 feet per minute.

280

10001930-002_AviationDictionary_2012_BOOK.indb 280 3/27/2012 9:38:26 AM

 service life • Seyboth fabric tester

service life — The expected length of time a unit, part, set screw — A small headless screw used to secure a wheel,
component, or piece of equipment is expected to operate pulley, or knob onto a shaft.
satisfactorily.
setback — The distance
service manual — A manual issued by the manufacturer of between the mold line
an aircraft, aircraft engine, or component and approved by and the bend tangent
the FAA. It describes the approved methods of servicing line on a sheet metal
and repairing the component. lay­out. For 90° bends,
setback is equal to the
serviceable — Equipment or parts in a condition that allows
inside radius of the bend
them to be returned to operational status on an aircraft.
plus the thickness of the
servicing diagram — Information furnished by the metal being bent.
manufacturer of an aircraft showing the proper access to
settling with power — In helicopters, a transient condition
all of the items or components requiring servicing.
of downward flight (descending through air that has just
servo — A motor or other form of actuator, that after been accelerated downward by the rotor) during which
receiving a small signal from the control device, exerts a an appreciable portion of the main rotor system is being
large force to accomplish the desired work. forced to operate at angles of attack above maximum.
Blade stall starts near the hub and progresses outward as
servo altimeter — An altimeter where the aneroid
the rate of descent increases.
mechanism moves a rotary pick‑off. Its signal is amplified
to drive a servomotor moving the drums and pointers. severe thunderstorm — A thunderstorm having a much
greater intensity, larger size, and longer lifetime than an
servo brake — A self-energizing drum brake that increases
airmass thunderstorm. Associated weather includes wind
braking action above that which would be applied without
gusts of 50 knots or more, and/or hail three-quarters of an
any assistance.
inch diameter or larger and/or strong tornadoes.
servo fuel — An intermediate metered fuel in the Bendix
severe weather avoidance plan — An approved plan to
RS fuel injection system controlling the opening of the
minimize the effect of severe weather on traffic flows
flow control valve based on the airflow into the engine.
in impacted terminal and/or ARTCC areas. SWAP is
servo loop — An automatic control system that sends a normally implemented to provide the least disruption to
signal to a servomotor to move a control device. The the ATC system when flight through portions of airspace
loop signal to a servomotor stops the servomotor when is difficult or impossible due to severe weather.
the control is moved the appropriate amount.
severe weather forecast alerts — Preliminary messages
servo system — An automatic control system that senses issued in order to alert users that a Severe Weather
changes in movement such as lowering the flaps. It sends Watch Bulletin (WW) is being issued. These messages
a feedback signal to the control motor to stop moving the define areas of possible severe thunderstorms or tornado
flaps when the correct position is obtained. activity. The messages are unscheduled and issued as
required by the National Severe Storm Forecast Center at
servo tab — An adjustable tab attached to the trailing edge
Kansas City, Missouri.
of a control surface. The tab moves opposite the direction
of the control and aids the pilot in moving the control. sewed seam — A seam in aircraft fabric made with a series
of stitches joining two or more pieces of material.
servomechanism — Automatic device controlling large
amounts of power using small inputs. A feedback system sewed‑in panel repair — A repair to fabric aircraft
allows it to produce only the required amount of control. covering with a panel extending from the leading edge to
the trailing edge and from rib to rib sewn in place. All of
servomotor — A motor that receives a signal due to the
the seams are suitably reinforced with surface tape.
action of the control system causing a mechanical
movement of a primary control. Servomotors have the sewed-patch repair — A repair to aircraft fabric covering
ability to move in either direction when the current of the where a patch is sewed into place and the seams are
correct polarity is sent to the servomotor. covered with surface tape.
servo-type carburetor — A carburetor using pressure sextant — An instrument used to measure the angular
drops across a servo metering jet to control the amount distance between the horizon and a navigational star to
of metered fuel. It is proportional to the amount of air determine geographic position or location.
allowed to flow to the cylinders.
Seyboth fabric tester — A patented, hand‑operated
sesquiplane — A biplane where the area of one of the wings precision device for testing the relative strength of
is less than one half the area of the other. The smaller installed aircraft fabric. It measures the amount of force
wing is usually the lower wing. required to punch a hole in the fabric with a specially
shaped punch.
281

10001930-002_AviationDictionary_2012_BOOK.indb 281 3/27/2012 9:38:26 AM

 S-glass • shielded ignition cable

S-glass — In composites, the S stands for structural shear point — An intentionally weakened point on a shaft
fiberglass. This type of fiberglass is for much of the such as in a dual element fuel pump. The shear point is
structural use in advanced composite structures. designed to break away if one element becomes jammed
A magnesium aluminosilicate composition that is and leaves the other element still functioning.
especially designed to provide very high tensile strength
shear section — A narrow portion of a drive coupling
glass filaments.
designed to shear in case of pump seizure and prevent
shaded-pole motor — A low‑torque AC induction motor. damage to either the pump or to the engine.
The rotating field is provided by the inductive action of
shear strength — The amount of force required to shear a
shaded poles on diametrically opposed pole pieces.
pin, bolt, or rivet.
shaft horsepower (SHP) — Turboshaft engines are rated in shear stress — Stress exerted on a material that tends to
shaft horsepower and calculated by use of a dynamometer slide it apart.
device. Shaft horsepower is exhaust thrust converted to a
rotating shaft. shear wave — A wave in which the particles vibrate at right
angles to the direction of the wave. Also referred to as a
shaft runout — An inspection performed on a rotating shaft transverse wave.
or component to determine the straightness of the item.
shearing gravity waves — Short atmospheric gravity wave
shaft turbine — A turbine engine used to drive an output disturbances that develop on the edges of stable layers
shaft commonly used in helicopters. in the presence of vertical shears. Wave amplitudes can
shall — As related to aircraft maintennace, means that the grow and overturn causing turbulence.
item is required, by the FAA, to be accomplished. shears — A cutting tool similar to scissors used to cut sheet
shank — A straight, metal.
narrow, essential part sheave — A wheel with a grooved center used as a pulley.
of a rotating body. An
example would be the sheet metal — Metal of any thickness up to 1/4”. Metal of a
portion of a twist drill beyond the flutes. (portion held by greater thickness is referred to as metal plate.
the drill chuck.) sheet metal drawing — A forming process where sheet
shank of a drill — The part of the body of the twist drill metal is pressed between dies to form the desired
that is round and smooth, not including the tip and flutes. compound‑curved shape.
The portion secured in the chuck of the drill motor. sheet metal layout — The pattern of a sheet metal part
shaping — A primary method of teaching that involves before forming, cutting, or drilling. Patterns allow a
the use of carefully designed stimuli and the correct great degree of accuracy in laying out the finished part.
Sheet metal layout consists of flat layout, duplication of
reinforcers for appropriate behavior. An instructor should
patterns, or projection through a set of points.
decide what behavior is desired from the students. Each
time they demonstrate the correct behavior, provide shelf cloud — A cloud that indicates the rising air over
positive reinforcement to help shape or develop this the gust front. Associated with the updraft of a multicell
behavior. thunderstorm it is located just above the gust front at low
levels.
shaving — A cutting operation in which thin layers of
material are removed from the outer surfaces of the shelf life — The period of time a material can be stored
product. and remain suitable for use. In composites, the time span
that a product will remain useful. This should be listed
shear — A stress exerted on a material that tends to slide on the label. Temperature during storage will affect the
it apart. shelf life.
shear failure — The failure of a riveted or bolted joint shell — The outer structure of an atom formed by the
caused by the rivets shearing rather than the sheet tearing. rotating electrons around the nucleus.
shear nut — A thin nut used on clevis bolts to prevent the shell‑type transformer — A transformer encased in steel
bolt from falling out. Shear nuts are only suitable for use containing the magnetic lines of flux.
in shear applications and must never be used in tensile
applications. shielded cable — An electrical conductor encased inside a
braided metal shielding. The shielding intercepts radiated
shear pin — A specially designed pin used in the drive shaft electrical energy and conducts it to ground rather than
of engine driven pumps to protect the accessory drive allowing it to cause radio interference.
train if the pump should seize.
shielded ignition cable — An electrical cable enclosed in a
metal braid. Used to carry high voltage from the distributor

282

10001930-002_AviationDictionary_2012_BOOK.indb 282 3/27/2012 9:38:26 AM

 shielded spark plug • shower

of the magneto to the spark plug. Its purpose is to prevent Shore scleroscope — A hardness tester used for metal,
radio interference caused by electromagnetic radiation. plastic, and rubber.
shielded spark plug — A spark plug completely encased short circuit — A path for electrons to flow from one
in a steel shell. The radiated energy from the spark is electrical potential to another without completing a
conducted to ground through the shielding and helps useful circuit.
prevent radio interference.
short range clearance — A clearance issued to a departing
shielded-arc welding — A method of gas welding in which IFR flight that authorizes IFR flight to a specific fix short
an inert gas such as argon, helium, or carbon-dioxide of the destination while air traffic control facilities are
is used as a covering shield around the arc. Preventing coordinating and obtaining the complete clearance.
the atmosphere from contaminating the weld results in a
stronger, more ductile, and more corrosion resistant weld. short stack — An exhaust system for aircraft reciprocating
engines consisting of a short exhaust pipe attached to the
shielding — Metal covers placed around electric and exhaust port of the cylinder. Short stacks use no collector
electronic devices to prevent the intrusion of external system.
electrostatic and electromagnetic fields.
short take off and vertical landing (STOVL) — A
shim — A thin piece of metal used to fill in a space between fixed-wing aircraft capable landing vertically and of
two objects in order to adjust a preload or the clearance clearing a 15-meter (50-foot) obstacle within 450 meters
between bearing parts. (1500 feet) of commencing takeoff run.
shimmy — A rapid and violent oscillation of a nose wheel short takeoff and landing aircraft — An aircraft that, at
or tail wheel of an airplane often caused by excessive some weight within its approved operating weight, is
wear in the support bearings. capable of operating from a STOL runway in compliance
with the applicable STOL characteristics, airworthiness,
shimmy damper — A hydraulic snubbing cylinder
operations, noise, and pollution standards.
installed between the nose wheel fork and the landing
gear structure. It is used to minimize shimmying of the short takeoff and landing (STOL) — The ability of an
nose wheel during takeoffs and landings. aircraft to take off and land in a distance of 1,000 feet
(sometimes 1,500 ft.) or less while clearing 50-foot
shock absorber — A device built into the landing gear of obstacles. These obstacles are located just after takeoff or
an aircraft to absorb the energy of the landing impact. just prior to landing.
shock loading — Stress loading for an extremely short short wave trough — Troughs in the mid- and upper
duration. troposphere and lower stratosphere that correspond to
shock mounted — Any device attached to the airframe with developing frontal lows. Short wave troughs are smaller
shock mounts to minimize the transmission of vibration in scale than long waves. They move toward the east,
or shock from one unit into another. averaging 600 nautical miles per day.

shock mounts — A shock absorbing attachment used to shorting switch — A multi-pole switch where one circuit is
mount an engine or instrument panel to an airframe to completed before another circuit is opened.
minimize vibration. shot peening — A process used to strengthen metal parts by
shock stall — Turbulent airflow on an airfoil that occurs blasting its surface with steel shot.
when the speed of sound is reached. The shock wave shoulder bolts — A bolt where the threaded portion is
distorts aerodynamic airflow causing loss of lift and stall. smaller than the shank. It is often used for the installation
shock strut — An aircraft landing gear shock strut that of plastic materials to prevent over tightening.
absorbs the initial landing impact by the transfer of oil shoulder-wing airplane — An airplane having one main
from one chamber to another through a restricting orifice. supporting wing surface mounted near the top but not
Taxi shocks are absorbed with compressed air or by a directly on top of the fuselage. Also referred to as the
spring. mid wing.
shock wave — A compression wave formed when a body show — Unless the context otherwise requires, means to
moves through the air at a speed greater than the speed show to the satisfaction of the Administrator.
of sound.
shower — Precipitation from a cumuliform cloud;
shop head — The upset head of an aircraft rivet. characterized by sudden onset and cessation, rapid
shop head rivet — The head formed on a rivet when it is change of intensity, and usually by rapid change in the
driven. appearance of the sky; showery precipitation can be in
the form of rain, ice pellets, or snow.

283

10001930-002_AviationDictionary_2012_BOOK.indb 283 3/27/2012 9:38:26 AM

 shower of sparks • signal generator

shower of sparks — The induction-vibrator-type starting shunt-wound motor — A motor in which electromagnetic
system used in some Bendix magnetos. A vibrator directs field windings are connected in parallel with the armature.
pulsating direct current into the primary circuit of one of
shut-off valve — A flow‑control valve used to shut off or
the magnetos when the points are closed. When the retard
stop a flow of fluid.
points open, pulsating current flows to ground through
the primary coil and induces a high voltage into the shuttle valve — A valve, mounted on critical components,
secondary winding. As long as both sets of points remain that directs system pressure into the actuator for normal
open, a shower of sparks occurs at the spark plug. operation but switches to emergency fluid when the
show-type finish — A glass-like aircraft finish achieved by emergency system is actuated.
applying many coats of dope and repeated sanding and side bands — The frequency bands on each side of a carrier
polishing. frequency produced by modulation.
shrink fit — Interference fit between parts when the female side stick — A primary flight control input located to the
part is heated and the male part is chilled before they are side of the pilot.
assembled. When they reach the same temperature, they
sideslip — An uncoordinated flight condition in which the
are essentially locked together.
aircraft moves downward and toward the inside of the
shrinking — The act of compressing a material into a turn. Sideslip can also result from the use of rudder to
smaller volume or area. maintain heading in an engine-out situation.
shrinking block — A sheet sidestep maneuver — A visual maneuver accomplished by
metal forming tool that a pilot at the completion of an instrument approach. It
clamps metal to prevent permits a straight-in landing on a parallel runway, which
it from buckling while must not be more than 1200 feet to either side of the
ham­mering its edge to approach runway.
shrink it. sight gauge — A glass tube or window attached to a
shrink-wrap — A method reservoir or tank that shows the quantity of fluid in the
used to protect products from dirt and dust while they are container.
held in storage. The part to be shrink‑wrapped is covered sight glass — A liquid level indicator located on the outside
with a film of transparent thermoplastic material. When heat of a reservoir that provides a visual indication of the level
is applied to the film, the film shrinks to encase the part. of liquid in the reservoir.
shroud — A cover or housing used to aid in confining an air sight line — A mark on a flat sheet of metal set even with
or gas flow to a desired path. the nose of the radius bar of a cornice or leaf brake. This
shroud ring — A stationary sealing ring positioned just placement puts the bend tangent line at the beginning of
outside the tip plane of rotating airfoils. Sometimes it is the bend.
the inner part of an outer casing. sigmet information [ICAO] — Information issued by a
shrouded-tip turbine blade — A blade with tip platforms meteorological watch office concerning the occurrence
that fit one to another to form a circular support ring. or expected occurrence of specified enroute weather
Often, the shrouds have thin abradable rims attached at phenomena that can affect the safety of aircraft operations.
their outer edge to act as air seals. SIGMET (WS) — This advisory describes conditions
shunt — An accurately calibrated resistor placed in parallel of higher intensity, which pose hazards to all aircraft,
with a meter movement for measuring current. Current flows including:
through the shunt and produces a voltage drop proportional a. severe icing not associated with thunderstorms,
to the amount of current. The ammeter movement measures
this voltage drop and displays it in amperes. b. severe or extreme turbulence or clear air turbulence
not associated with thunderstorms,
shunt circuit — A circuit that has several paths for electrons
c. dust storms, sand storms, or volcanic ash lowering
to flow.
surface visibilities to below three miles, and
shunt ohmmeter — An ohmmeter circuit used for
d. volcanic eruptions.
measuring low resistances. The unknown resistor is
placed in parallel (shunt) with the meter and resistance is signal — The intelligence or directive portion of a radio
measured by the amount of current the unknown resistor wave.
takes from the meter.
signal generator — A test unit designed to produce
shunt-wound generator — A generator in which the field reference electric signals that can be applied to electronic
and armature are connected in parallel. circuits for testing purposes.

284

10001930-002_AviationDictionary_2012_BOOK.indb 284 3/27/2012 9:38:26 AM

 signal-strength meter • simultaneous ILS approaches

signal-strength meter — In electronics, an instrument that silver brazing — Brazing (connecting two close fitting
indicates the signal strength being received. parts by the use of molten metal being drawn into the
joint by capillary action) using a silver alloy.
significant digits — Significant digits are those that
are statistically significant. In measurements, the last silver solder — An alloy of silver, copper, and nickel used
significant digit is the first one estimated (interpolated for hard soldering. It produces a joint that is stronger than
between two measured markings). For computations, a soft solder, but not as strong as some forms of brazing.
set of rules determines the number of significant digits.
All non-zero digits are counted as significant. Zeroes that silvered-mica capacitor — A capacitor made up of a mica
have non-zero digits to the left of them are significant dielectric coated with silver that makes up the plates of
zeroes. Examples: 0.005140 has four significant digits. the capacitor.
31.000 has five significant digits. simple flaps — Wing flaps lowered by pivoting them about
significant meteorological information — See SIGMET a point near their leading edge. They change the airfoil
section of the wing but do not affect the wing area.
significant point — A point, whether a named intersection,
a NAVAID, a fix derived from a NAVAID(s), or simple fraction — A fraction in which both the numerator
geographical coordinate expressed in degrees of latitude and the denominator are whole numbers.
and longitude. Established for the purpose of providing simple machine — A device that transforms energy or
separation, as a reporting point, or to delineate a route changes the direction of a force. The six simple machines
of flight. include the lever, pulley, wheel and axle, inclined plane,
silencer — A device used in cabin air distribution systems screw, and gear.
designed to minimize the noise created by pulsations in simple motion — Newton’s law of motion, which states
the air delivered from the cabin supercharger. that objects in motion tend to stay in motion.
silica gel — A desiccant used as a drying or moisture simplex communications — A method of communication
absorbing agent. Silica gel is often used to package where only one transmitter location can transmit at a time
products that can be damaged by excess moisture. while the other receives.
silicon — A natural element with a symbol of Si and an simplex fuel nozzle — A nozzle with one spray orifice and
atomic number of 14. Used to produce N- and P-type one spray pattern.
semiconductor devices having excellent thermal
characteristics. 1. N-Type: Silicon doped with an impurity simplex nozzle — A fuel discharge nozzle for turbine
having five valence electrons. 2. P-Type: Silicon doped engines fed from a single fuel manifold.
with an impurity having three valence electrons. simplified directional facility (SDF) — A NAVAID used for
silicon carbide — An abrasive used in the manufacture of nonprecision instrument approaches. The final approach
grinding stones and abrasive papers. course is similar to that of an ILS localizer except that the
SDF course can be offset from the runway, generally not
silicon controlled rectifier (SCR) — A gated rectifier more than 3 degrees, and the course can be wider than the
that allows current to flow only during that portion of localizer, resulting in a lower degree of accuracy.
the cycle when the gate has been triggered by a positive
pulse. simulate — To have the characteristics or appearance of
something that is real.
silicon glaze — A shiny, brown, glass-like deposit on the
nose insulator of a spark plug resulting from use in sandy simulated flameout — A practice approach by a jet
or dusty conditions. This glaze is non-conductive at aircraft (normally military) at idle thrust to a runway.
low temperatures, but at high temperatures it becomes The approach can start at a runway (high key) and can
conductive and causes the plug to short. continue on a relatively high and wide downwind leg
with a high rate of descent and a continuous turn to final.
silicon solar cell — A semiconductor device that develops a It terminates in a landing or low approach. The purpose
voltage when struck by light. of this approach is to simulate a flameout.
silicon steel — A steel alloy that contains silicon. simulator — An enclosed housing that duplicates all of the
silicone rubber — An elastic material made from silicone controls, instruments, furnishings, and environment of
elastomers. Silicone rubber is used with fluids that attack an actual airplane cockpit. The simulated environment
other natural or synthetic rubbers. reproduces the same sensations and indications found in
actual flight.
silver — A white, precious, metallic chemical element
with a symbol of Ag and an atomic number of 47. Very simultaneous ILS approaches — An approach system
malleable and a good conductor of electricity. permitting simultaneous ILS/MLS approaches to airports
having parallel runways separated by at least 4,300 feet

285

10001930-002_AviationDictionary_2012_BOOK.indb 285 3/27/2012 9:38:27 AM

 simultaneous MLS approaches • single-servo brakes

between centerlines. Integral parts of a total system are single-crystal turbine blade — A high temperature strength
ILS/MLS, radar, communications, ATC procedures, and blade with no grain boundaries. It is manufactured by an
appropriate airborne equipment. advanced casting process that produces the blade from a
single crystal of metal.
simultaneous MLS approaches — See simultaneous ILS
approaches. single-cut file — A hand file with a single row of teeth
extending across the piece at an angle.
sine — A trigonometric function found in a 90° triangle. It
is defined as the ratio of the length of the side opposite an single-engine absolute ceiling — In multi engine aircraft,
angle to the length of the hypotenuse. the density altitude an airplane is capable of reaching and
maintaining with the critical engine feathered and the
sine curve — 1. A
other at maximum power. This assumes the airplane is at
graphic represen­tation
maximum weight and in the clean configuration, flying
of the relationship
in smooth air. This is also the density altitude at which
be­tween an angle
VXSE and VYSE are the same airspeed. If flying above this
and its sine. 2. The
altitude and the engine fails, the plane will inevitably
curve show­ing the
descend until it reaches the single-engine absolute ceiling.
relation­ship between
the voltage or current single-engine service ceiling — The maximum density
and the angle through which the related rotary generator altitude at which the single-engine best rate-of-climb
has turned. airspeed (VYSE) produces a 50 f.p.m. rate of climb. The
ability to climb 50 f.p.m. in calm air is necessary simply
sine wave — The wave form of alternating current
to maintain level flight for long periods in turbulent air.
produced by a rotary generator. Its amplitude at any time
This ceiling assumes the airplane is at maximum gross
is proportional to the sine of the angle through which the
weight in the clean configuration, the critical engine (if
generator has turned.
appropriate) is inoperative, and the propeller is feathered.
single direction routes — Preferred IFR Routes that are In comparison, the multi-engine service ceiling is the
sometimes depicted on high altitude enroute charts and density altitude at which the best rate-of-climb airspeed
which are normally flown in one direction only. (VY) will produce a 100 f.p.m. rate of climb at maximum
gross weight in the clean configuration.
single flare — A flare used
for aircraft rigid tubing single-face repair — A repair to a bonded structure in
with a flange at the end which the damage extends through one face sheet and
of the tube. When a single into the core material.
flare is folded back over
single-loop rib-stitching — A method of attaching fabric
itself, it is referred to as a
double flare. covering to the ribs of an aircraft using only one loop of
ribstitch cord per stitch.
single frequency approach — A service provided under
a letter of agreement to military single-piloted turbojet single-piloted aircraft — A military turbojet aircraft
aircraft that permits use of a single UHF frequency during possessing one set of flight controls, tandem cockpits,
approach for landing. Pilots will not normally be required or two sets of flight controls but operated by one pilot.
to change frequency from the beginning of the approach C-onsidered single-piloted by ATC when determining the
to touchdown except that pilots conducting an enroute appropriate air traffic service to be applied.
descent are required to change frequency when control is single-point fueling — A method of fueling the aircraft
transferred from the air route traffic control center to the from a single point. It consists of a pressure fueling hose
terminal facility. and a panel of controls and gauges that permit one person
single sideband — Radio communications in which one to load or unload any of the fuel tanks of an aircraft. The
of the two sidebands used in amplitude modulation is panel has valves connecting the various tanks to the main
suppressed. fueling manifold. Fuel flows to each tank until the tank
has reached the desired level. Also referred to as pressure
single spread — A method of applying adhesive to only one fueling.
surface of a bonded joint.
single-point grounding — A method of electrically
single-acting actuator — A linear hydraulic or pneumatic grounding a circuit by connecting all of the ground wires
actuator that uses fluid power for movement in one to a single point.
direction and a spring force for its return.
single-servo brakes — Brakes that use the momentum
single-axis autopilot — An automatic flight control device of the aircraft to wedge the lining against the drum and
that controls the airplane only around the roll axis. assist in braking when the aircraft is rolling forward.

286

10001930-002_AviationDictionary_2012_BOOK.indb 286 3/27/2012 9:38:27 AM

 single-sideband • slag

single-sideband — A radio transmission in which only one ski plane — An airplane whose wheels have been replaced
of the sidebands in a signal is used. with skis for operation in snow or ice.
single-spool compressor — An axial flow compressor with skid — In a skid, the rate of turn is too great for the angle of
a single rotating mass. bank, and the ball moves to the outside of the turn.
single-spool turbine engine — A jet engine that has only skid fin — A longitudinal vertical airfoil usually placed
one turbine section connected to the compressor section. above the upper wing of a biplane to increase its lateral
Twin-spool turbines have two sections of each, operating stability.
at different speeds.
skid shoes — Plates attached to the bottom of a helicopter
single-throw switch — In electricity, a switch that has two skid‑type landing gear to protect the skid.
positions, ON and OFF. Can have multiple poles to turn
skills and procedures — The procedural, psychomotor,
ON and OFF multiple circuits simultaneously.
and perceptual skills used to control a specific aircraft or
sintered material — A heated material that has become a its systems. They are the stick and rudder or airmanship
coherent mass without melting. Used as an alternative to abilities that are gained through conventional training,
casting for small parts. are perfected, and become almost automatic through
experience.
sintered metal — A porous material made by fusing
powdered metal under heat and pressure. skin — The smooth outer cover of an aircraft.
sinusoidal curve — In mathematics, a curve with angle skin antenna — An antenna that is flush with the aircraft
degrees along the horizontal axis and sines of the angles skin.
along the vertical axis. This curve generally illustrates
skin effect — The tendency of high frequency alternating
the varying output voltage values of an AC generator as
currents to flow in the outer portion of a conductor. Skin
it turns through 360º.
effect can be reduced by using stranded rather than solid
siphon — A device that moves liquid from one container wire.
to a lower point. It consists of a flex tube in the liquid
skin friction — Aerodynamic drag caused by air flowing
and a suction device to start the flow of liquid. Gravity
over the surface of the aircraft.
and atmospheric pressure on the surface of the liquid
carry the liquid from the container to a point below the skip distance — The distance from a transmitter to the
container. point where a reflected sky wave first reaches the Earth.
siphon tube — A tube installed in a CO2 fire extinguisher skip welding — A welding technique used to prevent
cylinder assuring that CO2 directed to the discharge warping of the material. Skip welding is a series of short
nozzle remains in its liquid state. welded beads evenly spaced to anchor the entire length
of the weld. The remaining gaps are filled in after the skip
sites — Internet addresses that provide information and
welds are tacked in.
often are linked to other similar sites.
skull-cap spinner — A round nosed cover for the hub of
Sitka spruce — A tall spruce tree that has needle‑shaped
a fixed-pitch propeller. Normally the same diameter as
leaves, drooping cones, and berry‑like fruit. In the
the hub, it is usually attached to a bracket secured by
selection of wood for aircraft repairs, spruce is considered
propeller mounting bolts.
the standard to which other woods are compared.
skunk works — Slang. A loosely structured corporate
situational awareness — The accurate perception and
research and development unit formed to foster
understanding of all the factors and conditions within the
innovation. Most famous was Lockheed Aircraft’s Skunk
four fundamental risk elements that affect safety before,
Works®, headed up for years by Kelly Johnson.
during, and after the flight.
sky wave — The portion of a radio wave reflected from the
sizing — Material used in the manufacture of some fabrics
ionosphere.
to stiffen the yarn for ease of weaving. Aircraft fabric
should not contain sizing. Skydrol hydraulic fluid — A synthetic, nonflammable,
ester‑base hydraulic fluid used in modern high‑temperature
sizing up a situation — A colloquial term used to denote
hydraulic systems.
the process of analyzing a situation and deciding what
should be done. slab — An unfinished bar of metal.
sketch — A simple drawing made without the use of slag — A completely fused and brittle by-product caused by
drafting instruments. It usually shows a minimum of the flux used in welding. Slag separates from the metal in
detail and lacks precision. the process of welding.

287

10001930-002_AviationDictionary_2012_BOOK.indb 287 3/27/2012 9:38:27 AM

 slam acceleration • slotted flap

slam acceleration — Improper operation of a turbine sling psychrometer — In weather, a device used to measure
engine when the power control lever is moved forward the relative humidity. It consists of two thermometers,
too rapidly. A rich flameout is possible because the fuel one of which has wetted cloth wrapped around its bulb.
is metered before the airflow has increased sufficiently. Both thermometers are swung on the end of a cord. Due
More sophisticated fuel controls in recent turbine engines to evaporation, the thermometer with the wetted cloth
have minimized this problem. will read a lower temperature than the dry thermometer.
A chart of the differences is consulted to determine the
slant range — In radar, the line-of-sight distance from relative humidity.
radar to target as opposed to ground distance (from radar
to the position on the ground below the target). Also the slinger ring — A tubular ring mounted around the hub of
line-of-sight distance from an aircraft to a navigation aid a propeller where deicing fluid is directed and slung out
on the ground as opposed to the ground distance (from a onto the blades.
point under the airplane to the navigation aid). slip — 1. Propeller: The difference between geometric and
slant visibility — In weather, the distance from an airborne effective pitch of a propeller. Slip can be expressed as
observer to the farthest point visible on the ground. a percentage of the mean geometric pitch or as a linear
dimension. 2. Aircraft flight maneuver: A sideways
slant‑line distance — See slant range. aircraft maneuver used to descend at a steep angle or
slash — A radar beacon reply displayed as an elongated compensate for crosswind. 3. In a slip the rate of turn is
target. too slow for the angle of bank and the ball moves to the
inside of the turn.
slat — A movable auxiliary airfoil on the leading edge of
a wing. It is closed in normal flight but extends at high slip clutch mechanism — A typical installation on electric
angles of attack. This allows air to continue flowing over starter drives designed to prevent sudden high torque
to the engine. The clutch plates slip until torque on the
the top of the wing and delays airflow separation.
engine side matches the torque on the clutch side.
slave relay — A relay that operates in response to the actions
slip joint — A connection or joint in an induction system
of a relay in a primary circuit (activates an associated
that remains airtight even as the cylinders expand and
circuit).
contract with the temperature changes.
slaved gyro — Directional gyro slaved to the output of a flux
slip ring — A smooth circular ring used to put field current
valve. Gives a directional gyro synchronous attributes.
into the armature of a DC alternator.
sleet — Small, transparent or translucent, round or
slip stick — A slang term to describe a slide rule.
irregularly shaped pellets of ice. They can be (1) hard
grains that rebound on striking a hard surface or (2) slippage mark — A painted mark between a tire and a
pellets of snow encased in ice. wheel that indicates slippage. If the mark of the tire and
wheel are not lined up, the tire has slipped on the wheel.
sleeve — A tube or tube-like part that fits over or around
another part. slip-roll former — A metal working machine used to shape
sheet metal into cylindrical and curved shapes.
slide rule — A ruler-like instrument with a center slide. Both
the inner slide and fixed outer sections are marked with slipstream — A stream of air pushed back by a revolving
logarithmic scales. Slide rules are used for mathematical aircraft propeller.
calculations; however electronic calculators or computers sloshing sealing compound — A synthetic rubber sealant
are more widely used. poured inside a metal fuel tank to seal the tank and
slide switch — In electricity, a switch that consists of a prevent fuel leakage. It is poured into the tank and then
slider that moves across contacts to make and break one sloshed around until all surfaces are covered.
or more circuits. slot — A fixed, nozzle‑shaped opening near the leading edge
slide valve — A mechanical valve that opens and closes by of a wing that ducts air onto the top surface of the wing.
sliding a gate across a port. Its purpose is to increase lift at higher angles of attack.

slide-wire rheostat or potentiometer — In electricity, a slot time — See meter fix time/slot time.
variable resistor that changes resistance by moving a slider slot-headed screw — A screw with a single, straight groove
along a length of resistance wire. The amount of resistance cut across its head to fit the blade of a slotted screwdriver.
is proportional to the effective length of the wire.
slotted flap — A trailing edge wing flap that forms a duct
sliding support — A duct support attached to flexible when the flap is lowered. Air forced through the duct is
bellows. The sliding support allows movement of the held down on the upper surface of the flap allowing more
bellows while the duct is under pressure. flap extension before airflow separation.

288

10001930-002_AviationDictionary_2012_BOOK.indb 288 3/27/2012 9:38:27 AM

 slotted nut • social needs

slotted nut — Similar to a castle nut. A hexagon nut that has snap ring — A small, spring‑loaded, ring-type fastening
grooves cut across its top to fit a cotter pin or safety wire device that fits into a groove either outside of a shaft or
passing through a hole in the shank of a bolt. inside of a hole. Spring tension holds the ring in place.
slow taxi — To taxi a float plane at low power or low RPM. snap roll — An abrupt airplane maneuver where the airplane
rotates rapidly about its longitudinal axis. The maneuver
slow-blow fuse — A begins by entering an accelerated stall with abrupt
fuse that can take elevator movement, then adding full aileron and rudder
momentary overloads control in the direction of desired snap. Neutralizing all
but opens the circuit three controls terminates the maneuver.
when excess current
flows are sustained. Often used in motor circuits where snap-action electrical switch — An electrical switch that
current is high until the motor begins to turn. uses spring snaps to open and close the contacts when
the switch is moved. Positive action minimizes arcing
sludge — A heavy, slimy deposit in aircraft lubricating oil problems caused by slow opening or closing of the circuit.
resulting from oxidation of the oil and contamination by
water. snips — Hand shears used for cutting sheet metal.

sludge chamber — Tubes or thin sheet metal chambers snow — Water vapor that changes directly into crystals of
installed in the throws of an aircraft engine crankshaft. ice flakes when frozen in the upper air.
Sludge is forced into these chambers by centrifugal force snow depth — The depth of the snow actually on the
and held there until engine overhaul. ground.
slug — A gravitational unit of mass. A force of one pound snow grains — Precipitation of very small, white opaque
creates an acceleration of one foot per second. grains of ice, similar in structure to snow crystals.
slugging — A malfunction in a vapor cycle air‑conditioning The grains are fairly flat or elongated, with diameters
system where liquid refrigerant enters the compressor. generally less than 0.04 inch (1 mm.).

small aircraft — Aircraft having a certificated gross weight snow pellets — Precipitation consisting of white, opaque
of less than 12,500 lbs. approximately round (sometimes conical) ice particles
having a snow-like structure, and about 0.08 to 0.2 inch
small-scale integration — In electronics, the most basic in diameter; crisp and easily crushed, differing in this
of integrated circuits, consisting of up to nine gates or respect from snow grains; rebound from a hard surface
transistors. and often break up.
smaze — A mixture of fog vapor, smoke, dust (haze), and snubber — The portion of a hydraulic actuator that arrests
industrial smoke, with a lower moisture content than the motion of a piston at the end of its stroke. A snubber
smog. helps cushion the stopping action.
smile — The curved dimple around the edge of a rivet head soaking — Holding a metal at a specified temperature and
caused by a rivet set not being held squarely against the time for the purpose of heat treating or annealing.
head while bucking the rivet.
soap — Material mixed with water and used for cleaning.
smog — A mixture of smoke and fog. Soap is produced by mixing alkali and potash with fat or oil.
smoke — In weather, small particles of carbon, the result of soap bubble test — A method of testing for leaks in gas
combustion, which cause restrictions to visibility. Not to systems under pressure. A special non‑flammable soap
be confused with smog, which is a combination of smoke solution is brushed over the suspected fittings. If there is
and haze or fog. a leak escaping gas causes the soap to bubble.
smoke detector — A system that can detect the presence soapstone — A soft stone having a soapy feeling and
of smoke in an unoccupied aircraft compartment before composed essentially of talc. Used to mark steel parts
high temperatures actuate the fire warning system. prior to welding.
smolder — To burn without a flame. soaring — Flying without the use of an engine. The pilot
smoothing filter — A filter consisting of capacitors or uses rising air to remain aloft and reduce the rate of
inductors, or both, that attenuates the AC component in aircraft descent.
the output of a rectifier circuit. social needs — A level of Maslow’s hierarchy of needs.
snake drill — A long, flexible driving mechanism, one end After physical and safety needs are met, it becomes
of which is designed to be put in a drill chuck and the possible for students to satisfy their social needs. The
other designed to hold a twist drill. need to belong and to associate, as well as to give and
receive friendship and love.

289

10001930-002_AviationDictionary_2012_BOOK.indb 289 3/27/2012 9:38:27 AM

 socket wrench • sonic frequencies

socket wrench — A small cylindrical shaped wrench internally solid conductor — A wire made up of a single strand of
broached to fit the nut. It is equipped with a square hole in metal covered with insulating material.
its top that fits a square drive on the wrench handle.
solid fuel — Fuel such as wood or coal or one of the molded
socket-head screw — A screw with a hex-shaped socket solid propellant materials used in rocket engines.
recessed into its head.
solid solution — A mixture where two or more elements
sodium — A silver‑white, metallic, alkaline chemical or compounds combine with each other at an elevated
element with a symbol of Na and an atomic number of 11. temperature and remain in a combined solid state when
rapidly cooled.
sodium bicarbonate — A white powdery crystalline
compound. When mixed with water sodium bicarbonate solidity ratio — In rotorcraft, the ratio of the total rotor
neutralizes spilled battery acid. Also referred to as baking blade area to total rotor disc area.
soda.
solid-state device — An electronic device that controls the
sodium-vapor lamp — A bulb that glows from the flow of electrons without any mechanical operations.
excitation of sodium vapor atoms by an electric arc. Also referred to as a semiconductor.
soft magnetic material — A metal such as iron that readily solo flight — Refers to one person piloting an aircraft in
accepts lines of magnetic flux and is easily demagnetized. flight with no passengers.
soft solder — A physical alloy of lead and tin used to join solstice — Noon the first day of summer and the first day of
non-structural metal parts or to increase the electrical winter, when the sun has reached its highest and lowest
conductivity of a twisted wire joint. latitudes, respectively.
soft-faced hammer — A hammer with a wood, plastic, or soluble — Any substance that can be combined with
rubber face on the head. another substance. An example of this is mixing water
and crystalline sugar to form sugar water.
software — The programs, procedures, and documentation
associated with a computer system. solution — 1. A state in which base metal and alloying
agents are united to form a single, solid metal. 2. A
solar cell — A silicon semiconductor device that converts
combination of a solid, liquid, or gaseous substance
solar energy into electricity.
homogeneously mixed with a liquid, gas, or solid.
solar declination — The latitude where the sun is directly
solution heat treatment — A heat treatment of aluminum
overhead.
alloy where metal is raised to its heat treating temperature,
solar elevation angle — The angle of the sun above the held until uniform throughout, and then quenched. This
horizon measured in degrees. process covers alloying agents held in solid solution,
which increases the strength of the metal.
solar-radiation — Electromagnetic radiation from the sun.
solvent — A liquid used for dissolving and cleaning
soldered splice — A splice in electrical wiring made by
materials.
twisting the wires together and then flowing soft solder
over the joint. This type of splice is not recommended for sonar — A system that detects objects in the water by
aircraft use because it tends to be brittle. sending out sound waves and receiving the echoes.
Operates similar to radar. The acronym for SOund
soldering iron — An electrically heated hand‑held tool
NAvigation Ranging.
used to melt solder.
sonic — Relating to the speed of sound. Subsonic is speed
solderless connection — A terminal attached to an electrical
below the speed of sound; transonic is speed bridging
conductor by crimping it onto the wire.
the speed of sound; and supersonic refers to speed
solderless splice — A tubular fastener used to connect two greater than the speed of sound. The speed of sound is
or more wires. The fastener is crimped onto the wires. approximately 761 miles per hour at sea level, 59ºF.
solenoid — A remotely activated electrical device. A coil of sonic boom — A vibrational disturbance, heard as a loud
wire with a movable core is activated by completing an noise, caused by an airplane moving faster than the speed
electrical circuit. The movable core can be used to open of sound.
or close another electrical circuit or to achieve some
sonic cleaning — A method of cleaning parts using high
other mechanical action.
intensity sound waves in a cleaning fluid.
solid — 1. A geometric figure that has three dimensions:
sonic frequencies — High frequency vibrational disturbances
length, width, and height. 2. One of the three states of
that the human ear can detect, normally considered to be
matter having definite volume and shape and being
the frequencies between 20 and 20,000 Hz.
relatively firm or hard.

290

10001930-002_AviationDictionary_2012_BOOK.indb 290 3/27/2012 9:38:27 AM

 sonic soldering • spatial disorientation

sonic soldering — A method of soldering certain metals span of an airfoil — The length of an airfoil measured from
such as aluminum that are difficult to solder because tip to tip.
they quickly build up surface oxides. The tip of a sonic
spanner — A wrench consisting of a hook‑shaped arm with
soldering iron heats the surface by vibrating it at a sonic
a pin in its hooked end. Used for turning a ring‑shaped nut.
rate while simultaneously penetrating any surface oxide..
spanner nut — A shaft-retaining nut tightened using the
sonic speed — The speed sound travels through a medium.
notches in its face rather than from its outer surfaces as is
sonic vibration — A high‑frequency vibration caused by done with a conventional hex‑nut.
sound energy.
spanwise — From wing tip to wing tip.
soot — A black residue created during oxyacetylene
spar — The main, or principle, spanwise structural member
welding when the burning acetylene gas does not have
of a wing or other airfoil.
enough oxygen to be completely consumed.
spar varnish — A phenolic modified oil that cures by
sound — A mechanical radiant energy transmitted by
oxidation rather than evaporation of its solvents. Produces
longitudinal pressure waves in the material medium. Its
a tough, highly water-resistant film.
frequency is perceived by the human ear.
spark — Very brief discharge of electrical energy between
sound suppressor — Same as noise suppressor in reference
two conductors separated by air or other gas.
to engines. Also, a device on a test cell that reduces the
sound of exhaust stack noises. spark coil — A step‑up transformer that produces high
voltage for spark plugs.
sound waves — Longitudinal wave motion through matter.
Longitudinal waves vibrate back and forth longitudinally spark plug — A component in an aircraft engine that
in the direction of wave propagation. converts high voltage electricity from the magneto into
a high intensity spark for igniting fuel in the combustion
sounding — 1. In meteorology, an upper-air observation; a
chamber of a reciprocating engine.
radiosonde or rawinsonde observation. 2. The electrode
of a field‑effect transistor similar to the emitter of an spark plug bushing — A bronze or steel insert in the
ordinary transistor. 3. In communication, the sender, cast‑aluminum cylinder head of a reciprocating engine
speaker, transmitter, or instructor who composes and into which the spark plug. is screwed.
transmits a message made up of symbols, which are
spark plug resistor — A composition resistor installed
meaningful to listeners and readers.
in the barrel of most shielded spark plugs. The resistor
south geographic pole — The pole located at the 90th limits the current stored by the capacitive effect of the
degree of south latitude. The south geographic pole of the shielding, minimizing the erosion of the spark plug
Earth is located at the southern end of the Earth’s axis. electrodes.
south pole of a magnet — The pole of a magnet where lines spark suppressor — A device inside a magneto, such as a
of flux enter the magnet. Lines of flux are considered to capacitor, that is placed across a set of contacts to keep
leave the magnet at the north pole. the spark from jumping across the contact points as they
open.
space charge — The electric charge carried by a cloud of
electrons in the space between electrodes of an electron spark test — A common means of identifying various
tube. ferrous metals. In this test, the piece of iron or steel is
held against a revolving grinding stone and the metal is
space shuttle — A reusable aerospace vehicle designed
identified by the sparks thrown off. Each ferrous metal
for carrying passengers and cargo into Earth’s orbit and
has its own peculiar spark characteristics. The spark
subsequently returning for landing.
streams vary from a few tiny shafts to a shower of sparks
spacers — Devices or components used to take up space several feet in length.
between two objects.
spark-ignition — A method of providing ignition of the
spaghetti — Insulating tubing slipped over wires. fuel‑air mixture inside the cylinder of a reciprocating
engine by an electric spark.
spalling — A bearing defect in which chips of the hardened
bearing surface are broken out. spatial disorientation — A feeling of balance instability
caused by a conflict between the information relayed by
span — 1. Length dimension of a beam. 2. In rotorcraft, the
central vision and peripheral vision, which has virtually
dimension of a rotor blade or airfoil from root to tip.
no references with which to establish orientation.
span loading — The ratio between the weight of an airplane
and the span of its wings.

