1.1 Requests for the registration of, or modification of a three letter or telephony designator will only be recognized by ICAO when received from the State having jurisdiction over the aircraft operating agency, aeronautical authority or service concerned. Such requests should be made through the 3LD System at http://www.icao.int/3ld. Detailed process instructions on how to use the system are contained on the online webpage.
1.2 The same designator will not be registered for more than one aircraft operating agency, aeronautical authority or service.
1.3 No more than one three letter or telephony designator will be registered for each aircraft operating agency, aeronautical authority or service.
1.4 When a designator is no longer required, ICAO should be informed immediately. Any such designator so released will not be reassigned until a period of at least 60 days has elapsed.
1.5 Each Contracting State should review, at least annually, all of the designators and associated information in Doc 8585 for which it is responsible and advise ICAO of any other changes which should be made to this document in order to bring it up to date, such changes will be done through the 3LD System.
1.6 The rules governing the registration or change of three letter and telephony designators are as follows.
2. Three-letter designators
2.1 Three-letter designators are registered only for:
a) aircraft operating agencies engaged in air transport operations which in the opinion of the State of jurisdiction have a need for an exclusive designator;
b) governmental authorities and services which use and/or provide air navigation, communication and other facilities and services for international civil aviation;
c) organizations, other than governmental organizations, which provide services for international civil aviation.
2.2 a) A three letter designator should reflect to the maximum extent practicable, the name of the aircraft operating agency or its telephony designator, or the aeronautical service for which it is requested.
b) Designators for governmental organizations which provide civil aviation facilities and services are allocated only in the Y series.
c) Designators for governmental organizations which provide air traffic services are allocated only in the Z series (except ZXA to ZXZ).
d) The following designators are reserved for national allocation by Contracting States to national authorities and services and will not be used for other assignments by ICAO. The State may select and use any of these without referring the matter to ICAO:
YEY, YGY, YHY, YIY, YJY, YKY, YQY, YRY, YUY, YVY and ZXA to ZXZ groups.
2.3 The following three letter designators when appearing in the Shortened Address, the Address and/or in the Origin parts of an AFTN message, must be complemented with further identification of the aircraft operating agency, aeronautical authority or service concerned, in the beginning of the Text part of the message (see 126.96.36.199.2.1, and 188.8.131.52.2.2 of Annex 10, Volume II).
YXY – Military Service or organization
YYY – Aircraft operating agencies and organizations not allocated a three letter ICAO designator on an exclusive basis
ZZZ – Aircraft in flight.
2.4 In the registration of three-letter designators the following restrictions will apply:
a) To avoid conflict with the AFTN Start-of-Message Signal, combinations with CZ or ZC will not be used.
b) To avoid conflict with the AFTN End-of-Message Signal, combinations with NN will not be used.
c) PAN and SOS will not be assigned;
d) to avoid confusion with communications service codes, the following three letter combinations should not be used: QTA and SVC;
e) to avoid potential AFTN routing problems:
i) no further allocation of aircraft operating agency designators will be included in the Y and Z series; and
ii) no further allocation of any designators will be included in the Y series and ZAA to ZIZ, ZOA to ZUZ and ZYA to ZZY groups.
2.5 States which have introduced the Predetermined Distribution System for AFTN messages should inform each State from which AFTN messages for predetermined distribution are to be received of the three letter designators to be used for addressing such messages. These designators are not listed in this document.
Note.— For details, see Annex 10, Volume II, 184.108.40.206 and Appendix 5 to Annex 15 — Aeronautical Information Services.
3. Telephony designators
3.1 Telephony designators for aircraft operating agencies may be used as part of the aircraft radiotelephony call sign followed by the flight identification in radiotelephony communications, in accordance with the ICAO Radiotelephony Procedures (Annex 10, Volume II, 220.127.116.11.2 refers). Example: “AEROFLOT 301”.
3.2 In the registration of telephony designators the following rules will apply:
a) the telephony designator chosen should attempt to resemble the name of the aircraft operating agency or its function and be distinct and dissimilar from any other telephony designators in Doc 8585. Ideally it should reflect correlation between the three letter designator, the telephony designator and the name of the aircraft operating agency or its function (examples: ARO – ARROW – Arrow Aviation; RAJ – RAJI – Raji Airlines);
b) in order to reduce the length of transmission the telephony designator should be brief, comprising if possible one word of two or three syllables. It should not exceed two words;
c) three letter designators may not be used in phonetic form as telephony designators. However, telephony designators of long standing (such as KLM or TWA) may be retained, provided that an acceptable alphabetic representation is used (example: KAY ELL EMM); and
d) the telephony designator should be easily and phonetically pronounceable in at least one of the following languages: English, French, Russian, Spanish.
Note.— Resolution of similar sounding call signs:
1) In the interests of safety, simple procedures should be developed by States and aircraft operating agencies for detecting, reporting and eliminating those call-signs which, because of their similarities to other call-signs, may cause confusion or mistakes in identification. When call- sign similarity difficulties concern the telephony designator, the civil aviation authority concerned should coordinate efforts to resolve the problem. This may require submission to ICAO for a change in one or both of the conflicting telephony designators. Cooperation between civil aviation authorities is required when the aircraft operating agencies are from different States.
2) In the selection of the flight identification number the following is recommended:
a) flight numbers should be kept as short as possible and usually be limited to three figures;
b) flight numbers should be selected bearing in mind the flight numbers already in use by other operating agencies in the intended control environments; and
c) when practicable flight numbers other than those ending in a zero or five should be used.