aircraft address

‘aircraft address’ means a unique combination of 24 bits available for assignment to an aircraft for the purpose of air-ground communications, navigation and surveillance;

19a. ‘aircraft identification’ means a group of letters, figures, or a combination of them, which is either identical, or the coded equivalent, to the aircraft call sign to be used in air-ground communications, and which is used to identify the aircraft in ground–ground air traffic services communications;