UNIT- 2: Air Traffic Services

AREA CONTROL SERVICE:

The provision of air traffic control service for controlled flights, except for those parts of such flights
which are under the jurisdiction of Approach Control or Aerodrome Control to accomplish following
objectives:

a) prevent collisions between aircraft;

b) expedite and maintain an orderly flow of air traffic Area control shall provide the following
services: a) Control service; b) Traffic synchronisation as well as demand and capacity balancing to
all flights operating in controlled airspace and to IFR flights in Class F airspace wishing to enter
controlled airspace. c) Advisory service to IFR flights operating within advisory airspace. d) Flight
information service, Alerting service and assistance to organisations involved in SAR (search and
rescue)

Responsibilities: Area control is responsible for providing separation between aircraft operating in
controlled airspace and advice to aircraft in advisory airspace. Air traffic control clearances to
aircraft shall be based solely on the requirements for providing air traffic control services within such
airspace.

The area within which radar services are provided is determined by the radar coverage of the
equipment but may be further limited to areas defined in the unit operational manual.

ATC ROUTES AND SIGNIFICANT POINTS:

An ATS route is a designated route for channelling the flow of traffic as necessary for the provision of
air traffic services. This include jet routes, area navigation routes (RNAV), and arrival and departure
route. Routes may be defined with a designator; a path to and from significant points; distance
between significant points; reporting requirements; and the lowest safe altitude. Significant points:

A specified geographical location used in defining an ATS route or the flight path of an aircraft and for
other navigation and other ATS purposes (ICAO)

These significant points should be established, where possible, with reference to radio
navigational aids, preferably VHF (very high frequency) OR higher frequency aids. If no radio
navigational aids are available, a significant points should either be visually recognizable or
determinable by self-contained airborne navigational aids

A significant point is designated in plain language and is named with reference to an identifiable and
preferably prominent geographical location.

Area navigation (RNAV) is a method of instrument flight rules (IFR) navigation that allows an
aircraft to choose any course within a network of navigation beacons, rather than navigate directly to
and from the beacons. This can conserve flight distance, reduce congestion, and allow flights
into airports without beacons. Area navigation used to be called "random navigation", hence the
acronym RNAV.

Area navigation (RNAV) is a general term used to describe the navigation from point A to point B
without direct over flight of navigational aids, such as VOR stations or ADF nondirectional beacons. It
includes VORTAC (Very High Frequency Omni-Directional Radio Range Tactical Air Navigation Aid) and
VOR/DME based systems, as well as systems of RNAV based around LORAN (long range navigation),
GPS, INS (inertial navigation system), and the FMS (flight management system) of transport
category aircraft. However, until recently, the term RNAV was most commonly used to describe
the area navigation or the process of direct flight from point A to point B using VORTAC and VOR/DME
based references which are discussed in this section

All RNAV systems make use of waypoints. A waypoint is a designated geographical location or point
used for route definition or progress-reporting purposes. It can be defined or described by
using latitude/longitude grid coordinates or, in the case of VOR based RNAV, described as a
point on a VOR radial followed by that point’s distance from the VOR station (i.e., 200/25 means
a point 25 nautical miles from the VOR station on the 200° radial).

Below figure illustrates an RNAV route of flight from airport A to airport B. The VOR/DME and
VORTAC stations shown are used to create phantom waypoints that are overflown rather than
the actual stations. This allows a more direct route to be taken. The phantom waypoints are entered
into the RNAV course-line computer (CLC) as a radial and distance number pair. The computer creates
the waypoints and causes the aircraft’s CDI to operate as though they are actual VOR stations.
A mode switch allows the choice between standard VOR navigation and RNAV.

VOR based RNAV uses the VOR receiver, antenna, and VOR display equipment, such as the CDI
(course deviation indicator). The computer in the RNAV unit uses basic geometry and trigonometry
calculations to produce heading, speed, and time readouts for each waypoint. VOR stations need to
be within line-of sight and operational range from the aircraft for RNAV use.

RNAV has increased in flexibility with the development of GPS. Integration of GPS data into a
planned VOR RNAV flight plan is possible as is GPS route planning without the use of any VOR stations.

Fig: RNAV

RNP

Required navigation performance (RNP) is a type of performance-based navigation (PBN) that allows
an aircraft to fly a specific path between two 3D-defined points in space.
Area navigation (RNAV) and RNP systems are fundamentally similar. The key difference between
them is the requirement for on-board performance monitoring and alerting. A navigation specification
that includes a requirement for on-board navigation performance monitoring and alerting is referred
to as an RNP specification. One not having such a requirement is referred to as an RNAV specification.
Therefore, if ATC radar monitoring is not provided, safe navigation in respect to terrain shall be self-
monitored by the pilot and RNP shall be used instead of RNAV.

