airline in Lebanon (ceased 2015, but did actually fly to Sudan) IATA also issues an accounting or prefix code. This number is used on tickets as the first three characters of the ticket number. IATA airline designators are usually kept even if the airline changes name, so the code does not match the name anymore. For example, AY was given to Aero OY, now Finnair, and FI was given to Flugfélag Íslands, now Icelandair. ICAO airline designator The ICAO airline designator is a code assigned by the International Civil Aviation Organization (ICAO) to aircraft operating agencies, aeronautical authorities, and services related to international aviation, each of which is allocated both a three-letter designator and a telephony designator. These codes are unique by airline, unlike the IATA airline designator codes (see section above). The designators are listed in ICAO Document 8585: Designators for Aircraft Operating Agencies, Aeronautical Authorities and Services. ICAO codes have been issued since 1947. The ICAO codes were originally based on a two-letter system and were identical to the airline codes used by IATA. After an airline joined IATA its existing ICAO two-letter code was taken over as IATA code. Because both organizations used the same code system, the current terms ICAO code and IATA code did not exist until the 1980s. They were commonly called two-letter airline designators. At that time it was impossible to find out whether an airline was an IATA member or not just by looking at its code. In the 1970s the abbreviation BA was the ICAO code and the IATA code of British Airways, while non-IATA members like Court Line used their two-letter abbreviation as ICAO code only. In 1982 ICAO introduced the current three-letter system due to the increasing number of airlines. After a transitional period of five years, it became the official new ICAO standard system in November 1987 while IATA kept the older two-letter system that was introduced by ICAO in 1947. Certain combinations of letters are not allocated, to avoid confusion with other systems. Other designators, particularly those starting with Y and Z, are reserved for government organizations. The designator YYY is used for operators that do not have a code allocated. An example is: Operator: American Airlines Three-letter designator: AAL (the original ICAO-two-letter designator AA was officially used until 1987 and is also the IATA code of the airline) Telephony designator: AMERICAN A timeline of the airline