In the movie, Tom Hanks flies in two different FedEx A300s. The first one (Moscow-Memphis) has a real A300 flight deck, but the one that crashes has a totally fake flight deck.
Now, what's exactly supposed to have caused the accident? Like Lewis says, what originated the vacuum? While watching the scene of the accident, I was looking for broken windows or a hole in the fuselage that would cause a loss of pressurization but found none.
Shortly before ditching, the Captain lowers a lever located in the upper panel, meaning that engine 1 was on fire.
Anyway, let's just remember that this is just a MOVIE. We can't expect it to be real.
What I think was a great achievement in the crash scene, is how with great realism it reproduces the atmosphere of complete horror that I imagine is experienced during an accident.
"... for there you have been and there you will long to return."