Airports Authority of India Manual of Air Traffic Services – Part 1

CHAPTER 5

SEPARATION METHODS AND MINIMA

5.1 Provision for the separation of Whenever, as a result of failure or

controlled traffic degradation of navigation, communications,
altimetry, flight control or other systems,
5.1.1 Vertical or horizontal separation shall aircraft performance is degraded below the
be provided: level required for the airspace in which it is
a) between IFR flights in Class D and E operating, the flight crew shall advise the
airspaces except when VMC climb or ATC unit concerned without delay. Where the
descent is involved under the failure or degradation affects the separation
conditions specified in para 5.5.6; minimum currently being employed, the
b) between IFR flights and special VFR controller shall take action to establish
flights; [and another appropriate type of separation or
c) between special VFR flights separation minimum.

5.1.2 No clearance shall be given to

execute any manoeuvre that would reduce 5.2 Reduction in separation minima
the spacing between two aircraft to less than
the separation minimum applicable in the 5.2.1 In the vicinity of aerodromes
circumstances.
In the vicinity of aerodromes, the separation
5.1.3 Larger separations than the specified minima may be reduced if:
minima should be applied whenever a) adequate separation can be provided
exceptional circumstances such as unlawful by the aerodrome controller when each
interference or navigational difficulties call for aircraft is continuously visible to this
extra precautions. This should be done with controller; or
due regard to all relevant factors so as to b) each aircraft is continuously visible to
avoid impeding the flow of air traffic by the flight crews of the other aircraft
application of excessive separations. concerned and the pilots thereof report
that they can maintain their own
Note — Unlawful interference with an aircraft separation; or
constitutes a case of exceptional circumstances c) in the case of one aircraft following
which might require the application of separations
another. The flight crew of the
larger than the specified minima, between the
aircraft being subjected to unlawful interference
succeeding aircraft reports that the
and other aircraft.
other aircraft is in sight and separation
can be maintained.
5.1.4 Where the type of separation or
5.2.2 In the event of complete failure of
minimum used to separate two aircraft
radar equipment
cannot be maintained, another type of
separation or another minimum shall be
established prior to the time when the current As an emergency measure, use of flight
separation minimum would be infringed. levels spaced by half the applicable vertical
separation minimum may be resorted to
5.1.2 Degraded aircraft performance

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temporarily if standard non-radar separation 5.5.1 Vertical Separation Minimum

cannot be provided immediately.
a) A nominal 1000 feet below FL290 and
5.3 Loss of separation a nominal 2000 feet at or above FL290,
except as provided for in b) below; and
If, for any reason, a controller is faced with a
situation in which two or more aircraft are b) A nominal 1000 feet when both aircraft
separated by less than the prescribed are RVSM compliant and operating
minima due to reason other than ACAS RA within designated RVSM airspace.
(e.g. air traffic control errors or difference in
the pilot’s estimated and actual times over 5.5.2 Cruise climb
reporting points) controller is to
a) use every means at his / her disposal to Cruise climb is not permitted in Indian FIRs.
obtain the required minimum with the
least possible delay; and 5.5.3 Vertical Separation during
b) pass essential traffic information. climb and descent

5.4 Essential traffic information 5.5.3.1 An aircraft may be cleared to a

level previously occupied by another aircraft
5.4.1 Essential traffic is that controlled after the latter has reported vacating it,
traffic to which the provision of separation by except when:
ATC is applicable, but which, in relation to a a) severe turbulence is known to exist; or
particular controlled flight is not, or will not b) the aircraft concerned are established
be, separated from other controlled traffic by at the same holding pattern; or
the appropriate separation minimum. c) the difference in aircraft performance is
such that less than the applicable
5.4.2 Essential traffic information shall be separation minimum may result;
given to controlled flights concerned in which case such clearance shall be
whenever they constitute essential traffic to withheld until the aircraft vacating the level
each other. has reported at or passing another level
separated by the required minimum.
5.4.3 Essential traffic information shall
include: 5.5.4 Pilot in direct communication with
a) direction of flight of aircraft concerned; each other may, with their concurrence, be
b) type and wake turbulence category(if cleared to maintain a specified vertical
relevant) of aircraft concerned; separation between their aircraft during
c) cruising level of aircraft concerned and; ascent or descent.
i) estimated time over the reporting
point nearest to where the level will 5.5.5 Step climb and descents
be crossed; or
ii) relative bearing of the aircraft 5.5.5.1 The step climb / descent
concerned in terms of the 12-hour procedure may be used for simultaneous
clock as well as distance from the climb / descent of the aircraft to vertically
conflicting traffic; or separated levels provided that the lower /
iii) actual or estimated position of the higher aircraft is progressively assigned
aircraft concerned. levels that provide vertical separation with
the higher / lower aircraft.
5.5 Vertical separation

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5.5.5.2 When applying the step climb or

step descent procedures, pilot must be
advised that they are subject to a step climb
or descent.

