Airline codes

IATA expanded the two-character-system with codes consisting of a letter and a digit (or vice versa) e.g. EasyJet's U2 after ICAO had introduced its current three-letter-system in 1982.

These codes thus comply with the current airline designator standard, but use only a limited subset of its possible range.

There are three types of designator: unique, numeric/alpha and controlled duplicate (explained below): IATA airline designators are used to identify an airline for commercial purposes in reservations, timetables, tickets, tariffs, air waybills and in telecommunications.

After an airline is delisted, IATA can make the code available for reuse after six months and can issue "controlled duplicates".

For example, AY was given to Aero OY, now Finnair, and FI was given to Flugfélag Íslands, now Icelandair.

In 1982 ICAO introduced the current three-letter system due to the increasing number of airlines.

The flight number is published in an airline's public timetable and appears on the arrivals and departure screens in the airport terminals.

In cases of emergency, the airline name and flight number, rather than the call sign, are normally mentioned by the main news media.

This might be for historic reasons (South African Airways uses the callsign "Springbok", hearkening back to the airline's old livery which featured a springbok), or possibly to avoid confusion with a call sign used by an established airline.

Country names can also change over time and new call signs may be agreed in substitution for traditional ones.

The callsign should be easily and phonetically pronounceable in at least English, the international language of aviation.

For instance, Lufthansa Cargo (LH/GEC) has been assigned 020[4] as accounting code, and all the flight tickets issued by that airline start with "020-".