Don't airplanes have the same "visible spawn delay" that GV's do? The player spawns in and all is normal, but to others there is a delay before his vehicle is visible. The spawning player (in a GV) can be turning his turret to find that spawn camper and many times the spawn camper finally sees the player appear with the turret already pointing at him.
Perhaps because of the spawn visibility delay, by the time you see the other player's plane spawn, his engine is already running, the throttle is already open and he's already starting to roll...