De-Icing Policy and Procedures

Aircraft Operations in Adverse Weather

Introduction
The information in this manual is similar to other information published by:
● ICAO Document 9640 AN/940
● Aircraft Specific De-icing/Anti-icing Procedures (Located in the relevant sections of the Ground
Handling Manual).
● Federal Aviation Administration FAA 121.629
● FAA document, N8900.275 – Revised FAA-Approved Deicing Program Updates, Winter 2014-2015
● FAA – Official FAA Holdover Time Tables Winter 2014-2015, Revision 1.1
● AEA Recommendations for De-icing/Anti-icing Aeroplanes on the Ground - 29th Edition
● AEA Recommendations for De-icing/Anti-icing Aeroplanes on the Ground - ANNEX A Guidelines
for Holdover Times - 29th Edition
● AEA Training Recommendations and Background Information for De‐Icing / Anti‐Icing of
Aeroplane on the Ground - 11th Edition
The Southern Hemisphere winter season, in which de-icing is general performed in New Zealand, commences on 1st
April, and ends on the 31st October. Beware that it is not just limited to between these dates.
Please refer to Aircraft specific De-Icing Procedures, located in the relevant sections of the Ground Handling Manual.

Aviation Acronyms
Throughout this manual, abbreviations are used instead of the full name:
AFM – Aircraft Flight Manual
AMM – Aircraft Maintenance Manual
APU – Auxiliary Power Unit
CAA – Civil Aviation Authority
FAA – Federal Aviation Administration
FP – Freezing Point
HOT – Hold-over Time
IATA – International Air Transport Association
ICAO – International Civil Aviation Organisation
ISO – International Organisation for
Standardisation
LOP – Local Operating Procedure
LOUT – Lowest Operational Use Temperature
OAT – Outside Air Temperature
˚C – Degrees Celsius
˚F – Degrees Fahrenheit
PIC – Pilot-in-Command
RI – Refractive Index
SOP – Standard Operating Procedure
VHF – Very High Frequency
De-icing Policy
The rules governing aircraft cold weather operations are very specific and must be strictly adhered to.
The Pilot in Command shall not commence take-off unless the external surfaces are clear of any deposit which might
adversely affect the performance and/or the controllability of the airplane (Clean Aircraft Concept) except as permitted in
the Aircraft Flight Manual.
To ensure this, a contamination check is completed before departure by the Pilot in Command (PIC) or an Aircraft
Engineer. The ultimate decision to depart can only be made by the Pilot in Command (PIC).

Clean Aircraft Concept

During conditions conducive to aircraft icing during ground operations, take-off shall not be attempted when ice, snow,
slush, or frost is present or adhering to the wings, control surfaces, engine inlets or other critical surfaces. This is known as
the “Clean Aircraft Concept”.
Any deposit of ice, snow or frost on external surface of an aircraft, except as permitted in the Airplane Flight Manual or
Flight Crew Operations Manual, may drastically affect its performance due to reduced aerodynamic lift and increased drag
resulting from disturbed airflow. Furthermore, slush, freezing snow or ice may cause moving parts, such as control
surfaces and flap actuating mechanisms to jam, thus creating a hazardous situation. Numerous techniques for complying
with the Clean Aircraft Concept have been developed.
Proper and adequate de-icing, followed by an application of appropriate anti-icing fluid, provides the best protection
against contamination. A visual or physical check of the critical aircraft surfaces to confirm the treatment has been
effective and that the aircraft is in compliance with the Clean Aircraft Concept must be carried out when required.

Basic Aerodynamics
The Four Forces
Weight
Weight or gravity is the force which keeps things on the ground or a lack of it causes them to fall.
Lift
If you look closely at the wing of an aircraft, you will notice that the top of it is curved and the underneath is flatter. During
flight, the air which is moving over the top of the wing is moving faster than the air which is moving under it. This creates a
difference in air pressure with the over-wing being less than the under-wing. This creates ‘LIFT’ which overcomes the
weight.
Thrust
Thrust is the forward force that pushes an aircraft through the air. Air is drawn in through the front of the aircraft engine,
is compressed, mixed with fuel, and burned and the exhaust gases pushed out the back of the engine. The force of this is
sufficient to push the aircraft forward.
Drag
When an object is moving through the air it has to push the air out of its way and force its way through. This force
preventing the object moving freely through the air is called drag. The shape of the object influences the amount of drag -
hence aircraft are streamlined. This reduces drag and therefore less thrust or engine power is needed to fly.
For an aircraft to fly straight and level all these forces must be balanced and a change in any one of these forces will affect
this balance. The forces act together to help the pilot to:
1. Get the aircraft off the runway and to its intended altitude
2. Make sure that it stays at that altitude
3. Move the aircraft forward
4. Help the aircraft to slow down and land safely
Theory of Flight

An aircraft flies because the air flowing over its wings generates lift. To achieve this pre-calculated upward directional
force and to maintain the additional safety reserves needed, it is a pre-condition that the aircraft’s ‘critical’ surfaces are
‘smooth and clean’, prior to the start of the take-off roll. This requirement applies to the wings as well as the horizontal
and vertical tail surfaces

During ground icing conditions deposits of frost, ice, slush, and snow can accumulate on the critical wing surface, which
disturbs the smooth flow of air across the surfaces. This effectively reduces lift and increases drag.

As a result, aerodynamic safety margins, in regard to acceleration and lifting performance, will either be reduced or
completely eliminated. In the worst case, frozen deposits can cause the aircraft to stall.

