15.7.6.1 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.
15.7.6.1.1 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.
15.7.6.2 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.
15.7.6.3 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.
15.7.6.4 The appropriate ATC unit shall advise the aircraft concerned when it is to revert to the call sign indicated
by the flight plan.