291

10001930-002_AviationDictionary_2012_BOOK.indb 291 3/27/2012 9:38:27 AM

 spatula • specialized instructional services

spatula — A broad flat instrument used for spreading soft b. Controlled Firing Area – Airspace wherein activities
materials. are conducted under conditions so controlled as to
eliminate hazards to nonparticipating aircraft and
speak slower — Used in verbal communications as a
to ensure the safety of persons and property on the
request to reduce speech rate.
ground.
special activity airspace (SAA) — Any airspace with
c. Military Operations Area (MOA) – A MOA is airspace
defined dimensions within the National Airspace
established outside of Class A airspace area to separate
System wherein limitations can be imposed upon
or segregate certain nonhazardous military activities
aircraft operations. This airspace can be restricted areas,
from IFR traffic and to identify for VFR traffic where
prohibited areas, military operations areas, air ATC
these activities are conducted.
assigned airspace, and any other designated airspace
areas. The dimensions of this airspace are programmed d. Prohibited Area – Airspace designated under Part
into URET CCLD (User Request Evaluation Tool Core 73 within which no person may operate an aircraft
Capability Limited Deployment) and can be designated without the permission of the using agency.
as either active or inactive by screen entry. Aircraft
e. Restricted Area – Airspace designated under FAR
trajectories are constantly tested against the dimensions
Part 73, within which the flight of aircraft, while
of active areas and alerts issued to the applicable sectors
not wholly prohibited, is subject to restriction. Most
when violations are predicted.
restricted areas are designated joint use and IFR/
special aircraft and aircrew authorization required VFR operations in the area can be authorized by the
(SAAAR) — A method of FAA approval for instrument controlling ATC facility when it is not being utilized
flight porcedures that requires special aircraft equipment by the using agency. Restricted areas are depicted on
and/or crew training procedures. enroute charts. Where joint use is authorized, the name
of the ATC controlling facility is also shown.
special emergency — A condition of air piracy, or other
hostile act by a person(s) aboard an aircraft, which f. Warning Area – A warning area is airspace of defined
threatens the safety of the aircraft or its passengers. dimensions extending from 3 nautical miles outward
from the coast of the United States, that contains
special fastener — A fastener that differs in any respect
activity that can be hazardous to nonparticipating
from recognized standards.
aircraft. The purpose of such warning areas is to
special flight permit — A flight permit issued to an aircraft warn nonparticipating pilots of the potential danger.
that does not meet airworthiness requirements but is A warning area can be located over domestic or
capable of safe flight. A special flight permit can be issued international waters or both.
to move an aircraft for the purposes of maintenance
special VFR flight [ICAO] — A VFR flight cleared by
or repair, buyer delivery, manufacturer flight tests,
air traffic control to operate within Class B, C, D, and E
evacuation from danger, or customer demonstration.
surface areas in meteorological conditions below VMC.
Also referred to as a ferry permit.
special VFR operations — Aircraft operating in accordance
special instrument approach procedure — A procedure
with clearances within Class B, C, D, and E surface areas
approved by the FAA for individual operators, but not
in weather conditions less than the basic VFR weather
published in FAR 97 for public use.
minima. Such operations must be requested by the pilot
special use airspace — Airspace of defined dimensions and approved by ATC.
identified by an area on the surface of the Earth wherein
special VFR (SVFR) conditions — Weather conditions that
activities must be confined because of their nature and/
are less than basic VFR weather conditions, but permit
or wherein limitations can be imposed upon aircraft
flight under VFR within the lateral boundaries of the
operations that are not a part of those activities.
surface areas of Class B, C, D, or E airspace designated
Types of special use airspace are: for an airport. ATC authorization must be received.
a. Alert Area – Airspace that can contain a high volume specialized instructional services — Ground or flight
of pilot training activities or an unusual type of aerial instruction that is oriented to building knowledge and
activity, neither of which is hazardous to aircraft. skills in areas other than training pilots for specific
Alert Areas are depicted on aeronautical charts for the certificates or ratings. Some examples include flight
information of nonparticipating pilots. All activities reviews, instrument proficiency checks, and transition
within an Alert Area are conducted in accordance training. Others involve aircraft checkouts for tailwheel,
with Federal Aviation Regulations, and pilots of complex, high-performance, and high-altitude airplanes.
participating aircraft as well as pilots transiting the In addition, a flight instructor can help experienced
area are equally responsible for collision avoidance. military pilots transition to general aviation aircraft or
have an opportunity to provide instruction in homebuilt

292

10001930-002_AviationDictionary_2012_BOOK.indb 292 3/27/2012 9:38:27 AM

 specific fuel consumption • spindle

airplanes. Regional or local checkouts are additional speed of light — The speed at which light travels in a
areas where specialized instruction can benefit pilots and vacuum. 299,792.5 km/sec or 186,282 miles/sec.
increase safety.
speed of sound — The speed at which sound waves travel.
specific fuel consumption — Number of pounds of fuel At sea level, under standard atmospheric conditions,
consumed in one hour to produce 1 HP. sound travels 760 mph, 340 m/sec, or 1,116 ft./sec.
Referred to as Mach-one. Symbol M.
specific gravity — The ratio of the weight of a given
volume of a material to the same volume of pure water. speed segments — Portions of the arrival route between the
transition point and the vertex along the optimum flight
specific gravity adjustment — A fuel control adjustment
path for which speeds and altitudes are specified. There
that changes the fuel scheduling for use of fuels with
is one set of arrival speed segments adapted from each
differing specific gravities.
transition point to each vertex. Each set can contain up
specific heat — 1. The amount of heat required to raise to six segments.
the temperature of one gram of a substance one degree
speed sensitive switch — An automatic, flyweight‑operated
Celsius. 2. The ratio of the amount of heat required to
sequencing switch driven by the engine gearbox. Used for
raise the temperature of a body 1°, compared with the
completing electrical circuits for starting, ignition, fuel, etc.
amount of heat required to raise the temperature of an
equal mass of water 1°. speed to fly — In gliders, the optimum speed through the
(sinking or rising) air mass to achieve either the furthest
specific humidity — The percentage, by weight, of water
glide or fastest average cross-country speed depending
vapor in an air sample.
on the objectives during a flight.
specific thrust — A ratio of mass airflow and net thrust.
speeder spring — The control spring used in a centrifugal
One means of comparison between engines.
governor to establish a reference force opposed by the
specific weight — Density expressed in pounds per cubic centrifugal force of the spinning flyweights.
feet (lb./cu. ft.).
speed‑rated engine — A gas turbine with a rated thrust
specifications — Data concerning dimensions, weights, guaranteed to occur at a certain speed.
performance, locations, etc.
sphere — A geometric shape enclosed by a surface on
spectrometric oil analysis — A system of oil analysis in which all points are an equal distance from an enclosed
which a sample of oil is burned and the resulting light is point called the center.
examined for its wavelengths. This test can determine the
spherical — Having the form of a sphere.
amount of metals in the oil and can give warning of an
impending engine failure. spider — The portion of a propeller assembly used to
support propeller blades.
spectro-photometer — A special device used to determine
the way a surface reflects light waves of all frequencies. spike — A transient condition of increased voltage/current
It is used to analyze paint pigments. in an electrical circuit when the circuit is first closed.
speed — The act of moving swiftly, or the rate of movement. spillage — The movement of air from the bottom of the
wing to the top, outward and upward over the wing tip. It
speed adjustment — An ATC procedure used to request
is the cause of wing tip vortices.
pilots to adjust aircraft speed to a specific value for the
purpose of providing desired spacing. Pilots are expected spin — An aggravated stall that results in an airplane
to maintain a speed of plus or minus 10 knots or 0.02 descending in a helical, or corkscrew, path.
mach number of the specified speed.
spin certification — To be eligible for the flight
Examples of speed adjustments are: instructor-airplane or flight instructor-glider practical
test, an applicant must present a logbook endorsement
a. “Increase/reduce speed to mach point (number).”
from an appropriately certificated and rated flight
b. “Increase/reduce speed to (speed in knots)” or instructor certifying spin competency.
“Increase/reduce speed (number of knots) knots.”
spin training — When applying for an initial flight instructor
speed brakes — A control system that extends from the certificate, CFI students need to accomplish specific spin
airplane structure into the slipstream to produce drag and training in accordance with FAR Part 61.183.
slow the airplane.
spindle — The threaded part of a micrometer turned by the
speed handle — A crank‑shaped handle used to turn socket thimble that moves in and out of the frame.
wrenches more quickly.

293

10001930-002_AviationDictionary_2012_BOOK.indb 293 3/27/2012 9:38:28 AM

 spinner • sponson

spinner — The streamlined, bullet-shaped fairing that split needled — The position of the two hands on a
encloses a propeller hub assembly. A spinner streamlines helicopter’s engine/rotor tachometer. The two hands are
the propeller installation and contributes to engine cooling. not superimposed and the engine RPM and rotor RPM
spiral — A maneuver in which an airplane descends in a are unequal.
helix of small pitch and large radius, with the angle of split needles — A helicopter tachometer having two
attack within the normal range of flight angles. needles: one shows engine speed, the other shows rotor
spiral flutes — Twisted grooves that run from one end of system speed. When the clutch is fully engaged and the
an object to the other. The grooves on a twist drill are rotor is coupled to the engine, both needles show as one.
spiral flutes. When the needles are split, it indicates that the rotor
clutch is not fully engaged.
spirit level — A measuring tool used to determine the
relationship between a body and the horizon. The split spool compressor/turbine — Multiple-spool
measuring element is a curved glass tube filled with compressor/turbine. A turbine engine with two or more
liquid, but having a single bubble. The position of the separate spools (paired compressor and turbine) that
bubble in the tube is used to indicate the relationship. allows the engine to be more efficient and responsive to
varying power requirements.
spirit varnish — A wood finishing material made of resin
dissolved in solvent. The varnish forms a hard, resin film split steel lock washer — A heavy steel washer split and
on the wood when it dries. twisted to provide enough tension between the nut and the
surface of the material to prevent the nut from loosening.
splayed patch — A flush repair to a wood surface where
the edges of the patch are tapered, but the slope is steeper split-lock keys — Split, tapered,
than allowed in scarfing operations. cylindrical wedges used to lock
the valve spring retainers to the
splice — A process where two ends of a material are joined stem of a poppet valve in an
together. aircraft reciprocating engine.
splice connectors — Devices, such as insulated solderless split-phase induction motor
connectors, used for permanently connecting two ends of — An electric motor with an
electrical wiring. auxiliary winding that is out
splice knot — A knot used of phase with the main winding. The auxiliary winding
for joining two pieces helps to start rotate the motor and is disconnected when
of waxed rib-stitch the motor reaches operating speed.
cord. Unlike a square split-phase motor — An AC motor that utilizes an inductor
knot, a splice knot will not slip. or capacitor to shift the phase of the current in one of two
spline — Any of a series of uniformly spaced ridges on a field windings. This causes the resultant field to have a
shaft, parallel to its axis and fitting inside corresponding rotational effect.
grooves in the hub of a part. spoiler — Any device used to spoil lift by disrupting the
airflow over an aerodynamic surface.
splined shaft — A
shaft with a series of spoilers — Devices on the tops of wings to disturb (spoil)
grooves that meshes part of the airflow over the wing. The resulting decrease
with a drive unit in lift creates a higher sink rate and allows for a steeper
similarly configured so that the two units rotate as one, approach.
but are able to move laterally without interrupting the
spokeshave — A small woodworking tool with a blade
rotation.
mounted between two handles. The blade is drawn
split flaps — Wing flaps in which a portion of either the toward the operator and is used to round the edges of
underside or the trailing edge of the wing splits and folds sawn lumber.
downward to increase lift and drag.
spongy brakes — A brake malfunction caused by air in the
split lock washer — A heavy spring, steel lock washer split hydraulic fluid. Since air is compressible, the braking
at an angle across its face and twisted. Used with machine action will not have a positive feel. It will feel as though
screws or bolts where the self-locking or castellated‑type there were a sponge or spring between the brake and the
nut is not appropriate. The spring action of the washer brake pedal.
provides enough friction to prevent loosening of the nut
sponson — 1. A flange, or stub, projecting from the side
from vibration.
of a flying boat hull to increase the beam of the hull and
improve the lateral stability of the aircraft on the water.

294

10001930-002_AviationDictionary_2012_BOOK.indb 294 3/27/2012 9:38:28 AM

 spontaneous combustion • square knot

2. A projection from the side of the fuselage to support condition, spring steel is very hard, withstands high shear
auxiliary equipment such as weapons or cameras. and wear, and resists deformation. Used for making flat
springs and wire for coil springs.
spontaneous combustion — A condition that exists when
the temperature of a substance reaches its kindling spring tab — An auxiliary airfoil set into a control surface
temperature and self-ignites. No spark is required to start that, under conditions of high control forces, acts as a
the fire. servo‑tab providing an aerodynamic assist for the pilot.
spontaneous ignition — See spontaneous combustion. springback — The amount that metal springs back after it
has been bent to a specific angle. This must be allowed
spool — In an axial flow compressor, the spool shaped
for when making bends in sheet metal.
drum on which several stages of compressor blades are
mounted. spring-loaded — A condition where a spring holds one part
in a specific relationship with another. Spring loading
sport pilot — An FAA pilot certificate that allows operation
usually allows for some movement but returns the parts
of a light sport aircraft.
to their original relationship.
spot check — The random selection and inspection of
springwood — The light portion of wood that represents
manufactured products. The parts checked represent the
fast-growing wood from the spring of the year. Slower
quality of all the parts in that particular batch.
growing wood of the summer is darker. The two colors
spot facing — The process of using a rotary tool to remove create the rings seen in the cross section of a tree.
a small amount of surface material around a hole.
sprue — The filler hole in a mold. The resulting extension
spot welding — An electrical resistance welding where (the shape of the filler hole) of the part is also referred to
current is passed through sheets of metal stacked together. as the sprue.
When metal between the electrodes melts, it forms a
spur and pinion reduction gear system — A gear system
button of metal, joining the sheets.
used in reduction gearing. In a prop reduction gearing
spotlight — A strong beam of brilliant light used to system, the spur and pinion gears consist of a large
illuminate a particular area. driving gear, or sun gear, splined to the shaft. There is
also a large stationary gear, called a bell gear, and a set
spot-type fire detection system — Bi-metallic
of small spur planetary pinion gears mounted on a carrier
thermoswitches that close to initiate a fire warning
ring. When the engine is operating, the sun gear rotates.
signal any time the temperature in an area reaches a
Because the planetary gears are meshed with this ring,
predetermined value.
they rotate around the sun gear. The ring in which the
sprag clutch — A clutch joining two rotating shafts. The planetary gears are mounted rotates the prop shaft in the
clutch will ratchet and disengage when the driven shaft same direction as the crankshaft but at a reduced speed.
turns faster than the driving shaft.
spur gear — An external toothed gear.
sprag mount — An adjustable bracing system used on the
squall — A sudden increase in wind speed by at least 15
Bell 47 series helicopters.
knots to a peak of 20 knots or more and lasting for at
spray bar — An afterburner fuel nozzle that protrudes into least one minute. Essential difference between a gust and
the exhaust stream. a squall is the duration of the peak speed.
spray paint gun — An atomizing gun and reservoir device squall line — A line of thunderstorms often located along
that sprays liquid paint or finishing material onto a or ahead of a vigorous cold front. Squall lines can contain
surface being painted. severe thunderstorms. The term is also used to describe
a line of heavy precipitation with an abrupt wind shift
spray painting — A method of applying finish to a surface
but no thunderstorms, as sometimes occurs in association
using an atomizing gun and a reservoir filled with
with fronts.
properly thinned paint.
square — 1. A plane geometric shape having four equal
spray strip — Metal strips mounted on the side of a flying
sides with all four angles being right angles. 2. The
boat hull used to divert water away from the aircraft.
mathematical process of multiplying a number by itself.
spreader bar — A horizontal bar separating the floats of a
square engine — An engine whose bore and stroke are
twin‑float seaplane.
equal.
spring coupling — A spring loaded device in a gear drive
square file — A double-cut file with a square cross section,
train that protects a system from excessive shock loads.
tapered lengthwise. Used for filing slots for keyways.
spring steel — Steel containing carbon in percentages
square knot — A knot made up of opposite loops, each one
ranging from 0.50 to 1.05%. In the fully heat-treated
enclosing the parallel sides of the other.
295

10001930-002_AviationDictionary_2012_BOOK.indb 295 3/27/2012 9:38:28 AM

 square mil • stain

square mil — An area equivalent to a square having sides 1 St. Elmo’s Fire — A luminous brush discharge of electricity
mil (0.001 in.) in length. from protruding objects, such as masts and yardarms of
ships, aircraft, lightning rods, steeples, etc., occurring in
square root — The factor of a number that, when squared,
stormy weather.
will give the number. For example, the square root of 25
is ± 5. stabilator — A single-piece, horizontal tail component that
combines the functions of a stabilizer and an elevator.
square wave — The waveform of a multi-vibrator oscillator
where the leading edge and the trailing edge of the wave stability — 1. The property of a body that causes it,
are both vertical. when disturbed, to return to its original condition. 2.
In meteorology, a state of the atmosphere in which the
squaring shears — A large, floor‑mounted sheet metal tool
vertical distribution of temperature is such that a parcel
used to make square cuts across sheets of metal.
will resist displacement from its initial level.
squat switch — An electrical switch mounted on one of the
stabilizer — The fixed horizontal and vertical tail surfaces
landing gear struts. It is used to sense when the weight of
having the elevators and rudder hinged to the trailing edges.
the aircraft is on the wheels.
stabilizer bar — A dynamic component used on some Bell
squawk (mode, code, function) — Activate specific
helicopters to insure rotor stability.
modes/codes/functions on the aircraft transponder; e.g.,
“Squawk three/alpha, two one zero five, low.” See also stable operation — An operating condition where there
transponder. is no appreciable fluctuation in any of the operational
variables.
squealing brakes — A noise made by glazed brakes
chattering at such a high frequency that the sound stable oscillation — An oscillation whose amplitude does
resembles a squeal rather than a hammering. not increase.
squeegee — A long-handled rubber scraper blade used to stage — In turbine engine construction, a single turbine
remove liquid from a surface. wheel having a number of turbine blades.
squeeler tip — A tip of reduced thickness at the outer end stagger — The longitudinal relationship of the wings of a
of rotor blades. This section is designed to wear away biplane. If the upper wing is forward of the lower wing,
rather than damage the shroud ring if tip loading forces the airplane is said to have positive stagger.
cause contact.
stagger angle — Refers to blade twist design in an
squeeze bottle — A soft plastic bottle that, when squeezed, impulse‑reaction turbine blade.
forces the bottle contents out through its top.
staggered ignition — Dual ignition timed so that two firing
squeeze riveter — A pneumatic or hydraulic riveting gun in impulses do not occur at the same time.
which sets for both the manufactured head and the upset
staggered rings — A method of orienting the compression
head are mounted in the jaws of the large clamp. When
and oil control rings on a piston so that the gaps are
the squeeze-gun is actuated, the jaws come together just
not aligned with each other. This improves the overall
enough to form the proper size upset head. Also referred
compression of the engine.
to as a rivet squeezer.
staggered timing — A reciprocating engine ignition timing
squelch — A circuit in a communications receiver holding
method using a dual ignition system to provide spark
the output volume down until a signal is received.
plug firing at different points in the combustion cycle.
squelch circuit — See squelch.
staggerwires — The wire between the cabane struts of a
squib — A small electric device used to ignite a charge. biplane. These wires are used to adjust the stagger.
Found on aircraft where an action needs to be controlled
staging/queuing — The placement, integration, and
remotely, such as a fire extinguisher bottle in an engine
segregation of departure aircraft in designated movement
nacelle.
areas of an airport by departure fix, EDCT (expect
squirrel-cage induction motor — An induction motor departure clearance time), and/or restriction.
whose rotor resembles a squirrel cage.
stagnation point — The point on the leading edge of an
SRM (structural repair manual) — A manual developed airfoil where the airflow separates and results in some
by the manufacturer that covers all items not listed as going over the surface and some below.
minor maintenance, including instructions for structural
stain — An agent applied to wood to change the color
repair, major component removal, installation, and
and/or emphasize the grain. A protective finish such as
adjustment, setup, etc. Contains manufacturer-approved
varnish is usually applied over the stain.
data for major repairs and replacement.

296

10001930-002_AviationDictionary_2012_BOOK.indb 296 3/27/2012 9:38:28 AM

 stainless steel • standard terminal arrival route (STAR)

stainless steel — Steel, containing appreciable quantities standard atmospheric conditions — See standard
of chromium and nickel and used for applications where atmosphere.
resistance to corrosion is important.
standard barometric pressure — The weight of gases in
stake — Small, bench‑mounted, anvil-type sheet metal tool. the atmosphere sufficient to hold up a column of mercury
760 mm high (approximately 30”) at sea level (14.7 psi).
staking — A term used to denote the swaging of terminals
This pressure decreases with altitude.
onto an electrical conductor.
standard briefing — The most complete weather picture,
stall — Condition that occurs when the critical angle
tailored to your specific flight. Usually the briefing
of attack is reached and exceeded. Airflow begins to
includes adverse conditions, a weather synopsis,
separate from the top of the wing, leading to a loss of lift.
current weather, forecast weather, forecast winds and
A stall can occur at any pitch attitude or airspeed.
temperatures aloft, alternate routes, NOTAMs, ATC
stall strip — A spoiler attached to the inboard leading delays, and request for PIREPs.
edge of some wings causing the center section of the
standard cell — A cadmium‑mercury cell made in a specially
wing to stall before the tips. This assures aileron control
shaped glass container. The two electrodes are covered
throughout the stall.
with an electrolyte of cadmium sulfate. Voltage produced
stall warning transmitter — A device that produces a by a standard cell is 1.018636 volts at 20°C. Also referred
signal to warn the pilot of an impending stall. to as a Weston standard or a Weston normal cell.
stalled torque — The amount of rotative force provided standard day — Sea level, dry air, 59º F (15º C), no wind,
by a motor when properly powered with the rotor held 40º North or South latitude.
stationary.
standard fastener — A fastener that conforms in all
stalling angle — The angle of attack at which point the respects to recognized standards.
smooth flow of air over the wing ceases.
standard instrument approach procedure — See
stall/spin awareness — Stall/spin awareness training instrument approach procedure.
is designed to instill a trigger or early warning in the
standard instrument departure (SID) — A preplanned
mind of a pilot, which causes the proper reaction to
instrument flight rule (IFR) air traffic control departure
potential stall/spin situations in an immediate, positive
procedure printed for pilot use in graphic and/or textual
way. This training is required by the FAR’s. Many stall/
from. SIDs provide transition from the terminal to the
spin accidents occur as a result of pilot distraction while
appropriate enroute structure.
maneuvering close to the ground.
standard lapse rate — For 1,000 feet of altitude in the lower
stall-warning system — A system that warns the operator
atmosphere (below 36,000 feet), the standard pressure
when the aircraft is approaching the critical stall angle.
lapse rate is 1.00 in. Hg., and the standard temperature
stand by — Means the controller or pilot must pause for a lapse rate is 2°C (3.5°F).
few seconds, usually to attend to other duties of a higher
standard rate turn — A turn of three degrees per second.
priority. Also means to wait as in “stand by for clearance.”
The caller should reestablish contact if a delay is lengthy. standard sea level pressure — A standard value of
“Stand by” is not an approval or denial. pressure used as a reference for making aerodynamic
computations. It is 14.7 lb./sq. in., 29.92 inches of
standard — The test of quality required for a particular
mercury, or 1013.2 millibars.
purpose.
standard sea level temperature — A surface temperature
standard altimeter setting — Altimeter set to the standard
of 59°F or 15°C. See also standard atmosphere.
pressure of 29.92 in. Hg, or 1013.2 Mb.
standard temperature — 15º C (59º F).
standard atmosphere — At sea level, the standard
atmosphere consists of a barometric pressure of 29.92 standard terminal arrival — A preplanned instrument
inches of mercury (in. Hg.) or 1013.2 millibars, and a flight rule (IFR) air traffic control arrival procedure
temperature of 15°C (59°F). Pressure and temperature published for pilot use in graphic and/or textual form.
normally decrease as altitude increases. The standard STARs provide transition from the enroute structure to an
lapse rate in the lower atmosphere for each 1,000 feet of outer fix or an instrument approach fix/arrival waypoint
altitude is approximately 1 in. Hg. and 2°C (3.5°F). For in the terminal area.
example, the standard pressure and temperature at 3,000
standard terminal arrival route (STAR) — A preplanned
feet mean sea level (MSL) is 26.92 in. Hg. (29.92 - 3) and
instrument flight rule (IFR) air traffic control arrival
9°C (15°C - 6°C).
procedure published for pilot use in graphic and/or
textual form. STARs provide transition from the enroute

297

10001930-002_AviationDictionary_2012_BOOK.indb 297 3/27/2012 9:38:28 AM

 standard terminal arrival (STAR) charts • static flux

structure to an outer fix or an instrument approach fix/ starting torque — The amount of rotating force a motor
arrival waypoint in the terminal area. develops during start. Series-wound motors develop high
starting torque while shunt- (parallel) wound motors
standard terminal arrival (STAR) charts — Charts
develop very low starting torque.
designed to expedite air traffic control arrival procedures
and to facilitate transition between enroute and instrument starved area — In composites, an area in a plastic part
approach operations. Each STAR procedure is presented that has an insufficient amount of resin to wet out the
as a separate chart and can serve a single airport or more reinforcement completely.
than one airport in a given geographical location.
starved joint — In composites, an adhesive joint that has
standard-frequency signal — The National Institute been deprived of the proper film thickness of adhesive due
of Standards and Technology (NIST) broadcasts time to insufficient adhesive spreading or to the application of
and frequency information via WWV in Fort Collins, excessive pressure during the lamination process.
Colorado. The information is broadcast on frequencies of
statcoulomb — The amount of charge on each of two bodies
2.5, 5, 10, 15, and 20 MHz.
1 cm apart that causes them to exert a force of 1 dyne on
standard-rate turn — A rate of change in aircraft direction each other. The statcoulomb is the charge resulting from
of 3° per second, completing a 360° turn in two minutes. the addition of approximately 2 x 109 electrons to a body.
Higher speed jet aircraft use a half-standard-rate turn of
state aircraft — Aircraft used in military, customs and
1½ º per second, completing a 360° turn in four minutes.
police service, in the exclusive service of any government,
standing waves — Stationary waves occurring on an or of any political subdivision, thereof including the
antenna or transmission line as a result of two waves, government of any state, territory, or possession of
identical in amplitude and frequency, traveling in the United States or the District of Columbia, but not
opposite directions along the conductor. including any government-owned aircraft engaged in
carrying persons or property for commercial purposes.
standpipe — A vertical standing pipe in a tank or reservoir.
It allows a space for a reserve of fluid between the top of state of charge — A measurement of the percent of charge
the standpipe and the bottom of the tank. Reserve fluid is condition of a battery. For lead-acid batteries, the state of
drawn from the bottom of the tank. charge is measured by determining the specific gravity of
the electrolyte. The state of charge of a nickel-cadmium
staple — 1. Wire: A u-shaped piece of fine wire with
battery can only be determined by a measured discharge.
sharp‑pointed ends, driven into a surface to hold or fasten
material to it. 2. Textile material: The average length of statement of demonstrated ability (SODA) — The official
textile material. Cotton fibers. 3. A chief item: Any chief term for a waiver. This is a form that can be issued in
item, part, or element of a raw material. conjunction with a student’s medical exam. SODAs can
only be issued by the FAA’s federal air surgeon and are
stapler — A machine or tool used for driving staples
granted for a condition normally requiring a denial that is
through a piece of wood or stack of paper for the purpose
not necessarily a safety factor.
of binding them together.
static — 1. Still. Not moving. A condition of rest. 2. The
starboard side — The right-hand side of an aircraft or ship
noise produced in a radio or television receiver by
as viewed from aboard the craft and facing the front of
atmospheric or man-made electrical disturbances.
the craft.
static balance — 1. A condition of balance that does not
start end of runway (SER) — The beginning of the takeoff
involve any dynamic forces. 2. When a body stands in
runway available.
any position as the result of counterbalancing and/or
start winding — An auxiliary winding that is out of phase reducing heavy portions, it is said to be in standing or
with the main winding. The auxiliary winding helps to static balance.
start rotate the motor and is disconnected when the motor
static charge — The electrical charge that builds up on a
reaches operating speed.
nonconductive surface by friction. Friction between the
starter — A unit that uses electrical, pneumatic, or hydraulic airframe and the air creates a static charge.
energy to rotate an engine for starting.
static discharger — A device used to dissipate static
starter solenoid — An electrically operated switch that electricity from a control surface before it builds up to a
uses a small current controlled from the cockpit to close highly charged state.
the high current‑carrying contacts in the starter circuit.
static electricity — An electrical charge that can be built up
starter-generator — A combined unit used on turbine on a nonconductive surface by friction.
engines The device acts as a starter for rotating the
static flux — Concentration of lines of flux in the frame
engine, and after running, internal circuits are shifted to
of a magneto due to the rotation of the magnet. At full
convert the device into a generator.
298

10001930-002_AviationDictionary_2012_BOOK.indb 298 3/27/2012 9:38:28 AM

 static friction • stay

register, lines of flux are at maximum, while at neutral static thrust — The thrust produced by a turbine engine not
positions, lines of flux are at minimum. moving through the air.
static friction — The friction on an object when an attempt static tube — A cylindrical tube with a closed end and a
is made to slide the object along a surface. Once in number of small openings normal to the axis, pointed
motion the object slides more easily. upstream, and used to measure static pressure.
static instability — The characteristic of an aircraft that, static wick — A small device made of metal braid or
when disturbed from a condition of rest, tends to move it graphite‑impregnated cotton attached to the trailing edge
further from its original condition. of a control surface to dissipate accumulated electrical
charges into the air.
static interference — The noise in a radio caused by static
electricity moving between two structures having no station — The location of a point within an aircraft identified
common ground. by distance in inches from the datum.
static port — A small hole, flush with the side of the aircraft, station “0”(zero) — The reference point from which
through which static pressure is taken to operate the fuselage stations are measured. On some aircraft the
airspeed indicator, altimeter, and vertical speed indicator. point might be the firewall or the leading edge of the
wing. Stations in front of this would have negative
static pressure — Atmospheric pressure measured at a
station numbers and those aft would have positive station
point where there is no external disturbance and the flow
numbers. Station zero is sometimes placed at a point in
of air over the surface is smooth.
space in front of the aircraft so that all station numbers
static pressure pickup — A part of the static instrument are positive.
system. The location on the surface of an aircraft where
station declination — The orientation with respect to
static air pressure is picked up from port holes or static
true north of VHF transmitted signals. The orientation
ports. This data is supplied to the altimeter, airspeed
is originally made to agree with the magnetic variation
indicator, and vertical speed indicator.
(an uncontrollable global phenomenon) at the site.
static radial engine — An engine with cylinders radiating Hence station declination (fixed by man) may differ from
out from a small central crankcase. A single‑throw changed magnetic variation until the station is reoriented.
crankshaft is used for each row of cylinders. Most
station pressure — The actual atmosphere pressure at the
single‑row radial engines have an odd number of
observing station.
cylinders, but two or more rows can be used if more
power is required. station web — A built‑up section located at some point of
applied force, such as attachments for wings, stabilizer, etc.
static restrictions — Those restrictions that are usually not
subject to change, fixed, in place, and/or published. stationary front — Same as quasi‑stationary front.
static RPM — The maximum RPM a reciprocating engine stationary reservations — Altitude reservations that
can produce when the aircraft is not moving through the encompass activities in a fixed area. Stationary
air. The static RPM is lower than the RPM the engine reservations can include activities, such as special tests
develops while airborne because forward movement of weapons systems or equipment, certain U.S. Navy
rams additional air pressure into the carburetor inlet. carrier, fleet, and anti-submarine operations, rocket,
missile and drone operations, and certain aerial refueling
static stability — The initial tendency to return to a state of
or similar operations.
equilibrium when disturbed from that state.
stator — 1. The stationary part of an electrical machine
static stop — In rotorcraft, a device used to limit the blade
such as a motor or alternator. 2. The stationary portion
flap, or rotor flap, at low r.p.m. or when the rotor is
of an axial flow turbojet compressor. 3. The discs in a
stopped.
multiple‑disc brake that are keyed to the axle and do not
static system — Plumbing that connects the altimeter, rotate.
airspeed indicator, and vertical speed indicator to the
stator case — The outer engine casing that houses either
outside static air source of the airplane. An alternate
compressor or turbine stator vanes.
source is usually included in this system.
stator vane — Stationary vane, either compressor or
static temperature — A temperature measurement of air
turbine.
not in motion.
statute mile — A measure of land distance equal to 5280
static test — A method of testing the structural integrity of
ft. or 1.609 km.
an airplane to determine its ability to withstand loads that
could possibly be encountered in flight. stay — A cable or wire, loaded in tension only, used as a
structural member in a truss.

299

10001930-002_AviationDictionary_2012_BOOK.indb 299 3/27/2012 9:38:28 AM

 steady-state condition • stop altitude squawk

steady-state condition — The condition of any system that stepped solvents — Solvents in a finish that have different
exists when all of the measured values are stable. rates of evaporation. Some evaporate almost instantly,
while others evaporate slowly. This variance provides
steady-state flight — A condition when a rotorcraft is in
the desired film.
straight-and-level, unaccelerated flight, and all forces are
in balance. stepped stud — A stud replacement for one that has been
stripped out. The hole is drilled and tapped for a larger
steam — An invisible vapor created when water is heated
stepped stud.
to the boiling point
stepping relay — A rotary electrical switch that switches
steam fog — Sea smoke, evaporation fog.
from one set of contacts to another whenever its solenoid
steatite — The massive form of talc. Used for making receives a pulse.
ceramic insulating material for high‑voltage systems.
step-up transformer — A device that steps up voltages
steel — A hard and tough carbon-iron alloy. and is made with an iron core, a primary winding, and
a secondary winding. The step‑up transformer has less
steel wool — An abrasive material made of long, fine, steel
turns of wire in the primary winding than the secondary
shavings and used for scouring steel parts.
winding. This difference, depending on the turns‑ratio,
steering damper — A hydraulically actuated device used determines the step‑up of the secondary voltage.
to absorb shimmy vibrations from the nose wheel of an
stereo route — A routinely used route of flight established
aircraft.
by users and ARTCCs identified by a coded name; e.g.,
stellite — An extremely hard, wear-resistant metal used ALPHA 2. These routes minimize flight plan handling
for valve faces and stem tips. Contains cobalt, tungsten, and communications.
chromium, and molybdenum.
sterile cockpit — A crew resource management concept
stem — The part of a multiple-choice test item consisting of that specifically prohibits crewmember performance
the question, statement, or problem. of nonessential duties or activities while the aircraft is
involved in taxi, takeoff, landing, and all other flight
step — A break in the form of the bottom of a float or
operations conducted below 10,000 feet MSL, except for
hull. Designed to diminish resistance, lessen the suction
cruise flight.
effects, and improve longitudinal control.
stiffener — A structural member attached to an aircraft skin
step leader — The first of a series of events that make
for the purpose of making it stiffer. It is quite often an
up lightning. Nearly invisible to the eye, it is the path
extruded angle or a formed hat-shaped section.
that carries electrons from the base of the clouds to the
ground, creating an ionized channel for the subsequent stiffness — The relationship of load and deformation. The
discharge. ratio between the applied stress and resulting strain.
step taxi — To taxi a float plane at full power or high RPM stimulants — Drugs that excite the central nervous system
in order to obtain a speed that causes the plane to rise up and produce an increase in alertness and activity
on the planing portion of the floats.
Stoddard solvent — A petroleum product similar to
step turn — A maneuver used to put a float plane in a naphtha used as a solvent or cleaning agent.
planing configuration prior to entering an active sea lane
stoichiometric — A chemical relationship in which all of
for takeoff. The STEP TURN maneuver should only be
the constituents are used in the reaction. In the case of a
used upon pilot request.
stoichiometric mixture, all of the oxygen and hydrocarbon
step up coil — A transformer where a secondary winding fuel are used.
has more turns than the primary. The voltage in the
STOL aircraft — An aircraft that can perform short takeoff
secondary winding will be stepped up.
and landing procedures.
stepdown fix — A fix permitting additional descent within
stop — A device used to limit the throw or travel of a
a segment of an instrument approach procedure by
control.
identifying a point at which a controlling obstacle has
been safely overflown. stop altitude squawk — Used by ATC to inform an aircraft
to turn-off the automatic altitude reporting feature of
step-down transformer — A device that steps down
its transponder. It is issued when the verbally reported
voltages and is made with an iron core, a primary winding,
altitude varies 300 feet or more from the automatic
and a secondary winding. The step‑down transformer
altitude report.
has more turns of wire in the primary winding than
the secondary winding. This difference determines the
stepped down secondary voltage.

300

10001930-002_AviationDictionary_2012_BOOK.indb 300 3/27/2012 9:38:28 AM

 stop and go • strainer

stop and go — A procedure wherein an aircraft will land, straight roller bearings — Roller bearings used where the
make a complete stop on the runway, and then commence bearing is subjected to radial loads only.
a takeoff from that point.
straight shank drill — A twist drill with a straight shank,
stop burst — Used by ATC to request a pilot to suspend distinguishable from a twist drill with a tapered shank.
electronic countermeasure activity.
straightedge — Wood, metal, or plastic having a perfectly
stop buzzer — Used by ATC to request a pilot to suspend straight edge used in drawing straight lines, or to check
electronic countermeasure activity. for the straightness of a piece of material.
stop countersink — A countersink with a collar that doesn’t straight-in approach-IFR — An instrument approach
allow the cutter to cut too deeply into the metal skin. wherein final approach is begun without first having
executed a procedure turn, not necessarily completed
stop drill — A hole drilled in the end of a crack in aircraft
with a straight-in landing or made to straight-in landing
structural material to distribute stresses and stop the
minimums.
crack from proceeding further.
straight-in approach-VFR — Entry into the traffic pattern
stop nut — A nut used to prevent another nut from backing
by interception of the extended runway centerline (final
off due to vibrations. A stop nut is either a self-locking
approach course) without executing any other portion of
nut or a nut that can be torqued against the primary nut
the traffic pattern.
while the primary nut is being held in place.
straight-in landing — A landing made on a runway
stop squawk (mode or code) — Used by ATC to tell the pilot
aligned within 30° of the final approach course following
to turn specified functions of the aircraft transponder off.
completion of an instrument approach.
stop stream — Used by ATC to request a pilot to suspend
straight-in landing minimums — A statement of MDA and
electronic countermeasure activity.
visibility, or DH and visibility, required for straight-in
stopover flight plan — A flight plan format that permits landing on a specified runway.
in a single submission the filing of a sequence of flight
straight-in minimums — See straight-in landing
plans through interim full-stop destinations to a final
minimums.
destination.
straight-polarity arc welding — Electric arc welding
stopway — An area beyond the takeoff runway, no less
where the electrode is connected to the negative terminal
wide than the runway and centered upon the extended
of the power supply.
centerline of the runway, able to support the airplane
during an aborted takeoff, without causing structural straight-run gasoline — Gasoline that is refined from crude
damage to the airplane, and designated by the airport oil using the fractional distillation process to produce
authorities for use in decelerating the airplane during an straight‑run gasoline. In this method, the crude oil is
aborted takeoff. heated at atmospheric pressure in a heating container. The
various hydrocarbon liquids in the crude oil vaporize first,
storage battery — A secondary cell. An electrical device followed by those of higher boiling points. Straight-run
in which electrical energy is converted into chemical gasoline has an octane rating of approximately 70.
energy and stored. When needed it is converted back into
electrical energy. strain — 1. Deformation in a material caused by stress.
2. The process of exerting a force beyond the normal
storage life — In composites, the period of time during physical capacity of the material.
which a liquid resin, packaged adhesive, or pre-preg can
be stored under specified temperature conditions and strain gauge — An extremely tiny conductor bonded to the
remain suitable for use. The storage life should be printed surface of a component on which strain is to be measured.
on the label. Also referred to as shelf life. When the surface stretches the cross section of the strain
gauge becomes smaller and its resistance increases. The
storm detection radar — A radar optimized to show strain gauge is extremely sensitive and measures the
returns of precipitation rather than clouds as in a normal change.
weather radar.
strain hardening — The increase in strength and hardness
straight mineral oil — Oil, such as petroleum, derived of a metal by work hardening or cold working. Strain
from a mineral source as opposed to oils derived from hardening is normally done after a piece of material
plants and animals. Straight mineral oil would have no has been heat treated. If an aluminum alloy is not
additives. Often used during break-in of an engine. heat-treatable, strain hardening is the only way it can be
straight peen hammer — A metal beading hammer with hardened.
one flat face and one face with a vertical edge. strainer — A very fine mesh screen located in the fuel
system and used to remove impurities.

301

10001930-002_AviationDictionary_2012_BOOK.indb 301 3/27/2012 9:38:29 AM

 strand • structural icing

strand — Normally, an untwisted bundle or assembly of stress crack — In composites, external or internal cracks
continuous filaments used as a unit. Sometimes a single in a plastic caused by tensile stresses less than that of its
fiber or filament is referred to as a strand. short-time mechanical strength. The stresses that cause
cracking can be present internally or externally or can be
stranded conductor — An electrical conductor made up of
combinations of these stresses.
many strands of wire covered with an insulating material.
stress management — Personal analysis of stress being
stranded wire — Electrical wire made up of many smaller
wire strands. experienced and the application of appropriate coping
mechanisms.
strap pack — A tension-torsion system using sheet steel
lamination to carry the loads of the rotor blades to the stress relieve — A general term describing the process of
head. Used by Hughes Helicopters. relieving internal stresses within metals by controlled
heating and cooling. Annealing and normalizing are
strategic planning — Planning whereby solutions are more specific terms for this process.
sought to resolve potential conflicts.
stress riser — A location on a part that due to shape, or
stratification — Formed in layers. due to a defect, is more prone to failure as the result of
stratiform — Descriptive of clouds of extensive horizontal stress than the rest of the part. This could be due to a
development, as contrasted to vertically developed drastic change in cross-section or where the part has been
cumuliform clouds; characteristic of stable air. gouged or scratched. Stresses become concentrated at
such locations.
stratiform clouds — Clouds formed in layers.
stressed-skin structure — Aircraft skin designed to
stratocumulus — Stratified cumulus consisting of low gray carry the tension and compression stresses of structural
clouds, which are formed in layers, and that often cover loads. Stressed-skin structured aircraft have few internal
the whole sky especially in winter. structural members.
stratopause — The top stratosphere, approximately stretching — A sheet metal forming operation in which
160,000 feet MSL. the material is mechanically stretched over dies to form
stratosphere — The first layer above the troposphere compound curves.
extending to a height of approximately 160,000 feet, with stringer — A thin metal or wood strip running the length of
a composition much like the troposphere. the fuselage to fill in the shape of the formers.
stratus — Low gray uniform clouds that generally extend stroboscope — A device that can be adjusted to flash at
over a large area at altitudes of 2000 to 7000 feet (600 to specific rates. It can be used to “freeze” the apparent
2100 meters).
motion of propellers, pulleys, belts, rotors, etc., in order
streamline flow — A fluid flow without turbulence. All to inspect the action as if it is stopped.
lines of flow are in straight lines.
stroboscope tachometer — A variation of a stroboscope.
streamlined — Having a shape or contour that presents The stroboscope tachometer is shown on a rotating
a minimum resistance to the air with a minimum of unit and adjusted until apparent rotation is stopped.
turbulence. The sequenced flashing rate of the scope is then read to
determine the RPM of the unit being observed.
strength — The ability of a material to withstand forces
that attempt to deform it. The ability of a material to stroke — In a reciprocating engine, the distance a piston
resist stress without breaking. travels from bottom dead center (BDC) to top dead center
(TDC). Stroke is two times the crankshaft throw.
strength‑to‑weight ratio — The ratio of a material’s
strength to its weight. structural adhesive — In composites, adhesive used for
transferring required loads between two cured parts. An
stress — The internal resistance or change in shape or size
adhesive can also be used to bond metal to a composite
expressed in force per unit area. A stress concentration
structure.
is an area where the level of an applied stress causes a
notch, void, hole, or inclusion. structural bond — A bond that joins basic load-bearing
stress analysis — A mathematical determination of the loads parts of an assembly. The load can be either static or
experienced by a structure under specific circumstances. dynamic.

stress corrosion — Intergranular corrosion that forms structural failure — When a structure fails to withstand
within metals subject to tensile stresses and in a corrosive the stresses imposed upon it.
environment. Exposure to such an environment alone structural icing — The formation of ice on the exterior or
would not have caused corrosion. Tends to separate the structure of an aircraft.
grain boundaries.
302

10001930-002_AviationDictionary_2012_BOOK.indb 302 3/27/2012 9:38:29 AM

 structural machine screws • suction

structural machine screws — Machine screws having an subrogate — A legal term, which means to pursue action
unthreaded portion of the shank and made of high‑strength against a third party determined to be responsible for an
alloy steel. Used in place of an aircraft bolt to carry shear accident, and attempt to recover damages from them over
loads and some tensile loads. the amount of the deductible.
structural member — Any part of an aircraft structure subsidence — A slow descending motion of air in the
designed to carry loads or stress. atmosphere over a rather broad area; usually associated
with divergence and stable air.
structural steel — An alloy steel used for parts of an
aircraft subjected to high structural loads. subsonic flight — Flight when the air flowing over the
aircraft structure is moving slower than the speed of
strut — 1. A compression member in a truss. 2. The external
sound.
bracing on a non-cantilever airplane. 3. The stub wing
assembly through which thrust loads are transmitted subsonic inlet — A divergent-shaped duct that acts as a
from a pod-mounted turbine engine into the fuselage. subsonic diffuser.
strux — In composites, a foam like material used to form subsonic speed — Speed below the speed of sound.
structural sections for stiffening.
subsonic-diffuser — A divergent diffuser where the
stub antenna — A short, UHF, quarter‑wavelength antenna airstream spreads out to increase pressure as axial
normally used for radar beacon transponders or distance velocity decreases.
measuring equipment.
substandard — Unacceptable quality in a manufactured
stud — A headless bolt object.
that has threads on
substitute — The replacement of an object with the same
each end. One end
or better quality material and which meets all of the
often has coarse
specifications of the original.
threads for screwing into a casting, while the other end
has fine threads to accept a nut. substitute route — A route assigned to pilots when any part
of an airway or route is unusable because of NAVAID
stuffing box — A box through which a rotating shaft passes.
status. These routes consist of:
It is packed with a material that inhibits leakage around
the shaft. a. Substitute routes shown on U.S. Government charts
[and published in the Jeppesen Chart NOTAMs
styrene — A liquid hydrocarbon used in the manufacture
(Enroute)].
of certain synthetic resins to improve their workability.
Also, any of various synthetic plastics made from styrene b. Routes defined by ATC as specific NAVAID radials or
by polymerization or copolymerization. courses.
Styrofoam — A rigid polymer of styrene plastic material. c. Routes defined by ATC as direct to or between
NAVAIDs.
subassembly — An assembly that is a component of a
larger assembly. substitutions — Users are permitted to exchange CTA’s
(controlled time of arrival). Normally, the airline
subfreezing temperature — Below freezing. Any
dispatcher will contact the ATCSCC with this request.
temperature below the freezing point of water, which is
The ATCSCC shall forward approved substitutions to
32 º F or 0 º C.
the TMU’s who will notify the appropriate terminals.
subject matter knowledge codes — The subject matter Permissible swapping must not change the traffic load
knowledge codes establish the specific reference for the for any given hour of an EQF Program.
knowledge standards on FAA knowledge examinations.
substrate — The supporting material on which an integrated
These codes are associated with each FAA knowledge
circuit chip is built.
question and are referred to in the results returned to the
examinee after an examination. subsystem — An operating unit or assembly that is a
component of a larger system.
sublimation — Process by which a solid is changed to a gas
without going through the liquid state. Such as, from ice subtropical jet stream — One of two jet streams commonly
to water vapor. associated with the westerlies. Located near 25 to 30º
latitude, it reaches its greatest strength in the wintertime
submerged-arc welding — A method of electric arc
and is nonexistent in the summer.
welding in which a bare rod, covered with granulated
flux, is used as an electrode. The granulated flux melts suction — The act of producing negative pressure.
in the arc and flows ahead of the weld to prevent the
formation of oxides in the bead.

