What caused the passengers in United 93 to not be able to get plane back on track?

I recently saw United 93 in the theater. At the end, the passengers were desperately trying to overpower the hijackers and getting the stalling plane back on course, but couldn't seem to move it. Was the cause of this the angle and the speed at which the plane was plunging at that made it uncontrollable?What caused the passengers in United 93 to not be able to get plane back on track?A plane needs to be moving at a certain speed and a certain angle of attack in order to generate enough lift to keep it in controlled flight. I'd imagine you'd have to be a pretty experienced pilot to pull a huge plane like that out of a stall; depending how much altitude you have to work with, it might be impossible.What caused the passengers in United 93 to not be able to get plane back on track?it was a passenger transport aircraft. Those things aren't made to fly like that : it stalled (ie : lost it's balance on air)