Required Navigation Performance (RNP) is a statement of the navigation performance necessary for
operation within a defined airspace. RNP includes both performance and functional requirements,
and is indicated by the RNP value. The RNP value designates the lateral performance
requirement associated with a procedure. The term RNP is also applied as a descriptor for airspace,
routes, and procedures — including departures, arrivals, and instrument approach procedures
(IAPs). The descriptor can apply to a unique approach procedure or to a large region of airspace. RNP
applies to navigation performance within a designated airspace, and includes the capability of both
the available infrastructure (navigation aids) and the aircraft.

The RNP value designates the lateral performance requirement associated with a procedure.
The required performance is obtained through a combination of aircraft capability and the level of
service provided by the corresponding navigation infrastructure. From a broad perspective:

Aircraft Capability + Level of Service = Access

In this context, aircraft capability refers to the airworthiness certification and operational
approval elements (including avionics, maintenance, database, human factors, pilot procedures,
training, and other issues). The level of service element refers to the NAS infrastructure, including
published routes, signal-in-space performance and availability, and air traffic management. When
considered collectively, these elements result in providing access. Access provides the desired benefit
(airspace, procedures, routes of flight, etc.). A key feature of RNP is the concept of on-board
monitoring and alerting. This means the navigation equipment is accurate enough to keep the
aircraft in a specific volume of airspace, which moves along with the aircraft. The aircraft is expected
to remain within this block of airspace for at least 95 percent of the flight time. Additional airspace
outside the 95 percent area is provided for continuity and integrity, so that the combined areas ensure
aircraft containment 99.9 percent of the time. RNP levels are actual distances from the centerline of
the flight path, which must be maintained for aircraft and obstacle separation. Although additional
FAA-recognized RNP levels may be used for specific operations, the United States currently supports
three standard RNP levels:

RNP 0.3 – Approach

RNP 1.0 – Terminal

RNP 2.0 – Terminal and En Route

RNP 0.3 represents a distance of 0.3 nautical miles (NM) either side of a specified flight path
centerline. The specific performance required on the final approach segment of an instrument
approach is an example of this RNP level.
Fig: Required Navigation Performance

VERTICAL, LATERAL AND LONGITUDINAL SEPARATIONS BASED ON TIME / DISTANCE:

TYPES OF SEPARATION

There are 2 main types of separation:

Vertical separation

Horizontal separation

VERTICAL SEPARATION

Vertical separation is obtained by requiring aircraft to use prescribed altimeter settings procedures
to operate at different levels in terms of flight level or altitude.
VERTICAL SEPARATION MINIMUM – VSM

The vertical separation minimum (VSM) is 300m (1000ft) below FL290 and 600m (2000ft) above
FL290

For the airspace where reduced vertical separation minimum (RVSM) is applicable, the
separation minimum between FL290 and FL410 is reduced to 300m (1000ft)

HORIZONTAL SEPARATION

There are two types of horizontal separation:

Lateral separation

Longitudinal separation

Lateral separation shall be applied so that the distance between those portions of the intended routes
for which the aircraft are to be laterally separated is never less than an established distance to account
for navigational inaccuracies plus a specified buffer.

LATERAL SEPARATION MINIMA

The lateral separation minima by use of the same navigation aid are: VOR: both aircraft are established
on radials which diverge by at least 15° and at least one aircraft is at a distance of 28km or 15NM or
more from the facility
*NDB: both aircraft are established on tracks to or from the NDB which diverge by at least 30° and at
least one aircraft is at a distance of 28km or 15NM or more from the facility

*Dead reckoning: both aircraft are established on tracks which diverge by at least 45° and at least one
aircraft is at a distance of 28km or 15NM or more from the point of intersection of the track and both
aircraft are established outbound from the intersection.

LATERAL SEPARATION OF AIRCRAFT ON PARALLEL OR NON-INTERSECTING TRACKS

Lateral separation of aircraft on parallel or non-intersecting tracks or ATS routes shall be established
in accordance with the following:

For a minimum spacing between tracks of 50NM or 93km when using a navigational performance of
RNAV10 (RNP10) or RNP4
For a minimum spacing between tracks of 30NM or 55.5km when using a navigational performance of
RNP4

LONGITUDINAL SEPARATION GENERAL

Longitudinal separation shall be applied so that the spacing between the estimated positions of
the aircraft being separated is never less than a prescribed minimum.