303

10001930-002_AviationDictionary_2012_BOOK.indb 303 3/27/2012 9:38:29 AM

 suction cup gun • superheterodyne

suction cup gun — A paint gun in which material held in a superadiabatic lapse rate — A lapse rate greater than the
cup is attached to the gun and drawn into the air by suction. dry adiabatic lapse rate.
suction gauge — An aircraft instrument used to measure supercell thunderstorm — A severe thunderstorm that
negative pressure or suction in an aircraft vacuum system. almost always produces one or more of the extremes of
convective weather: Very strong horizontal wind gusts,
suction relief valve — A control valve in an instrument
large hail, and/or tornadoes. The supercell can occur
pneumatic system that provides a constant negative
anywhere in the mid-latitudes, but by far the favored
pressure. It opens the system to the outside air when the
area is the southern Great Plains of the United States.
vacuum rises above the preset value.
The supercell is so named because it requires extreme
suction vortex — A small vortex, about thirty feet in instability and a special combination of boundary layer
diameter, embedded in a tornado funnel. and high-level wind conditions.
sudden stoppage — A condition in which the aircraft engine supercharger — An engine or exhaust driven air compressor
has come to a complete stop in less than one revolution, used to provide additional pressure to the induction air so
usually caused by the propeller hitting an immovable the engine can produce additional power.
object. Sudden stoppage requires a special inspection to
supercharger control system — The system of controlling
determine internal engine damage.
the supercharger to maintain a constant manifold pressure
sulfate radical — A combination of chemical elements that as the altitude changes.
acts as though it were only one atom. In the case of a
supercharging — Increasing the cylinder pressure of a
sulfate radical, the S04 behaves in the chemical action
reciprocating aircraft engine by introducing compressed
of battery charging or discharging as though it were only
air into the cylinder on the intake stroke.
one element.
superconduction — The effect experienced at very low
sulfated — The condition of plates in a discharged lead‑acid
temperatures (approaching absolute zero) when atomic
battery. The lead has turned to lead sulfate. If allowed
vibration ceases. Conduction electrons are free to drift
to remain for a long period of time, the sulfate becomes
through conductors without opposition or loss of energy.
impossible to remove by normal charging action.
superconductivity — A reaction of certain chemical
sulfur — A pale yellow, non-metallic chemical crystal
elements when they are cooled and held at or near
element with a symbol of S and an atomic number of 16.
absolute zero degrees. At absolute zero degrees, these
sum — 1. The result obtained by adding two or more elements lose almost all of their electrical resistance and
numbers together. 2. Total. become strongly diamagnetic.
sump — 1. A low area in a fuel tank where water will supercooled water — Water that has been cooled below the
normally collect. 2. The component of an aircraft engine freezing point, but is still in a liquid state. Supercooled
used to hold the lubricating oil. water forms solid ice as soon as it is disturbed.
sump jar — A small jar in the vent line of a battery box supercritical wing — An aerodynamic wing design that
containing a pad wet with a chemical such as bicarbonate enhances the range, cruising speed, and fuel efficiency of
of soda or boric acid. Fumes given off by the battery jet aircraft by producing weaker shock waves that create
while it charges are neutralized by this material. less drag and permits high efficiency.
sun gear — The center gear in a planetary gear system superheat — The heat energy added to a gas after
around which the planetary gears rotate. evaporation has been completed.
sunset and sunrise — The mean solar times of sunset and superheated vapor — Vapor that has been heated above its
sunrise as published in the Nautical Almanac, converted boiling point.
to local standard time for the locality concerned. Within
superheated water — The process of heating water to a
Alaska, the end of evening civil twilight and the beginning
temperature above 212°F when it normally changes from
of morning civil twilight, as defined for each locality.
a liquid state to a vapor. Water can be superheated by
super high frequency — The frequency band between heating it in a pressurized container. This is because more
3 and 30 gigahertz (gHz). The elevation and azimuth heat energy has to be added before the molecules move
stations of the microwave landing system operate from fast enough to become steam.
5031 MHz to 5091 MHz in this spectrum.
superheterodyne — A radio receiver circuit that mixes the
super high radio frequency — Frequencies between 3.0 radio frequency signal received with a frequency produced
and 30.0 gigahertz having wavelengths between 100 and in a local oscillator to create an intermediate frequency.
10 mm.

304

10001930-002_AviationDictionary_2012_BOOK.indb 304 3/27/2012 9:38:29 AM

 super-refraction • surge

super-refraction — A condition where radar beams are SUPPS — Refers to ICAO Document 7030 Regional
bent more than normal due to anomalies in temperature Supplementary Procedures. SUPPS contain procedures
or humidity. for each ICAO Region which are unique to that Region
and are not covered in the worldwide provisions identified
supersaturated — Any solution (such as sugar and water)
in the ICAO Air Navigation Plan. Procedures contained in
in which a solid is dissolved until no more of the solid can
chapter 8 are based in part on those published in SUPPS.
be added. This amount varies according to the temperature
of the liquid. As the temperature decreases more of the surface air temperature — In meteorology, the temperature
solid recrystallizes and drops out of the solution. of the air measured at 1.5 meters (about 5 feet) above the
ground.
supersede — To make obsolete by replacement. When a
manufacturer issues new maintenance manuals, the new surface area — The airspace contained by the lateral
manuals supersede the old ones. boundary of the Class B, C, D, or E airspace designated for
an airport that begins at the surface and extends upward.
supersonic — A speed greater than the speed of sound.
surface corrosion — Oxidation across the surface of
supersonic aerodynamics — The branch of aerodynamics
a metal. Primary protection against this corrosion is
that deals with the theory of flight at speeds faster than the
achieved by surface treatment such as painting, anodizing,
speed of sound. Aero means pertaining to air; dynamics
or alodining.
is that branch of physics that considers bodies in motion
and the forces that produce changes of bodies in motion. surface friction — The resistive force that arises from
the combination of skin friction and turbulence near the
supersonic diffuser — A converging diffuser where the
Earth’s surface.
supersonic airstream pressure is raised as velocity
decreases. surface movement guidance and control system (SMGCS)
— Provisions for guidance and control or regulation for
supersonic nozzle — A divergent-shaped duct designed to
facilities, information, and advice necessary for pilots of
allow gases to expand outward faster than they accelerate
aircraft and drivers of ground vehicles to find their way
rearward.
on the airport during low visibility operations and to keep
supersonic speed — Mach 1.0 to Mach 5.0. the aircraft or vehicles on the surfaces or within the areas
intended for their use. Low visibility operations for this
supersonic transport — The British‑French Concorde and
system means reported conditions of RVR 1200 or less.
the Russian TU-144. The only two types of supersonic
commercial aircraft presently in existence. surface tape — Strips of fabric made of the same material
used to cover an aircraft structure. It is applied over the
superstructure — Framework attached to an aircraft truss
seams, rib‑stitching, and edges to give the surface a
structure to provide the desired aerodynamic shape. It is
smooth, finished appearance. Sometimes referred to as
usually covered with lightweight sheet metal or aircraft
finishing tape.
fabric.
surface tension — A cohesive condition that exists on the
supplemental type certificate (STC) — A certificate
surface of a liquid because of molecular attraction.
authorizing an alteration to an airframe, engine, or
component, which has been granted an Approved Type surface treatment — 1. Any treatment that changes the
Certificate. chemical, physical, or mechanical properties of a surface.
2. In composites, a material (size or finish) applied
supplemental weather service location — Airport
to fibrous material during the forming operation or in
facilities staffed with contract personnel who take
subsequent processes. The process is used to enhance
weather observations and provide current local weather
bonding capability of fiber to resin.
to pilots via telephone or radio. (All other services are
provided by the parent FSS.) surface visibility — Visibility observed from eye‑level
above the ground.
supplementary angles — Two angles that add up to 180º.
surface-based inversion — An inversion with its base at the
supply-type test items — Questions where the student
surface, often caused by cooling of the air near the surface
supplies answers as opposed to selecting from choices
as a result of terrestrial radiation, especially at night.
provided. Essay or fill-in-the-blank type questions are
examples of supply-type test items. surficant — Wetting agent. In lubricating systems surficant
adheres to contaminants causing them to drop out of the
support clamp — A clamp used to support various fluid
fuel and settle to the bottom of the tank as sludge.
lines or wire bundles connected to the aircraft structure.
surge — The abrupt loss of the efficiency of the axial
suppressor grid — The electrode in a pentode vacuum tube
flow compressor in a turbine engine when the angle of
used to suppress secondary emissions from the plate.

305

10001930-002_AviationDictionary_2012_BOOK.indb 305 3/27/2012 9:38:29 AM

 surging • synoptic chart

attack of the compressor blades becomes excessive. Also syllabus — A step-by-step, building block progression
referred to as a compressor stall. of learning with provisions for regular review and
evaluations at prescribed stages of learning. The syllabus
surging — A change in engine RPM or power in an
defines the unit of training, states by objective what the
oscillatory manner. It is usually caused by a malfunction
student is expected to accomplish during the unit of
in the fuel control system.
training, shows an organized plan for instruction, and
SURPIC — A description of surface vessels in the area of dictates the evaluation process for either the unit or
a Search and Rescue incident including their predicted stages of learning.
positions and their characteristics.
symbol — Graphic representation used to represent shape,
surveillance approach (ASR) — An instrument approach size, or material on a mechanical drawing.
wherein the air traffic controller issues instructions, for
symbols — In communication, words, gestures, and facial
pilot compliance, based on aircraft position in relation
expressions are formed into sentences and paragraphs
to the final approach course (azimuth), and the distance
that mean something to the receiver of the information.
(range) from the end of the runway as displayed on the
controller’s radar scope. The controller will provide symmetrical — A condition in which both halves of an
recommend-ed altitudes on final approach if requested object are the same.
by the pilot.
symmetrical airfoil — An airfoil with the same shape on
sustained speed — The average wind speed over a one- or both sides of its center line. The location of the center of
two-minute period. pressure of a symmetrical airfoil changes very little as its
angle of attack varies.
sustaining speed — The speed of the engine compressor and
turbine at which a turbine engine can keep itself running symmetrical laminate — In composites, a laminate in
without having to depend on power from the starter. which the stacking sequence of plies below its midline is a
mirror image of the stacking sequence above the midline.
swage — To squeeze together.
symmetry check — A rigging check of an aircraft where
swaged terminals — Solderless terminals fastened to an
measurements are made to determine that points on both
electrical conductor by the swaging process.
sides of the airplane are equidistant from the center line.
sweat solder — A method of soldering two pieces of metal
synchro — A synchronous device in which a movable
together. Both pieces are tinned with solder and then
element is slaved to a similar element in a master unit or
heated to form a joint without the use of additional solder.
transmitter.
Sweeny tool — A gear reduction type torque wrench used
synchro system — See synchro.
to remove the mast nut from helicopter rotors.
synchronize — To cause two events to occur at exactly the
sweepback — A wing design in which the wings do not
same time.
form right angles with the longitudinal axis but instead
are angled backward from the wing root to the wingtip. synchronous motor — An AC motor in which the rotor is
an electromagnet and the stator has a pulsating magnetic
sweptback wing — A wing planform in which the tips of
field from the AC flowing within it. The rotor must have
the wing are farther back than the wing root.
a starting device, but once it is running, it will operate at
swing a compass — The process of aligning the aircraft on a constant speed, which is determined by the frequency
a series of known magnetic headings and adjusting the of the power source.
compensating magnets to bring the compass heading as
synchronous speed — The speed at which a synchronous
near the magnetic heading as possible.
motor rotates. It is dependent on the frequency of the
swirl frame — The inlet case on some turboshaft engines alternating current that excites the field and the number
that act as an inlet particle separator. of poles in the stator.-
swirl vanes — Air circulation vanes that surround fuel synchrophasing — In multi engine aircraft, a form of
nozzles creating a small vapor retaining vortex. Fuel propeller synchronization in which not only the r.p.m. of
vapor trapped in this way is recirculated and utilized the engines are held constant, but also the position of the
more efficiently. propellers with relation to each other.
Swiss pattern files — A set of precision files used for synchroscope — An instrument showing the relationship of
delicate metal work. the engine speeds on a multi‑engine aircraft.
switching diode — A semiconductor device that behaves synoptic chart — In weather, a map or chart that depicts
like an open switch at low voltage levels, but acts like a meteorological conditions over a large area at a given time.
closed switch when voltage rises to a trigger level.

306

10001930-002_AviationDictionary_2012_BOOK.indb 306 3/27/2012 9:38:29 AM

 synthetic fibers • system strategic navigation

synthetic fibers — Man-made products such as fiberglass,

polyester, and polyamide fibers used in the production of
aircraft covering fabric.
synthetic oil — A lubricating oil with a synthetic rather
than a petroleum base. It tends to be less likely to oxidize
and form sludge than petroleum oils. Synthetics are used
extensively in turbine engines and are gaining wide
acceptance in reciprocating engines.
synthetic rubber — Any of several types of man‑made
products that have characteristics similar to natural
rubber.
synthetic vision — An artificial information display, usually
in the form of graphical computer images, that represent
the real world and helps improve a pilot’s ability to retain
situational awareness and control of the aircraft.
system — A group of parts or components that work
together in order to accomplish a common goal.
system discharge indicator — A yellow disc or blow-out
plug on the side of an aircraft. When blown out, it indicates
that the fire extinguishing system has been discharged
normally rather than by an overheat condition.
system pressure regulator — The hydraulic component
that controls hydraulic system pressure. It unloads the
pump when a pre‑selected pressure is reached. It also
brings the pump back online when the pressure drops to
the desired kick-in pressure.
system strategic navigation — Military activity
accomplished by navigating along a preplanned route
using internal aircraft systems to maintain a desired track.
This activity normally requires a lateral route width of 10
NM and altitude range of 1,000 feet to 6,000 feet AGL
with some route segments that permit terrain following.

307

10001930-002_AviationDictionary_2012_BOOK.indb 307 3/27/2012 9:38:29 AM

 T • tailwheel checkout

T tacky — A gluey or sticky finish.

tactical air navigation — An ultra-high frequency
tab — A small auxiliary control surface hinged to an aircraft electronic rho-theta air navigation aid that provides
primary control surface. Tabs can be used to assist in the suitably equipped aircraft a continuous indication of
movement of a primary control surface or as a means of bearing and distance to the TACAN station.
trimming an aircraft.
tag wire — Thin diameter wire used to tie identification
TACAN — An acronym for Tactical Air Navigation tags to objects.
System. An electronic navigation system that provides an
indication of the distance the aircraft is from a ground tail boom — A spar or outrigger connecting the tail surfaces
station. TACAN operates in the UHF range of the radio to a pod-­type fuselage.
frequency spectrum. tail cone — 1. The conical-shaped portion of a turbine
TACAN-only aircraft — An aircraft, normally military, engine exhaust system used to produce the proper area
possessing TACAN with DME but no VOR navigational increase for the gases as they leave the engine. 2. The
system capability. Clearances must specify TACAN or rearmost part of an aircraft fuselage.
VORTAC fixes and approaches. tail load — A downward aerodynamic force produced by
tachometer — An instrument that measures the rotating the tail of an airplane to maintain dynamic longitudinal
speed of an engine. For reciprocating engines, the stability.
tachometer reads in RPMs. In most turbine engines, the tail pipe — That portion of the exhaust system of an aircraft
tachometer reads in percent of the maximum RPM. engine through which the gases leave the aircraft.
tachometer cable — The flexible cable used to drive a tail rotor — In helicopters, a rotor turning in a plane
mechanical tachometer from the engine. It is made of two perpendicular to that of the main rotor and parallel to the
layers of steel wire, spiraled in opposite directions about longitudinal axis of the fuselage. It is used to counteract
a central core. the torque of the main rotor and to provide movement
tachometer generator — A small electrical generator about the yaw axis of the helicopter.
supplying current at frequencies proportional to the tail section — The rear portion, or empennage, of an
speed of the unit on which it is mounted. airplane.
tachometer generator and indicator — The generator tail skid — 1. On modem jet aircraft, a portion of the
has three-phase AC output of approximately 20V. It is structure designed to absorb shock in case the tail strikes
a gearbox-driven accessory that produces power for a the runway during rotation for takeoff. 2. A skid that
motor-driven indicator. The indicator provides a RPM supports the tail of an airplane on the ground. Tail skids
indication in the cockpit. were used before the advent of tail wheels.
tack — In composites, stickiness of the adhesive of a tail surface — A stabilizing or control surface in the tail of
pre-preg material. an aircraft.
tack coat — In painting, a very light coat of material tail wheel — A small wheel located at the rear of the
sprayed on a surface and allowed to stay until the fuselage of an airplane having a conventional landing
solvents evaporate. It is then covered with the full wet gear. It is used as a support for the tail when the airplane
coat of material. is on the ground.
tack rag — A rag, slightly damp with thinner, used to wipe tail wind — A wind blowing in the same direction the
a surface after it has been sanded to prepare it for the airplane is flying.
application of the next coat of finish.
tail-heavy — A condition of balance in an aircraft in which
tack weld — Small temporary welds along a welded seam the center of gravity is behind the aft limit.
made for the purpose of holding the pieces of metal in
tailpipe inserts — Small, sheet metal, wedge‑shaped tabs
position until the weld is completed.
that are inserted into the tailpipe of some older engines to
tacking — Hand‑sewn temporary stitches removed prior to reduce the nozzle opening and increase thrust. Adjustment
machine sewing. of thrust is now done at the fuel control.
tackle — A pulley in the form of a wheel mounted on a tailwheel checkout — To act as PIC of a tailwheel airplane,
faced axis and supported by a frame. The wheel, or disk, FAR 61.31(g) requires a demonstration of competency
is normally grooved to accommodate a rope. The frame in normal and crosswind takeoffs and landings, wheel
that supports the wheel is called a block. Block and tackle landings (unless the manufacturer has recommended
consists of a pair of blocks. Each block contains one or more against such landings), and go-around procedures. Seek
pulleys and a rope connecting the pulley(s) of each block. a comprehensive tailwheel checkout from a qualified

308

10001930-002_AviationDictionary_2012_BOOK.indb 308 3/27/2012 9:38:29 AM

 tailwind • tape laying

instructor for each make and model of tailwheel airplane takeoff thrust — With respect to turbine engines, means
that will be used for instruction. If one has logged PIC the jet thrust that is developed under static conditions at
time in a tailwheel airplane prior to April 15, 1991, then a specific altitude and atmospheric temperature under the
a tailwheel endorsement is not required in one’s logbook. maximum conditions of rotorshaft rotational speed and
gas temperature approved for the normal takeoff, and
tailwind — Any wind more than 90 degrees from the flight
limited in continuous use to the period of time shown in
path of the aircraft. For takeoff, any wind more than 90º
the approved engine specification.
from the magnetic heading of the runway.
takeoff weight — The weight of an aircraft at liftoff. Also
tailwind component — The portion of the wind that acts
referred to as maximum takeoff weight.
directly on the tail of the airplane.
tandem — One behind the other.
takeoff — The beginning of flight in which an airplane is
accelerated from a state of rest to that of normal flight. tandem bearings — The placement of two ball bearings so
The final breaking of contact with the land or water. the thrust load is shared by both bearings.
takeoff area — Any locality either on land, water, or tandem wing — A configuration having two wings of
structures, including airports/heliports and intermediate similar span, mounted in tandem.
landing fields, used or intended to be used, for the
tang — The portion of a knife blade or file that fits into the
takeoff of aircraft whether or not facilities are provided
handle.
for the shelter, servicing, or for receiving or discharging
passengers or cargo. tangent — 1. A line that contacts the circumference of a
circle without penetrating to the inside of the circle. 2. A
takeoff briefing — A tool that pilots can use for takeoff
trigonometric function that is the ratio of the lengths of
planning where they verbally rehearse the entire takeoff
the side opposite and the side adjacent to the angle in a
and departure prior to taking the active runway. By
right triangle.
conducting a takeoff briefing, multi-engine operations
can be performed safer. The briefing should include both tangent point (TP) — The point on the VOR/DME RNAV
normal and emergency procedures just prior to taxiing route centerline from which a line perpendicular to the
onto the runway. Among other things, this enables pilots route centerline would pass through the reference facility.
to be better prepared to handle engine failures during the
tank — A container or reservoir used to hold liquids.
various phases of the takeoff profile. This takeoff briefing
should review appropriate actions for an engine failure tank circuit — A parallel resonant circuit including an
prior to VMC, before the landing gear is retracted, and inductance and a capacitance.
after the airplane is climbing in the clean configuration.
tank selector valve — A selector valve controlled by the
take-off distance available (TODA) — The length of the pilot with which they can select the fuel tank from which
take-off run available plus the length of the clearway, if they desire to operate the engine.
provided.
tantalum carbide — A rare, corrosion‑resistant, metallic
takeoff power — 1. With respect to reciprocating engines, chemical element mixed with carbon. Used in cutting
the brake horsepower developed under standard sea tools and instruments.
level conditions, and under the maximum conditions
tap — A tool used to cut threads on the inside of a hole in
of crankshaft rotational speed and engine manifold
metal, fiber, or other material.
pressure approved for the normal takeoff, and limited
in continuous use to the time shown in the approved tap drill — A twist drill used to drill a hole before it is tapped.
engine specification. 2. With respect to turbine engines, Charts have been developed to determine the correct size tap
the brake horsepower developed under static conditions drill to use to obtain the correct dimensions for a tapped hole.
at a specified altitude and atmospheric temperature, and
tap extractor — A tool used to extract taps that have broken
under the maximum conditions of rotor shaft rotational
off in the hole. It is equipped with projecting fingers that
speed and gas temperature approved for the normal
enter the flutes of the tap. The tap is then backed out of
takeoff, and limited in continuous use to the time shown
the hole by turning the extractor with a wrench.
in the approved engine specification.
tape — In composites, a term used for thin unidirectional
take-off run available (TORA) — The length of runway
material that is usually no wider than 12 inches. The
declared available and suitable for the ground run of an
material may or may not be a prepreg.
airplane taking off.
tape laying — In composites, a manufacturing process
takeoff safety speed — A referenced airspeed obtained
where prepreg tapes are laid across or overlapped to build
after lift-off at which the required one-engine-inoperative
up a shape. The parts are sometimes vacuum bagged and
climb performance can be achieved.

309

10001930-002_AviationDictionary_2012_BOOK.indb 309 3/27/2012 9:38:29 AM

 tape measure • TCAS I

cured. This process can be automated by the use of tape target — In radar: Generally, any discrete object that
laying equipment reflects or retransmits energy back to the radar equipment.
Specifically, an object of radar search or surveillance.
tape measure — A narrow strip (usually made of cloth or
steel tape) with graduations of centimeters, inches, feet, target blade — The identification of one blade of a
etc. used for measuring. helicopter during electronic balancing. It is the blade
with the double interrupter.
taper — A gradual decrease in width or thickness from one
end of an object to the other. target symbol — A computer-generated indication shown
on a radar display resulting from a primary radar return
taper in plan only — A gradual change (usually a decrease) or a radar beacon reply.
in the chord length along the wing span from the root to the
tip with the wing sections remaining geometrically similar. tarmac — A hard surfaced area of an airport used for
aircraft parking, tie‑down, and servicing.
taper in thickness ratio only — A gradual change in
the thickness ratio along a wingspan with the chord tarnish — A stain, blemish, or dull surface.
remaining constant. tarpaulin — A cover made of a large piece of heavy,
taper pin — A device used for fastening concentric shafts waterproof material fitted along its edges with eyelets so
together to prevent relative motion between them. The ropes can be used for tying.
tapered pin is pressed into a tapered hole. tasks — Knowledge areas, flight procedures, or maneuvers
taper reamer — A reamer used to smooth and “true” within an area of operation of a practical test standard.
tapered holes and recesses. Each task includes a list of the type of aircraft category or
class to which it applies and a reference to the applicable
taper tap — A hand-operated thread cutting tap used to regulation or publication.
start the tapping process in a drilled hole. The tap tapers
tautening dope — Aircraft dope consisting of nitrocellulose
for the first six or seven threads.
and a plasticizer. The dope is applied to the fabric surface
tapered crankshaft — The crankshaft to which a propeller to produce tautness, increase strength, protect the fabric,
is mounted by fitting over a tapered end. waterproof the fabric, and make it airtight.
tapered propeller shaft — See tapered crankshaft. taxi — The movement of an airplane under its own power
on the surface of an airport (FAR 135.100-Note). Also, it
tapered punch — A hand punch tapered in length and used describes the surface movement of helicopters equipped
to drive pins, bolts, or rivets from their holes. with wheels.
tapered roller bearings — An anti-friction bearing made of taxi into position and hold — Used by ATC to inform a
hardened steel cylinders rolling between two cone-shaped, pilot to taxi onto the departure runway in takeoff position
hardened steel races. Tapered roller bearings are designed and hold. It is not authorization for takeoff. It is used
to carry both thrust and radial loads. when takeoff clearance cannot immediately be issued
tapered-shank drill — A twist drill that has a tapered shank because of traffic or other reasons.
and is held in the chuck by friction taxi lights — Lights similar to landing lights on an aircraft,
tapped hole — A hole in a casting or other material with but specifically aimed to illuminate the runway or taxiway
threads cut on the inside. when the airplane is taxiing.

tapped resistor — A wire-wound resistor that has taps taxi patterns — Patterns established to illustrate the desired
along the length of the wire in order to provide a choice flow of ground traffic for the different runways or airport
areas available for use.
of multiple fixed resistances.
taxi weight — The maximum weight allowed for ground
tapped stud hole — A hole in which threads have been cut
maneuvering. Also referred to as ramp weight.
for installation of a stud.
taxiway — Airport pavement that allows aircraft to taxi
tappet — The component in an aircraft reciprocating
from the terminal or parking area to the runway.
engine that rides on the face of the cam and transmits a
reciprocating motion to the push rods to open the poppet taxonomy of educational objectives — A system of sorting
valves in the engine cylinders. The hydraulic valve lifters learning outcomes into the three domains of cognitive,
normally fit inside the tappets. affective and psychomotor and rank ordering learning
levels from least to most complex within each domain.
tare weight — The weight of all items such as blocks or
chocks used to hold an airplane on the scales when it is TCAS I — A TCAS (traffic collision avoidance system)
being weighed. Tare weight must be subtracted from the that utilizes interrogations of, and replies from, airborne
scale reading to determine the weight of the aircraft. radar beacon transponders and provides traffic advisories
to the pilot.
310

10001930-002_AviationDictionary_2012_BOOK.indb 310 3/27/2012 9:38:29 AM

 TCAS II • tempering

TCAS II — A TCAS (traffic collision avoidance system ) telling and doing technique — A technique of flight
that utilizes interrogations of, and replies from airborne instruction that consists of the instructor first telling
radar beacon transponders and provides traffic advisories about and demonstrating the new procedure. This is
and resolution advisories in the vertical plane. followed by the student telling and the instructor doing.
Third, the student talks about the new procedure while
TCAS III — A TCAS (traffic collision avoidance system)
doing it. Last, the instructor evaluates while the student
that utilizes interrogation of, and replies from, airborne
accomplishes the procedure.
radar beacon transponders and provides traffic advisories
and resolution advisories inthe vertical and horizontal temper — The condition of hardness or softness of metal.
planes to the pilot.
temperature — In general, the degree of hotness or
teaching — The systematic and deliberate creation of coldness as measured on some definite temperature scale
practical instructional events (experiences) that are by means of any of various types of thermometers. Also,
conducive to learning. a measure of the direction heat will flow proportional to
the mean kinetic energy of the molecules.
teaching lecture — An oral presentation that is directed
toward desired learning outcomes. Some student temperature amplifier — An electronic device used to
participation is allowed. amplify the exhaust temperature signal before being
passed on to the fuel control. Used to assist in scheduling
teardown area — The area in an overhaul shop where
fuel flow.
equipment is received, inventoried, cleaned, and
disassembled for overhaul. temperature bulb — A temperature sensor installed at
points such as the air intake or exhaust manifold. Output
technician — Aviation Maintenance Technician (AMT). A
is transmitted to temperature gauges in the aircraft
person skilled in repairing aircraft who has been issued a
cockpit or to the fuel control.
certificate from the FAA authorizing the holder to repair
aircraft. temperature coefficient of resistance — The rate of
change in resistance per degree centigrade of temperature
Tedlar® — In composites, a material used on the surface as
change.
a waterproof barrier.
temperature datum system — An electronic circuit in an
tee fitting — A plumbing
electrohydromechanical fuel control. Used to assist in
connector in the shape of a T.
scheduling fuel flow.
teetering hinge — In
temperature gradient — The change of temperature
rotorcraft, a hinge that
divided by the distance over which the change occurs.
permits the rotor blades of a
semirigid rotor system to flap as a unit. temperature inversion — In meteorology, an increase
in temperature with height — a reversal of the normal
Teflon — A proprietary name for a fluorocarbon resin used
decrease with height in the troposphere.
to make hydraulic and pneumatic seals and backup rings.
temperature ratio — A ratio of two engine temperatures
teleflex cable — A cable used to connect engine accessories
used in certain performance calculations.
to cockpit controls. Also used as a feedback cable.
temperature scales — 1. Celsius, formerly known as
telegraphing — In composites, dimpling of the fabric into
centigrade, is based on the freezing point of water as 0°
the honeycomb core.
and its boiling point as 100°. Absolute zero is equal to
telemetering — A system of sending data over great -273° on the Celsius scale. Kelvin is based on the freezing
distances by radio. point of water as 273°K and its boiling point as 373°. 2.
Fahrenheit is based on the freezing point of water as 32°
telephone information briefing service (TIBS) — Telephone
and its boiling point as 212°. Absolute zero is equal to -460°
recording of weather and/or aeronautical information.
on the Fahrenheit scale. Rankine is based on the freezing
telescope — To extend or collapse a series of interconnecting point of water as 492° and its boiling point as 672°.
sections in order to make a longer or shorter linear
temperature-dewpoint spread — The difference between
assembly.
the air temperature and the dewpoint.
telescoping gauge — A precision measuring device that
tempering — A heat‑treatment process in which some
consists of a spring‑loaded rod telescoping inside a tube.
of the hardness is removed from a metal to increase its
The gauge is adjusted to the width of a bore or a hole and
toughness and decrease its brittleness.
locked. It is then removed from the hole and the length is
measured with a micrometer.

311

10001930-002_AviationDictionary_2012_BOOK.indb 311 3/27/2012 9:38:30 AM

 template • terminal VFR radar service

template — A pattern made of any suitable material to terminal control area (TCA) — A control area normally
permit the layout of parts with a minimum expenditure of located where air traffic routes converge in the vicinity
time and effort. It should be rigid and accurate and have of one or more airfields. No longer valid for U.S. – still
pertinent data marked on it. valid for foreign airspace.
tensile load — An external force that tends to lengthen or terminal doppler weather radar (TDWR) — Installed
stretch a body. at many U.S. airports vulnerable to thunderstorms
and microbursts. The use of Doppler radar provides a
tensile strength — The ability of an object to resist forces
narrower radar beam and with greater power, a more
tending to stretch or lengthen it.
comprehensive wind shear picture is available for wind
tensile stress — The forces that attempt to pull an object apart. shear prediction.
tensiometer — A measuring instrument used to determine terminal forecast (FT) — Provides weather conditions
the installed tension of aircraft control cables. expected to occur within a five nautical mile radius of the
runway complex at an airport.
tension — The stress produced in a body by forces acting
along the same line but in opposite directions. terminal radar service area — Airspace surrounding
designated airports wherein ATC provides radar
tension adjusters — Devices installed in an aircraft control
vectoring, sequencing, and separation on a full-time
system that maintain a constant cable tension, regardless of
basis for all IFR and participating VFR aircraft. The AIM
the temperature-caused dimensional changes in the airplane.
[and Jeppesen ATC Section] contains an explanation of
tension regulators — See tension adjusters. TRSA. TRSA’s are depicted on VFR aeronautical charts.
Pilot participation is urged but is not mandatory.
tension torsion bar — A strap made of layers of sheet steel
used to absorb tension of centrifugal loads between the terminal radar service area (TRSA) (USA) — Airspace
rotor blades and the hub. The tension torsion bar also surrounding designated airports wherein ATC provides
absorbs the tension in the torque that results from blade radar vectoring, sequencing and separation on a full-time
pitch changes. basis for all IFR and participating VFR aircraft. Service
provided in a TRSA is called Stage III Service. Pilots’
tension torsion strap — A strap made of wire used to serve
participation is urged but is not mandatory.
the same purpose on a helicopter rotor head as the tension
torsion bar. terminal strip — A strip of insulating material that contains
terminal posts to which aircraft wiring is attached.
tentative calculated landing time (TCLT) — A projected
time calculated for adapted vertex for each arrival aircraft terminal velocity — The speed of an aircraft at which the
based upon runway configuration, airport acceptance drag has reached such an amount that the airplane will no
rate, airport arrival delay period, and other metered longer accelerate.
arrival aircraft. This time is either the VTA (vertex time
terminal very high frequency omni-directional range
of arrival) of the aircraft or the TCLT/ACLT (actual
station (TVOR) — A very high frequency terminal
landing time calculated) of the previous aircraft plus the
omni-range station located on or near an airport and used
AAI (arrival aircraft interval), whichever is later. This
as an approach aid.
time will be updated in response to an aircraft’s progress
and its current relationship to other arrivals. terminal VFR radar service — A national program
instituted to extend the terminal radar services provided
tera — Trillion. A metric prefix equal to 1 x 1012.
instrument flight rules (IFR) aircraft to visual flight rules
terminal — 1. A connecting fitting in the form of a ring that (VFR) aircraft. The program is divided into four types of
attaches to the end of a wire. Used for connection to a service referred to as basic radar service, terminal radar
battery, terminal strip, or other component. 2. A keyboard service area (TRSA) service, Class B service and Class
and video monitor that allows a user to interface with the C service. The type of service provided at a particular
computer. location is contained in the Airport/Facility Directory.
terminal area — A general term used to describe airspace in a. Basic Radar Service: These services are provided
which approach control service or airport traffic control for VFR aircraft by all commissioned terminal radar
service is provided. facilities. Basic radar service includes safety alerts,
traffic advisories, limited radar vectoring when
terminal area facility — A facility providing air traffic
requested by the pilot, and sequencing at locations
control service for arriving and departing IFR, VFR,
where procedures have been established for this
Special VFR, and on occasion enroute aircraft.
purpose and/or when covered by a letter of agreement.
terminal control area [ICAO] — A control area normally The purpose of this service is to adjust the flow of
established at the confluence of ATS routes in the vicinity arriving IFR and VFR aircraft into the traffic pattern
of one or more major aerodromes.
312

10001930-002_AviationDictionary_2012_BOOK.indb 312 3/27/2012 9:38:30 AM

 terminal voltage • thermal expansion

in a safe and orderly manner and to provide traffic tetraethyl lead — A heavy, oily, poisonous liquid
advisories to departing VFR aircraft. (Pb(C2H5)4) mixed into aviation gasoline to increase its
octane rating.
b. TRSA Service: This service provides, in addition
to basic radar service, sequencing of all IFR and tetrahedron — A device normally located on uncontrolled
participating VFR aircraft to the primary airport and airports and used as a landing direction indicator. The small
separation between all participating VFR aircraft. end of a tetrahedron points in the direction of landing. At
The purpose of this service is to provide separation controlled airports, the tetrahedron, if installed, should
between all participating VFR aircraft and all IFR be disregarded because tower instructions supersede the
aircraft operating within the area defined as a TRSA. indicator.
c. Class C Service: This service provides, in addition to tetrode — An electron tube having four active electrodes.
basic radar service, approved separation between IFR
T-handle — A T‑shaped handle used for turning sockets.
and VFR aircraft, sequencing of VFR aircraft, and
sequencing of VFR arrivals to the primary airport. that is correct — During communications, this indicates:
The understanding you have is right.
d. Class B Service: This service provides, in addition to
basic radar service, approved separation of aircraft theodolite — An optical instrument used to measure vertical
based on IFR, VFR, and/or weight, and sequencing of and horizontal angles. Theodolites are used for surveying
VFR arrivals to the primary airport(s). and weather observations.
terminal voltage — The potential difference or voltage theoretical pitch — An assumed pitch of the propeller
across the terminals of a power supply such as a battery blades. Also referred to as as geometric pitch.
of cells. As soon as the power source begins to supply
therapeutic adapter — An adapter for a continuous‑flow
current to a circuit its terminal voltage falls because some
oxygen mask that allows oxygen to flow approximately
electric potential energy is lost in driving current against
three times the normal rate. It is used for passengers that
the supply’s own internal resistance.
have heart or respiratory problems.
terminating decimal — A decimal fraction that ends with
thermal — Rising air that lifts because it is warmer than
a whole number.
surrounding air.
terneplate — Lead‑coated thin sheets of steel used in some
thermal anti-icing system — A heated leading edge of the
older aircraft for the construction of fuel tanks and for the
wing and tail surfaces to prevent the formation of ice.
tipping on their wooden propellers.
thermal circuit breaker — A circuit breaker that opens
terrain following — The flight of a military aircraft
a circuit when an excessive amount of current flows
maintaining a constant AGL altitude above the terrain
through it. Made up of a bimetallic set of contacts that
or the highest obstruction. The altitude of the aircraft
open when heated.
will constantly change with the varying terrain and/or
obstruction. thermal circulation — The movement of air resulting from
differential heating.
terrestrial radiation — The radiation emitted by the Earth
and its atmosphere. thermal coefficient of resistance — The amount a material’s
resistance changes with a change in temperature.
tertiary — Something at a third level of importance, rank,
or value. thermal conduction — The transfer of heat energy from
one object to another.
test — 1. To submit a unit, component, etc. to conditions that
will show its quality, strength, etc. 2. A set of questions, thermal conductor — A material, such as metal, that can
problems or exercises for determining whether a person easily transfer heat energy.
has a particular knowledge or skill.
thermal cutout switch — A circuit breaker, or switch, that
test club — A wide-blade, short-diameter propeller used for breaks the circuit at a predetermined temperature.
applying a load to a freshly overhauled aircraft engine for
thermal decomposition — A chemical action that
its initial run-in.
decomposes a material into simpler substances by the
test item — A question, problem, or exercise that measures action of heat.
a single objective and calls for a single response.
thermal efficiency — The ratio of the amount of heat
test stand — A stationary structure where engines, units, energy converted into useful work to the amount of heat
components, etc., can be mounted for testing. energy in the fuel used.
test switch — A switch used to test a system in order to thermal expansion — The expansion of a substance due
determine its operational condition. to heat.

