Your right, no way is that realistic. I think the movie had two endings.
The real ending; where Batman died and blew up with the bomb. Cuz even with autopilot, the batwing cant accelerate at that speed. Batman had to manuelly fly it.
Fake ending, for people that cant handle Batman dying.
Nolan knows they would be a huge public outcry if he left the movie with Batman dyiing plain and simple. Parents and media would try to have a field day on that. So he left two endings left for interpetation. Its been done in other movies. I.E.---G.I Joe The Moive (1986)
yall reachin they showed his face then showed the clock count down from about ten seconds
sh*t ive seen him vanish from a whole roof top in about 2.1 seconds !
so ejecting from a plane with more then 5seconds on it or hitting some switch thats dumps u straight into the water below really fast is nothin to the batman!