DEFINITION: SAME, RECIPROCAL AND CROSSING TRACKS

Same tracks are same direction tracks or intersecting tracks when angular difference of these
both tracks is less than 45° or more than 315°

Figure: Same track conditions

Reciprocal tracks are opposite direction tracks and intersecting tracks when angular difference of
these both tracks is more than 135° or less than 225°

Figure: Reciprocal track conditions

Crossing tracks are intersecting tracks in other conditions than “same track” and “reciprocal track”

Figure: Crossing track conditions

LONGITUDINAL SEPARATION MINIMA BASED ON DISTANCE

Separation shall be established by maintaining not less than specified distance between aircraft
positions as reported by reference to DME in conjunction with other appropriate navigation
aids and/or GNSS (GPS).

AIRCRAFT MAINTAINING SAME LEVEL ON SAME TRACK

Default minimum separation in each

Situation Default minimum separation case the preceding aircraft is
maintaining a true airspeed of
37km/h (20kt) or more faster than
the succeeding aircraft
Aircraft on same 20 NM 37 km 10 NM 19
track km
AIRCRAFT MAINTAINING SAME LEVEL ON CROSSING TRACK

Default minimum separation in each

Situation Default minimum separation case the preceding aircraft is
maintaining a true airspeed of
37km/h (20kt) or more faster than
the succeeding aircraft
Aircraft on crossing 20 NM 10 NM
track 37 km 19 km

This longitudinal separation shall also apply at the crossing point of the tracks and when the relative
angle between the tracks is less than 90 degrees
LONGITUDINAL SEPARATION MINIMA BASED ON TIME

AIRCRAFT MAINTAINING SAME LEVEL ON SAME TRACK

Default
minimum
Default separation
minimum in each
Default separation in case the
minimum each case the preceding
separation if preceding aircraft is
Default minimum navigation aids aircraft is maintaining
Situation separation permit maintaining a a true
frequent true airspeed of airspeed of
determination 37km/h (20kt) 74km/h
of position and or more faster (40kt) or
speed than the more
succeeding faster than
aircraft the
succeeding
aircraft
Aircraft
on 15 minutes 10 minutes 5 minutes 3 minutes
same
track
ATC CLEARANCE:

An ATC clearance means an authorization by ATC, for the purpose of preventing collision between
known aircraft, for an aircraft to proceed under specified conditions within controlled airspace.

Purposes

Clearances are issued solely for expediting and separating air traffic and are based on known traffic
conditions which affect safety in aircraft operation. The traffic conditions include:

aircraft in the air;

aircraft on the manoeuvring area;

vehicles on the manoeuvring area;

obstructions not permanently installed on the manoeuvring area.

Applicability

ATC clearances are issued for controlled flights only, i.e.:

When a flight plan specifies that the initial portion of a flight will be uncontrolled, the pilot needs to
obtain a clearance from the relevant ATC unit before entering controlled airspace.

When a flight plan specifies that the first portion of a flight will be subject to ATC, and that
the subsequent portion will be uncontrolled, the aircraft is normally cleared to the point at
which the controlled flight terminates.

For flights through intermediate stops, the initial clearance limit is be the first destination aerodrome
and new clearances are to be issued for each subsequent portion of flight. By prior arrangement
between ATC units and the operators however it is possible to clear the flight through intermediate
stops.

A flight is subject to ATC clearance depending on the flight rules and airspace class, i.e.:

IFR flights are subject to ATC clearance in airspace classes A, B, C, D and E.

VFR flights are subject to ATC clearance in airspace classes B, C and D. They are not permitted in class
A airspace and are not controlled in class E.

FLIGHT PLANS:

Flight plans are documents filed by a pilot or flight dispatcher with the local Air Navigation Service
Provider (e.g. the FAA in the United States) prior to departure which indicate the plane's planned
route or flight path. Flight plan format is specified in ICAO Doc 4444. They generally include basic
information such as departure and arrival points, estimated time en route, alternate airports in case
of bad weather, type of flight (whether instrument flight rules [IFR] or visual flight rules [VFR]),
the pilot's information, number of people on board and information about the aircraft itself. In
most countries, flight plans are required for flights under IFR, but may be optional for flying VFR unless
crossing international borders. Flight plans are highly recommended, especially when flying over
inhospitable areas, such as water, as they provide a way of alerting rescuers if the flight is overdue.
Fig: Example of Flight plan document

POSITION REPORT

Position Report means a message, in a specified form, containing information on the position
and progress of an aircraft.