313

10001930-002_AviationDictionary_2012_BOOK.indb 313 3/27/2012 9:38:30 AM

 thermal fatigue • thermoplastic resin

thermal fatigue — A condition in turbine metals caused by of applied heat. This is displayed as current by the meter
heating and cooling each time a power setting is changed. instrument.
thermal index (TI) — In soaring, an index used to indicate the thermocouple — A temperature measuring system
probability of thermals forming. It is the temperature, for any consisting of two dissimilar metal wires joined at a
given level, of the air parcel having risen at the dry adiabatic temperature sensing point. A current proportional to
lapse rate (DALR) subtracted from the ambient temperature. the temperature of the junction is produced. In aviation,
Experience has shown that a TI should be -2 for thermals to thermocouples are generally used as a temperature
form and be sufficiently strong for soaring flight. sensing device.
thermal insulator — Materials such as paper, wood, etc. thermocouple exhaust temperature probe — A bimetallic
that are poor conductors of heat energy. probe, generally of chromel and alumel alloy, located in
an exhaust stream. Heat causes a milliampere current
thermal output — Amount of heat being discharged.
to flow to a cockpit indicator that indicates degrees in
thermal relief valve — A pressure relief valve installed in Celsius.
a static portion of a hydraulic system to relieve pressure
thermocouple fire detector — A device that produces
built up due to heat induced expansion.
an electrical current flow by thermal action and which
thermal runaway — A condition existing in a ultimately illuminates a cockpit warning signal.
nickel‑cadmium battery when the cell resistances become
thermocouple oil temperature bulb — A thermocouple
unbalanced because of temperature. The resistance of
positioned in the oil flow to provide a cockpit indicator
some cells decreases and allows the cells to take more
with an oil temperature indication. It is generally made up
current, which lowers their resistance even further and
of bimetallic materials such as chromel and constantan.
creates more current. This action continues until the
battery is seriously damaged, sometimes exploding. thermodynamic diagram — A chart presenting isopleths of
pressure, temperature, water vapor content as well as dry and
thermal shock — A stress induced into a system or
saturated adiabats. Various forms exist, the most commonly
component due to a rapid temperature change.
used in the United States being the Skew-T/Log-P.
thermal stress cracking — In composites, the crazing and
thermodynamics — The branch of science that deals with
cracking of some thermoplastic resins from overexposure
mechanical actions caused by heat.
to elevated temperatures.
thermoelectricity — Electrical energy generated by the
thermal switch — A switch activated by heat.
action of heat on the junction of two dissimilar metals.
thermal turbulence — Low-level turbulence (LLT) that
thermograph — A thermometer that continuously records
is produced dry convection (thermals) in the boundary
temperatures on a chart.
layer.
thermometer — An instrument for measuring temperature.
thermal wave — Waves, often but not always marked by
cloud streets, that are excited by convection disturbing thermonuclear action — The release of heat, light, and
an overlying stable layer. Also referred to as convection electromagnetic radiation from the fusion or fission of
waves. nuclear material.
thermals — A rising bubble of warm air. An element of thermopile — A collection of thermocouples connected in
convection. a series used to measure minute changes in temperature
or changes in the flow of electrical current.
thermionic — The electron emission caused by an
incan­descent material. thermoplastic — A plastic material used in advanced
composites as a matrix material. Heat is used during the
thermionic current — Current flow in a conductor caused
forming operation. It is not a permanent shape, however,
by heat.
if heated again it will soften and flow to form another
thermistor — A semiconductor device with a core material shape (Plexiglas windshield).
whose electrical resistance changes with a change in
thermoplastic material — A resin‑based plastic material
temperature.
that can be softened by heat and cooled many times
thermoammeter — An instrument for measuring RF without losing its tensile strength.
(radio frequency) alternating current in a circuit. The
thermoplastic resin — A resin material that softens with
thermoammeter measures the RF alternating current by
the application of heat. Most aircraft windshields and
exposing a thermocouple to the RF energy. As the wire
side windows are made of this material.
heats, it produces a current proportional to the amount

314

10001930-002_AviationDictionary_2012_BOOK.indb 314 3/27/2012 9:38:30 AM

 thermosafety discharge indicator • three-sixty (360) overhead

thermosafety discharge indicator — A red blowout disc thixotropic agent — A substance added to a resin to
located on the outside of an aircraft fuselage or engine increase its resistance to flow.
nacelle that blows out to vent a cylinder of high‑pressure
thread — 1. Projecting helical grooves cut around the
gas in the event of an overpressure condition caused by heat.
outside of a bolt, fitting, or pipe and on the inside of a
thermoset — A plastic material used in advanced bolt or fitting. 2. A very fine strand of linen, cotton, or
composites as a matrix material. Heat is used to form other material used to make yarn or fabric.
and set the part permanently. Once cured, it cannot be
thread chaser — A tool used to remove contamination
reformed by applying heat. Most composite structural
from a threaded device.
components are made of thermoset plastics.
thread gauge — A gauge with a series of V-notches cut
thermosetting material — A plastic material that remains
along one edge. Used to check the number of threads, or
hard once it is hardened by chemical means or by heat
the pitch, of a screw or bolt.
and pressure.
thread insert — An internally threaded bushing designed
thermosetting resin — A widely used resin that usually
to be molded in or inserted into soft or brittle materials
sets by chemical means and maintains its hardness even
to increase their strength and minimize the wear of the
when heat is applied.
threaded assembly.
thermosphere — The area of the atmosphere above the
thread pitch — The distance from the peak of one thread
mesosphere that has little practical influence over the
to the peak of the next thread on a screw, bolt, or other
weather. The thermosphere is marked by generally
thread fitting. Also referred to as a screw pitch gauge.
increasing temperature with altitude.
thread plug gauge — A go/no‑go type gauge to be screwed
thermostat — A device that functions to establish or
into internal threads.
maintain a desired temperature produced by a heater or
air‑conditioning system. thread ring gauge — A ring‑type gauge used for checking
external threads.
thermostatic bypass valve — A temperature‑sensing
valve in an engine oil cooler, used to direct the oil either three-axis autopilot — An automatic flight control system
through the core of the cooler or around the inside of the that controls an aircraft about all three axes.
cooler shell to maintain the proper oil temperature.
three-D (3-D) cam — Part of a linkage system, this
thermoswitch fire detector — A device that closes an multi‑labeled cam can rotate and move up and down
electrical contact in the presence of heat, illuminating to allow a cam follower riding on its surface to seek an
a warning light in the cockpit. This is done by thermal infinite number of positions. Used to miniaturize linkage
expansion of metals. systems such as in fuel controls.
thickness gauges — A measuring tool consisting of a series three-dimensional object — An object that has three
of precision‑ground steel blades of various thicknesses. It dimensions: length, width, and depth.
is used to determine the clearance or separation between
three-phase system — An AC electrical system consisting
parts.
of three conductors, each carrying current 120° out of
thimble — The part of a micrometer caliper that is turned phase with the others. Three‑phase systems are used
to rotate the spindle. extensively in modern electrical and electronic actuating
systems.
thinner — A solvent used to reduce the viscosity of dope
or paint. three-point landing — The landing of an airplane in which
all three main wheels of the landing system touch the
third-class lever — A lever that provides a fractional
ground at the same time. Three‑point landings are not
disadvantage, i.e., one in which a greater force is required
recommended for most tricycle gear aircraft.
than the force of the load lifted. For example, if a muscle
pulls with a force of 1,800 lbs. in order to lift a 100 lb. three-pole, single-throw switch — An electrical switch
object, a mechanical advantage of 100/1,800 is obtained. with three sets of contactors, or poles, each of which
This is a fractional disadvantage, since it is less than 1. completes only one circuit. The switch is controlled by a
single operating toggle.
thixotropic — In composites, an agent used to thicken a
resin system without adding weight. Makes the resin three-sixty (360) overhead — A series of predetermined
system less dense. Thixotropic agents include chopped maneuvers prescribed for aircraft (often in formation)
fibers, microballons, and fiber flox. Some agents give for entry into the visual flight rules (VFR) traffic pattern
more strength than others. and to proceed to a landing. An overhead maneuver is not
an instrument flight rules (IFR) approach procedure. An

315

10001930-002_AviationDictionary_2012_BOOK.indb 315 3/27/2012 9:38:30 AM

 three-state buffer • thruster

aircraft executing an overhead maneuver is considered the throttle valves, main venturi, boost venturi, and the
VFR and the IFR flight plan is cancelled when the impact tubes.
aircraft reaches the “initial point” on the initial approach
throttle ice — Carburetor ice that forms on the rear side
portion of the maneuver. The pattern usually specifies the
of a throttle valve when the throttle is partially closed.
following:
Occurs because of the lower pressure causing a drop in
a. The radio contact required of the pilot. temperature.
b. The speed to be maintained. through bolts — Long bolts that pass completely through
an object to hold it together.
c. An initial approach 3 to 5 miles in length.
throw — That part of a crankshaft to which the connecting
d. An elliptical pattern consisting of two 180 degree
rods are attached.
turns.
throwaway part — A part that is not economical to repair
e. A break point at which the first 180 degree turn is
if it should fail and must be thrown away and replaced
started.
with a new one.
f. The direction of turns.
thrust — 1. A forward force that imparts momentum to a
g. Altitude (at least 500 feet above the conventional mass of air behind it. 2. produced by a reaction to the
pattern). exhaust gases escaping the nozzle of a jet engine. 3.
The forward force produced by the aerodynamic force
h. A “Roll-out” on final approach not less than 1/4 mile
of a propeller. 4. In helicopters, the force developed by
from the landing threshold and not less than 300 feet
the rotor blades acting parallel to the relative wind and
above the ground.
opposing the forces of drag and weight.
three-state buffer — A logic device used to place signals
thrust bearing — A bearing in a reciprocating aircraft
on a data bus where only one signal source is allowed to
engine that absorbs loads parallel to the length of the
be active at a time. It can have an output of High or Low
crankshaft.
or can be Off.
thrust, gross — The thrust developed by an engine, not
three-view drawing — An orthographic projection drawing
taking into consideration any pressure of initial air mass
that uses three views to portray an object.
momentum. Also referred to as static thrust (Fg).
three-way light switch — An electrical switch wired to
thrust horsepower — The amount of horsepower the
allow the same light to be turned on or off from either of
engine‑propeller combination transforms into thrust.
two separate locations.
thrust line — An imaginary line passing through the center
threshold — The beginning of that portion of the runway
of the propeller hub, perpendicular to the plane of the
usable for landing.
propeller rotation.
threshold crossing height — The theoretical height above
thrust loads — Loads imposed upon the engine crankshaft
the runway threshold at which the aircraft’s glideslope
and bearings when the propeller is pulling or pushing the
antenna would be if the aircraft maintains the trajectory
aircraft.
established by the mean ILS glideslope or MLS glidepath.
thrust, net — The effective thrust developed by a jet
threshold lights — See airport lighting.
engine during flight, taking into consideration the initial
throat microphone — A special microphone used in areas momentum of the air mass prior to entering the engine.
where there is high background noise. It is applied to a
thrust reverser — A device attached to a turbine engine
person’s throat and operates by picking up vibrations
tailpipe to reverse the exhaust gas flow. Reversers assist
directly from the voicebox.
aircraft brakes and provide aircraft control during landing
throatless shear — A heavy‑duty cutting implement used and during rejected takeoffs.
to shear large sheets of metal.
thrust specific fuel consumption (TSFC) — 1. An
throttle — The valve in a carburetor or fuel control unit equation, TSFC = WfFn, where Wf is fuel flow in pounds
that determines the amount of fuel‑air mixture to be fed per hour and Fn is the net thrust in pounds. Used to
to the engine. calculate the fuel consumption as a means of comparison
between engines. 2. The amount of fuel an engine burns
throttle body — One of the units of a carburetor system.
in one hour to produce one pound of thrust.
All air entering the cylinders flows through this body
and is measured by volume and weight so that the thruster — A miniature rocket engine fired to change
proper amount of fuel can be added to meet the engine orientation of space vehicles and orbiting satellites.
demands under all conditions. The throttle body contains

316

10001930-002_AviationDictionary_2012_BOOK.indb 316 3/27/2012 9:38:30 AM

 thumbscrew • tip path plane

thumbscrew — A machine screw that has a round flat time group — Four digits representing the hour and minutes
projection perpendicular to the screw shank. Thumb from the Coordinated Universal Time (UTC) clock. FAA
screws can be turned by hand and are used on access uses UTC for all operations. The term “ZULU” can be
panels where it is necessary to frequently open and close used to denote UTC. The word “local” or the time zone
the panel. equivalent shall be used to denote local when local time
is given during radio and telephone communications.
thunder — A loud noise heard when lightening occurs When written, a time zone designator is used to indicate
between clouds or between clouds and the ground. The local time; e.g., “0205M” (Mountain). The local time can
lightening generates instantaneous high heat, which be based on the 24-hour clock system. The day begins at
causes a violent expansion of the surrounding air. This 0000 and ends at 2359.
expanding air causes the shock wave or noise of thunder.
time in service — With respect to maintenance time
thundercloud — A cumulonimbus cloud. records, means the time from the moment an aircraft
thunderstorm — Cumulonimbus clouds charged with leaves the surface of the Earth until it touches it at the
electricity and producing lightning, thunder, rain, and hail. next point of landing.

thyratron — Gas-filled triode electron tube in which a time limited part — Any item, component, unit, etc. whose
continuous current is caused to flow by a momentary time in service is limited by hours, the number of times
signal applied to the grid. the unit is operated, or a calendar basis, and that must be
removed and replaced with a new or similar item. Also
thyratron tube — A triode tube into which a gas has been referred to as a time change item.
introduced to change its operating characteristics.
timed turn — The most accurate way to turn to a specific
thyristor — A semiconductor device that acts as a switch. heading without the heading indicator. Use the clock
tie bolt — Bolts used to assemble wheel halves on split instead of the compass card to determine when to roll out.
aircraft wheels. Time-Rite Indicator — A piston position indicator, made
tie rod — Tension rod used for internal and external bracing by Time‑Rite, used for locating the position of a piston in
of various component parts. The ends are threaded for the cylinder of a reciprocating engine for the purpose of
attachment and length adjustment. magneto or valve timing.
tiedown — A special anchoring provision on an airport timing chain — A metal chain that connects the crankshaft
surface to which airplanes can be secured when parked. to the camshaft of a reciprocating engine. Causes the
valves to open and close in proper coordination with the
tight-drive fit — An interference fit between parts.
motion of the pistons.
time and opportunity — A perception factor where
timing disc — A device or tool that can be mounted on an
learning something is dependent on the student having
accessory drive or on the propeller to indicate the amount
the time to sense and relate current experiences in context
of crankshaft travel for ignition or valve riming.
with previous events.
tin — A soft, silver-white, metallic chemical element with a
time between overhaul (TBO) — A recommendation of
symbol of Sn and an atomic number of 50. Alloyed with
the manufacturer of an aircraft engine as to the amount of
other metals in solders, utensils, and in making tin plate.
time that the engine can operate under average conditions
before it should be overhauled. tin snips — Hand-operated sheet metal shears.
time change item — Any item, component, unit, etc. whose tinned — Coated by soft solder. Two surfaces that have
time in service is limited by hours, the number of times been tinned can be pressed together and reheated to sweat
the unit is operated, or a calendar basis, and that must be solder the pieces together.
removed and replaced with a new or similar item. Also
referred to as a time limited part. tinned wire — Electrical wire that has been coated by a thin
coating of soft solder.
time constant — The time required for the voltage of a
capacitor in an RC circuit to increase to 63.2 percent of tinner’s rivet — A flat-headed solid rivet that is driven by
maximum value or decrease to 36.7 percent of maximum holding the flat head of the rivet on an anvil and upsetting
value. the rivet by peening the end over with a hammer.

time constant of an electric motor — The time required tinplated — Sheet steel coated with a thin layer of tin.
for a motor to accelerate from off to its rated no-load tip cap — A removable tip on the rotor blade tip. The tip
speed. cap is often used to hold spanwise balance weights.
time delay relay — A relay that delays the closing or tip path plane — The path followed by the tips of a
opening of the relay for a specified time after activation. propeller as it rotates.

317

10001930-002_AviationDictionary_2012_BOOK.indb 317 3/27/2012 9:38:30 AM

 tip pocket • torque tube

tip pocket — An area provided at the tip of a helicopter toluol — A commercial grade of toluene, which is a liquid
rotor blade to place weight for spanwise balance. aromatic hydrocarbon similar to benzene, but less
volatile, flammable, and toxic.
tip speed — The speed of a rotating airfoil. Generally
subsonic except for fan blade tips and the tip of centrifugal ton of refrigeration — A measure of the cooling capacity
compression blades. of an air conditioning system. It is the same cooling effect
as melting one ton of ice in 24 hours.
tip targets — Reflectors placed on helicopter blade tips to
determine track with a spotlight or a strobe light. tone — 1. A tint or shade of a color. 2. A variation of a hue.
3. A sound of a specific frequency.
tip weight — A weight placed in the tip of a helicopter rotor
blade for spanwise balance. tool — The mold used in manufacturing a composite
component.
tip-path plane — In rotorcraft, the imaginary circular plane
outlined by the rotor blade tips as they make a cycle of tool steel — Hard steel used in the making of tools.
rotation.
tooling resins — In composites, resins used to make molds.
tire — A ring or loop made of rubber compound for
top dead center (TDC) — The position of the piston
toughness and durability. Tires consist of tread, casing
within a cylinder when the piston has reached its furthest
plies/cord body, and beads. Tires provide a cushion of air
uppermost position.
that helps absorb the shocks and roughness of landings
and takeoffs. They support the weight of the aircraft top overhaul — The overhaul of the cylinders of an aircraft
while on the ground and provide the necessary traction engine. It consists of grinding the valves, replacing the
for braking and stopping aircraft upon landing. piston rings, and doing anything else necessary to restore
the cylinders to their proper condition. The crankcase of
tire bead — Bundles of steel wire embedded in the rubber
the engine is not opened.
around the inner circumference of an aircraft tire. Fits
onto the wheel to hold the tire in place. torching — Long plumes of flame extending from the
exhaust stack caused by an excessively rich mixture and
titanium — A dark-gray, silvery, lustrous, very hard, light,
traces of unburned fuel remaining in the exhaust. This
and corrosion‑resistant metallic element with a symbol of
unburned fuel will not ignite until oxygen in the air of the
Ti and an atomic number of 22.
exhaust system mixes with the charge.
title block — An information block in the lower right‑hand
tornado — A violently rotating column of air, which appears
corner of an aircraft drawing in which the name of the
as a pendant from a cumulonimbus cloud, and nearly
part, the part number, and other pertinent information is
always observable as “funnel‑shaped.” It is the most
displayed.
destructive of all small-scale atmospheric phenomena.
toe-in — Aircraft wheels that tend to converge toward the front.
toroidal wound coil — An electrical coil wound around a
Toe-in will cause the tires to try to move closer together.
ring or dough­nut-shape core.
toe-out — Aircraft wheels that tend to diverge toward the
torque — 1. A resistance to turning or twisting. 2. Forces that
rear of the wheels. Toe‑out will cause the tires to try to
produces a twisting or rotating motion. 3. In rotorcraft, in
move apart.
helicopters with a single, main rotor system, the tendency
To-From indicator — An indicator on the course deviation of the helicopter to turn in the opposite direction of the
indicator (CDI). During VOR operation the vertical main rotor rotation.
needle of the CDI is used as the course indicator. The
torque limited — A limitation placed on the drive train of a
vertical needle also indicates when the aircraft deviates
helicopter in regards to power output of the engine.
from the course and the direction the aircraft must be
turned to attain the desired course. The “TO‑FROM” torque link — The hinged
indicator indicates whether the course set in the indicator linkage between the piston
will take the aircraft to or from the station. and cylinder of an oleo
shock strut. The piston
toggle switch — An electrical switch in which a projecting
moves in and out, but is
knob or arm moving through a small arc causes the
restrained from rotating.
contacts to open or close rapidly.
Also referred to as scissors.
tolerance — An allowable variation in the dimensions of
torque nose — A mechanism
a part.
or apparatus at the nose section of the engine that senses
toluene — A colorless, water insoluble, flammable liquid the engine torque and activates a torquemeter.
(C6H5CH3) used as a solvent, paint remover, and thinner.
torque tube — A tubular member of a control system used
to transmit torsional movement to the control.
318

10001930-002_AviationDictionary_2012_BOOK.indb 318 3/27/2012 9:38:31 AM

 torque wrench • toxic

torque wrench — A precision hand tool used to measure touchdown zone — The first 3,000 feet of the runway
the amount of torque applied to a bolt or nut. beginning at the threshold. The area is used for
determination of Touchdown Zone Elevation in the
torquemeter — An indicator used on some large
development of straight-in landing minimums for
reciprocating engines or on turboprop engines to indicate
instrument approaches.
the amount of torque the engine is producing.
touchdown zone elevation — The highest elevation in the
torquemeter indicator — A turboprop or turboshaft
first 3,000 feet of the landing surface. TDZE is indicated
cockpit instrument used to indicate engine power output.
on the instrument approach procedure chart when
The propeller or rotor inputs a twisting force to an
straight-in landing minimums are authorized.
electronic or oil operated torquemeter that sends a signal
to the indicator. touchdown zone [ICAO] — The portion of a runway,
beyond the threshold, where it is intended landing aircraft
torsion — An external stress that produces twisting within
first contact the runway.
a body.
touchdown zone lighting — See airport lighting.
torsional force — A twisting force. Torsional forces act on
a rotating propeller as the result of aerodynamic twisting toughness — The property of a metal that allows it to be
force and tensile forces that try to pull it apart. deformed without breaking.
torsional strength — The strength of a material in a tow — In composites, an untwisted bundle of filaments.
direction that opposes a twisting force.
tow hook — A mechanism allowing the attachment and
toss-up — A question where all the alternative answers are release of a towrope on the glider or tow plane. On
equally good. gliders, it is located near the nose or directly ahead of the
main wheel. Two types of tow hooks commonly used in
total drag — The sum of parasite and induced drag.
gliders are manufactured by Tost and Schweizer.
total estimated elapsed time [ICAO] — For IFR flights, the
tower — A terminal facility that uses air/ground
estimated time required from takeoff to arrive over that
communications, visual signaling, and other devices to
designated point, defined by reference to navigation aids,
provide ATC services to aircraft operating in the vicinity
from which it is intended that an instrument approach
of an airport or on the movement area. Authorizes aircraft
procedure will be commenced, or, if no navigation aid is
to land or takeoff at the airport controlled by the tower
associated with the destination aerodrome, to arrive over
or to transit the Class D airspace area regardless of flight
the destination aerodrome. For VFR flights, the estimated
plan or weather conditions (IFR or VFR). A tower can also
time required from takeoff to arrive over the destination
provide approach control services (radar or nonradar).
aerodrome.
tower enroute control service — The control of IFR
total pressure — The pressure a moving fluid would have
enroute traffic within delegated airspace between two or
if it were stopped. No losses are considered.
more adjacent approach control facilities. This service is
total temperature — A temperature measurement of air in designed to expedite traffic and reduce control and pilot
motion. The total of static temperature plus temperature communication requirements.
rise due to ram effect.
tower to tower — See tower enroute control service.
totalizer — A single fuel quantity gauge that indicates the
tower visibility — Prevailing visibility determined from
total of fuel in all of the fuel tanks.
the control tower.
touch and go — An aircraft training technique in which the
towering cumulus — A rapidly growing cumulus cloud,
pilot practices a series of landings and takeoffs without
it is often typical of the cumulus stage of thunderstorm
coming to a complete stop. As the airplane lands, the pilot
development. Its top can reach 20,000 feet AGL or more
advances the power for another takeoff and go-around.
and have a width of three to five miles.
touch-and-go landing — See touch-and-go.
towing eye — A ring or hook on an aircraft structure to
touchdown — 1. The point at which an aircraft first which a tow bar can be attached for moving the airplane
makes contact with the landing surface. 2. Concerning a on the ground.
precision radar approach (PAR), it is the point where the
Townend ring — A cowling used on radial-engine aircraft
glide path intercepts the landing surface.
designed to improve airflow and engine cooling.
touchdown RVR — The runway visual range (RVR)
toxic — Poisonous.
visibility readout values obtained from RVR equipment
serving the runway touchdown zone.

319

10001930-002_AviationDictionary_2012_BOOK.indb 319 3/27/2012 9:38:31 AM

 TPX-42 • traffic management unit

TPX-42 — A numeric beacon decoder equipment/system. b. in anticipation of a handoff or point out, or

It is designed to be added to terminal radar systems for
c. in conjunction with a request for control of an aircraft.
beacon decoding. It provides rapid target identification,
reinforcement of the primary radar target, and altitude traffic advisories — Advisories issued to alert pilots to
information from Mode C. other known or observed air traffic that can be in such
proximity to the position or intended route of flight of
trace — When precipitation occurs in amounts too small to
their aircraft to warrant their attention. Such advisories
be measured, less than .01 inches
can be based on:
traceable pressure standard — The facility station pressure
a. Visual observation.
instrument, with certification/calibration traceable to the
National Institute of Standards and Technology. Traceable b. Observation of radar identified and nonidentified
pressure standards can be mercurial barometers, aircraft targets on an ATC radar display, or
commissioned ASOS or dual transducer AWOS, or
c. Verbal reports from pilots or other facilities.
portable pressure standards or DASI.
NOTE 1: The word “traffic” followed by additional
tracer — In composites, a fiber, tow, or yarn added to a
information, if known, is used to provide such advisories;
pre-preg for verifying fiber alignment or for distinguishing
e.g., “Traffic, 2 o’clock, one zero miles, southbound,
warp fibers from fill fibers.
eight thousand.”
track — 1. The path followed by the tip of a propeller or
NOTE 2: Traffic advisory service will be provided to the
rotor blade as it rotates. 2. The actual flight path of an
extent possible depending on higher priority duties of the
aircraft over the ground. Also referred to as ground track.
controller or other limitations; e.g., radar limitations,
track [ICAO] — The projection on the Earth’s surface of volume of traffic, frequency congestion, or controller
the path of an aircraft, the direction of which path at any workload. Radar/nonradar traffic advisories do not
point is usually expressed in degrees from North (True, relieve the pilot of his responsibility to see and avoid
Magnetic, or Grid). other aircraft. Pilots are cautioned that there are many
times when the controller is not able to give traffic
tracking — A process of navigation where a course is
advisories concerning all traffic in the aircraft’s proximity;
placed in the course selector and the course is maintain
in other words, a pilot should not assumewhen traffic
tracking flag — A wooden pole that supports a white cotton advisories are requested or received, that all traffic will
flag, used to touch the operating rotor blades that have be issued.
had their tips covered with colored chalk. The marks left
TRAFFIC ALERT (aircraft call sign), TURN (left/right)
on the nag indicate track of the main rotor.
IMMEDIATELY, (climb/descend) AND MAINTAIN
tracking reflectors — Reflectors placed on the blade tips to (altitude)
determine track with a spotlight or a strobe light.
traffic alert and collision avoidance system — An airborne
tracking stick — A stick, with a wick on one end, used collision avoidance system based on radar beacon signals
to touch the operating rotor blades in order to determine that operates independent of ground-based equipment.
track. TCAS-I generates traffic advisories only. TCAS-II
generates traffic advisories, and resolution (collision
tracking targets — Reflectors placed on the blade tips to
avoidance) advisories in the vertical plane.
determine track with a spotlight or strobe light.
traffic in sight — Used by pilots to inform a controller that
TRACON — Acronym for Terminal Radar Approach
previously issued traffic is in sight.
Control.
traffic information — See traffic advisories.
tractor propeller — A propeller mounted to the front of an
engine that pulls the airplane through the air. traffic management program alert — A term used in a
Notice to Airmen (NOTAM) issued in conjunction with
trade winds — Winds that blow toward the equator from
a special traffic management program to alert pilots to
the northeast on the north side of the equator and from
the existence of the program and to refer them to either
the southeast on the south side. Trade winds are caused
the Notices to Airmen publication or a special traffic
by the friction between the air and the Earth and by the
management program advisory message for program
rotation of the Earth.
details. The contraction TMPA is used in NOTAM text.
traffic — 1. A term used by ATC to refer to one or more aircraft.
traffic management unit — The entity in ARTCC’s and
2. A term used by a controller to transfer radar identification
designated terminals responsible for direct involvement
of an aircraft to another controller for the purpose of
in the active management of facility traffic. Usually
coordinating separation action. Traffic is normally issued:
under the direct supervision of an assistant manager for
a. in response to a handoff or point out, traffic management.
320

10001930-002_AviationDictionary_2012_BOOK.indb 320 3/27/2012 9:38:31 AM

 traffic no factor • transcribed weather broadcast (TWEB)

traffic no factor — Indicates that the traffic described in a used as a location or reference for many aerodynamic
previously issued traffic advisory is no factor. measurements in aircraft operations and designs.
traffic no longer observed — Indicates that the traffic trailing finger — An electrode in the distributor of an
described in a previously issued traffic advisory is no ignition system that uses a booster magneto for starting.
longer depicted on radar, but can still be a factor. The high voltage from the booster magneto enters through
a slip ring and is distributed through a finger that trails the
traffic pattern — The traffic flow that is prescribed for
normal ignition finger. In this way, the cylinder would
aircraft landing at, taxiing on, or taking off from an
receive a late, hot spark after the normal firing point in
airport. The components of a typical traffic pattern are
order to facilitate starting and to prevent kick-back.
upwind leg, crosswind leg, downwind leg, base leg, and
final approach. training course outline (TCO) — Within a curriculum,
describes the content of a particular course by statement
a. Upwind Leg – A flight path parallel to the landing
of objectives, descriptions of teaching aids, definition of
runway in the direction of landing.
evaluation criteria, and indication of desired outcome.
b. Crosswind Leg – A flight path at right angles to the
training manual — A technical publication used to explain
landing runway off its upwind end.
the operation of a system or a component. It is general in
c. Downwind Leg – A flight path parallel to the nature and is not considered FAA‑approved data.
landing runway in the direction opposite to landing.
training media — Any physical means that communicates
The downwind leg normally extends between the
an instructional message to students.
crosswind leg and the base leg.
training syllabus — A step-by-step, building block
d. Base Leg – A flight path at right angles to the landing
progression of learning with provisions for regular review
runway off its approach end. The base leg normally
and evaluations at prescribed stages of learning. The
extends from the downwind leg to the intersection of
syllabus defines the unit of training, states by objective
the extended runway centerline.
what the student is expected to accomplish during the
e. Final Approach – A flight path in the direction of unit of training, shows an organized plan for instruction,
landing along the extended runway centerline. The and dictates the evaluation process for either the unit or
final approach normally extends from the base leg to stages of learning.
the runway. An aircraft making a straight-in approach
trajectory — A URET CCLD (User Request Evaluation
VFR is also considered to be on final approach.
Tool Core Capability Limited Deployment) representation
traffic situation display (TSD) — TSD is a computer of the path an aircraft is predicted to fly based upon a
system that receives radar track data from all 20 CONUS Current Plan or Trial Plan.
ARTCC’s, organizes this data into a mosaic display, and
trajectory modeling — The automated process of
presents it on a computer screen. The display allows the
calculating a trajectory.
traffic management coordinator multiple methods of
selection and highlighting of individual aircraft or groups trammel points — Sharp points, usually mounted on a
of aircraft. The user has the option of superimposing long bar. Used to transfer dimensions from one location
these aircraft positions over any number of background to another.
displays. These background options include ARTCC
tramming — A means of checking the alignment of an
boundaries, any stratum of en route sector boundaries,
aircraft structure by making comparative measurements.
fixes, airways, military and other special use airspace,
airports, and geopolitical boundaries. By using the TSD, transceiver — A piece of electronic communications
a coordinator can monitor any number of traffic situations equipment in which the transmitter and receiver are
or the entire systemwide traffic flows housed in the same unit.
trailing edge — The rearmost edge of an airfoil. transconductance — In bipolar transistors or field-effect
transistors, the ratio of a small change in plate current
trailing edge flap —
to a small change in grid voltage. The larger the
Sections of the trailing
transconductance, the larger the gain.
edge of an airfoil that
can be bent down or transcribed weather broadcast (TWEB) — A continuously
extended in flight to broadcast weather information service on selected low
increase the camber of the airfoil, increasing both the lift and medium frequency nondirectional beacons, and
and drag. on VHF omni-directional ranges, (VOR). The TWEB
includes a synopsis and route forecast and is based on a
trailing edge mean aerodynamic chord (TEMAC) — The
route of flight format specifically prepared by the NWS.
trailing edge of the mean aerodynamic chord that is often

321

10001930-002_AviationDictionary_2012_BOOK.indb 321 3/27/2012 9:38:31 AM

 transducer • transmission line

transducer — An electrical device that either takes electrical transition — 1. The general term that describes the change
energy and changes it into mechanical movement or takes from one phase of flight or flight condition to another; e.g.,
mechanical movement and changes it into electrical energy. transition from enroute flight to the approach or transition
from instrument flight to visual flight. 2. A published
transfer — To carry, remove, or send from one place or
procedure (DP Transition) used to connect the basic DP to
position to another.
one of several enroute airways/ jet routes, or a published
transfer gearbox — In helicopters, a gearbox driven procedure (STAR Transition) used to connect one of
from the main rotor shaft that in turn drives the main several enroute airways/ jet routes to the basic STAR.
(accessory) gearbox.
transition altitude (QNH) — The altitude in the vicinity
transfer of control — 1. That action whereby the of an airport at or below which the vertical position of
responsibility for the separation of an aircraft is transferred an aircraft is controlled by reference to altitudes (MSL).
from one controller to another. 2. The act of turning over
transition height (QFE) — The height in the vicinity of an
control of the aircraft from one pilot to another.
airport at or below which the vertical position of an aircraft
transfer punch — A punch having an outside diameter the is expressed in height above the airport reference datum.
same as the rivet hole and a sharp point at its exact center. A
transition layer — The airspace between the transition
transfer punch is used to provide a punch mark for starting
altitude and the transition level. Aircraft descending
a drill in the exact center of the hole being transferred.
through the transition layer will use altimeters set to
transferring controller — A controller/ facility transferring local station pressure, while departing aircraft climbing
control of an aircraft to another controller/facility. through the layer will be using standard altimeter setting
(QNE) of 29.92 inches of Mercury, 1013.2 millibars, or
transferring facility — See transferring controller.
1013.2 hectopascals.
transferring unit/controller [ICAO] — Air traffic control
transition level (QNE) — The lowest flight level available
unit/air traffic controller in the process of transferring the
for use above the transition altitude.
responsibility for providing air traffic control service to
an aircraft to the next air traffic control unit/ air traffic transition point — A point at an adapted number of
controller along the route of flight. miles from the vertex at which an arrival aircraft would
normally commence descent from its enroute altitude.
transformer — An electrical device in which an AC voltage
This is the first fix adapted on the arrival speed segments.
is generated in one winding by mutual induction from AC
voltage in another winding. There does not need to be a transition training — An instructional program designed
physical connection between the two windings. Used to to familiarize and qualify a pilot to fly types of aircraft
change the level of voltage in a circuit. Works only in an not previously flown such as tailwheel aircraft,
AC circuit. high-performance aircraft, and aircraft capable of flying
at high altitudes.
transient conditions — Conditions that can occur briefly
while accelerating or decelerating, or while passing transitional airspace — That portion of controlled airspace
through a specific range of engine operations. wherein aircraft change from one phase of flight or flight
condition to another.
transient current — A momentary change in normal
current load. translating cowl — The portion of a turbine engine cowling
that moves back to form an exhaust nozzle for thrust
transient voltage — A momentary change in normal
reverse air.
voltage.
translating tendency — The tendency of the single-rotor
transistor — A semiconductor device having three
helicopter to move laterally during hovering flight. Also
electrodes: a base, a collector, and an emitter. Current
referred to as tail rotor drift.
flow between the collector and emitter is dependant on
the voltage applied to the base. The transistor serves as a translational lift — In helicopters, the additional lift
switch or an amplifier. obtained when entering forward flight, due to the
increased efficiency of the rotor system.
transistor voltage regulator — A voltage regulator for DC
alternators or generators that uses a transistor to control the translucent — The condition of a material to be transparent,
field current. A zener diode is used to set the voltage level. letting light pass through it but diffusing it so that objects
beyond cannot be seen clearly.
transistorized voltage regulator — A voltage regulator
for DC generators or alternators that uses a transistor to transmission line — A conductor, usually coaxial, used to
control the flow of field current, but uses vibrating points join a receiver or a transmitter to the antenna.
to sense the voltage and control the transistor.

322

10001930-002_AviationDictionary_2012_BOOK.indb 322 3/27/2012 9:38:31 AM

 transmissivity • trickle charging

transmissivity — Ratio of the amount of power transmitted trapezoid — A plane, four‑sided geometric figure having
through a radome to the amount of power that would be only two sides parallel.
transmitted with the radome removed.
trapped fuel — Undrainable fuel. The amount of fuel
transmissometer — An apparatus used to determine remaining in the system after draining. Trapped fuel is
visibility by measuring the transmission of light through considered a part of the empty weight of the aircraft.
the atmosphere. It is the measurement source for
traverse — Lying across a body.
determining runway visual range (RVR) and runway
visibility value (RVV). triac — A semiconductor device similar to a
silicon‑controlled rectifier that can be triggered by either
transmit — In communications, to send information out
a positive or a negative pulse applied to its gate.
from a transmitter.
trial plan — A proposed amendment that utilizes
transmitter — Electric device whose function is to collect
automation to analyze and display potential conflicts
information from one point and send it electrically to a
along the predicted trajectory of the selected aircraft.
remote indicator.
triangle — A three‑sided, enclosed plane figure.
transmitting in the blind — A transmission from one
station to other stations in circumstances where two-way triangulation — In navigation, a method of determining
communication cannot be established, but where it is location by drawing lines from two or more known
believed that the called stations can be able to receive the locations in order to determine the position of the
transmission. unknown point. The lines from the known locations,
drawn either by sight or electronically, will cross at the
transom — In aviation, the vertical bulkhead at the rear end
location of the unknown point.
of a seaplane float.
triboelectric series — A list of materials capable of
transonic flight — Aircraft in flight approximating 0.8 to
producing static electricity by contact, friction, or
1.2 times the speed of sound in air.
induction. Some materials that build up static electricity
transonic speed — The speed of a body relative to the easily are flannel, silk, rayon, amber, hard rubber, and
surrounding fluid that is in some places subsonic and in glass. In the following list, materials at the top of the list
other places supersonic; usually from Mach 0.8 to 1.2. become positive to materials lower on the list:
POSITIVE
transonic speed range — Generally stated as Mach 0.8 to
Glass
1.2 speed range, where some portions of the airfoil have
Mica
subsonic flow and others supersonic flow.
Nylon
transparent — The property of being easily detected or Fur
seen through. Silk
Paper
transpiration cooling — Refers to internal cooling air that
Cotton
exits through porous walls of turbine blades and vanes.
Wood
transponder — Radar beacon transponder. A radar Acrylic
transmitter‑receiver that transmits a coded signal every Polystyrene
time it is interrogated by a ground radar facility. Rubber
NEGATIVE
transponder codes — The number assigned to a particular
multiple pulse reply signal transmitted by a transponder. triboelectricity — The production of static electricity by
contact or friction between different materials.
transport category aircraft — An aircraft that is
certificated under FAR Part 25. trick questions — A question deliberately written in such
a way as to cause the student to select the wrong answer
transverse pitch — The perpendicular distance between
even though the student knows the material.
two rows of rivets. Also referred to as gauge.
trickle charger — A battery charger that applies a very
transverse wave — A wave that moves in a perpendicular
small constant charge to a battery in order to maintain a
direction to the direction the wave is moving.
full charge on the battery.
transverse-flow effect — In rotorcraft, a condition of
trickle charging — A constant current charging method that
increased drag and decreased lift in the aft portion of
keeps cells on standby service at full charge by passing a
the rotor disc caused by the air having a greater induced
small current through them until they are removed from
velocity and angle in the aft portion of the disc.
the charger and returned to service.

323

10001930-002_AviationDictionary_2012_BOOK.indb 323 3/27/2012 9:38:31 AM

 tri-cresyl-phosphate • troposphere

tri-cresyl-phosphate — 1. A plasticizer used as a triple thread — A system using three threads cut into a
rejuvenator to restore resilience to dope film. 2. A toxic fastener. The second and third threads begin 120º after
substance used in lubricants. the previous thread. This type fastener allows tightly
spaced threads without the small lead (distance fastener
tricycle gear — This type of fixed landing gear consists of
moves each revolution) that would normally result with a
two main wheels located on either side of the fuselage
fine threaded, single-thread fastener.
and a third wheel, nosewheel, positioned on the nose of
the airplane. triple-slotted flap — A high lift device used to reduce
the takeoff or landing speed by changing the lift
tricycle landing gear — The landing gear of an aircraft
characteristics of a wing during the landing or takeoff
positioned so the main wheels are behind the center of
phases. Triple‑slotted flaps extend downward and
gravity and the nose is supported with a nose wheel.
rearward away from the wing in three sections separated
trigger pulse — An electric pulse applied to certain by slots. The slots allow a flow of air over the upper
electronic circuit elements to start or trigger an operation. surface of the flap. The effect is to streamline the airflow
and improve the efficiency of the flap.
triggering transformer — A high‑voltage transformer
connected in series with an igniter in a high‑energy triple-spool engine — Usually a turbofan engine design
ignition system for a turbine engine. The transformer where the fan is the N1 compressor, followed by the
places a high voltage across the igniter, ionizing the gap N2 intermediate compressor, and the N3 high pressure
and producing the triggering spark. compressor, all of which rotate on separate shafts at
different speeds.
trigonometry — The branch of mathematics dealing with
the ratios between the sides of a right triangle and the tri-square — A layout tool that consists of
application of these facts in finding the unknown side of a metal rule set at 90º to a thicker base,
any triangle. usually made of wood or plastic. Used
to draw lines perpendicular to an edge
trijet — An aircraft propelled by three jet engines.
of a piece of material.
trim — The adjustment of an aircraft’s controls to get a
trituator — Solid waste grinder on
balanced or stable condition of flight.
airliners.
trim devices — Any device designed to reduce or eliminate
tropical airmass — An airmass with characteristics
pressure on the control stick or yoke. When properly
developed over low latitudes. Maritime tropical air
trimmed, an aircraft should fly at the desired airspeed
(mT), the principal type, is produced over the tropical
with no control pressure from the pilot (i.e., “hands off”).
and subtropical seas; very warm and humid. Continental
Trim mechanisms are either external tabs on the control
tropical (cT) is produced over subtropical arid regions
surface or a simple spring-tension system connected to
and is hot and very dry. Compare polar airmass.
the control stick or yoke.
tropical cyclone — A general term for a cyclone that originates
trim tab — A small auxiliary hinged portion of a movable
over tropical oceans. There are three classifications of
control surface that can be adjusted during flight to a
tropical cyclones according to their intensity:
position resulting in a balance of control forces.
1. tropical depression: winds up to 34 knots;
trimetrogon — A system of aerial photography that uses
one vertical and two oblique shots of terrain taken 2. tropical storm: winds of 35 to 64 knots; and
simultaneously in order to properly map the contours of
3. hurricane or typhoon: winds of 65 knots or higher.
the landscape.
tropical storm — See tropical cyclone.
trimmer — A potentiometer, generally with a
screwdriver-adjusted slider used for fine tuning a circuit. tropopause — The boundary layer between the troposphere
and the stratosphere.
triode — A vacuum tube having three active electrodes.
tropopause — An area at an average altitude of 36,000 feet
trip-free circuit breaker — A circuit protection device that
that acts as a lid to confine most of the water vapor, and
opens a circuit when a current overload exists regardless
the associated weather, to the troposphere.
of the position of the control handle.
tropopause — The boundary between the troposphere and
triphibian — An aircraft landing gear configuration with
stratosphere, usually characterized by an abrupt change
the ability to operate from the ground, on snow and ice,
of lapse rate.
and from water.
troposphere — That portion of the atmosphere from the
triplane — An airplane having three main supporting wing
Earth’s surface to approximately 36,000 feet MSL. The
surfaces, usually located one above the other.
troposphere is characterized by decreasing temperature
with height, and by appreciable water vapor.
324

10001930-002_AviationDictionary_2012_BOOK.indb 324 3/27/2012 9:38:31 AM

 troubleshooting • tungsten steel

troubleshooting — The systematic analysis of a malfunction truss fuselage — Fuselage usually constructed of welded
in a system or component done in order to determine the steel tubing to carry the tensile and compressive loads. A
cause of malfunction. superstructure or auxiliary framework is often attached to
the truss to give the structure a desirable aerodynamic shape.
trough — In meteorology, an elongated area of relatively
low atmospheric pressure and maximum cyclonic truss head — A low, rounded top surface with a flat bearing
curvature of the wind flow (isobars or contours). Also surface.
referred to as a trough line.
TSO (Technical Standard Order) — A standard
trough line — See trough. established by the FAA for quality control in avionics,
instruments, and other airborne equipment.
true air temperature — See outside air temperature (OAT).
T-square — An instrument used for making aircraft
true airspeed indicator — An airspeed indicator that takes
drawings. It consists of a head and a perpendicular blade
into consideration dynamic pressure, static pressure, and
and is shaped like the letter T.
free air temperature in order to provide a display of the
true airspeed. T-tail — An aircraft with the horizontal stabilizer mounted
on the top of the vertical stabilizer, forming a T.
true airspeed (TAS) — Calibrated airspeed corrected for
non‑standard temperature and altitude. The speed at tubing — A rigid, hollow, elongated cylindrical piece of
which an aircraft is moving relative to the surrounding air. material through which fluids or wiring is passed.
true altitude — The actual height of an object above mean tubing cutter — A tool consisting of a sharp wheel and a
sea level. set of rollers. The tube to be cut is clamped between the
cutter cutting wheel, and the rollers and the tool is rotated
true bearing — The direction measured in degrees
around the tube. The cutting wheel is fed into the groove
clockwise from true north.
as the tube is cut.
true course (TC) — A navigational direction or course of an
tumble limit — The number of degrees of pitch or roll
aircraft in flight as measured in relation to the geographic
a gyro can tolerate before it reaches its gimbal stops.
north pole.
Beyond this point, the gyro will tumble.
true heading (TH) — The direction the longitudinal axis
tumbling — 1. The process of cleaning or abrading parts
of the airplane points with respect to true north. True
in a rotating container, either with or without cleaning
heading is equal to true course plus or minus any wind
or abrasive materials. 2. The action of a gyro when it
correction angle.
has reached its gimbal stops. The gyro will assume an
true north — The direction on the Earth’s surface that erroneous indication that does not return to normal until
points toward the geographic north pole. corrected.
true power — The power that actually exists in an AC tuned circuit — An electrical circuit in which the inductive
circuit. It is the product of the voltage, current, and power reactance is equal to the capacitive reactance. They will
factor; or is the product of the voltage and the current that be equal at a particular frequency called the resonant
is in phase with that voltage. True power is expressed in frequency. The circuit can be made resonant by either
watts. varying the frequency until resonance occurs, or holding
the frequency constant and varying inductance or
true wind direction — The direction, with respect to true
capacitance to achieve resonance. Also referred to as a
north, from which the wind is blowing.
resonant circuit.
true-false — Test item that consists of a statement that the
tuned radio frequency receiver — A radio receiver in
student must determine is true or false.
which tuning and amplification are accomplished in the
true-false test items — Consist of a statement followed by RF section before the signal reaches the detector. After
an opportunity for the student to determine whether the the detector, one or more stages of AF amplification are
statement is true or false. employed to increase the output sufficiently to operate a
loudspeaker.
truncated — Cut off as having the angles of an object cut
off. tungsten — A gray‑white, heavy, high melting point,
hard metallic element with symbol of W and an atomic
truss — A frame arranged together in such a manner that
number of 74.
all members of the truss can carry both tension and
compression loads with cross‑bracing achieved by using tungsten steel — Steel with which tungsten has been
solid rods or tubes. alloyed. It is used in the manufacture of cutting tools
because of its hardness.

