5.4.2  Determination of level occupancy
5.4.2.1 The criterion which shall be used to determine that a specific level is occupied by an aircraft shall be ±90 m (±300 ft), except that appropriate ATS authorities may specify a smaller criterion but not less than ±60 m (±200 ft) if this is found to be more practical.
Note.— For a brief explanation of the considerations

underlying this value see the Air Traffic Services Planning
Manual (Doc 9426).
5.4.2.2 Aircraft maintaining a level. An aircraft is considered to be maintaining its assigned level as long as the SSR Mode C-derived level information indicates that it is within ±90 m (±300 ft) of the assigned level.
5.4.2.3 Aircraft vacating a level. An aircraft cleared to leave a level is considered to have commenced its manoeuvre and vacated the previously occupied level when the SSR Mode C-derived level information indicates a change of more than 90 m (300 ft) in the anticipated direction from its previously assigned level.
5.4.2.4 Aircraft passing a level in climb or descent. An aircraft in climb or descent is considered to have crossed a level when the SSR Mode C-derived level information indicates that it has passed this level in the required direction by more than 90 m (300 ft).
VI. Radar Services
5.4.2.5 Aircraft reaching a level. An aircraft is con-sidered to have reached the level to which it has been cleared when three consecutive renewals of Mode C-derived level information have indicated that it is within 90 m (300 ft) of its assigned level.
Note.— In automated ATS systems, the cycles of renewals of Mode C data may not be evident to controllers. It may, therefore, be necessary to specify in instructions to controllers the number of display repetition cycles, or a time interval, corresponding to three consecutive renewals of Mode C data.
5.4.2.6 Intervention by a controller shall only be required if differences in level information between that displayed to the controller and that used for control purposes are in excess of the values stated above.
6. General radar procedures
6.1 Performance checks

6.1.1 The radar controller shall adjust the radar display(s) and carry out adequate checks on the accuracy thereof, in accordance with the technical instructions prescribed by the appropriate authority for the radar equipment concerned.
6.1.2 The radar controller shall be satisfied that the available functional capabilities of the radar system as well as the information presented on the radar display(s) is adequate for the functions to be performed.
6.1.3 The radar controller shall report, in accordance with local procedures, any fault in the equipment, or any incident requiring investigation, or any circumstances which make it difficult or impractical to provide radar services.
6.2 Identification of aircraft

6.2.1 Establishment of radar identification
6.2.1.1 Before providing radar service to an aircraft, radar identification shall be established and the pilot informed. Thereafter, radar identification shall be maintained until termination of the radar service.
6.2.1.2 If radar identification is subsequently lost, the pilot shall be informed accordingly and, when applicable, appropriate instructions issued.
6.2.1.3 Radar identification shall be established by at least one of the following methods.
6.2.2 SSR identification procedures
6.2.2.1 Where SSR is used, aircraft may be identified by one or more of the following procedures:
a)  recognition of the aircraft identification in a radar label;
Note.— The use of this procedure requires that the code/call sign correlation is achieved successfully, taking into account the Note following b) below.
b)  recognition of an assigned discrete code, the setting of which has been verified, in a radar label;
Note.— The use of this procedure requires a system of code assignment which ensures that each aircraft in a given portion of airspace is assigned a discrete code (see 5.2.2.7).
　
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