Images: Theory of Flight

Definition and Purpose of De-icing/Anti-icing
De-icing
De-icing is the process by which frost, ice and snow deposits are removed from aircraft surfaces with a de-icing fluid in
order to provide clean surfaces. De-icing consists of the application of hot water or a hot mixture of anti-icing fluid and
water to remove any contamination.
Purpose of De-icing
Frost ice and snow deposits on an aircraft's surface can seriously affect that aircraft's performance and/or its’
controllability. Since safety is PARAMOUNT, the creation of situations that may lead to incidents or accidents cannot be
permitted or tolerated under any circumstances.

Anti-icing
Anti-icing is the application of a protective film which provides protection against the formation of frost or ice, and
accumulation of snow or slush on clean surfaces of the aircraft for a limited period of time (known as the holdover time).

Effect of Contamination on Aircraft Performance

Failure to remove deposits of frost, ice, slush, and snow from aircraft surfaces, prior to take-off, could result in:
● Degraded aerodynamic performance
● Restricted control surface movement
● Blocked sensors
● Ingestion damage to engines
● Damage to vertical or horizontal tail surfaces
● Increased weight and/or altered balance characteristics
● Degraded aerodynamic performance
Test data from the aircraft manufacturers indicates that frost, ice or snow deposits having a thickness and surface
roughness similar to medium to course sandpaper on the leading edge can reduce wing lift by as much as 30% and
increase drag by as much as 40%.
These changes in lift and drag significantly increase stall speed, reducing controllability and alter aircraft flight
characteristics. Thicker or rougher frozen contaminants can have increasing effects on lift, drag, stall speed, stability, and
control, with the primary influence being surface roughness on the critical portions of the aerodynamic surface. These
adverse effects on the aerodynamic properties of the aerofoil may result in sudden departure from the commanded flight
path and may not be preceded by any indications or aerodynamic warning to the pilot. Frozen accumulations on leading
edges can increase drag by 40% and reduce lift by 30%.
Frozen accumulations may destroy the lifting ability of aerofoils, including leading edge devices, resulting in failure of the
aircraft to become airborne.
Increased drag
An aircraft may fail to reach take-off speed within the calculated/available distance, because of the increased drag placed
on the aerofoil due to the presence of frozen contaminants.
Decreased control
Frozen accumulations may impair the function of control surfaces, such a rudder, elevators, and ailerons and trim tabs, to
such a degree that the aircraft cannot be controlled.
Loss of Lift
Frozen accumulations (increase overall weight of aircraft) may destroy the lifting ability of aero foils, including leading
edge devices, resulting in failure of the aircraft to become airborne.
Flutter
Accumulation of frozen contaminants may create conditions that result in separation of airflow and dynamic instability of
the aerofoil surface which, extreme cases, can cause destruction of aircraft parts.
Restricted control surface movement
Ice deposits may form in hinge areas of control surfaces and restrict or prohibit their movement.
Blocked sensors
Frozen contaminants blocking pilot probes, static ports, engine pressure sensing probes and inlets can cause serious
instrumentation errors.

Images: Pitot Tubes, Static Vents, and Angle of Attack Sensors commonly found on Air Chathams’ Aircraft.

Weather Terms
Freezing Drizzle
Fairly uniform precipitation composed exclusively of fine drops (diameter less than 0.5 mm (0.02 in)) very close together
which freezes upon impact with the ground or other exposed objects.
Freezing Fog
A suspension of numerous very small water droplets which freezes upon impact with the ground or other exposed objects
generally reducing visibility.
Frost/Hoar Frost
Ice crystals that form from ice saturated air at temperatures below 0°c by direct sublimation on the ground or other
exposed objects.
Hail
Precipitation of small balls or pieces of ice with a diameter ranging from 5 to >50 mm failing either separately or
agglomerated.
Ice Pellets
Precipitation of transparent (grains of ice), or translucent (small hail) pellets of ice, which are spherical or irregular, and
which have a diameter of 5 mm (0.2 in.) or less. The pellets of ice usually bounce when hitting hard ground.
Light Freezing Rain
Precipitation of liquid water particles which freezes upon impact with the ground or other exposed objects, either in the
form of drops of more than 0.5 mm (0.02 inch) or smaller drops which, in contrast to drizzle, are widely separated.
Measured intensity of liquid water particles is up to 2.5 mm/hour with a maximum of 0.25 mm (0.01 inch) in 6 minutes.
Moderate and Heavy Freezing Rain
Precipitation of liquid water particles which freezes upon impact with the ground or other exposed objects, either in the
form of drops of more than 0.5 mm (0.02 inch) or smaller drops which, in contrast to drizzle, are widely separated.
Measured intensity of liquid water particles is more than 2.5 mm/hour (0.10 inch/hour).
Radiation Cooling
A process by which temperature decreases due to an excess of emitted radiation over absorbed radiation. On a typical
calm clear night aircraft surfaces emit long wave radiation, however there is no solar radiation (shortwave) coming in at
night and this long wave emission will represent a constant net energy loss.
Under these conditions the aircraft surface temperatures may be up to 4°C or more below that of the surrounding air. Rain
or High Humidity (On Cold Soaked Wing) Water forming ice or frost on the wing surface when the temperature of the
aircraft wing surface is at or below 0°C (32°F).
Rain and Snow
Precipitation is formed from a mixture of rain and snow.
NOTE: For operation in light rain and snow, treat it as light freezing rain.
Rime Ice
Small frozen water droplets that appear to look like frost in a freezer. Typically rime ice has low adhesion to the surface
and its surrounding rime ice particles.
Snow
Precipitation of ice crystals, most of which are branched, star shaped or mixed with unbranched crystals. At temperatures
higher than -5°C (23°F), the crystals are generally agglomerated into snowflakes.
Snow grains
Precipitation of very small white and opaque particles of ice that is fairly flat or elongated with a diameter of less than 1
mm (0.04 in.). When snow grains hit hard ground, they do not bounce or shatter.
NOTE: For holdover time purposes, treat snow grains as snow.
Snow pellets
Precipitation of white, opaque particles of ice, these particles are round or sometimes conical. Snow pellets are brittle,
easily crushed; they do bounce and may break on hard ground.
NOTE: For holdover time purposes, treat snow pellets as snow.
Slush
Snow or ice that has been reduced to a soft watery mixture.
Types of De-icing Fluid
Composition of De-icing Fluid
ISO Type I Fluid
The vast majority of de-icing fluids contain one or more of the common glycols (Monoethylene, monopropylene or
diethylene) a wetting agent and an anti-corrosive agent. These are known as Type I fluids and more frequently used in
colder, drier climates.
These fluids have high glycol content and a low viscosity in their undiluted form. De-icing performance is good but due to
the low viscosity, the protection given to the aircraft surfaces is limited when freezing precipitation is occurring.
Type I is predominantly used for removing frozen contamination from aircraft surfaces either as the first step in a two-step
process, or in a one step process where precipitation has stopped.
As there is no thickening agent contained in this fluid, no additional holdover time is provided by strengthening the mix.
The only benefit would be that the freezing point would be lowered, due to the increased glycol level of the mix, allowing
for use in lower temperatures.
ISO Type I fluids are currently used by Air Chathams during De-Icing procedures.
De-icing Media
● Heated water
● Heated mixture of water and Type I fluid
● Heated Premix Type I fluid
De-icing fluids are heated to 85°C, although a minimum temperature of 60°C can be used for light deposits of frost.
De-icing Fluids
How the Fluids Work
To be effective de-icing fluids must be:
● Mixed with water to a pre-determined ratio
● Heated up to a maximum of 90°C
● Applied as close to the aircraft surface as is possible
When used as a de-icing treatment there is little difference between any of the media described above, in so far as their
effectiveness for removing frozen contamination. This is due to the fact that it is the heat of the mixture rather than any
chemical reaction that melts the frozen deposit; it is then removed by the pressure of the spray.
Once the frozen deposit is removed, then the glycol in the fluid (all the above except water) remaining on the wing
prevents the frozen contamination from reforming for a period of time. This is achieved by the glycol lowering the freezing
point of any dried residue and prevents it from re-freezing. The time that the glycol remains effective is dependent on the
type and mixture of the fluid used, as well as the outside air temperature (OAT) and the precipitation occurring.

