"2 or 3 character code as designated by International Air Transport Association (IATA) to uniquely designate an airline operator. Local (non-IATA) codes can be added as required as long as they are unique for airline operators within the defined context.
Ex: SK, DY. Two or three characters. IATA and ICAO codes can be identical.
Reference Document: IATA Airline Coding Directory. The IATA standard uses 2 character codes, but in cases where no IATA standard code exists, an alternative code can be used. This can often be the 3 character ICAO code if one exists."