5.5.6 VMC climb and descent:

When so requested by an aircraft and

provided it is agreed by the pilot of the other
aircraft, an ATC unit may clear a controlled
flight, including departing and arriving flights,
operating in airspace Classes D and E in 5.6.1.2 By using the same navigation aid
VMC during the hours of daylight to fly or method
subject to maintaining own separation to one
other aircraft and remaining in VMC. When a By requiring to fly on specified tracks which
controlled flight is so cleared, the following are separated by a minimum amount
shall apply: appropriate to the navigational aid or method
a) Clearances shall be for a specified employed. Lateral separation between two
portion of the flight at or below 10,000 aircraft exists when:
feet, during climb and descent;
b) Essential traffic information shall be a) VOR
passed; and
c) If there is possibility that flight under Both aircraft are established on radials
VMC may become impracticable, an diverging by at least 15 degrees and at least
IFR flight shall be provided with one aircraft is 15 NM or more from the
alternative instructions to be complied facility.
with in the event that in VMC cannot be
maintained for the term of clearance.

5.6 Horizontal separation

The three types of horizontal separation are:

a) Lateral separation;
b) Longitudinal separation;
c) Radar separation.

5.6.1 Lateral separation

Means by which lateral separation may be

applied include the following: b) NDB

5.6.1.1 By using the same or different Both aircraft are established on tracks to or
geographic locations: from the NDB, which are diverging by at least
30 degrees and at least one aircraft is 15 NM
By position reports which positively indicate or more from the facility.
the aircraft are over different geographic
locations as determined visually or by
reference to a navigation aid.

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than 45 degrees or more than 315

degrees, and whose protection areas
overlap.

c) DR (dead reckoning)

Both aircraft are established on tracks

diverging by at least 45 degrees and at least
one aircraft is 15 NM or more from the point
of intersection of the tracks, this point being
b) Reciprocal tracks
determined either visually or by reference to
a navigational aid and both aircraft are
Opposite tracks and intersecting tracks
established outbound from the intersection.
or portions thereof, the angular
difference of which is more than 135
degrees but less than 225 degrees, and
whose protection areas overlap.

5.6.2 Longitudinal separation

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.
c) Crossing Tracks
5.6.2.1 For the purpose of application of
longitudinal separation, the terms same
Intersecting tracks or portions thereof
track, reciprocal tracks and crossing tracks
other than those specified in a) and b)
shall have the following meanings:
above.
a) Same track: same direction tracks and
intersecting tracks or portions thereof,
the angular difference of which is less

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b) 10 minutes, if navigation aids permit

frequent determination of position and
speed;

5.6.2.2.2.2 Aircraft flying on crossing tracks:

a) 15 minutes;
5.6.2.2 Longitudinal separation minima
based on time:

5.6.2.2.1 Cross Check Calculations

a) Separation requirements must be

cross-checked to ensure the integrity of
calculations.
b) The cross-check is to validate the initial
calculation and to confirm that the
calculation is consistent with the traffic b) 10 minutes if navigation aids permit
disposition. frequent determination of position and
speed
5.6.2.2.2 Aircraft at the same cruising
level

5.6.2.2.2.1 Aircraft flying on the same track:

a) 15 minutes;

5.6.2.2.3 Aircraft climbing or descending

5.6.2.2.3.1 Traffic on the same track.

When an aircraft will pass through the level

of another aircraft on the same track, the

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following minimum longitudinal separation d) 5 minutes while vertical separation

shall be provided: does not exist, provided that the level
a) 15 minutes while vertical separation change is commenced within 10
does not exist minutes of the time the second
aircraft has reported over an exact
reporting point.

c) 10 minutes while vertical separation does

not exist, provided that such separation is
authorized only where navigation aids
permit frequent determination of position
and speed

Note.— To facilitate application of the procedure

where a considerable change of level is involved,
a descending aircraft may be cleared to some
convenient level above the lower aircraft, or a
climbing aircraft to some convenient level below
the higher aircraft, to permit a further check on
the separation that will obtain while vertical
separation does not exist.