Methods and Procedures for Removing and Preventing Contamination

Introduction
De-icing is the procedure by which frost, ice or snow is removed from aircraft surfaces.
To preserve holdover times the process should be continuous and as short as possible. As already stated for maximum
effect the fluid is:
● Mixed with water to a pre-determined ratio (see fluid manufacturers “data sheets”)
● Heated up to a maximum 90°C
● Applied as close to the aircraft surface as possible to minimise heat loss.
CAUTION:
It is the responsibility of the De-icing Operator to ensure that the treatment is performed symmetrically and that on
completion all frozen deposits (with the possible exception of frost, which may be allowed on the fuselage and under-
wing have been removed.)
Principles of De-icing
The fluid works as following: There are three components working in unison and with the following effect.
● THE GLYCOL in the fluid reduces the freezing point to below the ambient temperature.
 ● THE WETTING AGENT allows the fluid to form a uniform film over the aircraft's surfaces.
● THE THICKENING AGENTS in Type II and IV fluid enables the film to remain on the aircraft surfaces until
take-off.
NOTE: It is the heat of the mixture rather than any chemical reaction that melts the frozen deposit.
The pressure of the spray and heated fluid is then used to flush away any residue.
Methods of De-icing
General
De-icing is to commence after all ground services have been completed
i.e. Re-fuelling, Loading and Catering. All doors (passenger and cargo) must be closed prior to starting the de-icing process.
One Stage De-icing
One stage de-icing is carried out with a mixture of fluid / water with regard to the ambient temperature. This process
includes a built-in anti-icing treatment which is dependent on the type of fluid used. The hold-over time starts as soon as
the first drop of fluid touches the aircraft frame.
Requirements for De-icing
Summary
It is now generally accepted that it is permissible for aircraft to operate with thin hoar frost on fuselage surfaces and up to
1/8 inch (3mm) on under-wing surfaces if contained within the area of the fuel tanks. However, static vents MUST be clear.
During routine de-icing operations it will therefore usually be unnecessary for these surfaces to be treated, providing the
accumulation is within defined limits.
FLIGHT CREWS OR CERTIFIED ENGINEERS HAVE THE FINAL DECISION as to whether de-icing is required or not.
NOTE: The presence of clear ice can usually only be detected by touch.

