Separation

Separation

Concept of Separation

16.1 General Provisions for the Separation of Controlled Traffic. Separation methods and minima are stipulated in ICAO PANS Document 4444. Within CAS the ATC service will make sure that all controlled flights (flights provided with ATC) are separated from each other to comply with the first requirement of the service - to prevent collisions between aircraft. Separation can be either:

•Vertical or

•Horizontal or

•Composite (a mixture of both - see para. 16.3)

It is applied to a defined standard, known as the separation minima. Separation is also applied to achieve spacing between aircraft to counter the effects of wake vortices and to facilitate timed arrivals and departures from busy aerodromes. Separation is applied:

•Between all flights in class A and B airspaces

•Between IFR flights in class C, D and E airspaces

•Between IFR flights and VFR flights in class C airspace

•Between IFR flights and special VFR flights

•Between special VFR flights, when so prescribed by the appropriate ATS authority

Note: IFR flights in VMC during daylight hours in classes D and E airspace may be cleared to climb and descend whilst maintaining own separation.

16.2Minimum Separation. Clearance will not be given to execute any manoeuvre that would reduce the spacing between two aircraft to less than the separation minimum applicable. Larger separations than the specified minima will be applied whenever wake turbulence or exceptional circumstances such as unlawful interference call for extra precautions. Whenever the type of separation or minimum used to separate two aircraft cannot be maintained, action shall be taken to ensure that another type of separation exists, or is established, when the previously applied separation becomes insufficient.

16.3Composite Separation. In circumstances where (usually due to an emergency or a serious deterioration in operating capability) the aircraft cannot maintain the necessary requirements for normal navigation, a compromise separation standard may be specified (in accordance with a RAN agreement), whereby the aircraft will take up altitude and track spacing not less than half that specified in the standards for normal separation. The RTF failure procedure for the NAT region specifies composite separation; likewise, the suggested procedure for unlawful interference where the pilot cannot maintain two-way RTF also specifies composite separation.

16.4Essential Traffic Information. Essential Traffic is defined as that controlled traffic to which ATC separation is applicable but to which in relation to another controlled flight is not, or will not, be separated by the required minimum. ‘Essential traffic information’ will be passed to the controlled flights concerned when they constitute essential traffic to each other.

Vertical Separation

16.5 Vertical Separation Minima. Wherever possible, ATC will arrange vertical separation to maximize the use of airspace and minimize horizontal use of airspace. Vertical separation is obtained by requiring aircraft using the same altimeter setting to fly at different levels expressed in terms of flight levels or altitudes dependent upon the magnetic track of the aircraft. The vertical separation minimum (VSM) is:

16

Separation 16

Separation 16

FL110 300 ft

300 ft

FL100

ICAO LEVEL OCCUPANCY STANDARD = +/- 300 ft (UK applies +/- 200 ft standard)

Figure 16.1 ICAO level occupancy standard

16.6RVSM Cruising Levels. The RVSM cruising levels defined for domestic airspace (outside of the NAT MNPSA) are those between FL290 and FL410 inclusive. In other words, both FL290 and FL410 are RVSM levels.

16.7Minimum Cruising Level. Except when specifically authorized by the appropriate authority, cruising levels below the minimum flight altitudes (established by the State) shall not be assigned. Area Control Centres shall, when circumstances warrant it, determine the lowest usable flight level or levels for the whole or parts of the control area for which they are responsible, and use it when assigning flight levels and pass it to pilots on request. Unless otherwise prescribed by the State concerned, the lowest usable flight level is that which corresponds to, or is immediately above, the established minimum flight altitude. The portion of a control area for which a particular lowest usable flight level applies is determined in accordance with air traffic services requirements.

16.8Assignment of Cruising Level. An ACC will normally allocate only one cruising level to an aeroplane (except where cruise climb is authorized), for flight in the control area or for flight entering another control area.

16.9Level Change. If a change in cruising level is required, the aircraft is to request a level change en route (after initial clearance received). Aircraft, cruise climb authorized, will be cleared to operate between two levels. On ATS routes (airways) extending beyond the control area, level changes are to be effected over a radio navigation aid. If an aircraft has been cleared into a CTA below the minimum cruising level for that airspace, the ACC will issue a clearance to climb even though the pilot has not requested it. When necessary, an aircraft may be cleared to change cruising level at a specified time, place or rate.