These designators identify airlines for commercial purposes. The characters are assigned by
IATA in accordance with the provisions of Resolution 762, for use in
reservations,
timetables, tickets, tariffs, air waybills,
schedules publications and in airline interline telecommunications, as well as for the airline industry applications. IATA assigns three types of two character airline designators: unique,
alphanumeric and controlled duplicate codes.
Since 1987 ICAO (more concerned with how aviation operates than the business of airlines) has allocated three letter codes for use by air traffic controllers.
As most companies have the word 'air', 'airline' or 'airways' in their name, almost all IATA codes starting or ending with 'A' have been taken (although the demise of Ansett Airlines and Pan Am might lead to their codes being recycled). New airlines have a bad scrabble hand of letters (and now numbers) to use. Creatively, Virgin Blue uses DJ; its founder's link to the music industry being a mnemonic.