325

10001930-002_AviationDictionary_2012_BOOK.indb 325 3/27/2012 9:38:31 AM

 tuning • turn anticipation

tuning — The process of adjusting circuits to resonance at turbocompound engine — A reciprocating engine that
a particular frequency. supplements the internal supercharger by an external
power recovery turbine (PRT) driven by a portion of
tunnel diode — A semiconductor diode that exhibits
the exhaust gas from the aircraft engine. The PRT is
a negative resistance characteristic. Under certain
connected through a fluid coupling and gear arrangement
conditions, an increase in voltage across the tunnel diode
to help drive the crankshaft.
results in a decrease in current through it.
turbofan — An engine featuring a multi-bladed ducted
turbine — A rotary wheel device fitted with vane-like
propeller driven by a gas turbine engine.
airfoils and actuated by impulse or reaction of a fluid
flowing through the vanes, or blades. Multiple turbine turbojet aircraft — An aircraft having a jet engine in
wheels are arranged along a central shaft. which the energy of the jet operates a turbine that in turn
operates the air compressor.
turbine bucket — The blades on a turbine wheel.
turbojet engine — A turbine engine that produces its thrust
turbine disc — The metal disc to which turbine blades are
entirely by accelerating the air through the engine.
attached.
turboprop aircraft — An aircraft having a jet engine in
turbine discharge pressure (Pt7) — The total pressure at
which the energy of the jet operates a turbine that drives
the discharge of the low‑pressure turbine in a dual turbine
the propeller.
axial flow engine.
turboprop engine — A turbine engine that drives a
turbine efficiency — A ratio of actual work performed
propeller through a reduction gearing arrangement.
by the turbine wheel in ft lbs/Btus and the laboratory
Most of the energy in the exhaust gases is converted into
standard of 778 ft lbs of work in 1 Btu. Expressed as a
torque, rather than its acceleration being used to propel
percentage.
the aircraft.
turbine engine — An aircraft engine that consists of an air
turboshaft — A gas turbine engine geared to an output
compressor, a combustion section, and a turbine. Thrust
shaft. Usually for rotorcraft installation, but also for
is produced by increasing the velocity of the air flowing
many marine and industrial uses.
through the engine.
turboshaft engine — A gas turbine engine that delivers
Turbine Inlet Pressure (TIT) — Temperature taken in
power through a shaft to operate something other than
front of the first stage turbine nozzle vanes. The most
a propeller.
critical temperature taken within the engine for use in
fuel scheduling. turbulence — 1. In general, any irregular or disturbed flow
in the atmosphere. 2. In aviation, bumpiness in flight.
turbine inlet temperature (TIT) — Temperature taken in
front of the first stage turbine nozzle vanes. TIT is the turbulence in and near thunderstorms (TNT) — That
most critical temperature taken within the engine and turbulence that occurs within, below, above, and around
essential to the operation of the fuel control. developing convective clouds and thunderstorms.
turbine nozzle — The orifice assembly through which turbulent flow — A flow of fluid in an unsteady state.
exhaust gases are directed prior to passing into the
turbulent gusts — The atmospheric wind and vertical
turbine blades.
motion fluctuations caused by turbulent eddies.
turbine nozzle vanes — The stationary airfoils that precede
turbulent wake — The turbulent eddies created near
each turbine blade set. They function to increase gas
the ground when high surface winds are disrupted by
velocity and direct the gases into the turbine blade at the
obstacles, such as hangers and other large buildings
optimum angle.
located near an approach path. Also, the turbulent region
turbine stage — In gas turbine engines, a stage consists downwind of a thunderstorm.
of a turbine stator vane set followed by a turbine rotor
turn — To machine on a lathe.
blade set.
turn and bank indicator — A flight instrument consisting of
turbine wheel — A rotating device actuated by reaction,
a rate gyro to indicate the rate of yaw and a curved glass
impulse, or a combination of both. Used to transform
inclinometer to indicate the relationship between gravity
some of the kinetic energy of the exhaust gases into shaft
and centrifugal force. The turn and bank indicator indicates
horsepower to drive the compressors and accessories.
the relationship between angle of bank and rate of yaw.
turbocharger — An air compressor driven by exhaust
turn and slip indicator — See turn and bank indicator.
gases, which increases the pressure of the air going into
the engine through the carburetor or fuel injection system. turn anticipation — 1. Turning maneuver initiated prior
to reaching the actual airspace fix or turn point that is

326

10001930-002_AviationDictionary_2012_BOOK.indb 326 3/27/2012 9:38:31 AM

 turn coordinator • TYP

intended to keep the aircraft within established airway twist drill — A metal cutting tool that has a straight shank
or route boundaries. 2. The capability to manually or and deep spiral flutes in its side and provides a passage
automatically determine the point along a route of flight, for the chips to be removed from the hole it is cutting.
prior to a fly-by fix, where a turn should be initiated to
twist grip — In helicopters, the power control on the end of
provide a smooth path to the succeeding course. 3. The
the collective control.
capability of RNAV systems to determine the point along a
course, prior to a turn WP, where a turn should be initiated twisted pair — Two insulated wires twisted together. This
to provide a smooth path to intercept the succeeding configuration causes the magnetic fields from each of the
course, and to enunciate the information to the pilot. conductors to cancel out the magnetic field of the other.
These wires are used in circuits such as the lighting circuit
turn coordinator — A rate gyro that senses both roll and
for the standby magnetic compass, where magnetic fields
yaw.
would cause compass errors.
turn WP [turning point] — A WP that identifies a change
two view drawing — An orthographic projection drawing
from one course to another.
that uses two views to portray an object.
turnbuckle — A device used in a control system to adjust
two-axis automatic pilot — An automatic flight control
cable tension. A turnbuckle consists of a brass barrel with
system that operates only in the roll and yaw axes.
both left‑ and right‑hand threaded terminals.
two-axis autopilot — An automatic flight control system
turning error — One of the errors inherent in a magnetic
that controls the airplane about the roll and yaw axes.
compass caused by the dip compensating weight. It
shows up only on turns to or from northerly headings in two-cycle engine — A reciprocating engine in which a
the northern hemisphere and southerly headings in the power impulse occurs on each stroke of the piston. As
southern hemisphere. Turning error causes the compass the piston moves outward, fuel‑air mixture is drawn into
to lead turns to the north or south and lag turns away from the crankcase below the piston; while above the piston,
the north or south. the mixture is compressed. Near the top of the stroke,
ignition occurs. As the piston moves downward, power
turning points — Track changes often occur along initial
is produced by the crankshaft. Near the bottom of the
or intermediate approach segments of non-RNAV
stroke, exhaust action takes place on one side of the
procedures, some defined by DME and some defined by
cylinder and intake action occurs on the opposite side.
radials or bearings.
two-part adhesive — An adhesive that consists of two parts.
turpentine — A thinner and quick drying agent used in
One part is the base and the other part is the accelerator.
varnishes, enamels, and other oil‑based paints.
When the two are mixed together in the correct amounts,
turret — A tool mount on a lathe. The turret holds several the adhesive cures in a short time period.
tools that can be selected as needed.
two-state device — An electronic component that can be
turret lathe — A metal-turning lathe in which the cutting switched to a high or resistance state by a control signal.
tools are mounted in a turret for purpose of quick change.
two-stroke-cycle engine — See two‑cycle engine.
tweak test — A test of the output of a wheel speed sensor
two-way communications — The ability of both stations
made by tweaking or flipping the sensor blade with the
involved in communications to transmit and receive
fingers to rotate it enough for it to generate a voltage.
signals or information.
twelve point head — A standard head form for externally
two-way radio communications failure — Loss of the
wrenched screws designed for use in counter‑bored holes.
ability to communicate by radio. Aircraft are sometimes
twelve-point socket — A socket wrench that has a 12‑point referred to as NORDO (No Radio). Standard pilot
double hex opening that makes it easy to position on a procedures are specified in FAR 91. Radar controllers
bolt or nut. issue procedures for pilots to follow in the event of lost
communications during a radar approach when weather
twenty-minute rating — The ampere hour rating of a
reports indicate that an aircraft will likely encounter IFR
battery indicating the amount of current that can be drawn
weather conditions during the approach.
from a battery in order to discharge it in twenty minutes.
TYP — A mechanical drawing term that means “typical.”
twilight — Often called dusk, it is the period of decreasing
It is used to show that the part symbolized by the TYP
light from sunset until dark.
designator is typical for more than one area or part of the
twin-row radial engine — A radial engine having two rows drawing.
of cylinders, one behind the other.

327

10001930-002_AviationDictionary_2012_BOOK.indb 327 3/27/2012 9:38:32 AM

 type • Ty-Rap

type — 1. As used with respect to the certification,

ratings, privileges, and limitations of airmen, means
a specific make and basic model of aircraft, including
modifications thereto that do not change its handling or
flight characteristics. Examples include: DC-7, 1049,
and F-27. 2. As used with respect to the certification of
aircraft, means those aircraft similar in design. Examples
include: DC-7 and DC-7C; 1049G and 1049H; and F-27
and F-27F. 3. As used with respect to the certification of
aircraft engines means those engines similar in design.
For example, JT8D and JT8D-7 are engines of the same
type, and JT9D-3A and JT9D-7 are engines of the same
type.
Type Certificate Data Sheets — The official specifications
of an airplane, engine, or propeller. Type certificate data
sheets are issued by the FAA. In order for the device to be
airworthy, it must conform to these specifications.
Ty-Rap — A patented nylon cable wrap used to hold wire
bundles together.

328

10001930-002_AviationDictionary_2012_BOOK.indb 328 3/27/2012 9:38:32 AM

 U • underspeed condition

U communication to a rocket or spacecraft on the launching

pad prior to liftoff.
U-bolt — A U-shaped rod threaded on both ends. U‑bolts unable — Indicates inability to comply with a specific
are used to fasten cables around a thimble. instruction, request, or clearance.
ultimate load — The amount of load applied to a part unbalanced cell — A condition in a nickel‑cadmium
beyond which the part will fail. battery in which one cell has discharged more than the
ultimate strength — The tensile strength of a material that, other cells. This is the initial step in a thermal runaway.
when exceeded, leads to the material breaking. unbalanced transmission line — A cable that has one
ultrahigh frequency (UHF) — The frequency band between conductor grounded or exposed to the outside elements
300 and 3,000 MHz. The bank of radio frequencies used in greater magnitudes than the other conductor.
for military air/ground voice communications. In some uncontrolled airport — A nontower airport where control
instances this can go as low as 225 MHz and still be of VFR traffic is not exercised.
referred to as UHF
uncontrolled airspace — Class G airspace.
ultralight vehicle — An aeronautical vehicle operated
for sport or recreational purposes that does not require uncontrolled spin — A spin in an airplane in which the
FAA registration, an airworthiness certificate, nor pilot controls are of little or no use in effecting a recovery.
certification. They are primarily single occupant vehicles, under the hood — Indicates that the pilot is using a hood
although some two-place vehicles are authorized for to restrict visibility outside the cockpit while simulating
training purposes. Operation of an ultralight vehicle in instrument flight. An appropriately rated pilot is required
certain airspace requires authorization from ATC. in the other control seat while this operation is being
ultrasonic cleaner — A cleaning apparatus that utilizes conducted.
cleaning fluid agitated by sound waves transmitted undercarriage — An airplane’s entire landing gear.
through the fluid. This method is widely used for filter
and bearing cleaning. undercompounded generator — A compound generator
(both series and shunt-wound) that is more influenced by
ultrasonic frequencies — Frequencies above 20,000 Hz the shunt winding than the series winding. Voltage output
that cannot be heard by the human ear. drops as load increases.
ultrasonic inspection — A nondestructive inspection in undercurrent relay — An electrical circuit protection
which the condition of a material is determined by its device that opens the circuit when the current drops
ability to conduct ultrasonic vibrations. below a predetermined value.
ultrasonic soldering — A method of soldering in which underpowered — An undesirable condition in which
the tip of a soldering iron is vibrated at an ultrasonic an engine does not have enough power to achieve the
frequency. The vibration separates the oxide film on the desired result.
surface of the metal. A flux is melted over the surface of
the hot metal to prevent more oxide from forming. undershoot — A condition of flight in which a landing
aircraft touches the ground short of the runway or the
ultrasonics — A branch of science dealing with high landing strip.
frequency sound waves. Normally considered to be
above the audio frequency range of 20 to 20,000 hertz. underslinging — In helicopters, placing the main rotor
hub around and below the top of the mast as is done on
ultraviolet lamp — A lamp that produces a light wavelength semi‑rigid rotor systems.
slightly shorter than the wavelength of visible light.
underslung — In rotorcraft, a rotor hub that rotates below
ultraviolet radiation — Rays of light that are shorter than the top of the mast, as on semirigid rotor systems.
the wavelength of visible light. Produced by the sun or by
special lamps, exposure to these rays can damage organic underspeed condition — A condition resulting from the
materials. movement of the blades of a propeller to a higher angle
than that required for con­stant‑speed operation. When the
ultraviolet rays — See ultraviolet radiation. speed drops below the RPM for which the governor is set,
ultraviolet (UV) — Frequencies higher than blue, having the resulting decrease in centrifugal force exerted by the
relatively short wavelengths. governor flyweights permits the speeder spring to lower
the pilot valve, thereby opening the propeller‑governor
umbilical cord — 1. A cable used to carry power or meter­ing port. Oil is then directed to the prop in the
life support to an astronaut for operating outside a proper direction to flatten the pitch of the propeller and
space vehicle. 2. A cable used to deliver power and correct the underspeed condition.

329

10001930-002_AviationDictionary_2012_BOOK.indb 329 3/27/2012 9:38:32 AM

 understanding • unpublished route

understanding — Level of learning. Ability to comprehend universal chuck — The three clamping jaws of a drill used
something learned. to hold drill bits and other drill accessories.
understanding — A basic level of learning where a universal joint — A joint coupling that allows one shaft to
student comprehends or grasps the nature or meaning of drive another shaft at angles to each other.
something.
universal motor — A series‑wound motor that operates on
undervoltage relay — An electrical circuit protection either alternating or direct current.
device that opens the circuit when voltage drops below a
universal propeller protractor — A precision measuring
predetermined value.
device used to measure the amount of blade angle.
underwing fueling — A method of fueling an aircraft from
universal time (UT) — In the most common civil usage,
a single‑point pressure fueling port located under the
UT refers to a time scale called “Coordinated Universal
wing.
Time” (abbreviated UTC), which is the basis for the
Underwriter’s Laboratories (UL) — An independent, worldwide system of civil time. This time scale is kept
not-for-profit product-safety testing and certification by time laboratories around the world and is determined
organization. using highly precise atomic clocks. The International
Bureau of Weights and Measures makes use of data
undrainable fuel — The amount of fuel that remains in the
from the timing laboratories to provide the international
system after draining. Undrainable fuel is considered a
standard UTC, which is accurate to approximately a
part of the empty weight of the aircraft.
nanosecond (billionth of a second) per day. The length of
undrainable oil — The oil remaining after draining the oil a UTC second is defined in terms of an atomic transition
from an engine. Undrainable oil is considered a part of of the element cesium under specific conditions, and is
the empty weight. not directly related to any astronomical phenomena. The
times of various events, particularly astronomical and
unfeather — The action of turning the propeller blades to
weather phenomena, are often given in “Universal Time”
an angle not parallel with the airplane’s line of flight.
(abbreviated UT), which is sometimes referred to, now
unfeathered — Low blade angle condition of a propeller. colloquially, as “Greenwich Mean Time” (GMT). The
two terms are often used loosely to refer to time kept
UNICOM — A nongovernment communication facility
on the Greenwich meridian, five hours ahead of Eastern
that can provide airport information at certain airports.
Standard Time. Times given in UT are almost always
Locations and frequencies of UNICOMs are shown on
given in terms of a 24-hour clock. Thus, 14:42 (often
aeronautical charts and publications.
written simply 1442) is 2:42 p.m., and 21:17 (2117) is
unidirectional — In composites, a fabric, tape, or laminate 9:17 p.m. Sometimes a Z is appended to a time to indicate
with all the major fibers running in one direction, giving UT, as in 0935Z.
strength in that direction.
unleaded gasoline — Engine fuel that has not been treated
unidirectional current — A flow of electrons in one with lead or lead components.
direction throughout a circuit. See also direct current.
unlimited ceiling — A clear sky or a sky cover that does not
uniform acceleration — Increasing the speed of an object constitute a ceiling.
at an unvaried rate.
unloaded rotor — In helicopters, the state of a rotor
uniform surface corrosion — Unvaried corrosion across a when rotor force has been removed, or when the rotor is
surface. No pits or localized damage have formed. operating under a low or negative G condition.

unijunction transistor — A transistor that allows voltage to unloading valve — A pressure control valve used in aircraft
flow between its two bases when an appropriate voltage hydraulic systems to prevent excessive pressures from
is applied to its emitter. bursting lines and blowing out seals. When the pressure
reaches a predetermined value, the valve reroutes the
union — Connectors or fittings that attach one item, such as
high output pressure back to the pump inlet.
tubing, to another.
unmetered fuel — Fuel that enters the fuel control from
unit — A single piece of equipment.
the fuel pump.
United States — Geographically, the States, the District of
unpublished route — A route for which no minimum
Columbia, Puerto Rico, and the possessions, including
altitude is published or charted for pilot use. It can include
the territorial waters, and the airspace of those areas.
a direct route between NAVAIDS, a radial, a radar vector,
United States air carrier — A citizen of the United States or a final approach course beyond the segments of an
who undertakes directly by lease, or other arrangement, instrument approach procedure.
to engage in air transportation.

330

10001930-002_AviationDictionary_2012_BOOK.indb 330 3/27/2012 9:38:32 AM

 unscheduled maintenance • user-defined waypoint

unscheduled maintenance — Maintenance performed urgency — A condition of being concerned about safety,
as a result of discrepancies found by flight and ground and of requiring timely but not immediate assistance; a
personnel. potential distress condition.
unstable — 1. The characteristic of an aircraft that causes urgency [ICAO] — A condition concerning the safety of an
it, when dis­turbed from a condition of level flight, to aircraft or other vehicle, or of person on board or in sight,
depart further from this condition. 2. In meteorology, a but which does not require immediate assistance.
general term to indicate various states of the atmosphere
U.S. standards for instrument procedures (TERPS) —
in which spontaneous convection will occur when
An official FAA publication that prescribes standardized
prescribed criteria are met; indicative of turbu­lence. See
methods for use in designing instrument approach
also absolute instability, conditionally unstable air.
procedures.
unstable air — Air with a temperature lapse rate different
usability — Characteristic of a test being easy to read and
than the surrounding air.
clear in the use of directions, figures, and illustrations.
unstable oscillation — An oscillation whose amplitude
usable fuel — The portion of the total fuel load available to
continues to diverge from the initial amplitude with no
an aircraft in flight.
tendency to return toward the original amplitude.
USAFIB — Acronym for: U. S. Army Aviation Flight
unusable fuel — The small amount of fuel in the tanks that
Information Bulletin
cannot be safely used in flight or drained on the ground.
Unusable fuel is considered part of the empty weight of useful load — The difference between the empty weight
the aircraft. of the airplane and the maximum weight allowed by the
manufacturer’s specification.
unusable oil — Oil that cannot be drained from the engine.
useful load — 1. The weight of the occupants, baggage,
updraft — A localized upward current of air.
and usable fuel (Aircraft certified prior to FAR Part 23
updraft carburetor — A carburetor mounted on the include oil). 2. The difference between the empty weight
bottom of a reciprocating engine. All of the air entering of the aircraft and the maximum weight of the aircraft.
the engine flows upward through the venturi. Also referred to as the payload.
upholstery — Materials (fabric, padding, and springs) used user request evaluation tool core capability limited
to make a soft covering for a seating surface. deployment (URET CCLD) — User Request Evaluation
Tool Core Capability Limited Deployment is an
upper air temperature — The temperature that is
automated tool provided at each Radar Associate position
referenced to the height or pressure level where they are
in selected En Route facilities. This tool utilizes flight and
measured.
radar data to determine present and future trajectories for
upper deck pressure — The pressure of the air between all active and proposal aircraft and provides enhanced,
the compressor and the throttle plate on a supercharged, automated flight data management.
reciprocating engine. This air is also used for
user-defined waypoint — User-defined waypoints
pressurization of the cabin and the fuel injection system.
typically are created by pilots for use in their own
upper front — A front aloft not extending to the Earth’s random RNAV direct navigation. They are newly
surface. established, unpublished airspace fixes that are
designated geographic locations/positions that help
upset head — The end of the rivet opposite the manufactured
provide positive course guidance for navigation and a
head formed during the riveting process.
means of checking progress on a flight. They may or may
upsetting — The process of increasing the cross‑sectional not be actually plotted by the pilot on enroute charts, but
area of the end of a rivet or bolt by bucking or hammering would normally be communicated to ATC in terms of
it. bearing and distance or latitude/longitude. An example of
user-defined waypoints typically includes those derived
upslope fog — Fog formed when air flows upward over
from database-driven area navigation (RNAV) systems
rising terrain and is, consequently, adiabatically cooled
whereby latitude/longitude coordinate-based waypoints
to or below its initial dewpoint.
are generated by various means including keyboard
upslope wind — The deflection of the air by hills or input, and even electronic map mode functions used to
mountains, producing upward motions along the slopes establish waypoints with a cursor on the display. Another
of a mountain or hill. example is an offset phantom waypoint, which is a point
in space formed by a bearing and distance from navaids
upwind — In the direction from which the wind is blowing.
such as VORs, VORTACs, and TACANs, using a variety
upwind leg — See traffic pattern. of navigation systems.

331

10001930-002_AviationDictionary_2012_BOOK.indb 331 3/27/2012 9:38:32 AM

 utility category airplane • U-tube manometer

utility category airplane — An airplane certificated for

flight that includes limited acrobatics such as spins, lazy
eights, chandelles, and steep turns in which the bank
angle exceeds 60°.
utility finish — A finish used on aircraft that provides the
fabric with the necessary fill and tautness, but lacks the
glossy appearance of a showroom finish.
U-tube manometer — A “U”-shaped glass tube filled
with a liquid. Pressure is measured by connecting a gas
under pressure to one vertical of the manometer. The
pressure causes a differential between the levels in the
two verticals. This gives a differential pressure between
the gas pressure and atmospheric pressure. If the liquid is
water, the measurement is in water column inches (WCI).

332

10001930-002_AviationDictionary_2012_BOOK.indb 332 3/27/2012 9:38:32 AM

 V • valve seat

V valve duration — The length of time, measured in degrees

of crankshaft rotation, a valve in an aircraft engine
V speeds — Specific airspeeds given for individual aircraft. remains open.
An example of a V speed would be VNE, or never exceed valve face — The inner, tapered surface of an intake or
speed. V speeds are aircraft specific. exhaust valve that forms a seal against the valve seat in
vacuum — A negative pressure or pressure below the cylinder head when the valve is closed.
atmospheric pressure, usually expressed in inches of valve float — In reciprocating engines, a condition in which,
mercury (in. Hg). at high RPM, the valve lifters lose contact with the cam
vacuum bagging — In composites, a means of applying lobes because the valve springs are not strong enough
atmospheric pressure to a part while curing by sealing the to overcome the momentum of the various valve train
part in a plastic bag and removing most of the air. components. This allows the valve to open further and stay
open longer than design specifications call for. Extended
vacuum bottle — A container for keeping liquids hot or periods of valve float will damage the valve train.
cold. Has inner and outer walls with most of the air taken
from the space between the container walls in order to valve grinding — A process of removing part of a valve face
insulate the container. with a precision grinding machine. Grinding improves
the seal between the valves and their seats.
vacuum distillation — A distillation process that boils
liquids at very low pressures. This allows the liquids to valve guide — The component in an aircraft reciprocating
be distilled at lower temperatures than would otherwise engine cylinder head that guides the valve and holds the
be possible. valve head concentric with the valve seat.
vacuum forming — A thermoplastic forming that uses valve lag — The number of degrees of crankshaft rotation
vacuum and a heated die to form the plastic. after top or bottom center at which the intake or exhaust
valves open or close. For example, if the intake valve
vacuum pump — A device mounted on an aircraft engine closes at 60° of crankshaft rotation after the piston passes
that creates negative pressure used to drive some of the over top center and starts down on its intake stroke, the
gyroscopic flight instruments. exhaust valve lag is 60°.
vacuum tube — An evacuated glass or metal envelope valve lapping — A process in which a valve is matched to a
containing a cathode, heater, plate, and often one or more valve seat by using a fine abrasive compound. Valve lapping
grids. It serves as an electron control valve. removes any rough material to ensure an airtight seal.
vacuum-tube voltmeter — An electronic voltage-measuring valve lead — The number of degrees of crankshaft rotation
instrument used for electronic circuit testing. Its high before top or bottom center at which the intake or exhaust
input impedance prevents it from drawing appreciable valves open or close. For example, if an intake valve
power from the circuit being tested. opens 15° before the piston reaches top center on the
valence electron — 1. An outer electron that can be given exhaust stroke, it is said to have a 15° valve lead.
up or gained in the process of ionic compound formation. valve lift — The distance a valve is lifted off its seat when
2. An outer electron shared with another atom in the it is opened by the cam.
process of covalent compound formation.
valve overlap — The degrees of crankshaft rotation
valence shell — In physics, the electrons in the outer ring when both the intake and exhaust valves are open. In a
of an atom. four‑stroke‑cycle reciprocating engine, valve overlap
validity — Characteristic of a measuring instrument that improves the efficiency of engine operation by allowing
actually measures what it is supposed to measure and the low pressure caused by the exhaust gases leaving
nothing else. the cylinder to help the fresh charge of fuel-air in the
induction system to start moving into the cylinder.
valley breeze — An upslope wind flow caused by the
heating of the mountain slope that heats the adjacent air. valve ports — The intake and exhaust holes in the cylinder
of an aircraft reciprocating engine.
valve — A device that regulates the flow of a liquid or gas.
valve radius gauge — A gauge to determine if a valve has
valve clearance — The clearance between a valve head and the proper radius between the stem and the head. An
rocker arm when the valve is seated. improper radius is an indication of a stretched valve.
valve core — A spring‑loaded, resilient check valve inside valve seat — A hardened ring of steel or bronze, embedded
a valve stem that, when depressed, allows air to flow into in the cast aluminum cylinder head to provide proper
or out of a tire or chamber. seating for the poppet valve.

333

10001930-002_AviationDictionary_2012_BOOK.indb 333 3/27/2012 9:38:32 AM

 valve spring tester • variable geometry air inlet duct

valve spring tester — A machine used in engine overhaul vapor pressure — 1. The pressure, at a specific temperature,
to test the condition of valve springs by measuring the exerted by the vapor above a liquid. Vapor pressure can
force required to compress them to a specified height. prevent the release of additional vapor. 2. In meteorology,
the partial pressure of water vapor in the atmosphere.
valve springs — Helical-wound steel wire springs used to
close the poppet valves in an aircraft engine cylinder. vapor separator — A device in a pressure‑type carburetor
regulator unit that prevents air in the fuel from upsetting
valve stem — The portion of a poppet valve that rides in
the metering of the carburetor. The vapor separator
the valve guide and maintains concentricity between the
consists of a small float and needle valve positioned in
head of the valve and the valve seat.
the vapor separator chamber. When there are no vapors
valve stretch — Elongation of the valve stem caused by in the chamber, the fuel level raises the float and holds
overheating. the needle valve closed. As vapors gather, the fuel level
in the chamber drops, lowering the float until the needle
valve stretch gauge — A tool that measures the radius
valve opens, releasing the vapors back into the fuel tank.
between the valve head and the valve stem.
vapor trail — A cloudlike streamer frequently observed
valve timing — The relationship between the crankshaft
behind aircraft flying in clear, cold, humid air. The
rotation and the opening and closing of the intake and
pressure reduction above the wing surfaces and water
exhaust valves.
vapor in the engine exhaust gases combine to create a
valve train — Moving parts of the valve operating system. visible trail of condensed water vapor.
Includes lifters, springs, valves and associated installation
vapor-cycle air-conditioning system — A system for
parts.
cooling the air in an aircraft cabin in which the cabin
valve-timing clearance — The clearance to which poppet heat is absorbed into a liquid refrigerant, turning it into
valves using solid valve lifters are adjusted to set the a vapor. This vaporized refrigerant is carried into a
cam for valve timing. After the timing is set, the valve condenser outside the airplane where the heat is released
clearance is adjusted to the cold, or running, clearance. to the outside air, causing the refrigerant to revert back to
a liquid to begin the cycle over again.
vanadium — A malleable, ductile, silver-white metallic
chemical element with a symbol of V and an atomic vaporize — To change a liquid into a vapor.
number of 23. Alloyed with steel, it toughens and adds
vaporizing tube — A fuel nozzle that injects a fuel‑air
tensile strength to the steel.
mixture into the combustor. This nozzle is in a system
vanadium steel — A steel alloyed with 0.10% to 0.15% that operates at lower pressure than the atomizing type
vanadium to provide additional hardness and strength. fuel nozzle system.
Vanadium steel is used in the manufacture of technicians’
variable absolute pressure controller (VAPC) — The
tools.
intelligence of the turbo system. It monitors compressor
vane — Stationary airfoils within an engine. discharge pressure and limits the maximum pressure.
Also maintains the discharge pressure slightly higher
vane‑type pump — A constant
than manifold pressure. The VAPC controls the discharge
displacement, fluid-moving
pressure by regulating the oil flow through the waste gate
pump in which a rotor
actuator. The variable portion of the pressure controller
containing sliding vanes turns in
is mechanically connected to the throttle. Opening the
an eccentric cavity to force the
throttle to maintain a higher manifold pressure will
fluid through the pump.
also adjust the VAPC to maintain a higher compressor
vanishing point — Points in a discharge pressure. The system’s design prevents the
drawing that converge to give turbocharger from working at maximum output when the
the appearance of having depth. excess pressure is not needed.
vapor — The gaseous state of a material. variable capacitor — A capacitor whose capacity can be
changed by varying the distance between the plates.
vapor degreasing — A method of degreasing a part
Variable capacitors are commonly used in radio or radar
by treating it with the hot vapors of a solvent such as
tuning devices.
trichlorethylene.
variable displacement pump — A pump whose output can
vapor lock — A condition in a fuel system in which liquid
be varied. For high pressure applications, this is usually
fuel has turned into a vapor in the fuel lines. This vapor
done by varying the stroke of a piston‑type pump.
prevents the flow of liquid fuel to the carburetor or fuel
injectors. variable geometry air inlet duct — The inlet duct on a
supersonic turbojet aircraft whose area or shape can be

334

10001930-002_AviationDictionary_2012_BOOK.indb 334 3/27/2012 9:38:32 AM

 variable geometry aircraft • ventral fin

varied in flight. Provides the proper inlet pressure to vari-ramp — A movable ramp in a turbine engine inlet that
the first stage of the compressor as the airspeed of the controls supersonic diffusions and airflow velocity into
airplane changes. the compressor.
variable geometry aircraft — An aircraft with the ability varnish — 1. Surface finish: A preparation of resin dissolved
to alter the configuration of its wings. The wings are in oil or alcohol. Provides a glossy, protective surface for
swept forward for takeoff and low speed flight and then wood, metal, etc. 2. Engine deposit: A baked oil deposit
swept back for flight at supersonic speeds. formed on reciprocating engine components that have
been operated at excessively high temperatures.
variable inductor — In electricity, an inductor (coil) whose
inductance is changed by varying the number of coils or varsol — A petroleum product similar to naptha. Used as
the composition of the core. a solvent.
variable pitch propeller — A propeller whose blade pitch V-belt — A drive belt that has a cross section in the shape
can be changed while the engine is operating to obtain the of a “V.” V-belts are used to drive generators, pumps, and
most efficient operation. Also referred to as a controllable other accessories from a source of motorized power.
pitch or constant-speed propeller.
V-block — A block with a
variable resistor — An electronic resistance component V-notch cut across it. Used
that can be varied by rotating an adjusting screw or shaft for shrinking or stretching
or adjusting the position of a sliding contact. Rheostats sheet metal angles or flanges.
and potentiometers are variable resistors.
vector — 1. A variable that has
variable restrictor — A unit that can be adjusted to control magnitude and direction. For
the amount of fluid flow and thereby control the operating example, wind or pressure
speed of a unit. gradient.The line’s length indicates magnitude, and the arrow
point represents direction of action. 2. A heading issued to an
variable-angle stator vanes — Inlet guide vanes and
aircraft to provide navigational guidance by radar.
compressor stator vanes that can change their angle to the
accommodate the oncoming airstream. Variable-angle vector — A quantity with both magnitude and direction.
stator vanes are connected to the power lever and The length of the line indicates magnitude; the arrowhead
control engine stall tendencies during acceleration and indicates direction of motion or force.
deceleration.
vector sum — In mathematics, the resultant of adding two
variable-frequency oscillator (VFO) — An oscillator in a or more vectors.
radio receiver for generating a heterodyne signal that is
veering — In weather, the process of wind direction shifting
beat against the incoming signal to create an intermediate
clockwise, as from north to northeast.
frequency. If the intermediate frequency is at an audio
rate, it allows a signal to be presented to a speaker or velocity — The actual change of distance with respect
headphones. If the intermediate frequency is a radio to time. The average velocity is equal to total distance
frequency, it can be amplified and demodulated. divided by total time. Usually expressed in MPH or FPS.
Variac — The registered trade name for a brand of vendor — An individual or collective that sells goods or
autotransformer. In general usage it describes a variety of services.
autotransformers. An autotransformer is a single winding
veneer — 1. Any of the thin layers of wood bonded together
transformer having a carbon brush that can tap off any
to form plywood. 2. A layer of fine wood glued to the
number of turns for the secondary. It produces variable
surface of an inferior wood to provide a superior surface
voltage AC output.
or to create a more attractive appearance.
variation — The angular difference between the true, or
V-engine — An internal combustion engine with cylinders
geographic, poles and the magnetic poles at a given point.
arranged in two rows in the form of a “V,” with an angle
The compass magnet is aligned with the magnetic poles,
between the rows, i.e., 45° or 60°.
while aeronautical charts are oriented to the geographic
poles. This variation must be taken into consideration vent — An opening for the escape of a gas or liquid or for
when determining an aircraft’s actual geographic the relief of pressure.
location. Indicated on charts by isogonic lines, it is not
ventilate — To provide fresh air to the inside of a
affected by the airplane’s heading.
compartment.
variometer — Sensitive rate of climb or descent indicator.
ventral fin — A vertical, stabilizing fin on the lower rear
portion of an airplane fuselage. Its purpose is to increase
the directional stability of the airplane by increasing the
area behind the vertical axis.
335

10001930-002_AviationDictionary_2012_BOOK.indb 335 3/27/2012 9:38:32 AM

 venturi • very high frequency omni-directional range station

venturi — A specially shaped restrictor in a fluid flow the geometric descent path from the Final approach fix
passage used to increase the velocity of the fluid and (FAF), or on occasion from an intervening stepdown fix,
decrease its pressure. to the Threshold Crossing Height (TCH). This angle can
or can not coincide with the angle projected by a Visual
venturi tube — A source of vacuum for the operation
Glide Slope Indicator (VASI, PAPI, PLASI, etc.)
of gyroscopic instruments. It is a short tube with large
openings at both the front and rear with a specially vertical S — The basic vertical S begins with a climb at
designed restrictor between them. The velocity of the air a constant airspeed and rate. Once a particular cardinal
flowing through this tube is increased and its pressure altitude is reached, the climb is reversed and a constant
decreased as it passes the restriction. rate, constant airspeed descent is begun. The amount of
altitude between reversals can be varied. Once students
verify — Request confirmation of information; e.g., “verify
become proficient with the straight-ahead vertical S, turns
assigned altitude.”
are added to the problem. The vertical S is a good exercise
verify specific direction of takeoff (or turns after takeoff) to use in teaching students to transition from one set of
— Used by ATC to ascertain an aircraft’s direction conditions to another. These maneuvers are designed to
of takeoff and/or direction of turn after takeoff. It is improve students’ cross-check and aircraft control.
normally used for IFR departures from an airport not
vertical separation — Separation established by assignment
having a control tower. When direct communication with
of different altitudes or flight levels.
the pilot is not possible, the request and information can
be relayed through an FSS, dispatcher, or by other means. vertical speed indicator — A sensitive differential pressure
gauge that indicates the rate at which an aircraft is
vernier — A means of making extremely small divisions
climbing or descending. The vertical speed indicator
or measurements. It consists of a short scale made to
is connected to the static system and senses the rate of
slide along the divisions of a graduated instrument for
change of ambient pressure measured in feet per minute.
indicating parts of divisions.
vertical stabilizer — The fixed vertical surface of an
vernier caliper — A precision measuring tool used to
aircraft empennage to which the rudder is attached. Also
measure the inside or outside dimension of an object. An
referred to as vertical fin.
auxiliary or vernier scale is used to accurately divide the
increments of the regular scale. vertical takeoff and landing (VTOL) — An aircraft that
can takeoff and land without forward motion. Capable of
vernier micrometer caliper — A micrometer caliper with
vertical climbs and/or descents and of using very short
a vernier scale that allows each one thousandth‑inch
runways or small areas for takeoff and landings. These
increment to be subdivided into ten equal parts of one
aircraft include, but are not limited to, helicopters.
ten-thousandth of an inch.
vertical vibration — In helicopters, a vibration in which
vernier scale — See vernier.
the movement is in a vertical direction. One cause might
vertex — 1. In geometry, the point of a cone. 2. The last be a main rotor that is out of track.
fix adapted on the arrival speed segments. Normally, it
vertical visibility — The distance one can see upward into
will be the outer marker of the runway in use. However,
a surface based obscuration; or the maximum height from
it can be the actual threshold or other suitable common
which a pilot in flight can recognize the ground through a
point on the approach path for the particular runway
surface based obscuration.
configuration.
vertical wind shear — The change in wind speed and/or
vertex time of arrival — A calculated time of aircraft arrival
direction over a vertical distance. See also wind shear.
over the adapted vertex for the runway configuration in
use. The time is calculated via the optimum flight path vertigo — Spatial disorientation caused by the physical
using adapted speed segments. senses sending signals to the brain that create a feeling of
whirling and dizziness.
vertical axis — The axis of an airplane extending vertically
through the center of gravity. Also referred to as the yaw axis. very high frequency — The frequency band between 30
and 300 MHz. Portions of this band, 108 to 118 MHz,
vertical motion — Movement of air parcels in an upward
are used for certain NAVAIDs; 118 to 136 MHz are
or downward direction.
used for civil air/ground voice communications. Other
vertical navigation (VNAV) — A function of area frequencies in this band are used for purposes not related
navigation (RNAV) equipment that calculates, displays, to air traffic control.
and provides vertical guidance to a profile or path.
very high frequency omni-directional range station —
vertical path angle (VPA) (USA) — The descent angle The omni-directional, or all-directional, range station
shown on some non-precision approaches describing provides the pilot with a course from any point within its
service range It produces 360 usable radials or courses,
336

10001930-002_AviationDictionary_2012_BOOK.indb 336 3/27/2012 9:38:33 AM

 very high frequency omnirange (VOR) navigation equipment • vibration isolator

any one of which is a radio path connected to the station. rules is not recommended. To be given when the current
The radials can be considered as lines that extend from and/or forecast weather conditions are at or below VFR
the transmitter antenna like spokes of a wheel. Operation minimums. It does not abrogate the pilot’s authority to
is in the VHF portion of the radio spectrum (frequency make his own decision.
range of 109.0-117.95 MHz).
VFR over-the-top — With respect to the operation of aircraft,
very high frequency omnirange (VOR) navigation means the operation of an aircraft over-the-top under VFR
equipment — The omni-directional, or all‑directional, when it is not being operated on an IFR flight plan.
range station provides the pilot with a course from any
point within its service range It produces 360 usable VFR terminal area charts — Depict Class B airspace that
radials or courses, any one of which is a radio path provides for the control or segregation of all the aircraft
connected to the station. The radials can be considered as within the Class B airspace. The charts depict topographic
lines that extend from the transmitter antenna like spokes information and aeronautical information that includes
of a wheel. Operation is in the VHF portion of the radio visual and radio aids to navigation, airports, controlled
spectrum (frequency range of 109.0‑117.95 MHz). airspace, restricted areas, obstructions, and related data.

very low frequency (VLF) — The radio frequency range VFR waypoint — A predetermined geographical position
between 3 and 30 kHz. used for route/instrument approach definition, progress
reports, published VFR routes, visual reporting points or
VFR aircraft — An aircraft conducting flight in accordance points for transitioning, and/or circumnavigating controlled
with visual flight rules. and/or special use airspace. Defined relative to a VORTAC
VFR conditions — Weather conditions equal to or better station or in terms of latitude/longitude coordinates.
than the minimum for flight under visual flight rules. The VFR-on-top — ATC authorization for an IFR aircraft
term can be used as an ATC clearance/instruction only to operate in VFR conditions at any appropriate VFR
when: altitude (as specified in FAR and as restricted by ATC).
a. An IFR aircraft requests a climb/descent in VFR A pilot receiving this authorization must comply with
the VFR visibility, distance from cloud criteria, and
conditions.
the minimum IFR altitudes specified in FAR 91. The
b. The clearance will result in noise abatement benefits use of this term does not relieve controllers of their
where part of the IFR departure route does not conform responsibility to separate aircraft in Class B and Class C
to an FAA approved noise abatement route or altitude. airspace or TRSA’s as required by FAA Order 7110.65.
c. A pilot has requested a practice instrument approach VHF omni-directional range /tactical air navigation
and is not on an IFR flight plan. (VORTAC) — A navigation aid providing VOR azimuth,
TACAN azimuth, and TACAN distance measuring
All pilots receiving this authorization must comply
equipment (DME) at one site)
with the VFR visibility and distance from cloud
criteria in FAR 91. Use of the term does not relieve vibrating-reed frequency meter — An electronic meter
controllers of their responsibility to separate aircraft in that uses a series of reeds to indicate the tuned frequency.
Class B and Class C airspace or TRSA’s as required by The display has several reeds that are each tuned to vibrate
FAA Order 7110.65. When used as an ATC clearance/ at a specified and marked frequency. When a particular
instruction, the term can be abbreviated “VFR”; e.g., frequency is in tune, the associated reed vibrates and
“MAINTAIN VFR,” “CLIMB/ DESCEND VFR,” etc. appears as a wider band, thus indicating the frequency.
VFR cruising altitude — When flying above 3,000 feet vibrating-type voltage regulator — A voltage regulator
AGL on a magnetic heading of 0° to 179° you must fly for direct current generators or alternators. Uses vibrating
at odd thousand-foot altitudes plus 500 feet and on a points to sense the voltage and provide a varying
heading of 180° to 359° you are required to fly on even resistance for the generator field current.
thousands plus 500 feet up to the flight levels.
vibration — A quivering or trembling motion. The
VFR flight — Flight in accordance with visual flight rules. motion of the particles of an elastic body or medium is
in alternately opposite directions from the position of
VFR military training routes — Routes used by the
equilibrium when that equilibrium has been disturbed.
Department of Defense and associated Reserve and Air
Guard units for the purpose of conducting low-altitude vibration insulator — A resilient support that helps isolate
navigation and tactical training under VFR below 10,000 a system from steady state vibrations.
feet MSL at airspeeds in excess of 250 knots IAS.
vibration isolator — A flexible, shock-mount support
[Jeppesen does not chart these routes]
installed between a component and the structure.
VFR not recommended — An advisory provided by Vibration isolators reduce damage to electronic units
a flight service station to a pilot during a pre-flight or by keeping heavy vibrations in the structure from being
inflight weather briefing that flight under visual flight transmitted into the unit.