5.6.2.2.3.2 Traffic on crossing tracks:

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a) 15 minutes while vertical separation Where lateral separation is not provided,

does not exist vertical separation shall be provided for at
least ten minutes prior to and after the time
the aircraft are estimated to pass, or are
estimated to have passed.

Provided that it has been determined that the

b) 10 minutes while vertical separation aircraft have passed each other, this
does not exist if navigation aids permit minimum need not apply:
frequent determination of position and
speed. 5.6.2.3 Longitudinal separation minima
based on distance using DME
5.6.2.3.1 Separation shall be established by
maintaining not less than specified
distance(s) between aircraft positions as
reported by reference to DME in conjunction
with other appropriate navigation aids.

5.6.2.3.2 Direct controller-pilot

communication shall be maintained while
such separation is used.

5.6.2.3.3 All distance reports must be made

with reference to the same DME station.

5.6.2.3.4 Aircraft at the same cruising

level

5.6.2.3.4.1 Aircraft on the same track:

a) 20 NM, provided:
i) each aircraft utilizes “on-track” DME
stations; and
ii) separation is checked by obtaining
simultaneous DME readings from the
aircraft at frequent intervals to ensure
that the minimum will not be infringed.
5.6.2.2.3.3 Traffic on reciprocal tracks

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b) 10 NM provided:
i) the leading aircraft maintains a true
airspeed of 20 kts or more faster than
the succeeding aircraft;
ii) each aircraft utilizes “on-track” DME
stations; and
iii) separation is checked by obtaining
b) 10 NM provided:
simultaneous DME readings from the
i) the leading aircraft maintains a true
aircraft at such intervals as are
airspeed of 20 kts or more faster than
necessary to ensure that the minimum
the succeeding aircraft;
is established and will not be infringed.
ii) each aircraft utilizes “on-track” DME
stations and that the relative angle
between the tracks is less than 90
degrees; and
iii) separation is checked by obtaining
simultaneous DME readings from the
aircraft at such intervals as are
necessary to ensure that the minimum
is established and will not be infringed.
10 NM DME-based separation between aircraft
on same track and same level

5.6.2.3.4.2 Aircraft on crossing tracks:

a) 20 NM, provided:
i) each aircraft utilizes “on-track” DME
stations located at the crossing point of
the tracks and that the relative angle
between the tracks is less than 90
degrees; and
ii) separation is checked by obtaining
simultaneous DME readings from the
aircraft at frequent intervals to ensure
that the minimum will not be infringed.

5.6.2.3.5 Aircraft climbing or descending

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5.6.2.3.5.1 Aircraft on the same track Aircraft utilizing on-track DME may be
cleared to climb or descend to or through the
10 NM while vertical separation does not levels occupied by other aircraft utilizing on-
exist, provided: track DME, provided that it has been
a) each aircraft utilizes “on-track” DME positively established that the aircraft have
stations; passed each other and are at least 10 NM
b) one aircraft maintains a level while apart.
vertical separation does not exist; and
c) separation is established by obtaining
simultaneous DME readings from the
aircraft.

5.6.2.4 Longitudinal separation minima

with Mach number technique
based on time:

5.6.2.4.1 The following conditions shall be

met when the Mach number technique is
being applied:

a) Aircraft Types: Turbojet aircraft only.

b) Routes:
i) The aircraft concerned have
reported over the same reporting
point and follow the same track or
continuously diverging tracks until
some other form of separation is
provided; or
ii) If the aircraft have not reported over
Note.— To facilitate application of the procedure the same reporting point and it is
where a considerable change of level is involved, possible to ensure, by radar or
a descending aircraft may be cleared to some other means, that the appropriate
convenient level above the lower aircraft, or a time interval will exist at the
climbing aircraft to some convenient level below common point from which they
the higher aircraft, to permit a further check on either follow the same track or
the separation that will obtain while vertical
continuously diverging tracks.
separation does not exist.

5.6.2.3.5.2 Aircraft on reciprocal tracks c) Levels: The aircraft concerned are in

level, climbing or descending.

