The FlightStats Code is the unique code for the airline or airport. The FlightStats Code is a required field. The IATA and ICAO codes are optional. The FlightStats Code will sometimes be identical to either the IATA or ICAO code or it may be distinct.
We recommend once every 1-2 weeks customers download the airline reference data to keep their systems up-to-date of additions/mergers/bankruptcies in the airline industry.
Airline (reference) API:
Why am I matching the wrong airline? What is an IATA duplicate?