Explanation of each:
Make a model of the airfield, with a transport plane on top
Basically the war factory is just an airfield, with a transprt plane on it that just sits there the whole time, and when you build a unit it comes out the back of the transport. The easiest way to do it, but not realistic
Make a model of the airfield, but have the unit construct anim be a plane flying in
Probably the best way to do it, and the one I'm leaning towards. You know how the door goes up when you build something out of the war factory? Make the anim instead be a plane flying in from way up high and landing, then taking off. But I'd have to time it right so the unit appears as the plane lands, which will be difficult, but I'm sure doable.
Quit whining and do it the hard way
Phoib's method of creating a dummy unit, which automatically dies on creation, but signals the OCL to make a plane appear and (para)drop off units. Problem is, you need to edit the AI to make room for the extra dummies, and its buggy as all the values need to be perfect or it spawns a billion planes :!: . Not cool, but has potential if I find the patience
If you can understand all that, you're amazing
If you can't, just look at what it'll appear to be and forget all the technical crap
