Except, I can't let this comment slide. The possibility of too high or too low are infinitely greater than on target as they both extend infinitely in opposite directions. All kidding aside and I'll tell you why: A B 757 is a pretty tall plane. When you stand next to one on the ramp (obviously the gear is out), the cockpit looms over head - I'm guessing about 20 feet to the cockpit. Now consider you've never flown one but you have an idea about how far from the ground you are when the gear is out because you got on board at some point while it was on the ground - you have no idea how far away the ground is when the gear is up though! So you'd have to include this in your planning. I'm guessing the Pentagon is less than 100ft high. It's only about 5 stories right? Anyway, you now have a 20ft tall projectile for a 100 ft tall target which, by the way, is afixed to terra firma and not hanging in the sky. So, if you come in too low, you make a premature smoking hole. Given that too high and too low extend to infinity in either direction, we have rudimentary landing aid lights called VASI's - this is very basic stuff. But the Pentagon is not equipped with VASI lights. It's not like the plane skidded in from across the street and dug a ditch to the building, nor did it scrape it's belly across the shingles. Ground floor, nose first - that's pretty good really, all things considered. 100 ft target, 20 ft projectile at 600 mph. I made ALL this up in my head so ya know...go verify if you like. I'd be interested to see how far off I am anyway.