16.10Same Destination. If practicable, cruising levels of aircraft bound for the same destination will be assigned to facilitate the correct approach sequence at the destination.

16.11Priority. An aircraft at a cruising level will have priority over aircraft requesting that level. When two or more aircraft are at the same level, the preceding aircraft will have priority

16.12Allocation Separation. An aircraft may be assigned a level previously occupied by another aircraft after the latter has reported vacating it. In the case of severe turbulence or cruise climb, the assignment will be withheld until the other aircraft has reported at another level separated by the required minimum.

16.13Vertical Separation During Ascent or Descent. Pilots in direct communication with each other may, with their concurrence, be cleared to maintain a specified vertical separation between their aircraft during ascent or descent.

16.14Clearance to Maintain Own Separation in VMC. If requested by the pilot of an aircraft and it is agreed by the pilot of the other aircraft and authorized by ATC, a flight operating in classes D and E airspace in VMC during daylight, may be cleared to climb or descend maintaining own separation from one other aircraft providing:

•The clearance is specifically for the portion of flight below 10 000 ft;

•Alternative instructions are passed to the pilot to cover loss of VMC;

•If conditions deteriorate to the limits of VMC, the pilot is to inform ATC that he/she is complying with the alternative instructions.

Horizontal Separation

16.15 Definition. Horizontal separation relates to the distance between aircraft in the horizontal plane. This may be:

•Longitudinal (aircraft following the same route), where the separation standard is based on time (or distance) along track between aircraft, or

•Lateral.

Separation 16

Separation 16

16.16 Lateral 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. This buffer shall be determined by the appropriate authority and included in the lateral separation minima. Lateral separation of aircraft at the same level is obtained by requiring operation on different routes or in different geographical locations as determined by visual observation, by use of navigation aids or by use of area navigation (RNAV) equipment. The ‘buffer’ concept is applied to all methods of separation.

Minimum lateral separation

Figure 16.3

16.17 Lateral Separation Criteria and Minima. Means by which lateral separation may be achieved include the following:

•Geographical Separation. Separation positively indicated by position reports over different geographical locations as determined visually or by reference to a navigation aid.

•Track Separation. This can be achieved between aircraft using the same navigation aid or method. It is achieved by requiring aircraft to fly on specified tracks which are separated by a minimum amount (angle and distance) appropriate to the navigation aid or method employed as follows. For the three cases specified the distance required is 15 NM from the common position with track divergence as follows:

•VOR: Track divergence 15°

•NDB: Track divergence 30°

•DR Fix: Track divergence 45°

Separation 16

16.25 Longitudinal Separation Based on DME. Where DME information is available, separation can be established by maintaining not less than the specified distances between aircraft positions. In this case it is a requirement that direct pilot - controller communication is maintained.

Note: in the NAT region using HF, communication is via a radio operator not direct to the controller.

16.26 Aircraft at the Same Level. The previously defined same and crossing track situations apply:

•Same track. The normal standard is 20 NM provided each aircraft uses on-track DME stations and separation is checked by obtaining simultaneous DME readings from the aircraft at frequent intervals. The standard may be reduced to 10 NM provided the leading aircraft maintains a TAS 20 kt or more, faster than the succeeding aircraft.

•Crossing tracks. The same track standards apply to crossing traffic providing that each aircraft reports distance from the station located at the crossing point and that the relative angle of the tracks is less than 90°.

•Climbing or descending. The standard separation is 10 NM whilst vertical separation does not exist, providing each aircraft uses ‘on-track’ DME stations; one aircraft maintains a level whilst vertical separation does not exist, and separation is established by simultaneous DME readings from the aircraft.

•Reciprocal tracks. Aircraft using on-track DME may be cleared to climb or descend to or through levels occupied by other aircraft using on-track DME, provided it has been positively established that the aircraft have passed each other and are at least 10 NM apart (or such other value as the authority specifies).

