It's easy, anyone could do it

[Carsten Wiethoff]

Not only is it very difficult or impossible to fly a 757 in that way, it is also completely useless, risky and unnecessary. It would have been much easier to fly in a direct line into the upper floors of the inner ring than to clip an antenna and several lightpoles, flying low to the ground with high speed, risking premature destruction of the aircraft. You would also have had a better chance to hit Rumsfeld or other important brass. But maybe that was not the purpose.
Analysis of the flight recorder that was found in the Pentagon reveals some other strange behaviour, like that BOTH of the pilots in a time interval of a few seconds adjusted the altimeter to the correct barometric pressure, like professional pilots would do, when passing FL180. For people intending to crash into a building with near perfect visibility this is not a logical thing to do. There are also things that any AA pilot would have done before departure, which were NOT done in AA77, like the alignment of the inertial reference platform.
One possible explanation would be that the flight data recorder found in the Pentagon did not belong to AA77, but to a flight executed by professional military pilots, flying a military aircraft equipped with GPS. How it ended up in the Pentagon is the million dollar question.