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d) Mach Number Assignment: A Mach ? Assign revised Mach numbers

number (or, when appropriate, a range appropriate for the estimated
of Mach numbers) shall be issued to interval, or
each aircraft. ? Establish vertical separation.
Note: Turbojet aircraft shall adhere to the Mach NOTE-Control estimates are calculated by the
number approved by ATC and shall request ATC controller using known wind patterns, previous
approval before making any changes thereto. If it aircraft transit times, pilot progress reports, and
is essential to make an immediate temporary pilot estimates.
change in the Mach number (e.g. due to
turbulence), ATC shall be notified as soon as d) Relative Speeds
possible that such a change has been made.
The lead aircraft maintains the same or
If it is not feasible, due to aircraft performance, to
maintain the last assigned Mach number during
a greater Mach number than the
en-route climbs and descents, pilots of aircraft following aircraft; or
concerned shall advise ATC at the time of the If the following aircraft is faster than the
climb/descent request. lead aircraft, ensure that the
appropriate time interval will exist until
e) Separation Minima another form of separation is achieved.

i) When Mach number technique is NOTE- The calculation of ground speeds and
estimated times over significant points is a time-
applied, minimum longitudinal consuming process which, in dense traffic situations,
separation between turbojet aircraft on could result in unacceptable delays in issuance of
the same track, whether in level, clearances. A “rule of thumb” may be applied which
climbing or descending flight shall be allows clearances to be issued in a timely manner,
10 minutes; or the prescribed minima provided the expected minimum longitudinal separation
over the exit point is subsequently confirmed when the
based on application of differential calculated flight progress strip data become available.
Mach number on prescribed ATS This rule of thumb can be stated as follows: for each
routes. 600 NM in distance between the entry and exit points
ii) The applicable longitudinal separation of the area where the Mach number technique is used,
add one minute for each 0.01 difference in Mach
minima is maintained by: number for the two aircraft concerned to compensate
Ensuring that the spacing for the fact that the second aircraft is overtaking the
between the estimated positions first aircraft (See Table below.)
of the aircraft is not less than
the prescribed minimum.
Continuously monitoring aircraft Application of the Mach Number Technique
position reports and updating when the Following Aircraft is Faster
control estimates along the
aircraft's track(s). If after Distance to Fly and Separation (in
establishing the Mach number Minutes) Required at Entry Point
technique between aircraft,
control information indicates that 001- 601- 1201- 1801- 2401-
Difference
less than the applicable minima in Mach 600 1200 1800 2400 3000
between aircraft may exist, NM NM NM NM NM
immediately
Issue crossing restrictions to 0.01 11 12 13 14 15
ensure the appropriate
0.02 12 14 16 18 20
longitudinal minima at the next
significant point, or

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whether arriving, departing or en route,

0.03 13 16 19 22 25
whenever the other aircraft concerned are
within five minutes flying time of the holding
0.04 14 18 22 26 30
area or within a distance prescribed by the
0.05 15 20 25 30 35
appropriate authority.

0.06 16 22 28 34 40

0.07 17 24 31 38 45

0.08 18 26 34 42 50

0.09 19 28 37 46 55

0.10 20 30 40 50 60

5.7 Minimum separation between

When preceding aircraft is maintaining a Mach number departing aircraft
greater than the following aircraft separation minima of
9 and 5 minutes inclusive, on prescribed minima may
be applied in accordance with the following table: 5.7.1 One-minute separation if aircraft are to
fly on tracks diverging by at least 45 degrees
immediately after take-off so that lateral
Application of the Mach Number Technique
when the Preceding Aircraft is Faster
separation is provided.

Separation
Mach Number by which the
Minima in Preceding Aircraft is Faster
Minutes

09 0.02

08 0.03

07 0.04

06 0.05 Note 1.— Wake turbulence categorization of aircraft

and longitudinal separation minima are contained in
Para 5.9
05 0.06

5.7.2 Two minutes between take-offs when

5.6.2 Separation of aircraft holding in the preceding aircraft is 40 kt or more faster
flight than the following aircraft and both aircraft
propose to follow the same track.
5.6.1 Aircraft established in adjacent holding
patterns shall be separated by the applicable
vertical separation minimum.

5.6.2 Except when lateral separation exists,

vertical separation shall be applied between
aircraft holding in flight and other aircraft,

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of the direction of approach after the

arriving aircraft has started procedure
turn or base turn leading to final
approach, provided that the take-off
will be made at least three minutes
before the arriving aircraft is
estimated to be over the beginning of
the instrument runway.

