Note.— Guidance material relating to vertical separation is contained in the Manual on Implementation of a 300 m (1 000 ft) Vertical Separation Minimum Between FL 290 and FL 410 Inclusive (Doc 9574).
4. Minimum cruising level

4.1 Except when specifically authorized by the appro-priate authority, cruising levels below the minimum flight altitudes established by the State shall not be assigned.
4.2 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.
Note 1.— Unless otherwise prescribed by the State concerned, the lowest usable flight level is that flight level which corresponds to, or is immediately above, the established minimum flight altitude.
Note 2.— The portion of a control area for which a particular lowest usable flight level applies is determined in accordance with air traffic services requirements.
Note 3.— See Part II, Note 2 to Section 1.
5. Assignment of cruising levels

5.1 Except when traffic conditions and co-ordination procedures permit authorization of cruise climb, an area control centre shall normally authorize only one cruising level for an aircraft beyond its control area, i.e. that cruising level at which the aircraft will enter the next control area whether contiguous or not. Aircraft will be advised to request en route any subsequent cruising level changes desired.
5.1.1 Aircraft authorized to employ cruise climb techniques shall be cleared to operate between two levels or above a level.
5.2 If it is necessary to adjust the cruising level of an aircraft operating along an established ATS route extending partly within and partly outside controlled airspace and where the respective series of cruising levels are not identical, such adjustment shall, whenever possible, be effected within controlled airspace and, if suitably located, over a radio navigation aid.
5/11/98
No. 2

5.3 When an aircraft has been cleared into a centre’s control area at a cruising level which is below the established minimum cruising level for a subsequent portion of the route, action should be initiated by that area control centre to issue a revised clearance to the aircraft even though the pilot has not requested the necessary cruising level change.
5.4 When necessary, an aircraft may be cleared to change cruising level at a specified time, place or rate.
5.5 In so far as practicable, cruising levels of aircraft flying to the same destination shall be assigned in a manner that will be correct for an approach sequence at destination.
5.6 An aircraft at a cruising level shall normally have priority over other aircraft desiring that cruising level. When two or more aircraft are at the same cruising level, the preceding aircraft shall normally have priority.
5.7 An aircraft may be assigned a level previously occupied by another aircraft after the latter has reported vacating it. If, however, severe turbulence is known to exist, or the aircraft concerned is effecting a cruise climb, such assignment shall be withheld until the aircraft vacating the level has reported at another level separated by the required minimum.
5.8 The cruising levels, or, in the case of cruise climb, the range of levels, to be assigned to controlled flights shall be selected from those allocated to IFR flights in:
a)  the tables of cruising levels in Appendix 3 of Annex 2; or
b)  a modified table of cruising levels, when so prescribed in accordance with Appendix 3 of Annex 2 for flights above flight level 410;
except that the correlation of levels to track as prescribed therein shall not apply whenever otherwise indicated in air traffic control clearances or specified by the appropriate ATS authority in Aeronautical Information Publications.
　
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