Loose Screw #2
Oh really, here is a picture of the Pentagon. It is a bit hard to see through the smoke (click to enlarge), but that hole is a hell of a lot bigger than 16 feet. Compare it to the firetruck just in front of it, which is considerably more than 16 feet long.
If you look at the damage after the fire is put out, you also see the extent of the damage. Look at how much rubble is piled up in the front.
It is quite obvious the hole is around 40 meters across, which amazingly also happens to be the wingspan of a 757. What an amazing coincidence!
Purdue University, interestingly enough, came out with a computer simulation of the crash. It almost exactly mimics the damage, a wide hole in the outer ring, growing increasingly smaller through 2 more rings. You can see it here.