Contamination Check
A contamination check shall take place and cover all critical parts of the aircraft and shall be performed from points
offering sufficient visibility of these parts (e.g. from the de-icing step or any other suitable piece of equipment). Any
contamination found, except frost within defined areas and defined limits shall be removed by a de-icing treatment if
required.
A contamination check will look for the presence of frost (expect within guidelines), ice, slush, and snow accumulation.
Special attention should be given to: Wings, Horizontal and Vertical stabilisers and all flight control surfaces.
If after the contamination check has been completed and the presence of any contamination has been found, a request for
further de-icing is made.
Request for De-icing
A Request for De-icing will be made by the flight crew. On arrival at the aircraft the pilot will ascertain what part(s) of the
aircraft require de-icing.
The De-icing Log, is completed when the de-icing treatment is finished and all relevant details, such as type and amount of
fluid is annotated, this declaration then serves as an authority for the aircraft to be released.
NOTE: This form is to be signed by the PIC, who has the final say on whether the aircraft is suitably de-iced. By signing this
form, they confirm that they have performed their checks, in accordance to aircraft manuals, that the critical areas of the
aircraft have been de-iced appropriately.
Adverse Weather Conditions
The following conditions are most likely to produce frozen deposits on aircraft structures which may not be readily
detectable on the ground.
● Precipitation occurring whilst aircraft is on the ground.
● Ice build-up during descent through thick clouds or precipitation during an approach where ground
temperatures are low.
● Freezing fog.
● Slush on runways.
Clear Ice Formation
Clear ice can form on aircraft surfaces, below a layer of snow or slush. It is therefore important that surfaces are closely
examined following each de-icing operation, in order to ensure that all deposits have been removed.
Significant deposits of clear ice can form, in the vicinity of the fuel tanks, on wing upper surfaces as well as under-wing.
Aircraft are most vulnerable to this type of build-up when:
1) Wing temperatures remain well below 0°C (32°F) during the turnaround/transit.
2) Ambient temperatures between -2°C and +15°C (28°F and 59°F) are experienced.
3) Ambient humidity is high and/or precipitation occurs while the aircraft is on the ground.
This type of ice formation is extremely difficult to detect. However, frost or ice on the lower surface of either wing can
indicate the presence of clear ice on the upper wing surfaces.
Therefore, when the above conditions prevail, or when there is otherwise any doubt whether clear ice has formed, a close
examination shall be made immediately prior to departure, in order to ensure that all frozen deposits have in fact been
removed.
NOTE: Low wing temperatures associated with this type of build-up normally occur when large quantities of cold fuel
remain in wing tanks during the turnaround / transit and any subsequent re-fuelling does not cause a sufficient increase in
wing temperature.
Ice Build Up During Descent/Approach
Ice can build up on control surfaces when descending through thick cloud or precipitation during an approach. When
ground temperatures at the destination are low, it is possible for flaps to be retracted and for accumulations of ice to
remain undetected between stationary and moveable surfaces.
It is, therefore, important that these areas are checked prior to departure and any frozen deposits removed.
De-icing Procedure
Removal of Frost and Light Ice
NOTE: Requirements necessitate that there to be no ice on the upside of the fuselage. This means that if ice is present, it
must be de-iced.
The spray should be traversed over the frozen surfaces and, providing the hot fluid is applied at the correct distance from
the aircraft skin, a minimal amount of fluid will be required to melt the deposits. For efficient de-frosting, aim the
gun/nozzle at the area to be sprayed before pulling the trigger and release as the end of the sweep is reached. Operatives
should not drench the structure and surrounding area with vast amounts of fluid. This is totally unnecessary and wasteful
on fluid.
Under-wing De-icing Procedures
Treatments must be symmetrical and may include flaps lower surfaces. Spray the affected areas with a heated fluid/water
mix suitable for a one step procedure (see caution below) or a two-step procedure as required and then spray the same
areas under the other wing.
WARNING!
L&R WINGS MUST BE TREATED IDENTICALLY, (same areas, same amount, same type of fluid, and same mixture
strength), even if contamination is only present under one wing.
A trained and qualified person (de-icing operative or engineer) must check to confirm the treatment was carried out
symmetrically and that all frozen deposits have been removed, reporting the treatment details to the PIC.
CAUTION:
Under-wing frost and ice are usually caused by very cold fuel in the wing tanks. Ensure the mix of fluid is sufficient to
prevent re-freezing, i.e. concentration of fluid is sufficient for temperatures on the wing that can be several degrees
below the OAT.
CAUTION:
When it is confirmed that the treated areas are clean, the following statement shall be given to the PIC: “Under wing
De-icing only”
Removal of Local Area Contamination
When no precipitation is falling or expected a “local area” de-icing may be carried out under the below mentioned or
similar conditions. In some cases, a full or complete de-icing is unnecessary. When the presence of frost and/or ice is
limited to localised areas of the surfaces of the aeroplane and no holdover time is likely to be required, only the
contaminated areas will require treatment.
This type of contamination will generally be found on the wing and/or stabiliser leading edges or in patches on the wing
and/or stabiliser upper surfaces.
Spray the affected area(s) with a heated fluid /water mixture suitable for a one-step procedure, and then spray the same
area(s) on the other side of the aeroplane. BOTH SIDES of the aeroplane MUST BE TREATED IDENTICALLY, (same areas,
same amount, and type of fluid, and same mixture strength), even if contamination is only present on one side.
A trained and qualified person (de-icing operative or engineer) will ensure the treatment was carried out symmetrically
and that all frozen deposits have been removed. After this check has confirmed that the treated areas are clean, the
following statement shall be given to the PIC, either on the de-icing confirmation sheet or over the headset: “Local area
De-icing only”.
Image: Spray pattern for moderate accumulations of snow and ice.
Image: For frozen deposits that have bonded to the aircraft, the bond is broken by concentrating the spray in various
spots, until the aircraft surface is exposed, the heat will then be conducted along the wing.