337

10001930-002_AviationDictionary_2012_BOOK.indb 337 3/27/2012 9:38:33 AM

 vibration meter • visibility

vibration meter — In turbine engines, a meter that senses sounds, and images to reproduce electronic versions of
vibration, measured in MILS (thousandths of an inch) or real life experience.
in./sec. (inches per second) occurring at the engine outer
viscosimeter — An instrument used to measure the
casings. Typical limit: 3 to 5 MILS.
viscosity of a fluid.
vibration pickup — A small electrical generator that
viscosity — The resistance to flow. In composites, resins have
transmits a turbine engine’s vibration signal to a vibration
a viscosity rating that corresponds to how thick they are.
meter either in the aircraft or in a test cell.
viscosity index — The measure of a fluid’s change in
vibrator — A relay that makes and breaks the flow of direct
viscosity due to a change in temperature.
current to produce pulsating DC, which can be passed
through an induction coil to change its voltage. viscous — Having a thick, glutinous consistency, and a
relatively high resistance to flow.
vibrator ignition system — An older turbine engine
ignition system that uses no storage capacitors. viscous damping — Diminishing the amount of vibration
by use of a fluid that turns some of the vibration energy
vibratory torque control — The special patented
into heat by pushing fluid through an orifice. A fluid
coupling between the crankshaft and propeller shaft of a
viscous damper also dissipates energy by redirecting the
Continental Tiara engine. It incorporates a quill shaft to
force, producing a damping pressure that creates a force
absorb torsional vibrations and a centrifugally actuated
that is 90 degrees out of phase with the vibration.
mechanism to lock out the quill shaft for operation when
a solid shaft would be more advantageous. vise — An adjustable tool that holds work and has two jaws
that open and close by means of a screw, lever, or cam.
Victor Airway — An airway system based on the use
of VOR facilities. The north‑south airways have odd Vise-grip pliers — A brand
numbers (Victor 11), and the east‑west airways have even name of locking pliers.
numbers (Victor 14). Locking is ac­complished
by an over-center locking
video — The electronic circuit components controlling or
device. The grip width of the
producing the visual signals displayed on a CRT.
pliers is variable through an adjusting screw in the handle.
video amplifier — An electronic component that can
visibility — The ability, as determined by atmospheric
amplify signals over a bandwidth sufficient to cover the
conditions and expressed in units of distance, to see
requirements of color video recording and broadcasting.
and identify prominent unlighted objects by day and
This bandwidth must range from 5 Hz to in excess of 5
prominent lighted objects by night. Visibility is reported
MHz.
as statute miles, hundreds of feet or meters.
video map — An electronically displayed map on the radar
a. Flight Visibility – The average forward horizontal
display that can depict data such as airports, heliports,
distance, from the cockpit of an aircraft in flight, at
runway centerline extensions, hospital emergency landing
which prominent unlighted objects can be seen and
areas, NAVAIDs and fixes, reporting points, airway/
identified by day and prominent lighted objects can be
route centerlines, boundaries, handoff points, special use
seen and identified by night.
tracks, obstructions, prominent geographic features, map
alignment indicators, range accuracy marks, minimum b. Ground Visibility – Prevailing horizontal visibility
vectoring altitudes. near the Earth’s surface as reported by the United
States National Weather Service or an accredited
view limiting device — A device used to limit the viewing
observer.
field of a pilot. This is typically used during instrument
training in order to allow the pilot to view only the c. Prevailing Visibility – The greatest horizontal visibility
instruments directly in front of him or her, entirely equaled or exceeded throughout at least half the
blocking references outside the aircraft. Common horizon circle that need not necessarily be continuous.
view limiting devices include plastic hoods and frosted
d. Runway Visibility Value (RVV) – The visibility
goggles.
determined for a particular runway by a
virga — Water or ice particles falling from a cloud, usually transmissometer. A meter provides a continuous
in wisps or streaks, and evaporating before reaching the indication of the visibility (reported in miles or
ground. fractions of miles) for the runway. RVV is used in lieu
of prevailing visibility in determining minimums for a
virtual reality (VR) — A computer-based technology that
particular runway.
creates a sensory experience that allows a participant to
believe and barely distinguish a virtual experience from e. Runway Visual Range (RVR) – An instrumentally
a real one. VR uses graphics with animation systems, derived value, based on standard calibrations, that

338

10001930-002_AviationDictionary_2012_BOOK.indb 338 3/27/2012 9:38:33 AM

 visibility (ICAO) • visual separation

represents the horizontal distance a pilot will see down by radiating a directional pattern of high intensity red
the runway from the approach end. It is based on the and white focused light beams that indicate to the pilot
sighting of either high intensity runway lights or on the that he is “on path” if he sees red/white, “above path” if
visual contrast of other targets whichever yields the white/white, and “below path” if red/red. Some airports
greater visual range. RVR, in contrast to prevailing or serving large aircraft have three-bar VASIs that provide
runway visibility, is based on what a pilot in a moving two visual glide paths to the same runway.
aircraft should see looking down the runway. RVR is
visual climb over the airport (VCOA) — An option to
horizontal visual range, not slant visual range. It is
allow an aircraft to climb over the airport with visual
based on the measurement of a transmissometer made
reference to obstacles to attain a suitable altitude from
near the touchdown point of the instrument runway
which to proceed with an IFR departure.
and is reported in hundreds of feet. RVR is used in
lieu of RVV and/or prevailing visibility in determining visual descent point (VDP) — A defined point on the final
minimums for a particular runway. approach course of a non-precision straight-in approach
procedure from which normal descent from the MDA to
1. Touchdown RVR – The RVR visibility readout
the runway touchdown point can be commenced, provided
values obtained from RVR equipment serving the
the approach threshold of that runway, or approach lights,
runway touchdown zone.
or other markings identifiable with the approach end of
2. Mid RVR – The RVR readout values obtained from that runway are clearly visible to the pilot.
RVR equipment located midfield of the runway.
visual flight rules (VFR) — 1. The procedures for
3. Rollout RVR – The RVR readout values obtained conducting flight under visual conditions according to
from RVR equipment located nearest the rollout Federal Aviation Regulations (FARs). The FARs specify
end of the runway. minimum cloud clearance and visibility requirements. 2.
VFR is also used to describe weather conditions and is
visibility (ICAO) — The ability, as determined by
often used interchangeably with the term VMC (visual
atmospheric conditions and expressed in units of distance,
meteorological conditions).
to see and identify prominent unlighted objects by day
and prominent lighted objects by night. Flight Visibility visual holding — The holding of aircraft at selected,
is the visibility forward from the cockpit of an aircraft in prominent geographical fixes that can be easily
flight. Ground Visibility is the visibility at an aerodrome recognized from the air.
as reported by an accredited observer. Runway Visual
visual inspection — The inspection of a part or component
Range (RVR) is the range over which the pilot of an
by visual means.
aircraft on the centre line of a runway can see the runway
surface markings or the lights delineating the runway or visual learners — Students who learn best with their sense
identifying its centre line. of sight. They prefer to absorb the big picture first, then
break the information down into individual parts.
visible light — Light wavelength between 4,000 and 7,700
angstroms (.4 - .77 µM) that can be seen by the eye. visual meteorological conditions (VMC) — Meteorological
conditions expressed in terms of visibility, distance from
visible line — A line on an engineering drawing that
cloud, and ceiling equal to or better than specified minima.
represents a portion of an object that can be seen.
visual purple — The chemical created by the rods that
visual approach — An approach conducted on an
provides night vision acuity. The proper name is
instrument flight rules (IFR) flight plan that authorizes
rhodopsin.
the pilot to proceed visually and clear of clouds to the
airport. The pilot must, at all times, have either the airport visual range — See runway visual range.
or the preceding aircraft in sight. This approach must be
visual separation — A means employed by ATC to separate
authorized and under the control of the appropriate air
aircraft in terminal areas and enroute airspace in the NAS.
traffic control facility. Reported weather at the airport
There are two ways to effect this separation:
must have a ceiling at or above 1,000 feet and visibility
of three miles or greater. a. The tower controller sees the aircraft involved and
issues instructions, as necessary, to ensure that the
visual approach (ICAO) — An approach by an IFR
aircraft avoid each other.
flight when either part or all of an instrument approach
procedure is not completed and the approach is executed b. A pilot sees the other aircraft involved and upon
in visual reference to terrain. instructions from the controller provides his own
separation by maneuvering his aircraft as necessary to
visual approach slope indicator (VASI) — An airport
avoid it. This can involve following another aircraft or
lighting facility providing vertical visual approach
keeping it in sight until it is no longer a factor.
slope guidance to aircraft during approach to landing

339

10001930-002_AviationDictionary_2012_BOOK.indb 339 3/27/2012 9:38:33 AM

 vitrify • voltmeter sensitivity

vitrify — To convert a material into glass or a glass-like voltage amplifier — A circuit designed to maximize voltage
substance by heat and fusion. gain at the expense of current gain or power gain.
vivid color —Colors of very high intensity and/or chroma. voltage avalanche — The reverse voltage required to cause
Sometimes used on aircraft for maximum visibility. a zener diode to break down and begin conducting.
VMC — Minimum controllable airspeed. VMC changes with voltage divider — A series of resistors placed across
altitude and is considered the minimum airspeed at which the poles of a source to provide a number of different
control of a multi-engine airplane can be maintained with voltages.
one engine inoperative.
voltage doubler — A circuit that produces an output voltage
VMC demonstration — This demonstration is required twice that of the input.
during a multi-engine practical test to show the control
voltage drop — 1. The decrease in voltage in an electrical
pressures necessary to maintain directional control with
circuit due to an increase in load. 2. The loss in potential
one engine inoperative.
energy in a circuit when a current is made to flow through
voice switching and control system (VSCS) — The VSCS a load and some of the energy is converted from electrical
is a computer controlled switching system that provides energy into another form such as heat.
air traffic controllers with all voice circuits (air to ground
voltage dropping resistor — A resistor placed in series
and ground to ground) necessary for air traffic control.
with some other component in order to reduce the
void — 1. Unsatisfactory gaps in a weld. 2. An empty area terminal voltage across or limit the current through that
in the composite laminate. The term void can be used component.
in place of delamination. 3. Internal fissure in ferrous
voltage quadrupler — In electricity, an amplifier whose
materials. Also referred to as fish eye, chrome check,
output current is four times its input current.
shatter crack, and snowflake.
voltage regulation — Maintaining a constant voltage level
volatile — A fluid easily vaporizable at relatively low
despite fluctuating load current requirements.
temperatures.
voltage regulator — A device that maintains a constant‑level
volatile content — In composites, the percent of volatiles
voltage supply despite changes in input voltage or load.
that are driven off as a vapor from a plastic or an
impregnated reinforcement. voltage rise — An increase in voltage caused by a decrease
in load or by the addition of a source, such as a chemical
volatile liquid — A fast-evaporating fluid.
cell, connected in series aiding with the general current
volatile memory — In computers, a memory or storage flow in the circuit.
device that loses its storage capability when power is
voltage spike — A quick burst of high voltage.
removed.
voltage standing-wave ratio — The ratio of the maximum
volatile mineral spirit — A fast-evaporating petroleum
voltage to the minimum voltage along a circuit.
product used as a paint or varnish thinner and for
preparing surfaces prior to painting. voltaic cell — A device (battery) containing electrodes
and an electrolyte for generating electricity by chemical
volatiles — In composites, materials, such as water and
action. Also referred to as a “galvanic” cell.
alcohol, in a resin formulation, that are capable of being
vaporized at room temperature. voltammeter — A d’Arsonval meter movement that can
be used either as an ammeter or a voltmeter. Though
volatility — The ease with which a fluid changes from a
this type of meter is a current measuring instrument, it
liquid to a vapor.
indicates voltage by measuring the current flow through
volcanic ash — In general, particulates and gases from a a resistance of known value. Measurements are in volts.
volcanic eruption.
volt-amperes — The product of the voltage and current in
VOLMET broadcast — Routine broadcast of a circuit.
meteorological information for aircraft in flight.
voltmeter — An electrical measuring instrument used to
volt — A unit of electromotive force (EMF) or potential measure electrical pressure or voltage.
difference that is needed to force one ampere of electrical
voltmeter sensitivity — A method used to determine the
flow through a resistance of one ohm.
accuracy of a meter. The sensitivity of a voltmeter is
voltage — The electric potential or potential difference given in ohms per volt and is determined by dividing the
expressed in volts. resistance of the meter plus the series resistance by the
full scale reading in volts.

340

10001930-002_AviationDictionary_2012_BOOK.indb 340 3/27/2012 9:38:33 AM

 volt-ohm-milliammeter • V-speed

volt-ohm-milliammeter — A multi-range electrical vortices — Circular patterns of air created by the movement
measuring instrument. The instrument can measure volts, of an airfoil through the air when generating lift. As an
amps, or resistance by selecting one of the instrument airfoil moves through the atmosphere in sustained flight,
ranges, which in turn, changes the internal connections to an area of low pressure is created above it. The air
measure a wide range of values. flowing from the high pressure area to the low pressure
volume — The space an object occupies. It is measured in area around and about the tips of the airfoil tends to roll
cubic units, found by multiplying the area of the base of up into two rapidly rotating vortices, cylindrical in shape.
the container by its height. These vortices are the most predominant parts of aircraft
wake turbulence and their rotational force is dependent
volume control — The circuit in a receiver or amplifier that upon the wing loading, gross weight, and speed of the
varies loudness of output. generating aircraft. The vortices from medium to heavy
volumetric efficiency — In reciprocating engines, the aircraft can be of extremely high velocity and hazardous
ratio of the volume of the charge taken into a cylinder, to smaller aircraft.
reduced to standard conditions, to the actual volume of VOT — A ground facility that emits a test signal to check
the cylinder. VOR receiver accuracy. Some VOTs are available to the
VOR — A ground-based electronic navigation aid user while airborne, and others are limited to ground use
transmitting very high frequency navigation signals, only.
360 degrees in azimuth, oriented from magnetic north. V-speed — Velocities relating to aircraft operation:
Used as the basis for navigation in the National Airspace
System. The VOR periodically identifies itself by Morse V1 — Decision speed, up to which it should be possible
Code and can have an additional voice identification to abort a takeoff and stop safely within the remaining
feature. Voice features can be used by ATC or FSS for runway length. After reaching V1 the takeoff must be
transmitting instructions/ information to pilots. continued.
VOR test signal (VOT) — A ground facility that emits a VA — Design maneuvering speed. The speed below which
test signal to check VOR receiver accuracy. Some VOTs abrupt and extreme control movements are possible
are available to the user while airborne, and others are (though not advised) without exceeding the airframe’s
limited to ground use only. limiting load factors.
VORTAC — A navigation aid providing VOR azimuth, VFE – Maximum flap extension speed (top of white arc on
TACAN azimuth, and TACAN distance measuring ASI).
equipment (DME) at one site)
VFTO – Final takeoff speed.
vortex — 1. A whirling, circulatory fluid motion. 2. In
meteorology, any rotary flow in the atmosphere. VMCA – Minimum control speed (air). The minimum
speed at which control of a twin-engine aircraft can be
vortex compressor blade tip — Profile-tip. A turbine maintained after failure of one engine.
engine blade that provides a smooth airflow at its tip end.
VMCG – Minimum control speed (ground). The minimum
vortex generators — Vortex generators are small speed at which control of a multi-engine aircraft can be
airfoil-like surfaces on the wing, which project vertically maintained after failure of a wing mounted engine on the
into the airstream. Vortices are formed at the tip of these ground.
generators just as they are on ordinary wingtips. These
vortices add energy to the boundary layer (the layer of VNE – Never-exceed speed, `redline speed’ denoted by a
air next to the surface of the wing) to prevent airflow red radial on an ASI.
separation. This reduces stall speed and can increase VMO – Maximum operating speed. Also MMO, Mach
takeoff and landing performance. limit maximum operating speed.
vortex ring — A microscale circulation cell superimposed VNO – Normal operating speed. The maximum structural
on the overall rising motion of a thermal, similar to a cruising speed allowable for normal operating conditions
smoke ring. It has a relatively narrow core of upward (top of green arc on ASI).
motions surrounded by a broad region of weaker sinking
motions. VR – Rotation speed, at which to raise the nose for
take-off.
vortex ring state — In helicopters, a transient condition
of downward flight (descending through air after just VREF – Reference landing speed.
previously being accelerated downward by the rotor)
VSO – Stalling speed at max takeoff weight, in landing
during which an appreciable portion of the main rotor
configuration with flaps and landing gear down, at sea
system is being forced to operate at angles of attack above
level, ISA conditions (bottom of white arc on ASI).
maximum. Blade stall starts near the hub and progresses
outward as the rate of descent increases. VX – Best angle of climb speed on all engines.
341

10001930-002_AviationDictionary_2012_BOOK.indb 341 3/27/2012 9:38:33 AM

 V-tail • VYSE

VXSE – Best engine-out angle of climb speed.

VY – Best rate of climb speed on all engines.
VYSE – Best engine-out rate of climb speed, `blue line
speed’ (blue radial on airspeed indicators of light twins)
VSSE – In multi engine aircraft, intentional one engine
inoperative airspeed. VSSE is not an airspeed defined
by the FAA, but rather an airspeed developed by the
manufacturer. It is considered the minimum speed for
intentionally rendering one engine inoperative in flight
for pilot training.
V-tail — A glider with two tail surfaces mounted to form a
V. V-Tails combine elevator and rudder movements.
V-tail surface — An empennage consisting of two fixed
and two movable surfaces arranged in a V shape. These
two surfaces have the same aerodynamic function as the
more conventional three surfaces.
VTOL aircraft — An aircraft that can takeoff and land
without forward motion. Capable of vertical climbs and/
or descents and of using very short runways or small
areas for takeoff and landings. These aircraft include, but
are not limited to, helicopters.
vulcanize — A process of treating crude rubber with sulfur
and subjecting it to heat. Vulcanizing increases the
strength and elasticity of the rubber.
VXSE — In multi-engine aircraft, best angle of climb, single
engine airspeed. VXSE is used for obstruction clearance
with engine inoperative. It provides the greatest altitude
gain over a specified distance with one engine inoperative.
VYSE — In multi-engine aircraft, best rate of climb, single
engine airspeed. VYSE is the speed that produces the
greatest gain in altitude in a given amount of time with
one engine inoperative.

342

10001930-002_AviationDictionary_2012_BOOK.indb 342 3/27/2012 9:38:33 AM

 W • water-injection system

W warm-up time — The time needed for a component and all

of its parts to reach operating temperature.
wafer-type selector switch — A multiple-contact switch warning area — Airspace of defined dimensions, extending
with contacts arranged around the edge of a wafer with a from 3 nautical miles outward from the coast of the
knob in the center. United States, that contains activity that can be hazardous
waffle piston — A reciprocating engine piston that has fins to nonparticipating aircraft. The purpose of such warning
cast on the bottom of the inside of the piston head that areas is to warn nonparticipating pilots of the potential
look like the surface of a waffle. This type of forging danger. A warning area can be located over domestic or
provides added strength and additional surface area for international waters or both.
carrying heat away from the piston. warning lights — Annunciation lights in an aircraft cockpit
wake turbulence — The rapidly rotating air that spills over that warn the flight crew of a dangerous situation or the
an airplane’s wings during flight. The intensity of the failure of a system or component.
turbulence depends on the airplane’s weight, speed, and warp direction — The threads running the length of the
configuration. Also referred to as wing tip vortices. fabric as it comes off the bolt. Parallel to the selvage edge.
walk-around bottle — A pressurized container of warp face — The side of the fabric where the greatest
breathing oxygen that is small enough for a passenger number of yarns are parallel to the selvage edge.
or crewmember to carry around the airplane. It consists
of a strap for carrying, a mask, a regulator, and a volume warp threads — The threads parallel to the length of a
indicator. fabric.
wall cloud — The well-defined bank of vertically developed warpage — Dimensional distortion in a plastic object.
clouds having a wall-like appearance, which form the Warren truss — A truss structure used for aircraft fuselages
outer boundary of the eye of a well-developed tropical in which the diagonal members carry both tensile and
cyclone. Also the portions of the rain free base of a compressive loads
supercell thunderstorm that is lower in the vicinity of the
main updraft. Tornadoes often develop here. wash — The disturbance in the air produced by the passage
of an airfoil. Also referred to as the “wake.”
Wankel engine — A brand name of a rotary piston engines
where the crankshaft and pistons are replaced by a wash primer — A self-etching primer used on aluminum
rotary piston coupled to a rotating shaft. The pistons or magnesium. It is often used to prepare the surface for
are replaced with a rotor that rotates inside a chamber zinc chromate primer.
causing the fuel-air charge to be compressed. This rotor washout — Slight twist built in on the outboard portion of
performs a uniform or variable rotary movement without the wing, designed to improve the stall characteristics of
being affected by alternating inertial forces caused by the the wing.
constantly reversing direction of a piston/rod/crankshaft
assembly. Since the motion produced is rotary, it can be water absorption — The ratio of the weight of water
utilized directly without having to be transformed. absorbed by a material to the weight of the dry material.
warm — A condition of having or emitting heat to a water ballast — System in some gliders for increasing in wing
moderate or adequate degree. loading, thus enabling increased average cross-country
speeds, using releasable water in the wings (via integral
warm airmass — An airmass characterized by temperatures tanks or water bags). Some gliders also have a small water
warmer than the ground over which it is moving. ballast tank in the tail for optimizing flying CG.
warm downslope wind — A warm wind that descends a water break test — Spraying water on a part to be bonded
slope on the lee side of a mountain, often called a chinook to assure there is no oil or grease contamination on the
or Foehn, is produced by a warm, stable, updraft airmass surface. If oil or grease is present, the water will bead.
moving across a range of mountains at high levels.
water equivalent — The depth of water that would result
warm front — The boundary area formed when a warm from the melting of snow or ice.
air mass contacts and flows over a colder air mass. Warm
fronts cause low ceilings and rain. water jet — Used primarily in the manufacturing process
as a cutting tool. A very high-pressure stream of water is
warm front occlusion — Characterized by the warm front used to cut through the component.
remaining on the ground and the cold front moving aloft.
water vapor — The gaseous form of H2O.
warm sector — The area covered by warm air at the surface
and bounded by the warm front and cold front of a wave water-injection system — A system in which water is
cyclone. injected along with the fuel to avoid damage to the engine.

343

10001930-002_AviationDictionary_2012_BOOK.indb 343 3/27/2012 9:38:33 AM

 waterspout • weight and balance records

As compression ratios are raised, or supercharging/ waypoint — A specified geographic location used to define
turbocharging is added to engines, temperatures rise and an an area navigation route or flight path of an aircraft
increased chance of detonation arises. Adding water injection employing area navigation. Waypoints are identified as
provides a water/air/fuel mixture that not only burns more either fly-by or fly-over.
efficiently and avoids spontaneous detonation but also
wear pads — In aircraft brakes, steel pads riveted to the
provides additional inlet air cooling and, hence, denser air.
surfaces of the stationary disks, the pressure plate, and
waterspout — A tornado that occurs over water. the back plate to provide a wearing surface against
the sintered material on the rotating disks. It is more
watt — The basic unit of electrical power. One ampere
economical to replace the wear pads than the disks and
flowing under a pressure of one volt is equal to one watt.
the plates themselves.
One watt equals 1/746 HP.
weather — The instantaneous state of the atmosphere.
wattage rating — The maximum amount of power an
electrical component needs to operate an appliance or weather advisory — In aviation weather forecast practice,
device without damaging the device. an expression of hazardous weather conditions not
predicted in the area forecast, as they affect the operation
watt-hour — A unit of electrical energy equal to one watt
of air traffic and as prepared by the NWS (National
acting for one hour.
Weather Service).
wattmeter — An instrument designed to measure electric
weather vane — A wind vane.
power in watts.
weave — In composites, the particular manner in which a
watt-second — A unit of electrical energy equal to one watt
fabric is formed by interlacing yarns. Usually assigned
acting for one second.
a style number used in ordering for the repair of a
wave carrier — An electromagnetic wave of high-frequency component.
alternating current whose modulations are used to
web — The portion of any beam or channel that lies between
transmit speech, images, and other signals. The more
the flanges of a spar, rib, or channel section. Furnishes
common term is carrier wave.
the strength necessary for longitudinal shear loads.
wave cyclone — A cyclone that forms and moves along a
web browser — A software program that provides access to
front. The circulation about the cyclone center tends to
sites on the World Wide Web (WWW).
produce a wavelike deformation of the front.
web of a beam — The portion of a beam that lies between
wave soldering — A method of soldering printed circuit
the flanges of a spar, rib, or channel section. Furnishes
boards where the board is placed slightly above a
the strength necessary for longitudinal shear loads.
container of molten solder. A wave is induced in the
solder and the resultant rise in level coats the exposed weber — A basic metric unit of magnetic flux equal to
leads, simultaneously soldering all component leads on that flux produced in a single turn of wire when an EMF
the board. of one volt is reduced to zero at a uniform rate of one
ampere per second.
wave window — Special areas arranged by Letter of
Agreement with the controlling ATC wherein gliders wedge — A tapered hard piece of wood or metal that can be
can be allowed to fly under VFR in Class A Airspace at used for splitting, tightening, securing, or levering.
certain times and to certain specified altitudes.
weft direction — Fibers that are perpendicular to the warp
waveform — The shape of an electrical signal as seen on fibers. Sometimes referred to as the woof or fill.
an oscilloscope. Examples of wave forms are sine waves
weighing points — The locations on an aircraft where
and square waves.
the scales are placed for weighing the aircraft. The
waveguide — A hollow metal tube designed to guide manufacturer designates the weighing points.
electromagnetic energy.
weight — A measure of the heaviness of an object. The force
wavelength — The distance between the crests of a wave by which a body is attracted toward the center of the Earth
of energy. Wavelength is inversely proportional to the (or another celestial body) by gravity. Weight is equal to
frequency of the wave. the mass of the body times the local value of gravitational
acceleration. One of the four main forces acting on an
way point — A predetermined geographical position used
aircraft. Equivalent to the actual weight of the aircraft. It
for route/instrument approach definition, progress reports,
acts downward toward the center of the Earth.
published VFR routes, visual reporting points or points
for transitioning, and/or circumnavigating controlled and/ weight and balance records — The aircraft records that
or special use airspace. Defined relative to a VORTAC provide the required information on the weight of the
station or in terms of latitude/longitude coordinates. empty aircraft and the location of its center of gravity (CG).

344

10001930-002_AviationDictionary_2012_BOOK.indb 344 3/27/2012 9:38:33 AM

 weight arm • Whitworth thread

weight arm — Another term for moment. Weight multiplied wet takeoff — Takeoff by an aircraft that is equipped with
by arm equals moment. engines that use water injection during takeoff.
weight shift control — A powered aircraft with a framed wet wing — An integral fuel tank in an aircraft wing made
pivoting wing and a fuselage controllable only in pitch by sealing part of the structure to use as a fuel tank.
and roll by the pilot’s ability to change the aircraft’s
wet-bulb temperature — The temperature of the air
center of gravity with respect to the wing. Flight control
modified by the evaporation of water from a wick
of the aircraft depends on the wing’s ability to flexibly
surrounding the thermometer bulb. Wet bulb temperature
deform rather that the use of control surfaces.
is used in conjunction with dry bulb temperature to
weld bead — The metal deposited in a welded joint for calculate the dew point.
reinforcement.
wet-bulb thermometer — A thermometer with a
weld fusion zone — The junction area of a weld that has muslin-covered bulb used to measure wet‑bulb
been melted together by heat. The area of base metal temperature.
melted as seen in the cross section of a weld.
wet-out — In composites, the saturation of an impregnated
weld procedures — The steps necessary to prepare a weld. fabric in which all areas of the fibers are filled with resin.
These steps can include making certain the necessary
wet-sump system — An oil system in which the oil is
equipment is available, the welding connections are
carried in a sump that is an integral part of the engine.
properly connected, the equipment is in good working
order, and the material to be welded is properly prepared. Wheatstone bridge — An electrical measuring circuit in
which the current through the indicator is determined by
welded patch — A patch of thin sheet steel welded over a
the ratio of the resistances of the four resistors that form
dent in a steel tubular structure to reinforce the structure
the legs of the bridge.
at the point of the damage.
wheel well — The part of the aircraft that receives or
welding — A method of joining materials in which a portion
encloses the landing gear as it retracts.
of each piece is melted and combined in its molten state.
Filler material is usually added for extra mass at the joint. when able — When used in conjunction with ATC
instructions, gives the pilot the latitude to delay
welding flux — A material used in welding that melts and
compliance until a condition or event has been
flows over the weld material to exclude oxygen from
reconciled. Unlike “pilot discretion,” when instructions
the surface of the molten metal and prevent oxides from
are prefaced “when able,” the pilot is expected to seek
forming in the weld.
the first opportunity to comply. Once a maneuver has
weldment — An assembly that is welded together. been initiated, the pilot is expected to continue until the
specifications of the instructions have been met. “When
Weston meter — An electronic instrument that utilizes a
able,” should not be used when expeditious compliance
moving coil.
is required.
wet bulb — Contraction of either wet-bulb temperature or
whetstone — An abrasive stone used for sharpening cutting
wet-bulb thermometer.
tools.
wet cell — An electrical power supply with electrodes and
whiffletree — A steering bell crank. It allows forces to
a liquid electrolyte for the conversion of chemical into
combine to produce an output.
electrical energy.
whip antenna — A quarter‑wave antenna usually in the
wet grinder — A precision grinding machine that uses a
high‑ or very-high frequency range. It is normally
flow of liquid coolant over the grinding stone to remove
vertically polarized.
the heat caused by grinding, preventing heat damage to
the material being ground. whirlwind — A small, rotating column of air; can be visible
as a dust devil.
wet head — A helicopter rotor head that uses oil as its
lubricant. white dew — Frozen dew.
wet lay-up — In composites, a method of making a whiteout — A situation where all depth perception is poor.
reinforced product by applying the resin system as a Caused by a low sun angle, and overcast skies over a
liquid when the reinforcement is put in place. snow covered surface.
wet sump engine — An engine in which all of the oil supply Whitworth thread — A screw thread used principally in
is carried within the engine itself. A dry sump engine has Great Britain. Also referred to as the British Standard
the majority of the oil contained in a separate tank. Whitworth (B.S.W.).

345

10001930-002_AviationDictionary_2012_BOOK.indb 345 3/27/2012 9:38:34 AM

 wicking • wing tip vortices

wicking — Occurs when solder flows to the insulation of wind velocity — A vector that includes wind direction and
stranded electrical wire during the soldering process. wind speed.
wide-area augmentation system (WAAS) — The WAAS is windmilling — The rotation of an aircraft propeller created
a satellite navigation system consisting of the equipment by air flowing around it with the engine not operating.
and software that augments the GPS Standard Positioning
window de-mister — A system of keeping the windows of
Service (SPS). The WAAS provides enhanced integrity,
an aircraft free of condensed moisture by blowing warm
accuracy, availability, and continuity over and above
air over or between the layers of transparent material.
GPS SPS. The differential correction function provides
improved accuracy required for precision approach. windshield — A transparent screen device made of plastic
or glass located in front of the occupants of a vehicle to
Wiggins coupling — A connector that allows fluid lines to
protect them from the elements of wind, rain, and cold.
be connected and disconnected quickly.
wing — An airfoil whose main function is to provide lift.
WILCO — I have received your message, understand it,
and will comply with it. wing area — The total wing area measured in square feet
by multiplying the wing span by the average wing chord.
winch — A machine that converts rotary motion to a tensile
force used for hauling or hoisting. A hand crank or motor wing chord — An imaginary straight line connecting
is connected to a drum around which a rope or cable the leading edge and the trailing edge of a wing airfoil
winds as the load is lifted. section.
wind — Air in motion relative to the surface of the Earth; wing fillet — A streamlined fairing between a wing and the
generally used to denote horizontal movement. fuselage. Used to smooth out the airflow and minimize
the interference drag caused by the junction.
wind chill factor — The effect of wind on temperature that
causes it to feel colder than the temperature would be wing flaps — The movable control surfaces on the trailing
without wind.. It blows away the thin layer of warm air edge of a wing inboard of the ailerons. Wing flaps alter the
that normally surrounds the body, and it draws away body camber and sometimes the area of the wing, increasing
heat by quickly evaporating any moisture that forms on both the lift and the drag.
the skin.
wing heavy — A condition of flight in which one wing
wind correction angle (WCA) — The angular difference has a tendency to fly lower than the other wing about an
between the heading of the airplane and the course. aircraft’s longitudinal axis. This condition is corrected by
properly adjusting the flight control rigging system.
wind direction — The direction from which wind is
blowing. wing loading — The ratio of the weight of a fully loaded
aircraft to the total wing area.
wind grid display — A display that presents the latest
forecasted wind data overlaid on a map of the ARTCC wing nut — A nut with two wing-like projections that can
area. Wind data is automatically entered and updated be gripped with a thumb and forefinger and, thus, turned
periodically by transmissions from the National by hand.
Weather Service. Winds at specific altitudes, along with
wing panel — A removable access panel or wing section
temperatures and air pressure can be viewed.
attached with screws, bolts, or rivets.
wind shear — A sudden, drastic shift in wind speed and/
wing profile — The outline of the wing section.
or direction that occurs over a short distance. Often
associated with weather fronts. wing rib — A structural member that gives a wing its
desired aerodynamic shape.
wind sock — A truncated cloth cone open at both ends and
mounted on a freewheeling pivot to indicate the direction wing span — The distance from one wingtip to the other.
the wind is blowing.
wing stations — Points measured from the centerline of an
wind triangle — Navigational calculation allowing aircraft (buttock line zero) toward the wing tip. Indicates
determination of true heading with a correction for the distance in inches from the centerline.
crosswinds on course.
wing strut — A diagonal brace between the fuselage and
wind tunnel testing — A test that uses a tunnel-like passage the wing of a semi-cantilever wing.
through which air is forced at controllable speeds in
wing tip vortices — Circular patterns of air created by the
order to study the effects of wind pressure on and around
movement of an airfoil through the air when generating lift.
airfoils, scale models, or other objects.
As an airfoil moves through the atmosphere in sustained
wind vane — An instrument to indicate wind direction. flight, an area of low pressure is created above it. The air
flowing from the high pressure area to the low pressure

346

10001930-002_AviationDictionary_2012_BOOK.indb 346 3/27/2012 9:38:34 AM

 wing tip vortices • working memory

area around and about the tips of the airfoil tends to roll wire bundle — A group of electrical wires tied together and
up into two rapidly rotating vortices, cylindrical in shape. secured to the structure.
These vortices are the most predominant parts of aircraft
wire cloth — A mesh woven of fine wire used for filtering.
wake turbulence and their rotational force is dependent
upon the wing loading, gross weight, and speed of the wire edge — A sharp burr on the edge of sheet metal that
generating aircraft. The vortices from medium to heavy has been cut on a shear.
aircraft can be of extremely high velocity and hazardous
wire gauge — A gauge used to measure wire diameter.
to smaller aircraft.
wire group — Two or more wires going to the same location
wing tip vortices — The rapidly rotating air that spills over
and tied together to retain their identity.
an airplane’s wings during flight. The intensity of the
turbulence depends on the airplane’s weight, speed, and wire mesh — In composites, a fine wire screen is used to
configuration. Also referred to as wake turbulence. dissipate an electrical charge from lightning or static
buildup. It is used as lightning protection usually directly
wing twist — A change in the aerodynamic shape of a wing
under the top layer of fabric.
that effectively causes the outboard section of the wing to
have less angle of attack than the inboard sections. Wing wire stripper — A tool designed to remove the insulation
twist allows the outboard section of the wing to avoid from electrical wires.
stalling at higher angles of attack, allowing ailerons to
wireless — British term for radio.
effectively control the roll of the aircraft.
wire-wound resistor — An electrical resistor made up of a
winglet — A design that nearly blocks or diffuses wing
winding of high‑resistance wire covered with baked‑on
tip vortices. Winglets are nearly vertical extensions on
ceramic material.
the wingtips, which are actually carefully designed,
proportioned, and positioned airfoils with their camber wobble pump — A hand‑operated fluid pressure pump. The
toward the fuselage, and with span, taper, and aspect ratio name wobble comes from the movement of the pump
optimized to provide maximum benefit at a specific speed handle back and forth as it pulls fluid into one side of the
and angle of attack. Also referred to as tip fins. pump and forces it out the other side.
winglet — A short, almost vertical stabilizing fin projecting woodruff key — A hardened piece of metal shaped in a half
from the tip of an aircraft wing. The winglet alters the circle on one side and flat on the other side. The key fits
downwash that normally washes across the wing’s into a semi‑circular groove to secure a wheel, disk, or
surface. This reduces induced drag and actually provides gear to a shaft.
a small amount of forward thrust. These two effects more
Wood’s metal — An alloy of lead, tin, bismuth, and
than cancel the parasitic drag of the winglet and reduce
cadmium that melts at a temperature of 158°F.
the overall drag of the aircraft.
words twice — 1. As a request: “Communication is difficult.
wingtip vortices — Circular patterns of air created by an
Please say every phrase twice.” 2. As information:
airfoil when generating lift. Vortices from medium to
“Since communications are difficult, every phrase in this
heavy aircraft can be extremely hazardous to small aircraft.
message will be spoken twice.”
wink Zyglo — A non‑destructive inspection method
work — The product of force and the distance through
in which the part to be inspected is sprayed with a
which the force acts.
fluorescent penetrant liquid. The penetrant seeps into any
surface cracks in the part. The liquid is then washed from workability — The ease with which wood, metal, or plastic
its surface and the part is placed in a vibrating fixture can be formed or shaped.
and observed under an ultraviolet light. If the vibration
work-hardening — Increasing the` strength and hardness
causes a crack that contains the penetrant to open and
of a metal by work‑hardening or cold‑working. The
close, the black light will illuminate the penetrant and
strain‑hardening is normally done after a piece of
give the appearance of winking each time the crack opens
material has been heat treated. If an aluminum alloy is
up to expose the penetrant.
not heat-treatable, strain hardening is the only way it can
wiper — A movable electrical contact used in an electrical be hardened.
component.
working life — In composites, the period of time during
wire braid — A woven, flexible metal that covers an which a liquid resin or adhesive remains usable.
aircraft’s electrical wiring and is used to intercept and
working memory — The portion of the brain that receives
ground any radiated electrical energy from the wire to
information from the sensory register. This portion of
prevent radio frequency interference.
the brain can store information in memory for only a
short period of time. If the information is determined

347

10001930-002_AviationDictionary_2012_BOOK.indb 347 3/27/2012 9:38:34 AM

 working voltage • wye connection

by an individual to be important enough to remember, it written tests — Often used as an evaluation device. They
must be coded in some way for transmittal to long-term include computerized tests as well as paper-and-pencil
memory. Also referred to as short-term memory. tests, and are often referred to as knowledge tests. A
test is a set of questions, problems, or exercises used
working voltage — The maximum amount of electrical
to determine whether your students have a particular
voltage that can safely be applied to an appliance without
knowledge or skill.
damaging it.
wrought iron — An easily welded, forged, or shaped iron
workload management — Ensures that essential
that contains very little carbon.
operations are accomplished by planning, prioritizing,
and sequencing tasks to avoid work overload. wrought metal — A metal that has been worked by rolling,
drawing, or forging, and which has a different grain
world aeronautical chart (WAC) — Similar to a sectional
structure from that of cast metal.
chart, but with a scale of 1:1,000,000. Provide a standard
series of aeronautical charts covering land areas of the wye connection — An electrical circuit connection that
world at a size and scale convenient for navigation looks like the letter Y.
by moderate speed aircraft. Topographic information
includes cities and towns, principal roads, railroads,
distinctive landmarks, drainage, and relief. Aeronautical
information includes visual and radio aids to navigation,
airports, airways, restricted areas, obstructions and other
pertinent data.
world wide web (WWW) — A part of the Internet that
provides access through the network by means of
graphics and hypertext links to different Web sites. Also
referred to as the Web.
worm gear — A gear that
consists of a threaded shaft
and a toothed wheel that are
meshed to­gether.
worm screw — A
worm-shaped gear that
meshes with a cogged gear set. When turned, it imparts a
radial motion on the cogged set, creating a rotary motion
90º from the input.
woven fabric — A material constructed by interlacing
yarns, fibers, or filaments to form fabric patterns.
WOXOF — Pronounced “walks off”, a slang weather term
meaning visibility zero in fog. Also seen as WXOF and
WOXOFF.
wrench — A tool with fixed or adjustable jaws for gripping
a nut, bolt, or pipe, and a long handle for leverage in
turning.
wrinkle — In composites, a surface imperfection in
laminated plastics that has the appearance of a crease or
fold in one or more outer sheets of the paper, fabric, or
other base. Also occurs in vacuum bag molding when the
bag is improperly placed, causing a crease.
wrinkle finish — A paint finish that wrinkles as it dries to
give a rough appearance.
wrist pin — The hardened steel pin that attaches the small
end of a connecting rod to a piston.

348

10001930-002_AviationDictionary_2012_BOOK.indb 348 3/27/2012 9:38:34 AM

 X • xylol

X
x-axis — The longitudinal axis about which an aircraft
rolls. The ailerons are used to control this movement. The
vertical axis is the Z-axis and the lateral axis is the Y-axis.
X-band radar — Radar that operates in a frequency band
of between 5.2 and 10.9 gigahertz.
xenon — A heavy, colorless, inert chemical gas element
with a symbol of Xi and an atomic number of 54.
X-ray — An electromagnetic radiation with an extremely
short wavelength. Capable of penetrating solid objects
and exposing photographic film.
X-ray inspection — A nondestructive inspection in which
high-frequency, high-energy electromagnetic waves pass
through the material and expose a photographic film.
Defects or discontinuities within the material show up as
variations in the density of the image on the film.
xylene — A toxic, flammable, aromatic hydrocarbon,
similar to benzene. It is used as a solvent. Also referred
to as xylol.
xylol — See xylene.

349

10001930-002_AviationDictionary_2012_BOOK.indb 349 3/27/2012 9:38:34 AM

 Y • Y-winding

Y yoke — 1. The control column in an airplane cockpit that

connects to and controls the movement of the elevators
Yagi antenna — A directional transmitting or and ailerons. 2. A cross member in a control system that
receiving antenna that uses one active dipole links or joins something together.
element and one or more directing dipoles and Y-valve — The oil drain valve for a dry sump engine. It
one or more reflecting dipoles. The passive derives its name from its shape. One arm of the “Y” goes
dipoles, which are not connected electrically, to the pressure pump inlet, one arm to the oil tank, and
are aligned for physical position. They the lower arm is fitted with a valve. From this valve, the
interact with each other to form a directional oil can be drained from the tank. Fuel for oil dilution is
field pattern. Most home-type TV antennae also introduced in the Y-valve.
are of the Yagi type.
Y-winding — A method of connecting the phase windings
yard — A measure of length. One yard is equal of a three-phase AC machine in which one end of each of
to 3 feet, 36 inches, or .914 meters. the three phase windings is connected together to form a
yardstick — A graduated measuring device that common point or a neutral terminal.
is 3 feet long and marked in inches and feet.
yarn — Twisted filaments, fibers, or strands, forming a
continuous length that is suitable for use in weaving into
materials.
yaw — The movement of an aircraft about its vertical axis.
yaw damper — An automatic control device used to
keep an aircraft from yawing. Swept wing aircraft are
particularly susceptible to Dutch Roll, an undesirable
yawing and rolling motion. Yaw dampers overcome the
unwanted yawing condition.
yaw string — A demonstration used to show the existence
of slip. To accomplish a yaw string demonstration, tape
a piece of yarn to the windscreen or to the top of the
nose of the aircraft. It should be placed in an area of
undisturbed flow. During flight, you will be able to see
the yarn move depending on whether or not the aircraft is
in a zero sideslip configuration.
Y-axis — The lateral, pitch axis. Pitch movements are
controlled by the elevators.
Y-connected circuit — A three-phase, or polyphase,
alternating current circuit that has three single‑phase
windings spaced so that the voltage induced in each
winding is 120° out of phase with the voltages in the
other two windings.
yellow arc — A yellow marking on an instrument that
indicates a region of caution. On an airspeed indicator,
for instance, the yellow arc indicates a range of speeds
that are tolerable to fly in calm air, but not in turbulence.
yield point — The load on a material, expressed in lbs./
square inch, that causes the initial indication of permanent
distortion. Also referred to as yield strength.
yield strength — The load on a material, expressed in lbs./
square inch, that causes the initial indication of permanent
distortion.

