ICAO 8585/199 Designators for Aircraft Operating Agencies: 2022 [paper]

The designators consist of:

a) three-letter designators for use on the international aeronautical telecommunication service and for aircraft identification by air traffic control (ATC); and
b) telephony designators for aircraft operating agencies and for authorities and services operating aircraft, which may be used as appropriate.

Parts 1, 2 and 3 consist of encode and decode tables linking aircraft operating agencies, aeronautical authorities and services with their assigned ICAO three-letter and telephony designators. Addresses of government civil aviation authorities are listed in Part 4.