NOTE: To prevent damage to aircraft surfaces ensure that the maximum force of the solid flow of fluid on the surfaces is
not more than 10 psi on an area of 25 square inches. Do not exceed an impingement of 50 psi (345 kPa) at the surface.
NOTE: Non-metallic surfaces (e.g. composites) have a lower heat transfer than metallic surfaces. De-icing may take longer,
and more fluid may be needed.
NOTE: There are specific Aircraft Maintenance Manual requirements that stipulate the maximum pressure of the solid
flow of fluid on the aircraft surface. For certain aircraft, the spraying of de-icing fluids on the aircraft surfaces, especially
composite surfaces such as the radome, lower belly panels and flight control surfaces (including aileron, rudder and
elevator) the pressure shall not exceed 1.5 psi (10kPa). As this is a very low pressure, it requires special care and attention
by the de-icing operator to ensure these specific aircraft surfaces are not damaged during the de-icing process.
CAUTION:
DO NOT point a solid high-pressure flow of fluid directly at the aircraft surface for any extended period of time, as this
may cause structural damage.
Manual Removal of Ice and Snow
Heavy accumulation of snow will always be difficult to remove from aircraft surfaces and vast quantities of fluid will
invariably be consumed in the attempt. Under these conditions serious consideration should be given to manually
removing the worst of the snow, before attempting to de-ice.
Approval from the aircraft operator must be obtained before this process is carried out and must be overseen by an
engineer.
Equipment
● Soft Bristled Brushes or Broom (recommended)
● Ropes
● Squeegees
● Hot Air Blower
If snow or ice cannot be (manually) removed completely, perform a Type I fluid de- icing activity. In addition, if the aircraft
surface is still wet after manually removing snow and ice and the local conditions (i.e. low air temperature) provide a
potential for residual water to refreeze, it will also be necessary to perform a Type I fluid de-icing activity.
CAUTION:
Care must be taken to prevent damage to vortex generators, angle of attack sensors, pitot/static ports etc. when
manual methods of snow clearing are employed.
NOTE: All snow MUST be removed from the nose radome area, in order to prevent from blowing back and obscuring the
pilot’s vision during take-off.
NOTE: Non-metallic surfaces (e.g. composites) have a lower heat transfer than metallic surfaces. De-icing may take longer,
and more fluid may be needed.
Spraying Techniques
For the effective removal of snow and ice the following techniques should be used.
Wings / Tail
Spray from tip "sweeping" inboard to the wing root from the highest point of surface camber to create a bow wave effect.
Spraying from the rear of the wing is not allowed as fluid may enter flap bays with residual fluid crystallising with
subsequent re-hydration causing control problems.
If removal of contamination is required on the lower side of the wings and the horizontal stabiliser and elevator, de-icing
fluid shall be applied sparingly to minimise fluid flow into drain holes.
Note: Make sure that ice and/or snow is not pushed into the areas around the flight controls during ice and snow removal.
CAUTION: In the Trimmable Horizontal Stabilizer area of many aircraft (i.e. Metroliner) be especially careful to point the
spray from the front to the rear (which will prevent any de-/anti-icing fluid going into the THS or into the rear fuselage
non-pressurised compartment).

Vertical Surfaces
Start at TOP and work DOWN

Image: Direction of spray for the tail

NOTE: All De-icing operators need to be aware that the fluid comes out hot and with pressure.
CAUTION:
DO NOT POINT A SOLID FLOW OF FLUID DIRECTLY AT THE SURFACE. APPLY FLUID AT A LOW ANGLE TO PREVENT
DAMAGE TO THE AIRCRAFT SURFACES. DO NOT USE A HIGH-PRESSURE SPRAY TO BLOW THE ICE AND SNOW OFF THE
AIRCRAFT SURFACES. LET THE TEMPERATURE OF THE FLUID DO ITS WORK!!
Fuselage
Aim gun to sweep along top centre line. Do not spray over windscreens and passenger door unless the door is closed.
Nose/Radome Area and Flight Deck Windows
Type I water fluid mix is recommended or manual methods of removal such as squeegees or brushes.
When thickened fluids are used avoid spraying near flight-deck windows as fluid residues can cause a severe loss of
visibility during flight. Any thickened fluid remaining on nose areas, where it could blow back onto flight deck windows,
must be removed prior to departure using squeegees or equivalent.
If flight-deck windows are contaminated with thickened fluids, use water or an approved windshield cleaner (use of low
freezing point windscreen fluid is recommended when OAT is at or below 0°C).
Landing Gear and Wheel Bays
Under certain conditions, it may be possible to sweep off accumulations such as blown snow. However, where deposits
have bonded to surfaces, they can be removed by the application of hot air.
Image: Convair Wheel Axel & Brakes

WARNING!
UNDER NO CIRCUMSTANCES SHOULD DE-ICING FLUID BE SPRAYED ON TO WHEEL AXEL OR BRAKES
The aim should be to keep the application of fluid to this area to a minimum.
Engines
Where possible, deposits of snow should be manually cleared from engine intakes prior to departure under the
supervision of the PIC.
Snow may be removed from an engine inlet using a small soft bristled hand-held brush.
Look for any ice that is attached to the engine inlet surface from a distance of 4-feet or less. Ensure ice is removed from
any of the inlet probes or sensors and only with the permission and under the supervision of an Engineer
CAUTION:
UNDER NO CIRCUMSTANCE SHALL ANY HARD or SHARP TOOL/SCRAPER BE USED TO REMOVE ICE FROM ANY PART OF
THE ENGINES

General Information
If any fluid is inadvertently sprayed onto windows, then remove all of the fluid from the cockpit windows before the
departure.
Make sure you carefully examine the windows with the wipers installed. Make sure that fluid is removed from all the
forward areas where it could flow back on the windshields during the taxi and take-off. These areas must be clean before
the departure.
NOTE: De-icing/anti-icing fluid can be removed by rinsing with approved cleaner and a soft cloth or flushing with Type I de-
icing fluid.
De-icing process
Before each de-ice you must do the following checks.
• Make sure the fluid is up to temperature (run fluid from gun until hot fluid has pumped through) prior
to use.
• When aircraft is due for de-icing then communicate with the PIC to get the aircraft configured for de-
icing.
• When the configuration process is underway the following will be happening to the aircraft.

