Right now, obviously, anything we say about what actually happened on the planes themselves is pure speculation. But let's address some of the possibilities.
One would think that the terrorist, whom ever they are, would have used trained pilots on the planes. They would not have to this trouble only to risk having a pilot refuse the orders of a hijakcer ordering them to crash into the WTC, Pentagon or whatever.
If that is the case then what happened with the fourth plane that crashed in PA?
Was the hijacker an idiot and crashed before he could reach his target?
Were they counting on the pilots obeying orders and this one refused and elected to crash in a field?
Did the pilot or someone else on the crew or passenger struggle with the terrorist and force the crash there? (There are reports of passenger calling on a cell phone telling someone they were being hijacked.)
What type of training are pilots now going to receive to prevent this in the future?
It is all guessing right now but nonetheless things that make you go Hmmmmmmmmm.........