Put it this way: You need to know the intricacies of how the code works, how it runs, how it will call any given animation on the object, this inner workings of the code is NOT something they (or I!) want to become common knowledge.
The 3d object itself must be set up in a certain way, with a certain hierarchy of animations, and each animation might need special conditions, be they looping, reversing, whatever.
You can't just make a 3D object and expect it to be imported into the average game, because they're very much integrated. Some games go out of their way to code things so that certain objects can be imported (like your MMORPG, like Counter-Strike custom skins, and some others) but a majority of games are much more complex with regards to how they integrate 3D and game code.
It's not an easy proposition. I didn't get into it too heavily, even in my most advanced classes, but my instructor did broach the subject a few times and described a few things to the class regarding a simplified student project (basically making a 3D "Frogger" type game).
It's not so easy as it might seem.
EDIT: AH most probably uses a single model for aircraft.
