Witness accounts. Some calculations.
Hi,
This seems to be a reasonable place to put this...
According to [link|http://www.janes.com/aerospace/civil/news/jawa/boeing_767.shtml|Jane's], a 767 is around 180 feet long (160 - 200 feet depending on the version).
The outer wall of the outer ring of the Pentagon is [link|http://www.defenselink.mil/pubs/pentagon/facts.html|921 feet long].
[link|http://www.defenselink.mil/news/Sep2001/010915-D-6570C-004.jpg|Illustration of the path of the plane] that hit the Pentagon. Note that it penetrated the 3 outer rings.
[link|http://www.defenselink.mil/news/Sep2001/010915-D-6570C-009.jpg|Illustration of destroyed and damaged columns] illustrating the plane's path in the building.
[link|http://www.defenselink.mil/news/Sep2001/t09152001_t915evey.html|Briefing transcript]:
Q: That seems to indicate that it came to rest in ring C, the nose cone.
Evey: Let me talk to that, because you've asked a number of questions already about the extent of penetration, et cetera. This is an overhead of the building. The point of penetration was right here, and we blocked that out to show that's the area of collapse. The plane actually penetrated through the E ring, C ring -- excuse me -- E ring, D ring, C ring.
This area right here is what we call A-E Drive. And unlike other rings in the building, it's actually a driveway that circles the building inside, between the B and the C ring. The nose of the plane just barely broke through the inside of the C ring, so it was extending into A-E Drive a little bit. So that's the extent of penetration of the aircraft.
Q: It broke through which one?
Evey: The rings are E, D, C, B and A. Between B and C is a driveway that goes around the Pentagon. It's called A-E Drive. The airplane traveled in a path about like this, and the nose of the aircraft broke through this innermost wall of C ring into A-E Drive.
Q: One thing that's confusing -- if it came in the way you described, at an angle, why then are not the wings outside? I mean, the wings would have shorn off. The tail would have shorn off. And yet there's apparently no evidence of the aircraft outside the E ring.
Evey: Actually, there's considerable evidence of the aircraft outside the E ring. It's just not very visible. When you get up close -- actually, one of my people happened to be walking on this sidewalk and was right about here as the aircraft approached. It came in. It clipped a couple of light poles on the way in. He happened to hear this terrible noise behind him, looked back, and he actually -- he's a Vietnam veteran -- jumped prone onto the ground so the aircraft would not actually -- he thinks it (would have) hit him; it was that low.
On its way in, the wing clipped. Our guess is an engine clipped a generator. We had an emergency temporary generator to provide life-safety emergency electrical power, should the power go off in the building. The wing actually clipped that generator, and portions of it broke off. There are other parts of the plane that are scattered about outside the building. None of those parts are very large, however. You don't see big pieces of the airplane sitting there extending up into the air. But there are many small pieces. And the few larger pieces there look like they are veins out of the aircraft engine. They're circular.
Q: Would you say that the plane, since it had a lot of fuel on it at the impact, and the fact that there are very small pieces, virtually exploded in flames when it tore into the building? I mean, since there are not large pieces of the wings laying outside, did it virtually explode?
Evey: I didn't see it. My people who did see it enter the building describe it as entering the building and then there being flames coming out immediately afterwards. Whether you describe it as an explosion or not, people I talk to who were there, some called it an explosion. Others called it a large fire. I'm not sure. I wasn't there, sir. It's just a guess on my part.
I haven't been able to find dimensions between the various rings of the Pentagon, but from the illustration and the known length of the plane, I think a reasonable estimate of the penetration into the building is 200 - 300'. I've heard an estimate that the 767 was travelling at 450 mph (though that might have been the estimate of the WTC planes' speed).
Let's assume uniform deceleration (probably a very poor assumption, but it'll give us a ballpark figure.)
The speed of a body under uniform acceleration can be described by:
V(final)^2 = V(initial)^2 + 2 * A * D
Where V's are velocities, A is the acceleration, and D is the distance travelled subject to the acceleration.
450 mph = 660 feet per second.
In our case, V(final) = 0, V(initial) = 660 feet per second and D = 300 feet.
Then A = -726 feet per second per second.
1 g = 32 feet per second per second.
So the 767 underwent an acceleration of about -23 g's if it travelled 300 feet in about 0.91 seconds. If it travelled 200 feet, then the acceleration was about -34 g's.
It's not surprising that so little of the plane was left after impact.
Cheers,
Scott.