350

10001930-002_AviationDictionary_2012_BOOK.indb 350 3/27/2012 9:38:34 AM

 Z • Zyglo Inspection

Z zero sideslip — A control technique used following an

engine failure in a multi-engine aircraft where the pilot
Zahn cup — A cup of definite size and shape, with a hole maintains an attitude that minimizes drag, alleviating the
in its bottom used to measure the viscosity of a material sideslip of the airplane. As bank angle exceeds the zero
by the number of seconds required for the cup to empty. sideslip value, there is a sharp loss of climb performance.
Zero sideslip angle varies with the airplane type. Flying
Z-axis — The vertical axis of an object. Turning the nose at zero sideslip allows adequate directional control with
of the aircraft, for example, causes the aircraft to rotate the best climb performance possible.
about its vertical axis. Rotation of the aircraft about the
vertical axis is called yawing. This motion is controlled zero-lash valve lifter — A hydraulic device in a reciprocating
with the rudder. engine that reduces the slack between a valve and the valve
lifter due to changes in the engine operating temperatures.
zener diode — A diode rectifier designed to prevent the
flow of current in one direction until the voltage in the zero-lift line — A line through an airfoil, along which a
reverse direction reaches a predetermined value. At this flow of relative wind will produce no lift.
time, the diode permits a reverse current to flow. zero-time — An engine overhauled by the factory. Only a
zenith — The highest point directly overhead. factory overhaul can be called a zero-time engine.

zephyr — A west wind or a gentle breeze. zinc — A bluish‑white, crystalline metal with a symbol of
Zn and an atomic weight of 30. Zinc is ductile in its pure
Zeppelin — A rigid cylindrical airship supported by internal state but quite brittle in its commercial form. It is used in
gas cells. Invented by Count Ferdinand von Zeppelin. the production of electrical batteries and for coating steel
Zerk fitting — A grease fitting with a check valve that parts to protect them by means of sacrificial corrosion.
allows grease to be pumped through the fitting into a zinc chloride cell — In batteries, a chemical cell using
bearing surface. Removal of the grease gun allows the powdered manganese dioxide and zinc as its pole pieces
check valve to reseat preventing grease from leaking out and a solution of zinc chloride as its electrolyte.
and dirt from entering the fitting.
zinc chromate primer — An alkyd resin,
zero — 1. Numerical: 0. Having no value. Used as a corrosion‑inhibiting primer that can be used on almost all
reference point. 2. Temperature: A reference point on a metal surfaces. Moisture releases chromate ions to inhibit
Fahrenheit thermometer that is 32° below the freezing the formation of corrosion, and the alkyd resin forms a
point of water or the point on a Celsius thermometer good bond for aircraft finishes.
where water freezes.
Z-marker — A radio beacon that radiates in a vertical
zero adjustment — The adjustment on an instrument to a cone-shaped pattern. Z-markers are placed along airways
zero point, or to an arbitrary point from which all negative or approach courses to denote specific locations.
and positive measurements are to be adjusted.
zone numbers — The location marks on an aircraft
zero bleed — In composites, a laminate fabrication drawing, both vertical and horizontal. They are used to
procedure that does not allow loss of resin during cure. locate detail parts on the drawing.
zero fuel weight — The weight of the aircraft to include all Zulu time — The proper radio phraseology when making
useful load except fuel. Limits the ratio of loads between reference to coordinated universal time.
the fuselage and wings. The maximum load that an airplane
can carry also depends on the way the load is distributed. Zyglo Inspection — A penetrant inspection system in which
The weight of an airplane in flight is supported largely by a fluorescent dye is drawn into surface defects in a material.
the wings; therefore, as the load carried in the fuselage is The defects are made visible by a powder-type developer.
increased, the bending moment on the wings is increased.
zero fuel weight — The weight of an aircraft that includes
the entire useful load, minus the fuel.
zero gravity — The effect of gravity when it has been
nullified by parabolic flight.
zero lash — A condition in a valve train in a reciprocating
engine in which all of the clearance is kept out of the
valve train by the use of hydraulic valve lifters.

351

10001930-002_AviationDictionary_2012_BOOK.indb 351 3/27/2012 9:38:34 AM

10001930-002_AviationDictionary_2012_BOOK.indb 352 3/27/2012 9:38:34 AM
 ABBREVIATIONS/ACRONYMS

A — Acceleration ACFO — Aircraft Certification Field ADSIM — airfield delay simulation

Office model
A&P — airframe and powerplant
mechanic ACFT — aircraft ADSY — administrative equipment
systems
A/C — aircraft ACID — aircraft identification
ADTN — administrative data
A/FD — Airport/Facility Directory ACLS — automatic carrier landing
transmission network
system
A/G — air to ground
ADTN2000 — Administrative Data
ACLT — actual landing time
A/H — altitude/height Transmission Network 2000
calculated
AAC — Mike Monroney ADU — attitude direction unit
ACM — air cycle machine
Aeronautical Center
ADVO — administrative voice
ACO — Aircraft Certification Office
AAF — Army Air Field
AEG — aircraft evaluation group
ACW — air crew warning
AAI — arrival aircraft interval
AER — approach end of runway
AD — Airworthiness Directive
AAM — air-to-air missile
AERA — automated enroute air
AD — ashless dispersant
AAP — advanced automation traffic control
program ADA — Air Defense Area
AEX — automated execution
AAP — autoflight annunciator panel ADAP — Airport Development Aid
AF — airway facilities
Program
AAR — airport acceptance rate
af — audio frequency
ADAS — AWOS Data Acquisition
AAS — Airport Advisory Service
System AFB — Air Force Base
ABC — after bottom center
ADC — air data computer AFC — automatic frequency control
ABDIS — Automated Data
ADCCP — Advanced Data AFCS — automatic flight control
Interchange System Service B
Communications Control system
ABS — anti-skid brake system Procedure
AFDS — Autopilot Flight Director
AC — Advisory Circular ADCUS — advise customs System
AC — Air Corps ADDA — administrative data AFIS — automated flight inspection
system
AC — alternating current ADF — automatic direction finder
AFM — aircraft flight manual
AC — convective outlook (weather) ADI — attitude direction indicator
AFP — area flight plan
ACAIS — Air Carrier Activity ADI — automatic de ice and
Information System inhibitor AFRES — Air Force Reserve
Station
ACARS — aircraft communications ADIZ — Air Defense Identification
addressing and reporting system Zone AFS — Airways Facilities Sector
ACAS — aircraft collision ADL — aeronautical data link AFSFO — AFS Field Office
avoidance system
ADLY — arrival delay AFSFU — AFS Field Unit
ACC — area control center
ADM — aeronautical decision AFSOU — AFS Field Office Unit
ACCT — accounting records making (Standard is AFSFOU)
ACD — automatic call distributor ADO — Airline Dispatch Office AFSS — Automated Flight Service
Station
ACDO — Air Carrier District Office ADP — automated data processing
AFTN — Automated Fixed
ACF — Area Control Facility ADS — automatic dependent
Telecommunications Network
surveillance

353

10001930-002_AviationDictionary_2012_BOOK.indb 353 3/27/2012 9:38:37 AM

 AGL — above ground level AMSL — above mean sea level ARLNO — airline office
AHC — auto heading comparator AMT — aviation maintenance ARO — airport reservation office
technician
AHRS — attitude heading reference ARP — air data reference panel
system AMVER — Automated Mutual
ARP — airport reference point
Assistance Vessel Rescue System
AID — airport information desk
ARSA — airport radar service area
AN — Air Force-Navy Standard
AIG — Airbus Industries Group
ARSR — air route surveillance radar
ANC — alternate network
AIM — Aeronautical Information
connectivity ARTCC — Air Route Traffic
Manual
Control Center
AND — Air Force-Navy Design
AIP — Aeronautical Information
ARTS — Automated Radar Terminal
Publication ANG — Air National Guard
System
AIP — Airport Improvement Plan ANGB — Air National Guard Base
AS — Aeronautical Standard
AIRMET — Airman’s ANMS — automated network
ASA — American Standards
Meteorol­ogical Information monitoring system
ASAS — Aviation Safety Analysis
AIRNET — Airport Network ANP — actual navigation
System
Simulation Model performance
ASC — AUTODIN switching center
AIS — Aeronautical Information ANSI — American National
Service Standards Institute ASCP — aviation system capacity
plan
AIT — automated information AOA — angle of attack
transfer ASD — aircraft situation display
AOCC — airline operations control
ALD — available landing distance center ASDA — accelerate-stop distance
available
ALNOT — alert notice AP — acquisition plan
ASDAR — acft to satellite data relay
ALP — airport layout plan AP — autopilot system
ASDE — airport surface detection
ALS — approach lighting system APC — absolute pressure controller
equipment
ALSF1 — ALS with sequenced API — American Petroleum Institute
ASLAR — aircraft surge launch and
flashers I
APP — approach recovery
ALSF2 — ALS with sequenced
APP — auto-pilot panel ASM — air‑to‑surface missile
flashers II
APS — airport planning standard ASM — available seat mile
ALSIP — approach lighting system
improvement plan APU — auxiliary power unit ASOS — automated surface
observation system
ALTRV — altitude reservation APV — approach with vertical
guidance ASP — arrival sequencing program
AM — amplitude modulation
AQAFO — Aeronautical Quality ASQP — airline service quality
AMASS — Airport Movement Area
Assurance Field Office performance
Safety System
ARAC — Army Radar Approach ASR — airport surveillance radar
AMC — automatic mixture control
Control
ASTA — airport surface traffic
AMCC — ACF/ARTCC
ARAC — Aviation Rulemaking automation
Maintenance Control Center
Advisory Committee
ASTM — American Society of
AMOS — Automated
ARCTR — FAA Aeronautical Testing Materials
Meteorological Observation
Center or Academy
Station ASV — airline schedule vendor
ARF — airport reservation function
AMP — ARINC Message Processor AT — air traffic
ARFF IC — Aircraft Rescue And
AMP — Airport Master Plan AT&T — American Telephone and
Fire Fighting Incident Commander
Telegraph
AMS — Aeronautical Material
ARINC — Aeronautical Radio
Specification AT&T ASDC — AT&T Agency
Incorporated
Service Delivery Center
354

10001930-002_AviationDictionary_2012_BOOK.indb 354 3/27/2012 9:38:37 AM

 AT&T CSA — AT&T Customer ATP — Airline Transport Pilot BBS — bulletin board system
Support Associate
ATR — Airline Transport Rating BC — back course
ATA — actual time of arrival
ATS — air traffic service BCA — benefit/cost analysis
ATA — Air Transport Association
ATS — Air Traffic Services (FAA) BCD — binary coded decimal
ATAS — Airspace and Traffic
ATSCCP — ATS Contingency BCR — benefit/cost ratio
Advisory Service
Command Post
BDAT — digitized beacon data
ATC — after top center
ATT — attitude retention system
BDC — bottom dead center
ATC — air traffic control
ATTIS — AT&T Information
BFO — beat frequency oscillator
ATCAA — air traffic control Systems
mode of ADF
assigned airspace
AUL — Approved Unserviceable
BFO — beat‑frequency oscillator
ATCBI — air traffic control beacon List
indicator BHP — brake horsepower
AUTODIN — DoD Automatic
ATCCC — Air Traffic Control Digital Network BIM — blade inspection method
Command Center
AUTOVON — DoD Automatic BIS — blade inspection system
ATCO — air taxi commercial Voice Network
BL — bend tangent line
operator
AVAIDS — navigational aids
BMEP — brake mean‑effective
ATCRB — air traffic control radar
AVC — automatic volume control pressure
beacon
AVGAS — Aviation gasoline BMP — best management practices
ATCRBS — Air Traffic Control
Radar Beacon System AVN — Aviation Standards National BOC — Bell Operating Company
Field Office
ATCSCC — Air Traffic Control BPCU — bus power control unit
System Command Center AVON — AUTOVON Service
bps — bits per second
ATCT — airport traffic control AVTUR — Aviation turbine fuel
BRI — basic rate interface
tower
AWC — aviation weather center
BRITE — Bright Radar Indicator
ATD — actual time of departure
AWG — American Wire Gauge Terminal Equipment
ATD — along track (straight line)
AWIS — airport weather BRL — building restriction line
distance
information
BSFC — brake specific fuel
ATE — actual time enroute
AWOS — Automated Weather consumption
ATIS — Automatic Terminal Observing System
BTC — before top center
Information Service
AWP — aviation weather processor
BUEC — back-up emergency
ATISR — ATIS recorder
AWPG — aviation weather products communications
ATM — air traffic management generator
BUECE — back-up emergency
ATM — air turbine motor AWS — air weather station communications equipment
ATM — asynchronous transfer mode AWSS — Automated Weather C — Celsius (Centigrade)
Sensor System temperature
ATMS — Advanced Traffic
Management System BANS — BRITE alphanumeric C/A — coarse acquisition
system
ATN — Aeronautical CAA — Civil Aviation Authority
Telecommunications Network BART — Billing Analysis Reporting
CAB — Civil Aeronautics Board
Tool (GSA software tool)
ATODN — AUTODIN terminal
CADC — central air data comp
(functional unit or system) BASIC — basic contract observing
station CAP — Civil Air Patrol
ATOMS — Air Traffic Operations
Management System BASOP — military base operations CARF — Central Altitude
Reservation Facility
ATOVN — AUOTVON (facility) BBC — before bottom center

355

10001930-002_AviationDictionary_2012_BOOK.indb 355 3/27/2012 9:38:37 AM

 CAS — calibrated airspeed CENTX — central telephone COE — U.S. Army Corps of
exchange Engineers
CASFO — Civil Aviation Security
Office CEQ — Council on Environmental COMCO — command
Quality communications outlet
CAT — category
CERAP — central radar approach Consol — kind of low or medium
CAT — clear air turbulence
frequency long range navigational
CERAP — combined Center/
CAT II — Category II approach aid
Rapcon
CAU — crypto ancillary unit Consolan — a kind of low or
CFA — controlled firing area
medium frequency long range
CAVU — clear, and visibility
CFC — central flow control navigational aid
unlimited
CFCF — central flow control CONUS — Continental United
CAWS — central aural warning
facility States
system
CFCS — central flow control service CORP — Private Corporation other
CBI — computer based instruction
than ARINC or MITRE
CFI — certificated flight instructor
CC&O — customer cost and
CP — center of pressure
obligation CFIT — controlled flight into terrain
CPDLC — Controller Pilot Data
CCAS — cockpit crew alerting CFR — Code of Federal Regulations
Link Communications
system
CFR — Cooperative Fuel Research
CPE — customer premise equipment
CCC — communications command
CFWP — central flow weather
center CPMIS — consolidated personnel
processor
management information system
CCCC — staff communications
CFWU — central flow weather unit
CPU — central processing unit
CCCH — central computer complex
CG — center of gravity
host CPU — control protection unit
CGAS — Coast Guard Air Station
CCL — convective condensation CRA — conflict resolution advisory
level CGCC — center of gravity control
CRDA — converging runway
computer
CCLD — Core Capability Limited display aid
Deployment CIG — ceiling
CRM — crew resource management
CCS-7NI — Communication CIT — compressor inlet temperature
CRT — cathode ray tube
Channel Signal-7 Network
CL — coefficient of lift
Interconnect CSA — communications service
CLC — course line computer authorization
CCSD — command communications
service designator CLIN — contract line item CSD — constant-speed drive
CCU — central control unit CLT — calculated landing time CSEU — control system electronic
unit
CD — common digitizer CM — circular mils
CSG — slide graphic computer
CD — controller display CM — commercial service airport
CSIS — centralized storm
CD — Convergent-Divergent duct CMNPS — Canadian Minimum
information system
(venturi) Navigation Performance
Specification Airspace CSO — customer service office
CDI — course deviation indicator
CNS — consolidated NOTAM CSR — communications service
CDP — compressor discharge
system request
pressure
CNSP — consolidated NOTAM CSS — central site system
CDR — cost detail report
system processor
CTA — control area
CDT — controlled departure time
CO — carbon monoxide
CTA — controlled time of arrival
CDTI — cockpit display of traffic
CO — central office
information CTA — current transformer
CO2 — carbon dioxide assembly
CDU — central data unit

356

10001930-002_AviationDictionary_2012_BOOK.indb 356 3/27/2012 9:38:38 AM

 CTA/FIR — control area/flight DARC — direct access radar DFDR — digital flight data recorder
information region channel
DFGC — direct flight guidance
CTAF — Common Traffic Advisory dBA — decibels A, weighted computer
Frequency
DBCRC — Defense Base Closure DFGS — direct flight guidance
CTAS — center TRACON and Realignment Commission system
automation system
DBMS — data base management DFI — direction finding indicator
CTC — cabin turbo compressor system
DG — directional gyro
CTMA — Center Traffic DBRITE — digital bright radar
DGPS — differential global
Management Advisor indicator tower equipment
positioning satellite (system)
CTOT — constant torque on takeoff DBU — database unit
DH — Decision Height
CUD — course unit display DC — direct current
DID — direct inward dial
CUPS — consolidated uniform DC — Divergent-Convergent duct
DIN — AUTODIN Service
payroll system
DCA — Defense Communications
DIP — drop and insert point
CVFP — charted visual flight Agency
procedure DIRF — direction finding
DCA — Ronald Reagan Washington
CVFR — controlled visual flight National Airport DITCO — Defense Information
rules Technology Contracting Office
DCAA — dual call, automatic
Agency
CVR — cockpit voice recorder answer device
DME — distance measuring
CVRS — computerized voice DCAS — digital core avionic system
equipment
reservation system
DCCU — data communications
DME/N — standard DME
CVTS — compressed video control unit
transmission service DME/P — precision distance
DCE — data communications
measuring equipment
CW — carrier wave equipment
DME/P — precision DME
CW — continuous wave DCP — data collection package
DMN — data multiplexing network
CW — continuous wave NDB DDA — dedicated digital access
signals DNL — day light equivalent sound
DDD — direct distance dialing
level (also called LDN)
CWA — center weather advisory
DDM — difference in depth of
DoD — Department of Defense
CWP — cockpit warning panel modulation
DOD — direct outward dial
CWS — central warning system DDS — digital data service
DOI — Department of Interior
CWSU — center weather service DEA — Drug Enforcement Agency
unit DOS — Department of State
DECM — defensive electronic
CWY — clearway counter measures DOT — Department of
Transportation
DA — decision altitude DECU — digital elect control unit
DOTCC — Department of
DA — density altitude DEDS — data entry and display
Transportation Computer Center
system
DA — descent advisor
DOTS — dynamic ocean tracking
DEIS — draft environmental impact
DA — direct access system
statement
DABBS — DITCO Automated DP — instrument departure
DEP — departure
Bulletin Board System procedure
DER — departure end of runway
DADC — digital air data computer DPDT — double‑pole,
DEWIZ — Distant Early Warning double‑throw
DAIR — direct altitude and identity
Identification Zone
readout DPST — double‑pole, single‑throw
DF — direction finder
DAR — designated agency DPU — data processor unit
representative DFAX — digital facsimile
DR — dead reckoning
357

10001930-002_AviationDictionary_2012_BOOK.indb 357 3/27/2012 9:38:38 AM

 DSCS — digital satellite EFIS — electronic flight information ETA — estimated time of arrival
compression service systems
ETD — estimated time of departure
DSUA — dynamic special use EFIS — electronic flight instrument
ETE — estimated time enroute
airspace (indication) system
ETG — enhanced target generator
DTS — dedicated transmission EGT — exhaust gas temperature
service ETMS — enhanced traffic
EIAF — expanded inward access
management system
DUAT — Direct User Access features
Terminal ETN — electronic
EICAS — engine indication and
telecommunications network
DUATS — Direct User Access crew alerting system
Terminal System EU — European Union
EICAS — engine indication central
DVA — diverse vector area alert system EVAS — enhanced vortex advisory
system
DVFR — day visual flight rules EIS — environmental impact
statement EVBC — engine variable bleed
DVFR — defense visual flight rules
control
ELT — emergency locator
DVOR — doppler very high
transmitter EVC — engine vane control
frequency omni directional range
ELWRT — electrowriter EVCS — emergency voice
DVRCR — differential voltage
communications system
reverse current relay EMF — electromotive force
(voltage) EWCG — empty weight center of
DYSIM — dynamic simulator
gravity
EMPS — enroute maintenance
EADI — electronic attitude direction
processor system EWR — Newark International
indicator
Airport
EMSAW — Enroute Minimum Safe
EARTS — Enroute Automated
Altitude Warning F&E — facility and equipment
Radar Tracking System
ENAV — enroute navigational aids F/F — Fuel Flow
EAS — equivalent airspeed
EOF — emergency operating facility FA — aviation area forecast
EC — European Community
EPA — Environmental Protection FAA — Federal Aviation
ECCM — electronic counter-coun-
Agency Administration
termeasures
EPC — external power container FAAAC — FAA Aeronautical
ECM — electronic countermeasures
Center
EPE — estimated position error
ECOM — enroute communications
FAACIS — FAA Communications
EPR — engine pressure ratio
ECU — electronic control unit Information System
EPROM — erasable programmable
ECU — engine control unit FAA-PMA — Federal Aviation
read only memory
Administration - Parts
ECVFP — expanded charted visual
EPS — engineered performance Manufacturing Approval
flight procedures
standards
FAATC — FAA Technical Center
EDC — engine driven compressor
EPSS — enhanced packet switched
FAATSAT — FAA
EDCT — expect departure clearance service
Telecommunications Satellite
time
ERAD — enroute broadband radar
FAC — facility
EDP — engine driven pump
ESEC — enroute broadband
FAD — Fuel Advisory Departure
EDP — expedite departure path secondary radar
FAF — final approach fix
EEC — electronic engine computer ESF — extended superframe format
FAP — final approach point
EEL — emergency exit lights ESFC — equivalent specific fuel
consumption FAPM — FTS2000 Associate
EFAS — enroute flight advisory
Program Manager
service ESP — enroute spacing program
FAR — Federal Aviation Regulation
EFC — expect further clearance ESV — expanded service volume
FAST — final approach spacing tool
ESYS — enroute equipment systems
358

10001930-002_AviationDictionary_2012_BOOK.indb 358 3/27/2012 9:38:38 AM

 FAWP — final approach waypoint FGC — flight guidance computer fps — feet per second
FAX — facsimile equipment FIFO — flight inspection field office FRC — request full route clearance
FB — fly by FIG — flight inspection group FREQ — frequency
FBO — fixed-base operator FINO — Flight Inspection National FSAS — flight service automation
Field Office system
FBS — fall back switch
FIPS — Federal Information FSDO — Flight Standards District
FCC — Federal Communications
Publication Standard Office
Commission
FIR — Flight Information Region FSDPS — flight service data
FCLT — freeze calculated landing
processing system
time FIRE — fire station
FSEP — facility/service/equipment
FCOM — FSS Radio Voice FIRMR — Federal Information
profile
Communications Resource Management Regulation
FSEU — flap/slat electronic unit
FCPU — facility central processing FISDL — flight information services
unit data link FSN — Fuel Spray Nozzle
FCU — Fuel Control Unit FL — flight levelFLIP — flight FSP — flight strip printer
information publication
FD — flight director system FSPD — freeze speed parameter
FLOWSIM — traffic flow planning
FD — winds and temperatures aloft FSS — Flight Service Station
simulation
forecast
FSSA — Flight Service Station
FM — fan marker
FDAT — flight data entry and Automated Service
printout (FDEP) and flight data FM — frequency modulation
FSTS — federal secure telephone
service
FMA — final monitor aid service
FDAU — flight data acquisition unit
FMC — flight management FSYS — flight service station
FDC — Flight Data Center computer equipment systems
FDE — flight data entry FMCS — flight management ft/sec — Feet per second
computer system
FDEP — flight data entry and FTS — Federal Telecommunications
printout FMEP — friction mean effective System
pressure
FDI — integrated flight indicator FTS2000 — Federal
FMF — facility master file Telecommunications System 2000
FDIO — flight data input/output
FMIS — FTS2000 Management FUS — functional units or systems
FDIOC — flight data input/output
Information System
center FWCS — flight watch control
FMS — flight management system station
FDIOR — flight data input/output
remote FMSP — flight management system GA — general aviation
procedure
FDM — frequency division GAA — general aviation activity
multiplexing FNMS — FTS2000 Network
GAAA — general aviation activity
Management System
FDP — flight data processing and avionics
FO — fly over
FED — federal GADO — General Aviation District
FOB — fuel on board Office
FEIS — final environmental impact
statement FOD — foreign object damage gal — Gallon
FEP — front end processor FOIA — Freedom of Information GBAS — ground based
Act augmentation system
FET — field effect transistor
FP — flight plan GCA — ground control approach
FFAC — from facility
fpm — feet per minute GCO — ground communication
FFG — fuel flow governor
outlet
FPNM — feet per nautical mile
FFR — fuel flow regulator
GCU — generator control unit

359

10001930-002_AviationDictionary_2012_BOOK.indb 359 3/27/2012 9:38:38 AM

 GEO — geostationary satellite HAT — height above touchdown Hz — hertz
zone
GFP — Ground Fine Pitch I/AFSS — International AFSS
HAZMAT — hazardous materials
GLS — GNSS landing system IA — indirect access
HCAP — high capacity carriers
GNAS — General National Airspace IA — inspection authorization
System HDME — NDB with distance
IAF — initial approach fix
measuring equipment
GNSS — global navigation satellite
IAP — instrument approach
system HDQ — headquarters
procedure
GNSS — Global Navigation Satellite HDTA — high density traffic
IAPA — instrument approach
System airports
procedures automation
GNSSP — global navigation satellite HE — High Energy
IAS — indicated airspeed
system panel
HELI — heliport
IAWP — initial approach waypoint
GOES — Geostationary Operational
HF — high frequency
Environ­mental Satellite IBM — International Business
Hg — Mercury Machines
GOESF — GOES Feed Point
HGS — head-up guidance system IBP — international boundary point
GOEST — GOES terminal
equipment HH — NDB, 2kw or more IBR — intermediate bit rate
GPA — gas path analysis HI EFAS — high altitude EFAS IC — integrated circuit
(enroute flight advisory service)
gph — gallons per hour ICA — initial climb area
HIG — hermetically sealed
GPS — global positioning satellite ICAO — International Civil
integrating gyro
Aviation Organization
GPS — global positioning system
HIRL — high intensity runway
ICSS — International
GPU — ground power unit lights
Communications Switching
GPWS — ground proximity warning HIWAS — hazardous inflight Systems
system weather advisory service
IDAT — interfacility data
GRADE — graphical airspace HLDC — high level data link
IDG — integrated drive generator
design environment control
IEC — integral electronic control
GRI — group repetition interval HMU — hydromechanical unit
IEPR — integrated engine pressure
GS — glide slope HOC — high oil consumption-jet
ratio
engine
GS — groundspeed
IF — intermediate fix
HOV — high occupancy vehicle
GSA — General Services
if — intermediate frequency
Administration HP — High Pressure
IFCP — interfacility
GSD — geographical situation HP — Horse Power
communications processor
display
hr — hour
IFDS — interfacility data system
GSE — ground support equipment
HSI — horizontal situation indicator
IFEA — in flight emergency
GSI — glide slope indicator
HSTCU — horizontal stabilizer trim assistance
GTE — Gas Turbine Engine control unit
IFF — Identification, Friend or Foe
GUS — ground uplink station HUD — head‑up display
IFIM — International Flight
H — Non Directional Radio Homing HUD — Housing and Urban Information Manual
Beacon (NDB) Development
IFO — International Field Office
HAA — height above airport HVOR — high altitude VOR
IFR — instrument flight rules
HAL — height above landing HWAS — hazardous in flight
IFS — integrated flight system
weather advisory
HARS — high altitude route system
IFSS — international flight service
HYD ISO — hydraulic isolation
HASOV — hot air shut-off valve station

360

10001930-002_AviationDictionary_2012_BOOK.indb 360 3/27/2012 9:38:38 AM

 IGFET — insulated gate field effect ITT — inlet turbine temperature LAN — local area network
transistor
ITT — intermediate turbine LASCR — light‑activated silicon
IGV — inlet guide vane temperature control rectifier
IHP — indicated horsepower ITWS — integrated terminal LAT — latitude
weather system
ILS — instrument landing system LATA — local access and transport
IVRS — interim voice response area
IM — inner marker
system
LAWRS — limited aviation weather
IMC — instrument meteorological
IVSI — instant vertical speed reporting station
conditions
indicator
lb — pound
IMEP — indicated mean effective
IVSI — instantaneous rate of climb
pressure LCD — liquid crystal display
indicator
in. Hg — inches of mercury LCF — local control facility
IW — inside wiring
INM — integrated noise model LCN — local communications
j — joule (energy unit)
network
INS — inertial navigation system
JATO — jet assisted takeoff
LDA — landing directional aid
Int — intersection
JFC — jet fuel control
LDA — landing distance available
INU — inertial navigation unit
JFET — junction field effect
LDIN — lead in lights
IOAT — indicated outside air transistor
temperature LEC — local exchange carrier
JFK — John F. Kennedy
IOC — initial operational capability international airport LED — light emitting diode
IPB — illustrated parts breakdown JPT — jet pipe temperature LEMAC — leading edge of the
mean aerodynamic chord
IPC — illustrated parts catalog Kbps — kilobits per second
LF — low frequency
IPL — illustrated parts list KE — Kinetic Energy
LF/MF — low/medium frequency
IPM — illustrated parts manual kHz — kilohertz
LFR — low-frequency radio range
IR — IFR military training route KIAS — knots indicated airspeed
LGA — LaGuardia Airport
IR — infrared kt — Knot (1 nm/hr)
LH — left‑hand (threads)
IRAN — Inspect and Repair As KTAS — knots true airspeed
Necessary LINCS — Leased Interfacility NAS
KVAR — kilovolt amperes reactive
Communications System
IRBM — intermediate‑range
KVDT — keyboard video display
ballistic missile LIRL — low intensity runway lights
terminal
IRMP — information resources LIS — Logistics and Inventory
L/MF — low/medium frequency
management plan System
LA — power lever angle
IRS — inertial reference system LLWAS — Low Level Wind Shear
LAA — local airport advisory Alert System
IRU — inertial reference unit
LAAS — local area augmentation LMM — compass locator at middle
ISA — International Standard
system marker
Atmosphere
LAAS — Low Altitude Alert System LMM — locator middle marker
ISDN — integrated services digital
network LABS — leased A B service LMS — LORAN monitor site
ISMLS — interim standard LABSC — LABS GS 200 Computer LNAV — lateral navigation
microwave landing system
LABSR — LABS remote equipment LOC — ILS localizer
ISOV — isolation shutoff valve
LABSW — LABS switch system LOCID — location identifier
ISU — inertial sensing unit
LAHSO — land and hold short LOI — letter of intent
ITI — interactive terminal interface operations

361

10001930-002_AviationDictionary_2012_BOOK.indb 361 3/27/2012 9:38:38 AM

 LOM — compass locator at outer Mbps — megabits per second MIRL — medium intensity runway
marker lights
MCA — minimum crossing altitude
LONG — longitude MIS — meteorological impact
MCAS — Marine Corps Air Station
statement
LOP — line of position
MCC — Maintenance Control
MISC — miscellaneous
LOP — low oil pressure Center
MISO — Manufacturing Inspection
LORAN — long range navigation MCD — metal chip detector
Satellite Office
system
MCDU — multipurpose control
MIT — miles in trail
LOX — liquid oxygen display unit)
MITP — metal in tail pipe
LP — low pressure MCL — middle compass locater
MITRE — Mitre Corporation
LRCO — limited remote MCS — maintenance and control
communications outlet system MLS — Microwave Landing System
LRNAV — long range navigation MDA — minimum descent altitude MM — ILS Middle Marker
LRR — long range radar MDT — maintenance data terminal MMC — maintenance monitoring
console
LRRA — low range radio altimeter MEA — minimum enroute altitude
mmf — magnetomotive force
LSB — least significant bit MEA — minimum enroute IFR
altitude MMS — maintenance monitoring
LSI — large scale integration
system
MEC — main engine control
LVOR — low altitude VOR
MNPS — minimum navigation
MEF — maximum elevation figure
M — mach performance specification
MEK — methyl-ethyl-ketone
MAA — maximum authorized MNPSA — minimum navigation
altitude MEL — minimum equipment list performance specifications
airspace
MAA — maximum authorized IFR METAR — aviation routine weather
altitude report MOA — memorandum of agreement
MAC — mean aerodynamic chord METI — meteorological MOA — military operations area
information
MAHWP — missed approach MOCA — minimum obstruction
holding waypoint METO — maximum except takeoff clearance altitude
power
MALS — medium intensity MODE C — altitude encoded
approach lighting system MF — middle frequency beacon reply
MALSF — MALS with sequenced MFDU — multi function display MODE S — mode select beacon
flashers unit system
MALSR — MALS with runway MFJ — modified final judgment MOS — metal oxide semiconductor
alignment indicator lights
MFQ — main fuel quantity MOSFET — metal oxide
MAP — maintenance automation semiconductor field effect
MFT — meter fix crossing time/slot
program transistor
time
MAP — military airport program MOU — memorandum of
MH — magnetic heading
understanding
MAP — missed approach point
MHA — minimum holding altitude
mph — miles per hour
MAP — modified access pricing
MHz — megahertz
MPO — Metropolitan Planning
MAP — monitor alert parameter
MIA — minimum IFR altitudes Organization
MAWP — missed approach
MIDO — Manufacturing Inspection MPS — maintenance processor
waypoint
District Office subsystem
MB — magnetic bearing
MIG — metal inert gas MPS — master plan supplement
MB — marker beacon
MILSPEC — military specifications MRA — minimum reception altitude
mb — millibars
MRC — monthly recurring charge
362

10001930-002_AviationDictionary_2012_BOOK.indb 362 3/27/2012 9:38:38 AM

 MS — military standard NAS — National Airspace System NFIS — NAS Facilities Information
System
MSA — minimum safe altitude NAS — Naval Air Station
NI — network interface
MSAW — minimum safe altitude NASA — National Aeronautics and
warning Space Administration NICS — National Interfacility
Communications System
MSB — most significant bit NASDC — National Aviation Safety
Data NIDS — National Institute for
MSD — most significant digit
Discovery Sciences
NASP — National Airspace System
MSI — medium‑scale integration
Plan NIMA — National Imagery and
MSL — mean sea level Mapping Agency
NASPAC — National Airspace
MSN — message switching network System Performance Analysis NM — nautical mile
Capability
MTCS — modular terminal NMAC — near mid air collision
communications system NATCO — National
NMC — National Meteorological
Communications Switching
MTI — moving target indicator Center
Center
MTR — military training route NMCE — network monitoring and
NATO — North Atlantic Treaty
control equipment
MULTICOM — frequency used at Organization
airports without a tower, FSS, or NMCS — network monitoring and
NAVAID — navigation aid
UNICOM control system
NAVMN — navigation monitor and
MUX — multiplexer NOAA — National Oceanic and
control
Atmospheric Administration
MVA — minimum vectoring altitude
NAWAU — National Aviation
NOC — notice of completion
MVFR — marginal VFR Weather Advisory Unit
NOPAC — North Pacific
MVFR — marginal visual flight NAWPF — National Aviation
rules Weather Processing Facility NoPT — no procedure turn required
N — Rotational speed, RPM NBCAP — National Beacon Code NOS — National Ocean Service
Allocation Plan
n.m. — nautical miles NOTAM — notice to airmen
NCAR — National Center for
N1 — Low pressure spool NPA — nonprecision approach
Atmospheric Research
N2 — High pressure spool NPDES — National Pollutant
NCF — National Control Facility
Discharge Elimination System
N2O — Nitrous oxide
NCIU — NEXRAD communications
NPIAS — National Plan of
NAAQS — National Ambient Air interface unit
Integrated Airport Systems
Quality Standards
NCS — National Communications
NPN — negative, positive, negative
NACO — National Aeronautical System
transistor
Charting Office
NDB — nondirectional radio beacon
NPRM — notice of proposed rule
NADA — NADIN concentrator
NDB(ADF) — nondirectional making
NADIN — National Airspace Data beacon (automatic direction
NRC — non recurring charge
Interchange Network finder)
NRCS — National Radio
NADSW — NADIN switches NEPA — National Environmental
Communications Systems
Policy Act
NAF — Naval Aircraft Factory
NSA — national security area
NEXRAD — next generation
NAILS — National Airspace
weather radar NSAP — National Service
Integrated Logistics Support
Assurance Plan
NFAX — National Facsimile Service
NAPRS — National Airspace
NSSFC — National Severe Storms
Performance Reporting System NFDC — National Flight Data
Forecast Center
Center
NAS — National Aerospace
NSSL — National Severe Storms
Standard NFDD — National Flight Data
Laboratory; Norman, OK
Digest
NAS — National Aircraft Standard
NSW — no significant weather
363

10001930-002_AviationDictionary_2012_BOOK.indb 363 3/27/2012 9:38:38 AM

 NSWRH — NWS Regional OPSW — operational switch PCG — positive course guidance
Headquarters
OPX — off premises exchange PCL — pilot controlled lighting
NTAP — Notices to Airmen
ORD — Chicago O’Hare PCM — pulse code modulation
Publication
International Airport
PCU — prop control unit
NTP — National Transportation
ORD — operational readiness
Policy pd — potential difference
demonstration
NTS — negative torque sensor PDAR — preferential arrival and
OROCA — off-route obstruction
departure route
NTSB — National Transportation clearance altitude
Safety Board PDC — performance data computer
ORTAC — VOR combined with
NTZ — no transgression zone UHF tactical air navigation PDC — pre departure clearance
NWS — National Weather Service OTR — oceanic transition route PDC — program designator code
NWSR — NWS Weather excluding OTS — organized track system PDN — public data network
NXRD
P — pressure PDR — preferential departure route
NXRD — advanced weather radar
p.s.i. — pounds per square inch P-factor — an element of
system
asymmetrical thrust
P/CG — pilot/controller glossary
O — oxygen
PFC — passenger facility charge
P/S — power section
OAG — Official Airline Guide
PFD — personal flotation device
P1 — pressure at Station 1 (engine
OALT — operational acceptable
nose) PGB — propeller gear box
level of traffic
P7 — tailpipe pressure PIBAL — pilot balloon observation
OASIS — Operation and
Supportability Implementation PA — precision approach PIC — pilot in command
System
PA — pressure altitude PIC — principal interexchange
OAT — outside air temperature carrier
PABX — private automated branch
OAW — off airway weather station exchange PIDP — programmable indicator
data processor
OBS — omni bearing selector PAD — packet assembler/
disassembler PinS — point in space
OCS — obstacle clearance surface
PAM — peripheral adapter module PIREP — pilot weather report
ODAL — omnidirectional approach
lighting system PAPI — precision approach path PK — Parker-Kalon screw
indicator
ODAPS — Oceanic Display and PLASI — pulsating approach slope
Processing Station PAR — precision approach radar indicator
OEI — one engine inoperative PAR — preferential arrival route PM — phase modulation
OFA — object free area PAR — preferred arrival route PMC — power management control
OFDPS — Offshore Flight Data PATWAS — pilots automatic PMS — program management
Processing System telephone weather answering system
service
OFT — outer fix time PNP — positive, negative, positive
PBCT — proposed boundary transistor
OFZ — obstacle free zone
crossing time
POB — persons on board
OM — ILS outer marker
PBRF — pilot briefing
POH — pilot’s operating handbook
OMB — Office of Management and
PBX — private branch exchange
Budget POI — principal operations
PC — personal computer inspector
ONER — oceanic navigational error
report PCA — positive control airspace POLIC — police station
OPLT — operational acceptable PCA — positive control area POP — point of presence
level of traffic
PCB — printed circuit board POT — point of termination

364

10001930-002_AviationDictionary_2012_BOOK.indb 364 3/27/2012 9:38:39 AM

 PPI — plan-position indicator RAIL — runway alignment indicator RCO — remote communications
lights outlet
PPIMS — Personal Property
Information Management System RAIM — receiver autonomous RCU — remote control unit
integrity monitoring
PPS — precise positioning service RDAT — digitized radar data
RAPCO — Radar Approach Control
PR — primary commercial service RDP — radar data processing
(USAF)
airport
RDSIM — runway delay simulation
RAPCON — Radar Approach
PRBCV — pressure ratio bleed model
Control (FAA)
control valve
REIL — runway end identifier lights
RAREP — radar weather report
PRI — primary rate interface
RF — radio frequency
RAT — ram air temp
PRM — precision runway monitor
RFI — radio-frequency interference
RAT — ram air turbine
PROM — programmable read‑only
RHI — range-height indicator
memory RATCC — Radar Air Traffic
(scope)
Control Center
PRT — power recovery turbine
RII — required inspection item
RATCF — Radar Air Traffic Control
PRV — Pressure Relief Valve
Facility (USN) RL — general aviation reliever
PSDN — public switched data airport
RATO — rocket-assisted takeoff
network
RLIM — runway light intensity
RB — relative bearing
PSEU — proximity sense elect unit monitor
RBC — rotating beam ceilometer
psi — pounds per square inch RMCC — remote monitor control
RBDPE — radar beacon data center
PSN — packet switched network
processing equipment
RMCF — remote monitor control
PSS — packet switched service
RBDT — ribbon display terminals facility
PSTN — public switched telephone
RBN — radio beacon RMI — radio magnetic indicator
network
RBSS — Radar Bomb Scoring RMK — remark
PSU — passenger service unit
Squadron
RML — radio microwave link
PT — procedure turn
RCAG — remote center air/ground
RMLR — RML repeater
PTS — practical test standards
RCAG — remote communications
RMLT — RML terminal
PTU — power transfer unit air/ground
RMM — remote maintenance
PUB — publication RCC — rescue coordination center
monitoring
PUP — principal user processor RCCB — remote control circuit
RMMS — remote maintenance
breaker
PV — Pressure-Volume (diagram) monitoring system
RCCC — Regional Communications
PVC — permanent virtual circuit RMS — remote monitoring
Control Centers
subsystem
PVC — polyvinyl chloride
RCF — remote communication
RMS — root mean square
PVD — plan view display facility
RMSC — remote monitoring
QC — quality control RCIU — remote control interface
subsystem concentrator
unit
QEC — quick engine change
RNAV — area navigation
RCL — radio communications link
QECA — quick engine change
RNP — required navigation
assembly RCLM — runway centerline
performance
marking
r.p.m. — revolutions per minute
ROD — record of decision
RCLR — RCL repeater
R-12 — refrigerant 12
ROSA — report of service activity
RCLS — runway centerline lighting
RA — resolution advisory
system ROT — runway occupancy time
RAF — Royal Air Force
RCLT — RCL terminal RP — restoration priority

365

10001930-002_AviationDictionary_2012_BOOK.indb 365 3/27/2012 9:38:39 AM

 RPC — restoration priority code SAC — Strategic Air Command sfc — surface
RPG — radar processing group SAE — Society of Automotive SFL — sequenced flashing lights
Engineers
RPM — Revolutions per minute SFR — special flight rules
SAFI — semi automatic flight
RPZ — runway protection zone SG — Specific Gravity
inspection
RR — low or medium frequency SHF — super high frequency
SAI — standby attitude indicator
radio range station
SHP — Shaft Horse Power
SALS — short approach light system
RRH — remote reading
SHPO — State Historic Preservation
hygrothermometer SAR — search and rescue
Officer
RRHS — remote reading SAS — stability augmentation
SI — international system of units
hydrometer system
SIAP — standard instrument
RRWDS — remote radar weather SAT — static air temperature
approach procedure
display
SATCOM — satellite
SIC — service initiation charge
RRWSS — remote radar weather communications
display (RWDS) sensor site SID — standard instrument
SAWRS — Supplementary Aviation
departure
RSS — remote speaking system Weather Reporting System
SID — station identifier
RT — remote transmitter SBC — surge bleed control
SIF — stall indicator failure
RT & BTL — radar tracking and SCAT 1 DGPS — special category 1
beacon tracking level differential GPS SIGMET — significant
meteorological information
RTAD — remote tower SCATANA — Security Control of
alphanumeric display Air Traffic and Air Navigation SIMMOD — airport and airspace
Aids simulation model
RTCA — Radio Technical
Commission for Aeronautics SCC — System Command Center SIP — state implementation plan
RTM — resin transfer molding SCVTS — Switched Compressed SM — statute mile
Video Telecommunications
RTOP — reserve takeoff power SMGC — surface movement
Service
guidance and control
RTR — remote transmitter/receiver
SD — radar weather report
SMGCS — surface movement
RTRD — remote tower radar display
SDF — simplified direction finding guidance control system
RVDT — rotary variable display
SDF — simplified directional facility SMPS — sector maintenance
transmitter
processor subsystem
SDF — software defined network
RVR — runway visual range as
SMS — simulation modeling system
measured in the touchdown zone SDIS — switched digital integrated
area service SNR — signal to-noise ratio
RVV — runway visibility value SDP — service delivery point SNR or S/N — signal to noise ratio
RW — runway SDS — switched data service SOC — service oversight center
RWDS — remote radar weather sec — second (time) SODA — statement of demonstrated
display ability
SEL — single event level
RWP — real time weather processor SOIR — simultaneous operations on
SELF — simplified short approach
intersecting runways
rwy — runway lighting system with sequenced
flashing lights SOIWR — simultaneous operations
S/G — starter-generator
on intersecting wet runways
SER — start end of runway
S/S — sector suite
SPECI — aviation selected special
SFAR 38 — Special Federal
SAA — special activity airspace weather report
Aviation Regulation 38
SAAR — special aircraft and SPR — single point refueling
SFC — Specific Fuel Consumption
aircrew authorization required
SPS — standard positioning service

