Automatically on passing the next reporting point, or when instructed by ATC to do so.
Only when instructed to REVERT TO FLIGHT PLAN CALL SIGN GOLF ALFA CHARLIE ZULU GOLF.
When instructed by ATC to do so, or automatically at 15:45.
Automatically on making the next frequency change, or when instructed by ATC to do so.
ICAO Doc 4444
15.7.6 Change of radiotelephony call sign for aircraft
220.127.116.11 An ATC unit may instruct an aircraft to change its type of RTF call sign, in the interests of safety, when similarity between two or more aircraft RTF call signs are such that confusion is likely to occur.
18.104.22.168.1 Any such change to the type of call sign shall be temporary and shall be applicable only within the airspace(s) where the confusion is likely to occur.
22.214.171.124 To avoid confusion, the ATC unit should, if appropriate, identify the aircraft which will be instructed to change its call sign by referring to its position and/or level.
126.96.36.199 When an ATC unit changes the type of call sign of an aircraft, that unit shall ensure that the aircraft reverts to the call sign indicated by the flight plan when the aircraft is transferred to another ATC unit, except when the call sign change has been coordinated between the two ATC units concerned.
188.8.131.52 The appropriate ATC unit shall advise the aircraft concerned when it is to revert to the call sign indicated by the flight plan.
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