Airnav, might be worth changing the primary key on the table. When I originally created the primary keys, I made C3 the primary key, and prevented duplicates. Suggest we make C2 the primary key, and prevent duplicates, if that's going to be the main use for this table now.
Beware.
Because of the relatively small number of combinations available, IATA have made provision for what they refer to as "controlled duplication" of codes, so you could in theory see the same code used by two small, local airlines on opposite sides of the world or, in some cases, a code used by one passenger carrier and another all-cargo airline.
Having said that, I can't think of any current examples off the top of my head, apart from the aforementioned XM.
It's also true, of course, that many operators have ICAO codes but no IATA code, which might affect the ability to create a PK on C2.