All airlines have an alphabetic identification code issued by ICAO. From 1947, when ICAO was formed, until 1982, ICAO codes were two letters long;1 in the latter year, due to the increasing number of airlines in the world, ICAO lengthened its airline codes to three letters (although the preexisting two-letter codes remained valid until 1987).
Does anyone know when in 1982 ICAO introduced three-letter airline codes? (I'm writing about an accident that occurred in 1982, and I can't tell if I should list the two-letter or three-letter ICAO designator for the flight.)
1: When IATA got into the business of issuing airline codes in the early 1950s, its members adopted their preexisting ICAO codes as their new IATA codes (this is why IATA codes are two characters long2).
2: Although the IATA system makes formal provision for three-character airline codes, it has never actually issued those, because airlines don't want to have to replace ancient equipment that can't handle airline codes longer than two characters.