Record the start time on the De-Icing Log as you begin the de-icing process.
Deice the aircraft starting with the fuselage first if required.
Once finished, carry out a final check of the aircraft to ensure there is no further evidence of ice or snow and then pass the
de-icing form to the PIC.
Final Checks Following De-icing
Post De-icing Check
Immediately prior to departure, check that the aircraft is prepared for flight in accordance with these general
requirements and that the critical aircraft surfaces are clean of all frost, ice, slush, and snow accumulations in accordance
with the following requirements.
Special attention will be given to:
Wings, tail, and control surfaces
Wings, tail and control surfaces shall be free of ice, snow, slush, and frost except that a coating of frost may be present on
wing lower surfaces in areas cold soaked by fuel between forward and aft spars in accordance with the aircraft
manufacturer's published manuals.
NOTE: Frost or other frozen contamination is not acceptable on the underside of horizontal stabiliser and elevator, unless
otherwise specified by aircraft manufacturer, the notification of such specification being the responsibility of the PIC or
Airline Engineer.
Pilot heads and static ports
Pilot heads and static ports shall be clear of ice, frost, snow, and fluid residues.
Engine inlets
Engine inlets shall be clear of internal ice and snow and fan shall be free to rotate.
Air conditioning inlets and exits
Air conditioning inlets and exits shall be clear of ice, frost, and snow. Outflow valves shall be clear and unobstructed.
Landing gear and landing gear doors
Landing gear and landing gear doors shall be unobstructed and clear of ice, frost, and snow.
Fuel tank vents
Fuel tank vents shall be clear of ice, frost, and snow.
Fuselage
Frost may be present on the fuselage per the direction of the PIC or a company engineer.
Nose/Radome Area and Flight Deck Windows
Any significant deposits of snow slush or ice on the windscreens or on areas forward of the windscreens shall be removed
prior to departure.
Flight control check
A functional flight control check using an external observer may be required after de- icing depending upon aircraft type.
This is particularly important in the case of an aircraft that has been subjected to an extreme ice or snow covering.

NOTE: An aircraft shall not be dispatched after a de-icing until the aircraft has received the following visual check by the
flight crew.
This check shall cover wings, horizontal stabilizer, vertical stabilizer, and fuselage, plus all other parts of the aircraft on
which a de-icing treatment was performed according to the requirements identified during the contamination check.
The check shall be performed from points offering sufficient visibility of these parts (e.g. from the de-icer itself or another
elevated piece of equipment). If contamination is found or the holdover time expires, de-icing must be used to remove any
fluid still settled on the wing before a further anti-icing treatment can be performed.

Before take-off, the PIC must ensure that he has received confirmation that this Post De-icing Check has been
accomplished.

NOTE: For specific aircraft types, additional requirements may be necessary e.g. special clear ice checks, such as tactile
checks on wings. These special checks are not covered by the Post De-icing Check.
a) As the de-icing operation progresses, the De-icing Operator will closely monitor the surface receiving treatment
in order to ensure that all forms of frost, ice, slush, or snow are removed.
 b) Once the operation has been completed, the De-icing Operator will carry out a close visual check of the surface
where treatment commenced in order to ensure it has remained free of contamination.
NOTE: This procedure is not required under ‘frost only’ conditions.
c) Where the request for de-icing did not specify all of the following surfaces, i.e. wing, horizontal stabilizer and
fuselage, the surfaces omitted from the request shall also receive a close visual check at this time in order to
confirm that they have also remained free of contamination
d) Any evidence of contamination that is outside the defined limits shall be reported to the PIC immediately.
Pre-Take-Off Checks
Pre-take-off Check (Flight Crew)
The PIC prior to take-off shall assess whether the applied holdover time is still appropriate. This check is normally
performed from inside the flight deck and is based on the information recorded on form PB.1 – Aircraft De-icing Log.
Aircraft Type Specific – Special Checks
Special or additional checks required by specific types of aircraft i.e. special clear ice checks such as tactile checks on
wings, that are not covered by the contamination check must be addressed separately by the aircraft operator or
engineer.
Hold Over Time (HOT)
Holdover Times
Holdover times commence with the START of a one-step procedure and with a two-step de-icing procedure at the START
of the second step.

Holdover times are provided to assist:

● Ground Staff in providing the operating Captain with an aircraft in a fully de-iced condition.
● The operating Captain in carrying out his responsibility for ensuring that the aircraft remains free of
contamination until take-off.

Where appropriate, they should be used in conjunction with a visual pre-take-off check of the wing, in order to ensure
compliance with the 'clean aircraft' concept. The judgment and experience of the Captain will be required to assess the
nature and rate of precipitation and the holdover time applicable to the actual conditions.
Holdover time is obtained by de-icing fluids remaining on and protecting aircraft surfaces for a period of time. With a one-
step de-icing operation holdover begins at the start of the operation and with a two-step, at the start of the second (anti-
icing) step. Holdover time will have effectively run out when frozen deposits start to form/accumulate on aircraft surfaces.
ISO Type I fluid forms a thin liquid wetting film which rapidly flows off the aircraft surfaces, giving a more limited
holdover time than Type II/IV fluids. With this type of fluid, no additional holdover would be provided by increasing the
concentration of fluid in the fluid/water mix.

