And just for reclarification, IATA or ICAO airline codes. (Eg. QF or QFA)
Neither, because lots of ground operators are not airlines and sometimes we have more than one variation for the same operator, so they don't have an ICAO or IATA code, so we used what is really a "GSX code", that can specify both airlines and ground operators too. For airlines, sometimes it's the IATA, sometimes it's the ICAO.
If you want to know for sure which code operators have in GSX, look in the rules_handling.cfg file, located in Addon Manager\texture folder. The name of the
sections, the ones inside square brackets are the code so, for example:
American Airlines has two codes,
AA and
AA_white, the second it's a reversed white on blue livery, an example why we couldn't "just" use an ICAO or a IATA code.
Aerogate it's just
Aerogate. This is a ground handling company, not an airline, which is another example why we couldn't "just" use an ICAO/IATA code.
KLM has also two variations,
KL and
KL_white, the second being a white on light blue color scheme.
Those are the codes you must place in the atc_parking_codes, which will drive ONLY the selection of the ULD containers. You can use multiple codes too so, for example, if you set it like this:
atc_parking_codes = LH, DLH ( for Lufthansa )
The LH code will work for GSX, the DLH code will (in theory) be used by the default ATC in the sim to assign you by preference to gates with the DLH codes, although I don't think it's really supported.