366

10001930-002_AviationDictionary_2012_BOOK.indb 366 3/27/2012 9:38:39 AM

 SRAP — sensor receiver and TACAN — tactical air navigation TDWR — terminal Doppler weather
processor system radar
SRL — single red line (computer) TACR — TACAN at VOR, TACAN TDZL — touchdown zone lights
only
SSALF — SSALS with sequenced TEC — tower enroute control
flashers TAF — aviation terminal forecast
TEHP — Thrust Equivalent Horse
SSALR — simplified short approach TAI — tail anti-ice Power
lighting system
TARS — terminal automated radar TELCO — telephone company
SSALS — simplified short approach service
TELMS — Telecommunications
light system
TAS — true airspeed Management System
SSALSR — simplified short
TAT — total air temperature TEL-TWEB — telephone access to
approach light system with
TWEB
runway alignment indicator lights TATCA — terminal air traffic
control automation TEMAC — trailing edge of the
SSB — single side band
mean aerodynamic chord
TAVT — terminal airspace
SSB — split system breaker
visualization tool TERPS — terminal instrument
SSI — small‑scale integration procedures
TBO — time between overhaul
SSU — Saybolt Seconds Universal TET — Turbine Entry Temperature
TC — true course
STAR — standard terminal arrival TFAC — to facility
TCA — terminal control area
route
TGT — turbine gas temperature
TCA — Traffic Control Airport or
STC — Supplemental Type
Tower Control Airport TH — threshold
Certificate
TCACCIS — Transportation THP — Thrust Horse Power
STD — standard
Coordinator Automated Command
TIBS — telephone information
STMP — special traffic management and Control Information System
briefing service
program
TCAS — Traffic Alert and Collision
TIG — tungsten inert gas
STMUX — statistical data Avoidance System
multiplexer TIMS — telecommunications
TCAS II — traffic collision
information management system
STOL — short takeoff and landing avoidance system
TIPS — terminal information
STOVL — short takeoff and vertical TCC — DOT Transportation
processing system
landing Computer Center
TIR — total indicator reading
SURPIC — surface picture TCCC — tower control computer
complex TIT — turbine inlet temperature
SVFR — special VFR
TCE — tone control equipment TL — taxilane
SVFR — special visual flight rules
TCH — threshold crossing height TLS — transponder landing system
SWSL — supplemental weather
service TCLT — tentative calculated TM&O — Telecommunications
landing time Management and Operations
T — Temperature (Absolute)
TCO — Telecommunications TMA — Traffic Management
T — Thrust
Certification Officer Advisor
T/R — thrust reverser system
TCOM — terminal communications TMC — Traffic Management
T1MUX — T1 multiplexer Coordinator
TCS — tower communications
TA — traffic advisory system TMC/MC — Traffic Management
Coordinator/Military Coordinator
TAA — terminal arrival area TD — time difference
TMCC — Terminal Information
TAAS — terminal advance TDC — top dead center
Processing System
automation system
TDLS — tower data link services
TMCC — traffic management
TAC — terminal area chart
TDMUX — time division data computer complex
multiplexer
367

10001930-002_AviationDictionary_2012_BOOK.indb 367 3/27/2012 9:38:39 AM

 TMF — traffic management facility TSCU — torque signaling condition URET CCLD — User Request
unit Evaluation Tool Core Capability
TML — television microwave link
Limited Deployment
TSEC — terminal secondary radar
TMLI — television microwave link
service USAF — United States Air Force
indicator
TSFC — thrust specific fuel USAFIB — U.S. Army Aviation
TMLR — television microwave link
consumption Flight Information Bulletin
repeater
TSO — technical standard order USCG — United States Coast Guard
TMLT — television microwave link
terminal TSP — telecommunications service USOC — Uniform Service Order
priority Code
TMP — traffic management
processor TSR — telecommunications service USS — United States, standard
request
TMS — thrust management system UTC — coordinated universal time
TSYS — terminal equipment (Zulu time)
TMS — traffic management system
systems
UV — Ultra Violet
TMSPS — traffic management
TTL — total torque limiter
specialists UWS — urgent weather SIGMET
TTMA — TRACON traffic
TMU — traffic management unit V — volume
management advisor
TNAV — terminal navigational aids V1 — maximum speed in the takeoff
TTY — teletype
at which the pilot must take the
TODA — takeoff distance available
TVOR — terminal VOR first action (e.g., apply brakes,
TOF — time of flight reduce thrust, deploy speed
TW — taxiway
brakes) to stop the airplane within
TOFMS — time of flight mass
TWEB — transcribed weather the accelerate-stop distance. V1
spectrometer
broadcast also means the minimum speed
TOPS — Telecommunications in the takeoff, following a failure
TWR — tower (non controlled)
Ordering and Pricing System of the critical engine at VEF, at
(GSA software tool) TY — Type (FAA Communications which the pilot can continue the
Information System ) takeoff and achieve the required
TORA — take off run available
height above the takeoff surface
TYP — typical (mechanical
TPP — terminal procedures within the takeoff distance.
drawing)
publications
V1 — Pulse jet powered flying bomb
U.S. — United States
TPU — transit pressure unit
V2 — Liquid fuel rocket
UAS — uniform accounting system
TR — telecommunications request
V2 — takeoff safety speed
UBR — utility bus relay
TRACAB — terminal radar
V2 MIN — minimum takeoff safety
approach control in tower cab UER — unscheduled engine removal
speed
TRACON — terminal radar UFO — unidentified flying object
VA — design maneuvering speed
approach control
UHF — ultra high frequency
VAC — volts of alternating current
TRAD — terminal radar service
UNC — United National, coarse
VAFTAD — volcanic ash transport
TRF — tuned radio frequency
UNF — United National, fine and dispersion chart
(receiver)
UNICOM — aeronautical advisory VAPC — variable absolute pressure
TRI — thrust rating indicator
station controller
TRNG — training
URA — Uniform Relocation VAR — volcanic activity reporting
TRSA — terminal radar service area Assistance and Real Property
VAR — volt‑ampere reactive
Acquisition Policies Act of 1970
TRU — transformer rectifier unit
VASI — visual approach slope
URET — User Request Evaluation
TSA — taxiway safety area indicator
Tool
TSCU — torque sensing control unit VB — design speed for maximum
gust intensity

368

10001930-002_AviationDictionary_2012_BOOK.indb 368 3/27/2012 9:38:39 AM

 VBV — variable blade vane VMC — minimum control speed with VSTOL — vertical or short takeoff
the critical engine inoperative and landing
VC — design cruising speed
VMC — visual meteorological VSV — variable stator vane
VCOA — visual climb over the
conditions
airport VSW — speed at which onset of
Vmini — minimum speed natural or artificial stall warning
VD — design diving speed
occurs
VMO/MMO — maximum operating
VDA — vertical descent angle
limit speed VSWR — voltage standing‑wave
VDC — volts of direct current ratio
VMU — minimum unstick speed
VDF/MDF — demonstrated flight VTA — vertex time of arrival
VNAV — vertical navigation
diving speed
VTAC — VOR collocated with
VNE — never-exceed speed
VDME — VOR with distance TACAN
measuring equipment VNO — maximum structural cruising
VTOL — vertical takeoff and
speed
VDP — visual descent point landing
VNTSC — Volpe National
VEF — speed at which the critical VTOSS — takeoff safety speed for
Transportation System Center
engine is assumed to fail during Category A rotorcraft
takeoff VON — virtual on net
VTS — voice telecommunications
VF — design flap speed VOR — very high frequency omni system
directional range
VF — voice frequency VTVM — vacuum‑tube voltmeter
VOR/DME — collocated VOR and
VFC/MFC — maximum speed for VV — vertical visibility
DME navaids
stability characteristics
VVI — vertical velocity indicator
VORTAC — collocated VOR and
VFE — maximum flap extended
TACAN VX — speed for best angle of climb
speed
VOT — VOR test facility VY — speed for best rate of climb
VFO — variable‑frequency
oscillator VR — rotation speed w/m — Water/methanol coolant mix
VFR — visual flight rules VR — VFR military training route WA — AIRMET
VFTO — final takeoff speed VREF — reference landing speed WAAS — wide area augmentation
system
VGSI — visual glide slope indicator VRS — voice recording system
WAC — world aeronautical chart
VH — maximum speed in level flight VS — stalling speed or the minimum
with maximum continuous power steady flight speed at which the WAN — wide area network
airplane is controllable
VHF — very high frequency WARP — weather and radar
VS0 — stalling speed or the minimum processor
VHF/DF — VHF direction finder
steady flight speed in the landing
WC — work center
VIP — very important person configuration
(dignitary) WCA — wind correction angle
VS1 — stalling speed or the minimum
VIP — video integrator and steady flight speed obtained in a WCP — weather communications
processor (thunderstorm intensity specific configuration processor
standard)
VSCS — voice switching and WECO — Western Electric
VLE — maximum landing gear control system Company
extended speed
VSI — vertical speed indicator WESCOM — Western Electric
VLF — very low frequency Satellite Communications
VSR — reference stall speed
VLO — maximum landing gear WEU — warning electronic unit
VSR1 — reference stall speed in a
operating speed
specific configuration WFO — weather forecast office
VLOF — lift-off speed
VSRO — reference stall speed in the WGS84 — World Geodetic System
VLV — valve landing configuration of 1984

369

10001930-002_AviationDictionary_2012_BOOK.indb 369 3/27/2012 9:38:39 AM

 WH — hurricane advisory
whr — watthour
WMO — World Meteorological
Organization
WMS — wide area master station
WMSC — weather message
switching center
WMSCR — weather message
switching center replacement
WOW — weight on wheels (squat
switch)
WOXOF — weather, zero visibility
in fog
WP — waypoint
WRS — wide area ground reference
station
WS — SIGMET
WSCMO — weather service
contract meteorological
observatory
WSFO — Weather Service Forecast
Office
WSMO — Weather Service
Meteorological Observatory
WSO — Weather Service Office
WSP — weather system processor
WST — convective SIGMET
WST — convective significant
meteorological information
WSW — wind shear warning
WTHR — weather
WW — Severe Weather Watch
Bulletin
WX — weather
WXOF — weather, zero visibility
in fog
WXR — weather radar

370

10001930-002_AviationDictionary_2012_BOOK.indb 370 3/27/2012 9:38:39 AM

 GREEK LETTERS

Α α alpha Ν ν nu
Β β beta Ξ ξ xi
Γ γ gamma Ο ο omicron
Δ δ delta Π π pi
Ε ε epsilon Ρ ρ rho
Ζ ζ zeta Σ σ sigma
Η η eta Τ τ tau
Θ θ theta Υ υ upsilon
Ι ι iota Φ φ phi
Κ κ kappa Χ χ chi
Λ λ lamda Ψ ψ psi
Μ μ mu Ω ω omega

371

10001930-002_AviationDictionary_2012_BOOK.indb 371 3/27/2012 9:38:39 AM

 STANDARD ABBREVIATIONS/SYMBOLS

α — temperature coefficient of cm — centimeter mi — mile(s)

resistance cos — cosine mm — millimeter
CO — carbon monoxide cu cm — cubic centimeter(s) MPH — miles per hour
CO2 — carbon dioxide cu in — cubic inch(es) mv — millivolt
Fg — static thrust or gross thrust cu ft — cubic foot (feet) neg — negative
Fn — net thrust cu m — cubic meter(s) oz — ounce(s)
Gm — transconductance dB — decibel pf or μμf — picofarad
H2 — hydrogen deg — degree pos — positive
HCl — hydrochloric acid ESHP — equivalent shaft horsepower PPH — pounds per hour
k — dielectric constant f — farad PPM — parts per million
Nf — RPM of a free turbine F — Fahrenheit psi — pounds per square inch
N1 — RPM of a low‑pressure ft — foot (feet) PSIA — pounds per square inch
compressor ft lb — foot‑pound absolute pressure
N2 — RPM of a high‑pressure com- ft lbs — foot‑pounds PSID — pounds per square inch dif-
pressor g — gram ferential pressure
P — power gal — gallon PSIG — pounds per square inch
Pb — lead HP — horsepower gauge
Pb — bumer pressure hr — hour pt — pint
Pt2 — inlet pressure Hz — hertz qt — quart
Pt4 — compressor discharge pressure in — inch(es) R — Rankine
PT7 — turbine discharge pressure in hg — inch(es) of mercury rev — revolution(s)
R — resistance IPS — inches per second RPM — revolutions per minute
Tt2 — inlet temperature k — kilo sec — second
V1 — takeoff decision speed K — Kelvin SHP — shaft horsepower
V2 — minimum takeoff safety speed kg — kilogram sin — sine
Xc — capacitive reactance kHz — kilohertz sq cm — square centimeter(s)
Z — impedance km — kilometer sq in — square inch(es)
+ — positive kM — kilomega sq ft — square foot (feet)
‑ — negative kw — kilowatt sq m — square meter
Ω — ohm kw‑hr — kilowatt hour sq mi — square mile(s)
º — degree l — liter sq mil — square mil
“ — inch(es) lb — pound tan — tangent
‘ — foot (feet) lbs — pounds TEHP — thrust equivalent horse-
amp — ampere m — meter power
Btu — British thermal unit mb — milibar THP — thrust horsepower
C — Celsius mf or μf — microfarad U.S. — United States
cal — calorie(s) mHz — millihertz V — volt
Cal — large calorie(s) MHz — megahertz yd — yard

372

10001930-002_AviationDictionary_2012_BOOK.indb 372 3/27/2012 9:38:40 AM

 CHEMICAL ELEMENTS

actinium — Ac gold — Au potassium — K

aluminum — Al hafnium — Hf praseodymium — Pr
americum — Am hahnium — Ha promethium — Pm
antimony — Sb hassium — Hs protactinium — Pa
argon — Ar helium — He radium — Ra
arsenic — As holmium — Ho radon — Rn
astatine — At hydrogen — H rhenium — Re
barium — Ba illnium — Il rhodium — Rh
berkelium — Bk indium — In rubidium — Rb
beryllium — Be iodine — I ruthenium — Ru
bismuth — Bi iridium — Ir rutherfordium — Rf
bohrium — Bh iron — Fe samarium — Sm
boron — B joliotium — Jl scandium — Sc
bromine — Br krypton — Kr seaborgium — Sg
cadmium — Cd lanthanum — La selenium — Se
calcium — Ca lawrencium — Lr silicon — Si
californium — Cf lead — Pb silver — U
carbon — C lithium — Li sodium — Na
cerium — Ce lutetium — Lu strontium — Sr
cesium — Cs magnesium — Mg sulfur — S
chlorine — Cl manganese — Mn tantalum — Ta
chromium — Cr meitnerium — Mt technetium — Tc
cobalt — Co mendelevium — Md telllurium — Te
columbium — Cb mercury — Hg terbium — Tb
copper — Cu molybdenum — Mo thallium — TI
curium — Cm neodymium — Nd thorium — Th
dubnium — Db neon — Ne thulium — Tm
dysprosium — Dy neptunium — Np tin — Sn
einsteinium — Es nickel — Ni titanium — Ti
emanation — Em niobium — Nb tungsten — W
erbium — Er nitrogen — N uranium — U
europium — Eu nobelium — No vanadium — V
fermium — Fm osmium — Os wolfram — W
fluorine — F oxygen — O xenon — Xe
francium — Fr palladium — Pd ytterbium — Yb
gadolinium — Gd phosphorus — P yttrium — Y
gallium — Ga platinum — Pt zinc — Zn
germanium — Ge plutonium — Pu zirconium — Zr
glucinium — Gl polonium — Po

373

10001930-002_AviationDictionary_2012_BOOK.indb 373 3/27/2012 9:38:40 AM

 ATA/JASC CODES
(AIR TRANSPORT ASSOCIATION [ATA] SPECIFICATION 100 or
JOINT AIRCRAFT SYSTEM COMPONENT [JASC] CODES)

Note: General Aviation is gradually beginning to use ATA/JASC Codes, but presently might also be using either GAMA
(General Aviation Maintenance Association) Codes which are similar to ATA/JASC Codes, or manufacturer specific codes.

05 MAINTENANCE CHECKS 2120 — AIR DISTRIBUTION 2212 — ALTITUDE CONTROLLER

(OPERATOR DERIVED) SYSTEM
2213 — FLIGHT CONTROLLER
2121 — AIR DISTRIBUTION FAN
2214 — AUTOPILOT TRIM
10 PARKING AND MOORING 2130 — CABIN PRESSURE INDICATOR
(OPERATOR DERIVED) CONTROL SYSTEM
2215 — AUTOPILOT MAIN SERVO
2131 — CABIN PRESSURE
CONTROLLER 2216 — AUTOPILOT TRIM SERVO
11 PLACARDS AND MARKINGS
2132 — CABIN PRESSURE 2220 — SPEED-ATTITUDE
1100 — PLACARDS AND INDICATOR CORRECT. SYSTEM
MARKINGS
2133 — PRESSURE REGUL/ 2230 — AUTO THROTTLE
OUTFLOW VALVE SYSTEM

12 — SERVICING 2134 — CABIN PRESSURE 2250 — AERODYNAMIC LOAD

SENSOR ALLEVIATING
1210 — FUEL SERVICING
2140 — HEATING SYSTEM
1220 — OIL SERVICING
2150 — CABIN COOLING 23 — COMMUNICATIONS
1230 — HYDRAULIC FLUID
SYSTEM
SERVICING 2300 — COMMUNICATIONS
2160 — CABIN TEMPERATURE SYSTEM
1240 — COOLANT SERVICING
CONTROL SYSTEM
2310 — HF COMMUNICATION
2161 — CABIN TEMPERATURE SYSTEM
18 — HELICOPTER VIBRATION CONTROLLER
2311 — UHF COMMUNICATION
2162 — CABIN TEMPERATURE SYSTEM
1800 — HELICOPTER VIB/NOISE
ANALYSIS INDICATOR
2312 — VHF COMMUNICATION
2163 — CABIN TEMPERATURE SYSTEM
1810 — HELICOPTER
VIBRATION ANALYSIS SENSOR
2320 — DATA TRANSMISSION
2170 — HUMIDITY CONTROL AUTO CALL
1820 — HELICOPTER NOISE
ANALYSIS SYSTEM
2330 — ENTERTAINMENT
SYSTEM

22 — AUTO FLIGHT 2340 — INTERPHONE & PA

21 — AIR CONDITIONING
SYSTEM
2100 — AIR CONDITIONING 2200 — AUTO FLIGHT SYSTEM
2350 — AUDIO INTEGRATING
SYSTEM
2210 — AUTOPILOT SYSTEM SYSTEM
2110 — CABIN COMPRESSOR
2211 — AUTOPILOT COMPUTER
SYSTEM
374

10001930-002_AviationDictionary_2012_BOOK.indb 374 3/27/2012 9:38:40 AM

 2360 — STATIC DISCHARGE 25 — EQUIPMENT/ 27 — FLIGHT CONTROLS
SYSTEM FURNISHINGS
2700 — FLIGHT CONTROL
2370 — AUDIO/VIDEO 2500 — CABIN EQUIPMENT/ SYSTEM
MONITORING FURNISHINGS
2701 — CONTROL COLUMN
2510 — FLIGHT COMPARTMENT SECTION
EQUIPMENT
24 — ELECTRICAL POWER 2710 — AILERON CONTROL
2520 — PASSENGER COMPART- SYSTEM
2400 — ELECTRICAL POWER MENT EQUIPMENT
SYSTEM 2711 — AILERON TAB CONTROL
2530 — BUFFET/GALLEYS SYSTEM
2410 — ALTERNATOR-GENERA-
TOR DRIVE 2540 — LAVATORIES 2720 — RUDDER CONTROL
SYSTEM
2420 — AC GENERATION 2550 — CARGO COMPARTMENTS
SYSTEM 2721 — RUDDER TAB CONTROL
2551 — AGRICULTURAL SPRAY SYSTEM
2421 — AC GENERATOR- SYSTEM
ALTERNATOR 2722 — RUDDER ACTUATOR
2560 — EMERGENCY EQUIPMENT
2422 — AC INVERTER 2730 — ELEVATOR CONTROL
2561 — LIFE JACKET SYSTEM
2423 — PHASE ADAPTER
2562 — EMERGENCY LOCATOR 2731 — ELEVATOR TAB
2424 — AC REGULATOR BEACON CONTROL SYSTEM
2425 — AC INDICATING SYSTEM 2563 — PARACHUTE 2740 — STABILIZER CONTROL
SYSTEM
2430 — DC GENERATING 2564 — LIFE RAFT
SYSTEM 2741 — STABILIZER POSITION
2565 — ESCAPE SLIDE
INDICATING
2431 — BATTERY OVERHEAT
WARN. SYSTEM 2570 — ACCESSORY COMPART-
2742 — STABILIZER ACTUATOR
MENT
2432 — BATTERY/CHARGER 2750 — TE FLAP CONTROL
SYSTEM 2571 — BATTERY BOX
SYSTEM
STRUCTURE
2433 — DC RECTIFIER- 2751 — TE FLAP POSITION IND.
CONVERTER 2572 — ELECTRONIC SHELF
SYSTEM
SECTION
2434 — DC GENERATOR- 2752 — TE FLAP ACTUATOR
ALTERNATOR
2760 — DRAG CONTROL
2435 — STARTER-GENERATOR 26 — FIRE PROTECTION
SYSTEM
2436 — DC REGULATOR 2600 — FIRE PROTECTION
2761 — DRAG CONTROL
SYSTEM
ACTUATOR
2437 — DC INDICATING SYSTEM
2610 — DETECTION SYSTEM
2770 — GUST LOCK/DAMPER
2440 — EXTERNAL POWER
2611 — SMOKE DETECTION SYSTEM
SYSTEM
2612 — FIRE DETECTION 2780 — LE FLAP CONTROL
2450 — AC POWER DISTRIBU-
SYSTEM
TION SYSTEM
2613 — OVERHEAT DETECTION
2781 — LE FLAP POSITION IND.
2460 — DC POWER/DISTRIBU-
2620 — EXTINGUISHING SYSTEM
TION SYSTEM
SYSTEM
2782 — LE FLAP ACTUATOR
2621 — FIRE BOTTLE, FIXED

2622 — FIRE BOTTLE,

PORTABLE 375

10001930-002_AviationDictionary_2012_BOOK.indb 375 3/27/2012 9:38:40 AM

 28 — FUEL 2917 — HYDRAULIC PRESSURE 3060 — PROP/ROTOR ANTI-ICE/
REGULATOR-MAIN DE-ICE SYSTEM
2800 — AIRCRAFT FUEL
SYSTEM 2920 — HYDRAULIC, 3070 — WATER LINE ANTI-ICE
AUXILIARY SYSTEM SYSTEM
2810 — FUEL STORAGE
2921 — HYDRAULIC ACCUMU- 3080 — ICE DETECTION
2820 — ACFT FUEL DISTRIB. LATOR-AUXILIARY
SYSTEM
2922 — HYDRAULIC FILTER-
2821 — ACFT FUEL FILTER/ AUXILIARY 31 — INSTRUMENTS
STRAINER
2923 — HYDRAULIC PUMP- 3100 — INDICATING/
2822 — FUEL BOOST PUMP AUXILIARY RECORDING SYSTEM

2823 — FUEL SELECTOR/ 2925 — HYDRAULIC PRESSURE 3110 — INSTRUMENT PANEL

SHUTOFF VALVE RELIEF-AUXILIARY
3120 — INDEPENDENT INSTRU-
2824 — FUEL TRANSFER VALVE 2926 — HYDRAULIC RESERVOIR- MENTS (CLOCK, ETC.)
AUXILIARY
2830 — FUEL DUMP SYSTEM 3130 — DATA RECORDERS (FLT/
2927 — HYDRAULIC PRESSURE MAINT)
2840 — ACFT FUEL INDICATING
REGULATOR-AUX.
3140 — CENTRAL COMPUTERS
2841 — FUEL QUANTITY (EICAS)
2930 — HYDRAULIC SYSTEM
INDICATOR
INDICATING
3150 — CENTRAL WARNING
2842 — FUEL QUANTITY
2931 — HYDRAULIC PRESSURE
SENSOR 3160 — CENTRAL DISPLAY
INDICATOR
2843 — FUEL TEMPERATURE 3170 — AUTOMATIC DATA
2932 — HYDRAULIC PRESSURE
INDICATING
SENSOR
2844 — FUEL PRESSURE
2933 — HYDRAULIC QUANTITY 32 — LANDING GEAR
INDICATOR
INDICATOR
3200 — LANDING GEAR SYSTEM
2934 — HYDRAULIC QUANTITY
29 — HYDRAULIC POWER SENSOR 3201 — LANDING GEAR/WHEEL
FAIRING
2900 — HYDRAULIC POWER
SYSTEM 3210 — MAIN LANDING GEAR
30 — ICE AND RAIN
2910 — HYDRAULIC, MAIN PROTECTION 3211 — MAIN LANDING GEAR
SYSTEM ATTACH SECTION
3000 — ICE/RAIN PROTECTION
2911 — HYDRAULIC POWER- SYSTEM 3212 — EMERGENCY
ACCUMULATOR-MAIN FLOTATION SECTION
3010 — AIRFOIL ANTI/DE-ICE
2912 — HYDRAULIC FILTER- SYSTEM 3213 — MAIN LANDING GEAR
MAIN SYSTEM STRUT/AXLE/TRUCK
3020 — AIR INTAKE ANTI/
2913 — HYDRAULIC PUMP. DE-ICE SYSTEM 3220 — NOSE/TAIL LANDING
ELECT-ENG.-MAIN GEAR
3030 — PITOT/STATIC ANTI-ICE
2914 — HYDRAULIC HAND- SYSTEM 3221 — NOSE/TAIL LANDING
PUMP-MAIN GEAR ATTACH SECTION
3040 — WINDSHIELD/DOOR
2915 — HYDRAULIC PRESSURE RAIN/ICE REMOVAL 3222 — NOSE/TAIL LANDING
RELIEF VLV-MAIN GEAR STRUT/AXLE
3050 — ANTENNA/RADOME
2916 — HYDRAULIC RESER- ANTI-ICE/DE-ICE SYSTEM 3230 — LANDING GEAR
VOIR-MAIN RETRACT/EXT. SYSTEM
376

10001930-002_AviationDictionary_2012_BOOK.indb 376 3/27/2012 9:38:40 AM

 3231 — LANDING GEAR DOOR 34 — NAVIGATION 3436 — WIND SHEAR
RETRACT SECTION DETECTION SYSTEM
3400 — NAVIGATION SYSTEM
3232 — LANDING GEAR DOOR 3440 — INDEPENDENT POS.
ACTUATOR 3410 — FLIGHT ENVIRONMENT DETERMINING SYSTEM
DATA
3233 — LANDING GEAR 3441 — INERTIAL GUIDANCE
ACTUATOR 3411 — PITOT/STATIC SYSTEM SYSTEM

3234 — LANDING GEAR 3412 — OUTSIDE AIR TEMP. 3442 — WEATHER RADAR
SELECTOR IND./SENSOR SYSTEM

3240 — LANDING GEAR BRAKE 3413 — RATE OF CLIMB 3443 — DOPPLER SYSTEM
SYSTEM INDICATOR
3444 — GROUND PROXIMITY
3241 — BRAKE ANTI-SKID 3414 — AIRSPEED/MACH SYSTEM
SECTION INDICATING
3445 — AIR COLLISION
3242 — BRAKE 3415 — HIGH SPEED WARNING AVOIDANCE SYSTEM (TCAS)

3243 — MASTER CYL/BRAKE 3416 — ALTIMETER, BAROMET- 3446 — NON RADAR WEATHER
VALVE RIC/ENCODER SYSTEM

3244 — TIRE 3417 — AIR DATA COMPUTER 3450 — DEPENDENT POSITION

DETERMINING SYSTEM
3245 — TIRE TUBE 3418 — STALL WARNING
SYSTEM 3451 — DME/TACAN SYSTEM
3246 — WHEEL/SKI/FLOAT
3420 — ATTITUDE AND 3452 — ATC TRANSPONDER
3250 — LANDING GEAR DIRECTION DATA SYSTEM SYSTEM
STEERING SYSTEM
3421 — ATTITUDE GYRO & IND. 3453 — LORAN SYSTEM
3251 — STEERING UNIT SYSTEM
3454 — VOR SYSTEM
3252 — SHIMMY DAMPER 3422 — DIRECTIONAL GYRO &
IND. SYSTEM 3455 — ADF SYSTEM
3260 — LANDING GEAR
POSITION & WARNING 3423 — MAGNETIC COMPASS 3456 — OMEGA NAVIGATION
SYSTEM
3270 — AUXILIARY GEAR (TAIL 3424 — TURN & BANK/RATE OF
SKID) TURN INDICATOR 3457 — GLOBAL POSITIONING
SYSTEM
3425 — INTEGRATED FLT.
DIRECTOR SYSTEM 3460 — FLIGHT MANAGE.
33 — LIGHTS COMPUTING SYSTEM
3430 — LANDING & TAXI AIDS
3300 — LIGHTING SYSTEM
3431 — LOCALIZER/VOR
3310 — FLIGHT COMPARTMENT SYSTEM 35 — OXYGEN
LIGHTING
3432 — GLIDE SLOPE SYSTEM 3500 — OXYGEN SYSTEM
3320 — PASSENGER COMPART-
MENT LIGHTING 3433 — MICROWAVE LANDING 3510 — CREW OXYGEN SYSTEM
SYSTEM
3330 — CARGO COMPARTMENT 3520 — PASSENGER OXYGEN
LIGHTING 3434 — MARKER BEACON SYSTEM
SYSTEM
3340 — EXTERIOR LIGHTING 3530 — PORTABLE OXYGEN
3435 — HEADS UP DISPLAY SYSTEM
3350 — EMERGENCY LIGHTING SYSTEM

377

10001930-002_AviationDictionary_2012_BOOK.indb 377 3/27/2012 9:38:40 AM

 36 — PNEUMATIC 4940 — APU START/IGNITION 5260 — ENTRANCE STAIRS
SYSTEM
3600 — PNEUMATIC SYSTEM 5270 — DOOR WARNING
4950 — APU BLEED AIR SYSTEM SYSTEM
3610 — PNEUMATIC DISTRIBU-
TION SYSTEM 4960 — APU CONTROLS 5280 — LANDING GEAR DOORS

3620 — PNEUMATIC INDICAT- 4970 — APU INDICATING

ING SYSTEM SYSTEM
53 — FUSELAGE
4980 — APU EXHAUST SYSTEM
5300 — FUSELAGE STRUCTURE
37 — VACUUM 4990 — APU OIL SYSTEM (GENERAL)

3700 — VACUUM SYSTEM 5301 — AERIAL TOW EQUIPMENT

3710 — VACUUM DISTRIBUTION 51 — STANDARD PRACTICES/ 5302 — ROTORCRAFT TAIL

SYSTEM STRUCTURES BOOM

3720 — VACUUM INDICATING 5100 — STANDARD PRACTICES/ 5310 — FUSELAGE MAIN

SYSTEM STRUCTURES STRUCTURE

5101 — AIRCRAFT STRUCTURES 5311 — FUSELAGE MAIN

FRAME
38 — WATER/WASTE 5102 — BALLOON REPORTS
5312 — FUSELAGE MAIN
3800 — WATER & WASTE BULKHEAD
SYSTEM
52 — DOORS 5313 — FUSELAGE MAIN
3810 — POTABLE WATER LONGERON/STRINGER
SYSTEM 5200 — DOORS
5314 — FUSELAGE MAIN KEEL
3820 — WASH WATER SYSTEM 5210 — PASSENGER/CREW
DOORS 5315 — FUSELAGE MAIN FLOOR
3830 — WASTE DISPOSAL BEAM
SYSTEM 5220 — EMERGENCY EXIT
5320 — FUSELAGE MISCELLA-
3840 — AIR SUPPLY (WATER 5230 — CARGO/BAGGAGE
NEOUS STRUCTURE
PRESS. SYSTEM) DOORS
5321 — FUSELAGE FLOOR
5240 — SERVICE DOORS
PANEL
45 — CENTRAL MAINT. 5241 — GALLEY DOORS
5322 — FUSELAGE INTERNAL
SYSTEM MOUNT STRUCTURE
5242 — E/E COMPARTMENT
4500 — CENTRAL MAINT. DOORS
5323 — FUSELAGE INTERNAL
COMPUTER STAIRS
5243 — HYDRAULIC COMPART-
MENT DOORS
5324 — FUSELAGE FIXED
5244 — ACCESSORY COMPART- PARTITIONS
49 — AIRBORNE AUXILIARY
POWER MENT DOORS
5330 — FUSELAGE MAIN PLATE/
5245 — AIR CONDITIONING SKIN
4900 — AIRBORNE APU SYSTEM
COMPART. DOORS
5340 — FUSELAGE MAIN
4910 — APU COWLING/CON-
5246 — FLUID SERVICE DOORS ATTACH FITTINGS
TAINMENT
5247 — APU DOORS 5341 — WING ATTACH FITTINGS
4920 — APU CORE ENGINE
(ON FUSELAGE)
4930 — APU ENGINE FUEL & 5248 — TAIL CONE DOORS
5342 — STABILIZER ATTACH
CONTROL
5250 — FIXED INNER DOORS FITTINGS

378

10001930-002_AviationDictionary_2012_BOOK.indb 378 3/27/2012 9:38:40 AM

 5343 — LANDING GEAR 5520 — ELEVATOR STRUCTURE 5630 — DOOR WINDOWS
ATTACH FITTINGS
5521 — ELEVATOR SPAR/RIB 5640 — INSPECTION WINDOWS
5344 — FUSELAGE DOOR STRUCTURE
HINGES
5522 — ELEVATOR PLATES/SKIN
5345 — FUSELAGE EQUIPMENT STRUCTURE 57 — WINGS
ATTACH FITTINGS
5523 — ELEVATOR TAB 5700 — WING STRUCTURE
5346 — POWERPLANT ATTACH STRUCTURE
5710 — WING MAIN FRAME
FITTINGS
5530 — VERTICAL STABILIZER STRUCTURE
5347 — SEAT/CARGO ATTACH STRUCTURE
5711 — WING SPAR STRUCTURE
FITTINGS
5531 — VERTICAL STABILIZER
5712 — WING RIB STRUCTURE
5350 — FUSELAGE AERODY- SPAR/RIB STRUCTURE
NAMIC FAIRINGS 5713 — WING LONGERON/
5532 — VERTICAL STABILIZER
STRINGER
PLATES/SKIN
5714 — WING CENTER BOX
54 — NACELLES/PYLONS 5533 — VENTRAL STRUCTURE
(ON VERT. STAB) 5720 — WING MISCELLANEOUS
5400 — NACELLE/PYLON
STRUCTURE
STRUCTURE 5540 — RUDDER STRUCTURE
5730 — WING PLATES/SKINS
5410 — MAIN FRAME (ON 5541 — RUDDER SPAR/RIB
NACELLE/PYLON) STRUCTURE 5740 — WING ATTACH FITTINGS
5411 — FRAME/SPAR/ 5542 — RUDDER PLATE/SKIN 5741 — WING, FUSELAGE
RIB(NACELLE/PYLON) STRUCTURE ATTACH FITTINGS
5412 — BULKHEAD/FIREWALL 5543 — RUDDER TAB 5742 — WING, NAC/PYLON
(NAC/PYLON) STRUCTURE ATTACH FITTINGS
5413 — LONGERON/STRINGER 5550 — EMPENNAGE FLT. CONT. 5743 — WING, LANDING GEAR
(NAC/PYLON) ATTACH FITTING ATTACH FITTINGS
5414 — PLATE SKIN (NAC/ 5551 — HORIZONTAL STABILIZER 5744 — CONTROL SURFACE
PYLONS) ATTACH FITTING ATTACH FITTINGS
5415 — ATTACH FITTINGS (NAC/ 5552 — ELEVATOR/TAB ATTACH 5750 — WING CONTROL
PYLON) FITTINGS SURFACE STRUCTURE
5553 — VERT. STAB. ATTACH 5751 — AILERON STRUCTURE
FITTINGS
55 — STABILIZERS 5752 — AILERON TAB
5554 — RUDDER/TAB ATTACH STRUCTURE
5500 — EMPENNAGE FITTINGS
STRUCTURE 5753 — TE FLAP STRUCTURE
5510 — HORIZONTAL STABI- 5754 — LEADING EDGE DEVICE
LIZER STRUCTURE 56 — WINDOWS STRUCTURE
5511 — HORIZONTAL STABILIZER 5600 — WINDOW/WINDSHIELD 5755 — SPOILER STRUCTURE
SPAR/RIB SYSTEM

5512 — HORIZONTAL STABI- 5610 — FLIGHT COMPARTMENT

LIZER PLATE/SKIN WINDOWS

5513 — HORIZONTAL STABILIZER 5620 — PASSENGER COMPART-

TAB STRUCTURE MENT WINDOWS

379

10001930-002_AviationDictionary_2012_BOOK.indb 379 3/27/2012 9:38:40 AM

 61 — PROPELLERS/ 6321 — MAIN ROTOR BRAKE 71 — POWERPLANT
PROPULSORS
6322 — ROTORCRAFT COOLING 7100 — POWERPLANT SYSTEM
6100 — PROPELLER SYSTEM FAN SYSTEM
7110 — ENGINE COWLING
6110 — PROPELLER ASSEMBLY 6330 — MAIN ROTOR TRANS- SYSTEM
MISSION MOUNT
6111 — PROPELLER BLADE 7111 — COWL FLAP SYSTEM
SECTION 6340 — ROTOR DRIVE INDICAT-
ING SYSTEM 7112 — ENGINE AIR BAFFLE
6112 — PROPELLER DE-ICE SECTION
BOOT SECTION
7120 — ENGINE MOUNT
6113 — PROPELLER SPINNER 64 — TAIL ROTOR SECTION
SECTION
6400 — TAIL ROTOR SYSTEM 7130 — ENGINE FIRESEALS
6114 — PROPELLER HUB
SECTION 6410 — TAIL ROTOR BLADE 7160 — ENGINE AIR INTAKE
SYSTEM
6120 — PROPELLER CONTROL 6420 — TAIL ROTOR HEAD
SYSTEM 7170 — ENGINE DRAINS
6440 — TAIL ROTOR INDICAT-
6121 — PROPELLER SYNCHRO- ING SYSTEM
NIZER SECTION
72 — TURBINE/TURBOPROP
6122 — PROPELLER GOVERNOR ENGINE
65 — TAIL ROTOR DRIVE
6123 — PROPELLER FEATHER- 7200 — ENGINE (TURBINE/
6500 — TAIL ROTOR DRIVE TURBOPROP)
ING/REVERSING
SYSTEM
6130 — PROPELLER BRAKING 7210 — TURBINE ENGINE
6510 — TAIL ROTOR DRIVE REDUCTION GEAR
6140 — PROPELLER INDICAT- SHAFT
ING SYSTEM 7220 — TURBINE ENGINE AIR
6520 — TAIL ROTOR GEARBOX INLET SECTION
6540 — TAIL ROTOR DRIVE 7230 — TURBINE ENGINE COM-
62 — MAIN ROTOR INDICATING SYSTEM PRESSOR SECTION

6200 — MAIN ROTOR SYSTEM 7240 — TURBINE ENGINE COM-

BUSTION SECTION
6210 — MAIN ROTOR BLADES 67 — ROTORS FLIGHT
CONTROL 7250 — TURBINE SECTION
6220 — MAIN ROTOR HEAD
6700 — ROTORCRAFT FLIGHT 7260 — TURBINE ENGINE
6230 — MAIN ROTOR MAST/ CONTROL ACCESSORY DRIVE
SWASHPLATE
6710 — MAIN ROTOR CONTROL 7261 — TURBINE ENGINE OIL
6240 — MAIN ROTOR INDICAT- SYSTEM
ING SYSTEM 6711 — TILT ROTOR FLIGHT
CONTROL 7270 — TURBINE ENGINE
BYPASS SECTION
6720 — TAIL ROTOR CONTROL
63 — MAIN ROTOR DRIVE SYSTEM

6300 — MAIN ROTOR DRIVE 6730 — ROTORCRAFT SERVO

SYSTEM SYSTEM

6310 — ENGINE/TRANSMISSION
COUPLING

6320 — MAIN ROTOR GEARBOX

380

10001930-002_AviationDictionary_2012_BOOK.indb 380 3/27/2012 9:38:40 AM

 73 — ENGINE FUEL & 7421 — SPARK PLUG/IGNITER 7720 — ENGINE TEMP. INDICAT-
CONTROL ING SYSTEM
7430 — IGNITION SWITCHING
7300 — ENGINE FUEL & 7721 — CYLINDER HEAD TEMP
CONTROL (CHT) INDICATING

75 — AIR 7722 — ENG. EGT/TIT INDICAT-

7310 — ENGINE FUEL DISTRI-
ING SYSTEM
BUTION
7500 — ENGINE BLEED AIR
7730 — ENGINE IGNITION
7311 — ENGINE FUEL-OIL SYSTEM
ANALYZER SYSTEM
COOLER
7510 — ENGINE ANTI-ICING 7731 — ENGINE IGNITION
7312 — FUEL HEATER SYSTEM ANALYZER

7313 — FUEL INJECTOR NOZZLE 7520 — ENGINE COOLING 7732 — ENGINE VIBRATION
SYSTEM ANALYZER
7314 — ENGINE FUEL PUMP 7740 — ENGINE INTEGRATED
7530 — COMPRESSOR BLEED
7320 — FUEL CONTROLLING CONTROL INSTRUMENT SYSTEM
SYSTEM
7531 — COMPRESSOR BLEED
7321 — FUEL CONTROL/ GOVERNOR 78 — ENGINE EXHAUST
ELECTRONIC 7800 — ENGINE EXHAUST
7532 — COMPRESSOR BLEED
7322 — FUEL CONTROL/ VALVE SYSTEM
CARBURETOR 7810 — ENGINE COLLECTOR/
7540 — BLEED AIR INDICATING TAILPIPE/NOZZLE
7323 — TURBINE GOVERNOR SYSTEM
7820 — ENGINE NOISE
7324 — FUEL DIVIDER SUPPRESSOR

7330 — ENGINE FUEL INDICAT- 76 — ENGINE CONTROLS 7830 — THRUST REVERSER

ING SYSTEM
7600 — ENGINE CONTROLS
7331 — FUEL FLOW INDICATING 79 — ENGINE OIL
7601 — ENGINE SYNCHRONIZING
7332 — FUEL PRESSURE INDI- 7900 — ENGINE OIL SYSTEM
CATING 7602 — MIXTURE CONTROL (AIRFRAME)

7603 — POWER LEVER 7910 — ENGINE OIL STORAGE

7333 — FUEL FLOW SENSOR
(AIRFRAME)
7334 — FUEL PRESSURE 7620 — ENGINE EMERGENCY
7920 — ENGINE OIL DISTRIBU-
SENSOR SHUTDOWN SYSTEM
TION (AIRFRAME)
7921 — ENGINE OIL COOLER
77 — ENGINE INDICATING
74 — IGNITION 7922 — ENGINE OIL TEMP.
7700 — ENGINE INDICATING REGULATOR
7400 — IGNITION SYSTEM SYSTEM
7923 — OIL SHUTOFF VALVE
7410 — IGNITION POWER 7710 — POWER INDICATING
7930 — ENGINE OIL INDICAT-
SUPPLY SYSTEM
ING SYSTEM
7711 — ENGINE PRESSURE
7411 — LOW TENSION COIL 7931 — ENGINE OIL PRESSURE
RATIO (EPR)
7412 — EXCITER 7932 — ENGINE OIL QUANTITY
7712 — ENGINE BMEP/TORQUE
INDICATING 7933 — ENGINE OIL TEMPERA-
7413 — INDUCTION VIBRATOR TURE
7713 — MANIFOLD PRESSURE
7414 — MAGNETO/DISTRIBUTOR (MP) INDICATING
7420 — IGNITION HARNESS 7714 — ENGINE RPM INDICAT-
(DISTRIBUTION) ING SYSTEM

381

10001930-002_AviationDictionary_2012_BOOK.indb 381 3/27/2012 9:38:40 AM

 80 — STARTING
8000 — ENGINE STARTING
SYSTEM
8010 — ENGINE CRANKING
8011 — ENGINE STARTER
8012 — ENGINE START VALVES/
CONTROLS
81 — TURBOCHARGING
8100 — EXHAUST TURBINE
SYSTEM (RECIP)
8110 — POWER RECOVERY
TURBINE (RECIP)
8120 — EXHAUST TURBO-
CHARGER

82 — WATER INJECTION
8200 — WATER INJECTION
SYSTEM

83 — ACCESSORY GEARBOXES
8300 — ACCESSORY
GEARBOXES
85 — RECIPROCATING ENGINE
8500 — ENGINE (RECIPROCAT-
ING)
8510 — RECIPROCATING
ENGINE FRONT SECTION
8520 — RECIPROCATING
ENGINE POWER SECTION
8530 — RECIPROCATING
ENGINE CYLINDER SECTION
8540 — RECIPROCATING
ENGINE REAR SECTION
8550 — RECIPROCATING
ENGINE OIL SYSTEM

382

10001930-002_AviationDictionary_2012_BOOK.indb 382 3/27/2012 9:38:40 AM