The tables provided by the Aircraft Flight Manuals give an approximate indication of the holdover times that could
reasonably be expected during freezing precipitation. Many variables can influence holdover and these times should
therefore not be considered as absolute. The actual time of protection may be extended or reduced, depending upon the
ambient conditions. The lower limit of the published time span approximates to the estimated time of protection during
moderate precipitation and the upper limit to the estimated time of protection during light precipitation.
These tables shall be reviewed and confirmed at the start of each de-icing/anti-icing season.
NOTE: In heavy precipitation holdover times may not be achievable
SAE TYPE I FLUID – ALUMINIUM SURFACES
SAE TYPE I FLUID – COMPOSITE SURFACES
Fluid Limitations
ISO TYPE I FLUIDS
The freezing point of the ISO Type I fluid used for either one-step de-icing or as the first step in a two-step operation shall
be at least 10°C below the ambient temperature. In no case shall this temperature be lower than the lowest operational
use temperature (LOUT)
Warning!
Type I fluids supplied as concentrates for dilution with water prior to use shall not be used undiluted.
Fluid Application Table Type I Fluid / Water Mixtures
Guidelines for the application of Type I Fluid/Water mixtures (minimum concentration) as a function of OAT (Outside Air
Temperature)

FAA GUIDELINES FOR THE APPLICATION OF SAE TYPE I FLUID MIXTURE MINIMUM CONCENTRATIONS AS A FUNCTION
OF OUTSIDE AIR TEMPERATURE

Outside Air One-step Procedure De- Two-step Procedure

Temperature icing/Anti-icing1
First step: Deicing Second step: Anti- icing1,2
(OAT)

Heated water or a mix

of fluid and water
-3C (27F) heated to 60C (140F)
and above Mix of fluid and water minimum at the nozzleMix of fluid and water
heated to 60C (140F) heated to 60C (140F)
minimum at the nozzle, with minimum at the nozzle, with
a freezing point of at least Freezing point of a freezing point of at least
10C (18F) below OAT heated fluid mixture 10C (18F) below OAT
Below shall not be
-3C (27F) more than 3C (5
° F) above OAT
1) Fluids must only be used at temperatures above their lowest operational use
temperature (LOUT).
2) To be applied before first-step fluid freezes, typically within 3 minutes. (This time may be
higher than 3 minutes in some conditions, but potentially lower in heavy precipitation,
colder temperatures, or for critical surfaces constructed of composite materials. If
necessary, the second step shall be applied area by area.)
Notes:

● Upper temperature limit shall not exceed fluid and aircraft manufacturers’ recommendations.
● To use Type I holdover time guidelines in all conditions including active frost, at least 1 litre per
square meter (2 gal. per 100 square feet) fluid must be applied to the de-iced surfaces.
● This table is applicable for the use of Type I Holdover Time Guidelines in all conditions, including
active frost. If holdover times are not required, a temperature of 60 °C (140 °F) at the nozzle is
desirable.
● The lowest operational use temperature (LOUT) for a given Type 1 fluid is the higher of:
a) The lowest temperature at which the fluid meets the aerodynamic acceptance test for a
given aircraft type, or
b) The actual freezing point of the fluid plus a freezing point buffer of 10°C (18°F).
Caution: Wing skin temperatures may differ and, in some cases, be lower than OAT. A
stronger mix (more glycol) may be needed under these conditions.
NOTE: If removal of contamination is required on the lower side of the wings and the horizontal stabiliser and elevator, de-
icing fluid shall be applied sparingly to minimize fluid flow into drain holes.

Procedure Precautions
One Step De-icing
One-step de-icing is performed with a heated fluid. The fluid used to de-ice the aircraft remains on aircraft surfaces to
provide limited anti-ice capability. The correct fluid concentration shall be chosen with regard to desired holdover time
and is dictated by outside air temperature and weather conditions.
CAUTION:
Wing skin temperatures may be lower than OAT. If this condition is identified, a stronger mix (more glycol) may need to
be used to ensure a sufficient freeze point buffer.
CAUTION:
In order to detect dried residues, it may help to spray a water mist onto the affected surfaces. This causes the dried
residues to rehydrate and swell into a kind of gel.
Before De-icing
Inform the PIC that de-icing is about to commence. The aircraft needs to be configured so that whilst anti-icing and de-
icing is being carried out, the moveable surfaces shall be in a position as specified by the aircraft manufacturer. This is the
responsibility of ONLY the operating crew or an engineer.
When the APU is running APU ‘AIR’ must be selected “OFF” and when slush, ice or snow is to be removed from the tail
plane areas of most aircraft the horizontal stabiliser must be positioned in the leading edge “UP” position. When PIC are
not in attendance and one or more of the requirements are not met, Engineering should be requested to configure the
aircraft, before starting de-icing operations - See operator manual regarding specific instructions for different aircraft
types.
Check the fluid for optimum temperature. For effective de-icing, the temperature of the fluid needs to be hot, up to 90°C
in the vehicle tank. If the fluid is not at this temperature, significantly more fluid will be required, and it will take longer to
complete the operation. It is the heat not the chemical reaction that de-ices the aircraft.
Ensure that the optimum removal ‘technique’ has been selected. The basic de-icing requirement is to apply the fluid close
to the aircraft, in order to minimize heat loss and obtain maximum benefit from the force of the fluid spray.
Observe the basic spraying requirements detailed in 6.5 – Spraying Techniques and observe the no-spray areas. Failure to
observe the no spray areas could potentially affect the safety of the aircraft. It is vital therefore that all operatives have a
good understanding of the requirements.
During De-icing
‘NO SPRAY’ AREAS
The de-icing operative should be aware of the No Spray areas and ensure to the best of their ability that fluid is no sprayed
or resting on the following areas:
• Flight Deck Windows
• Pitot / Static Ports and Vents

• Engine Intakes

• Passenger Doors and Windows

Images: Examples of No Spray Areas on Air Chathams Aircraft

As well as the ‘NO SPRAY’ areas shown above, there are also windows, doors/seals, brakes/landing gear, vents, probes,
sensors, cavities, and any opening where sprayed fluid is not allowed. These are only a general guide to the “NO SPRAY“
areas. For further information consult with PIC for company specific ‘NO SPRAY ‘areas from the AMM.
NOTE: The following sample diagram shows the essential ‘NO SPRAY areas. Information on specific aircraft types as per
your station operations should be obtained from the aircraft operator.