5.8.2 If an arriving aircraft is making a

Note: Calculations, based on TAS, of speed straight-in approach, a departing aircraft may
differentials of aircraft during climb may not be
sufficiently accurate in all circumstances for take off:
determining if the procedures in 5.8.2 can be applied, a) in any direction until five minutes
in which case calculations based on IAS may be more before the arriving aircraft is estimated
suitable. to be over the instrument runway;
b) in a direction which is different by at
5.7.3 Five-minute separation while vertical least 45 degrees from the reciprocal of
separation does not exist if a departing the direction of approach of the arriving
aircraft will be flown through the level of a aircraft:
preceding departing aircraft and both aircraft i) until three minutes before the arriving
propose to follow the same track. Action aircraft is estimated to be over the
must be taken to ensure that the five-minute beginning of the instrument runway, or
separation will be maintained or increased
while vertical separation does not exist. Note: Lateral separation is considered to exist
between an arriving aircraft that subsequently
commenced final approach and the departing
aircraft that has established on a course diverging
by at least 45 degrees from the reciprocal of the
final approach course.

5.8 Separation of departing aircraft

from arriving aircraft

The following separation shall be applied

when take-off clearance is based on the
position of an arriving aircraft:

5.8.1 If an arriving aircraft is making a

complete instrument approach, a departing
aircraft may take off:

a) in any direction until an arriving

aircraft has started its procedure turn
or base turn leading to final approach;
b) in a direction which is different by at Note: Use of runway other than runway- in-
least 45 degrees from the reciprocal use for the purpose of application of

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separation vide para 5.8.1.a and 5.8.2.a is not HEAVY MEDIUM 2 min
authorized. HEAVY LIGHT 3 min
or
5.9 Non-radar wake turbulence MEDIUM
longitudinal separation minima
5.9.5 Departing aircraft
5.9.1 Categorization of aircraft: Wake
turbulence separation minima should be Leading Following Separation Minima
based on a grouping of aircraft types into Aircraft Aircraft
HEAVY MEDIUM Departing from
three categories according to the maximum
or a) the same
certificated take-off mass. LIGHT runway
b) parallel runway 2 min
Category Maximum Certified separated by
take off mass less than 760 m
c) crossing
Heavy 1,36,000 kg or more runways if the
Medium Less than 1.36,000 kg projected flight
but more than 7000 path of the
kg second aircraft
will cross the
Light 7000 kg or less projected flight
path of the first
MEDIUM LIGHT
5.9.2 The ATC unit concerned shall not be aircraft at the
required to apply wake turbulence same altitude or
less than 1 000
separation: ft below;
a) for arriving VFR flights landing on the d) Parallel runways
same runway as a preceding landing separated by
HEAVY or MEDIUM aircraft; and 760 m or more,
if the projected
b) between arriving IFR flights executing
flight path of the
visual approach when the aircraft has second aircraft
reported the preceding aircraft in sight will cross the
and has been instructed to follow and projected flight
maintain own separation from that path of the first
aircraft at the
aircraft. same altitude or
less than 1 000
5.9.3 The ATC unit shall, in respect of the ft below.
flights specified in 5.10.2 a) and b) as well as
when otherwise deemed necessary, issue a
caution of possible wake turbulence. HEAVY MEDIUM Departing from 3 min
(Full or a) an
5.9.4 Arriving aircraft length LIGHT intermediate
Except as provided in 5.10.2 a) and b), the take-off) part of the
MEDIUM LIGHT same runway;
following minima shall be applied to aircraft or
(Full
landing behind a HEAVY or a MEDIUM length b) an
aircraft: take-off) intermediate
part of a
Leading Following Separation parallel
Aircraft Aircraft Minima runway;

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5.9.6 Opposite direction

A separation minimum of 2 minutes shall be
applied between a LIGHT or MEDIUM
aircraft and a HEAVY aircraft and between a
LIGHT aircraft and a MEDIUM aircraft when
the heavier aircraft is making a low or missed
approach and the lighter aircraft is:

a) utilizing an opposite-direction runway for

take-off;

or
b) landing on the same runway in the
opposite direction, or on a parallel
opposite-direction runway separated by
less than 760 m.

5.9.7 Displaced landing threshold

A separation minimum of 2 minutes shall be

applied between a LIGHT or MEDIUM
aircraft and a HEAVY aircraft and between a
LIGHT aircraft and a MEDIUM aircraft when
operating on a runway with a displaced
landing threshold when:
a) a departing LIGHT or MEDIUM aircraft
follows a HEAVY aircraft arrival and a
departing LIGHT aircraft follows a
MEDIUM aircraft arrival; or
c) an arriving LIGHT or MEDIUM aircraft
follows a HEAVY aircraft departure and

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an arriving LIGHT aircraft follows a

MEDIUM aircraft departure if the
projected flight paths are expected to
cross.
Note: Wake Vortex generation begins when the nose
wheel lifts off the runway on take-off and continues
until the nose wheel touches down on landing.

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