16.27 Longitudinal Separation with Mach Number Technique Based on Time. The Mach number technique requires turbojet aircraft to fly at the Mach number approved by ATC, and to request approval before making any speed changes. If it is essential to make immediate temporary changes to speed (e.g. due to turbulence), ATC is to be informed as soon as possible. If it is not feasible due to aircraft performance to maintain the last assigned Mach number during en route climbs and descents, pilots are to advise ATC at the time clearance to climb or descent is requested. Separation will be deemed to exist when the required time interval exists providing:

•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

•It is possible to ensure, by radar or other means, that the appropriate time interval will exist at the common point from which they will either follow the same track or continuously diverge, if the aircraft have not already reported over the same point.

16.28 Time Intervals. When the Mach number technique is applied, minimum longitudinal separation between turbojet aircraft on the same track, whether in level, climbing or descending flight is:

•10 minutes providing the preceding aircraft maintains a Mach speed equal to or greater than that maintained by the following aircraft, or

•Between 9 and 5 minutes inclusive, providing the preceding aircraft is maintaining a Mach number greater than the following aircraft in accordance with the following:

Figure 16.12 Mach number separation

16.29 Longitudinal Separation Based on RNAV. This is applicable to RNAV aircraft operating along RNAV routes or ATS routes defined by VOR. In this case, separation is established by maintaining the specified distance between aircraft positions reported by reference to the RNAV equipment. It is a requirement that direct controller/pilot communications are maintained. RNAV positions are defined as standard way points common to both aircraft subject to separation. The minimum is 150 km (80 NM) distance based separation instead of the normally required 10 minutes. It is also essential that the Mach number technique is applied. In the event of equipment failure reducing the navigation capability to less than the RNAV requirement, the normal longitudinal separation will be applied. The specific separation requirements are:

•Same cruising level. 150 km (80 NM) providing each aircraft reports position from same point and separation is checked by obtaining simultaneous RNAV distance readings from the aircraft at frequent intervals.

•Climbing or descending on same track. 150 km (80 NM) whilst vertical separation does not exist, provided each aircraft reports distance from same way point, one aircraft maintains level flight whilst vertical separation does not exist, and separation is established by obtaining simultaneous RNAV distance readings from the aircraft.

•Reciprocal tracks. Aircraft may be permitted to climb or descend through levels occupied by other aircraft providing it has been positively established by simultaneous RNAV distance readings to or from the same on-track way point that the aircraft have passed each other by at least 150 km (80 NM).

Separation 16

Separation 16

16.30 Longitudinal Separation Based on RNAV where RNP is Specified. For aircraft cruising, climbing or descending on the same track in an RNP RNAV environment, the separation standards detailed in the table below may be used. During the application of the 50 NM minimum, if an aircraft fails to report its position, the controller is to take action within 3 minutes to establish communications. If communication has not been established within 8 minutes, alternative separation is to be applied. An aircraft may climb or descend through an occupied level once it has been established that the aircraft concerned have passed.

Figure 16.13 RNP RNAV separation

16.31 Reduction in Separation Minima. The separation minima may be reduced as determined by the appropriate ATS authority, after prior consultation with the aircraft operators, as appropriate, in the following circumstances:

•When special electronic or other aids enable the pilot-in-command of an aircraft to determine accurately the aircraft’s position and when adequate communication facilities exist for that

position to be transmitted without delay to the appropriate air traffic control unit; or

•When, in association with rapid and reliable communication facilities, radar-derived information of an aircraft’s position is available to the appropriate air traffic control unit; or

•When special electronic or other aids enable the air traffic controller to predict rapidly and accurately the flight paths of an aircraft and adequate facilities exist to verify frequently the actual aircraft positions with the predicted positions; or

•When RNAV-equipped aircraft operate within the coverage of electronic aids that provide the necessary updates to maintain navigational accuracy.

•In accordance with RAN agreements, after prior consultation with the aircraft operators, when:

•Special electronic, area navigation and other aids enable the aircraft to closely adhere to their current flight plans; and

•The air traffic situation is such that the conditions regarding communications between pilots and the appropriate ATS unit or units need not necessarily be met to the degree specified therein, in order to maintain an adequate level of safety.