I just checked my visitor message thingy. A TRUE airport, (name, adf, radios, AI landing/takeoff, all that fun stuff), is not possible from what I know without the tools which are not publicly released. I believe static objects will work but there might be issues with the game engine recognizing it as something that an aircraft can land on without blowing up at a certain speed. Having a static object with refueling trucks etc so the player can rearm/refuel....not sure. It might have to be tied to a TRUE airport, but never tested it.