This I know. And when do you think the plane is most difficult to control? During ordinary level flight at high speed, or during a slow approach with gear down and flaps fully extended?

Allow me to answer...

LANDING is the hardest part of flying a plane. Second hardest is TAKEOFF. Once you have the sucker airborne, it's actually very easy. If you have even basic hand-eye coordination and decent spatial reckoning skills, you can grab the yoke of anything from a Piper Cub to a 747 Jumbo and steer it around without much trouble, once it is already in flight. These guys didn't need to worry about landing; all they had to do was hit a building.

Seriously, flying a plane once it is already in the air is about as difficult as driving a car. And yes, I have flown a plane.

The Pentagon wall was the terminus of a descending turn at high speed, much more difficult than level flight.

And I say again, given enough time to practice the approach, it would not be that difficult to execute this maneuver. The flight path very closely resembles that used by fighter planes to rapidly descend from high altitudes. I cannot readily recall what the name is (Immelman, maybe?), but it essentially places the plane on its side and allows it to drop while at the same time turning to reverse course, rapidly descending and increasing to combat speed. Granted, fighters do it a whole hell of a lot faster, but there is no reason why a larger plane would be incapable of that maneuver as long as the airframe isn't overstressed.

Get a copy of MS Flight Sim and try it out. I did it lastnight to see if I could do a flyover runway approach and managed to line up on the runway from 12,000 feet at 500 KIAS on the 4th attempt.