that could explain the large debris field. Airliners aren't built to withstand high g loads. It's possible the hijacker pilot might've decided that if he wasn't going to accomplish his mission due to the passenger revolt, he wasn't going to let anyone else on board live, either. All he would've had to do is put the plane into a high-speed power dive (full throttle and drop the nose 20-30 degrees), exceed red-line within a matter of seconds, then pull abruptly. It's even possible this happened accidentally as the passengers and hijackers struggled for control of the plane. In any event, the airliner would've started shedding pieces in pretty short order. The higher it was when it began breaking up, the bigger the debris field.

As for shooting the plane down, why would they bother to keep that secret under the circumstances? After having suffered 3 attacks that morning, we would've been fully justified in shooting down an airliner under the circumstances, just as those pilots who are flying Combat Air Patrols over the US are prepared to do today if necessary. It's a grim responsibility but one the pilots are prepared to accept.