Basic areas of caution when de-icing/anti-icing are engine-inlets, APU inlet/exhaust, windows, doors/seals, brakes/landing
gear, vents, probes, sensors, cavities, and any opening where sprayed fluid is not allowed.

Additionally, composite parts may have their own limitations regarding de-icing fluids and temperatures, such as
composite propellers. There are many variations, but these general areas shall be avoided whenever possible. Some
splashes of fluid and fluid drained cannot be avoided but direct spray on these parts is not allowed. Areas where fluid is
allowed to be sprayed (e.g. the radome), but from where fluid flow-off can cause some problems (e.g. fluid flowing from
the nose section on the windows during take-off), should be noted and the procedure should be discussed together with
the PIC. The reasons why these areas are restricted and the consequences of what might happen if glycol/fluid is sprayed
should be understood. Such incidents may be that sensors give false readings, engine and APU produce smoke inside the
aeroplane via the air intake (or break), glycol may stick on heated cockpit windows causing restricted view for the flight
crew etc.

Image: No Spray Areas (Advanced)

De-icing Fluid
Requirements
Fluid Temperature check
Once the fluid has come to the desired temperature and the hose has been purged you need to take the infrared
thermometer and check that the fluid is at the right temperature at the nozzle between 60 and 80 degrees.
Fluid Storage and Handling
It has previously been determined that careful handling is required at the pre-aircraft stage, in order to ensure that the
fluids are not degraded, either prior to or during application.
The methods employed to store, transport, heat, pump and apply these fluids must be in line with the manufacturers
recommendations if the fluid is to be maintained in an acceptable condition from 'delivery to take-off. The basic effect of
this type of degradation is to reduce the viscosity of the fluid thereby allowing it to flow off prematurely. This leaves the
external surfaces of the aircraft unprotected and therefore vulnerable to the effects of freezing precipitation. Under these
conditions the published holdover time may NOT be achievable.
Fluid Handling
De-icing fluid is a chemical product with environmental impact. During fluid handling, avoid any unnecessary spillage and
comply with local environmental and health laws and the manufacturer's safety data sheet.
Storage
As per the instructions of the manufacturer, de-icing must be kept in cool conditions, avoiding direct sunlight, UV light and
must not be exposed to temperatures of more than 60oC. Designated fluid storage areas need to be identified within a
facility.
All de-icing fluid that is on a mobile platform needs to be regularly checked to ensure the mobile barrow has not been
(inadvertently) repositioned or the UV resistant cover is still adequately covering all the fluid stock.
Pumping
Type I de-icing fluids do not get adversely affected by the type of mechanical shearing action of some de-icing pumps;
however, Type IV fluid is subject to degradation (shearing) if used with mechanical (e.g. gear type) pumps. Therefore, only
compatible pumps and spraying nozzles shall be used with this sort of fluid.
Heating
De-icing fluids shall be heated according to the fluid manufacturer’s guidelines.
Prolonged or repeated heating of fluids (directly or indirectly) may result in loss of water which can lead to performance
degradation of the fluid.
Any of the following situations or a combination of them can accelerate the fluid performance degradation:
● Low fluid consumption
● Tanks being in standby mode with heating system on for extended periods of time
● High temperatures in fluid tanks
● High temperatures in water tanks which are in direct contact with the fluid tanks (if applicable)
Application
Application equipment shall be cleaned thoroughly before being initially filled with de- icing fluid in order to prevent fluid
contamination. The integrity of the fluid at the nozzle shall be checked periodically.
Fluid Tank Filling
When required, the fluid tanks are filled so that the fluid is mixed to the correct concentration. One on one unit of the
batch of fluid to ensure that liquid is at 100% concentration and one when the filling process is complete to ensure that
liquid is at the mixed ratio required.
To ensure that the correct concentration is reached, it is vital that each container of fluid used is monitored and the
following procedure is followed.
● Empty one fluid container into appropriate tank.
● Fill same container to the same level with water that the fluid was before emptying into tank.
Once the desired levels of mixed fluid have been reached ensure that all containers are empty.
Communication Procedure
De-icing Communication
An aircraft shall not be dispatched after a de-icing operation until the aircraft has received the following visual check by a
trained and qualified person.
This check shall cover wings, horizontal stabilizer, vertical stabiliser, and fuselage, plus all other parts of the aircraft on
which a de-icing/anti-icing treatment was performed according to the requirements identified during the contamination
check.
NOTE: Where the request for de-icing/anti-icing did not specify the fuselage, it shall also receive a visual check at this time,
in order to confirm that it has remained free of contamination.
The check shall be performed from points offering sufficient visibility of these parts. Any contamination found, shall be
removed by further de-icing treatment and the check repeated.
Before take-off, the PIC will request confirmation that the aircraft is CLEAN.
NOTE: For specific aircraft types, additional requirements may be necessary e.g. special clear ice checks, such as tactile
checks on wings.
NOTE: A de-icing treatment should be continuous and as short as possible. If a treatment is interrupted, the PIC shall be
immediately informed stating:
a) reason for interruption.
b) actions to be taken (in consultation with the PIC).
c) expected time of delay.
Before continuing the treatment:
a) inform the PIC.
b) establish (in consultation with the PIC), further treatment to be carried out, including any surfaces
requiring re-treatment (in relation to Holdover time).
Carry out treatment as agreed.

Documentation
The De-Icing Log needs to be completed and returned signed to the PIC before dispatching the aircraft.