The introduction of ICAO designators

The international civil aviation network carries over four billion passengers around the world annually. In celebrating ICAO's 75th Anniversary Celebrations, we will be highlighting some of the crucial safety achievements that have enabled this. We hope you follow our series throughout the year, and we encourage you to use the #ICAO75 hashtag to share your thoughts and memories with us through social media.


On 7 December 1944, the Convention on International Civil Aviation (also known as Chicago Convention) was signed by 52 States. Pending ratification of the Convention by 26 States, the Provisional International Civil Aviation Organization (PICAO) was established. It functioned from 6 June 1945 until 4 April 1947. By 5 March 1947 the 26th ratification was received and ICAO came into being on 4 April 1947.[i]

Going back to when ICAO was still PICAO, the importance of being able to identify newly created airlines in flight was already clear.  The COM panel of PICAO was the group that provided the groundwork for the Three-letter and Telephony identifiers that we use today.

Initially, there were only telephony designators assigned, as you can see in the excerpt from the final COM report in 1947.  The small number of airlines listed is astounding when compared to the over 5,800 designators currently listed in our 3LD database today.

As the number of airlines increased it was decided that States would also make requests to ICAO to assign two-letter designators along with a telephony designator.  The ICAO two-letter designators for airlines were distributed in “Communication Codes and Abbreviations” (Doc 2560 COM 164). [ii] These designators consisted of a unique two-letter code which could be used in aircraft identification in the flight plan and/or a telephony designator, which then could be used as part of an aircraft’s radiotelephony call sign.

This document then evolved into Doc 506 and then into Doc 6938 and then into the Designators for Aircraft Operating Agencies, Aeronautical Authorities and Services (Doc 8585), that is used worldwide today.

In November of 1981 (C-WP/7342), ICAO proposed the change from the old two-Letter designator system to the current Three-Letter Designator system due to the increasing number of airlines.  The Doc 8585 supplement dated July 1987 is the first appearance in print of the Three-Letter Designators as we know them today.

In Assembly A37 of 2010, (A37-WP/71), ICAO’s Technical Commission announced an initial set of safety tools, one of which was the online Aircraft Safety Information Service (OASIS), which included the database for Designators for Aircraft Operating Agencies, Aeronautical Authorities and Services (Doc 8585). This database and the related print document contained the listing of three-letter and telephony designators assigned by ICAO, including a list of any changes to the designators since the previous issue was published.

In October 2014 State letter 2014/72 announced the new web-based request system for three-letter and telephony Designators called 3LD. The new online system, which was implemented on 1 November 2014i, was a welcome replacement for the slow and antiquated paper-based system of requesting and assigning designators to States.

The 3LD request system allows airlines to request designators themselves directly, and have those requests automatically forwarded to the 3LD Focal Points assigned by each State.  An airline can click on Request New Designator (under Industry), purchase a PIN, and fill in the form with their suggestions for a Three-letter and Telephony designator, before submitting the request.

The State focal point then receives each new request for review and approval online. The focal point can then forward the request to ICAO to assign the designators by a click of a button.  The request is reviewed through ICAO ATM and OPS experts, helping to achieve global suitability and non-duplication of designators. Once assigned, the request follows the reverse path back to the requesting airline.

The transition to an online system provided states with the ability to trace designator requests online and enabled the option for states to receive timely data downloads of the updated designators, an accomplishment which supported ICAO’s new strategies to provide safety data as required in a timely and reliable manner.

ICAO is currently looking into ways to expand and improve 3LD’s dataset and delivery methods to respond to the increasing demands for safety data globally. Based on ICAO’s preliminary compilation of annual global statistics, the total number of passengers carried on scheduled services rose to 4.1 billion in 2017, which is 7.2 per cent higher than the previous year, while the number of departures reached 36.7 million in 2017, a 3.1 per cent increase compared to 2016. [iii], a huge change from 1947, when this volume of flights was not even imaginable.

In June of 2019, ICAO will hold its first 3LD User’s Forum Meeting to align itself with the future needs of State’s 3LD Focal Points in consideration of the upcoming improvements of the online 3LD system.

The expansion of air traffic will only continue, with ICAO at the forefront, ensuring that this expansion will be accommodated in the safest manner possible.

About the Author

Sharron Morin is a Programme Associate and Administrator for the Three-Letter and Telephony Designator database (3LD), producing the ICAO Document 8585, Designators for Aircraft Operating Agencies, Aeronautical Authorities and Services, currently working in the Operational Safety Section of the International Civil Aviation Organization (ICAO).  Sharron has worked with ICAO for over 20 years and previously operated the ICAO world-wide aircraft accidents database for 10 years, as well as being an ADREP/ECCAIRS trainer.

[i] Doc 7300

[ii] Please note:  these ICAO designators are not to be confused with the IATA two letter reservation codes which were at that time used to identify an airline for commercial purposes and were based on the

ICAO designators.  These IATA codes are no longer in sync with ICAO designators.

[iii] Annual Report 2017