Originally Posted by KRL

I think you have to put speed into perspective here. If you've ever seen a really nasty car crash, where the car was going super fast, there's not much left as a single structure.

Now you figure a fully fueled jet going full speed at over 500 MPH.

Do the physics. The energy of that mass at that velocity going into a heavily reinforced structure like the Pentagon will completely disintegrate quite compactly.