The International Air Transport Association, or IATA, assigns a two-digit code to most of the worlds’s airlines. Though actually having provided for a three-digit code, the first two digits being alphanumeric and the third an optional alpha character, in the format “xx(a)”, the IATA has never used the third digit; they reserve the option to do so, but will not yet, until all airlines’ computer reservation systems are able to acknowledge the three-character combination. These two/three letters make up the airline designator.
A flight designator is the IATA’s system of using the airline designator to identify every specific flight. The flight designator appears on passengers’ tickets and boarding passes. It starts with the airline designator, then is followed by up to 4 digits, representing the numeric flight number, and then sometimes followed by an optional “operational suffix”. Airline designators are used to identify an airline for purposes such as reservations, timetables, tickets, tariffs, air waybills and in interline communications.
The IATA airline codes should not be confused with the International Civil Aviation Organization’s(ICAO) airline designators, though the IATA’s codes are the most widely used.