Official Pentagon Investigations
Sketchy Reports by Volunteer Investigators and Academics
As in the case of the World Trade Center site, the Federal Emergency Management Agency (FEMA) took control of the crime scene and supervised the official investigation of it. Also as in Manhattan, FEMA officials in Washington appointed volunteers from the American Society of Civil Engineers (ASCE) to investigate the crime and write a report. The team was dubbed the BPS (Building Performance Study). The BPS investigated the response of the building to the crash, not the crash itself, evidence of which was not available to them. 1
By the time the full Pentagon BPS team visited the site, all debris from the aircraft and structural collapse had been removed and shoring was in place wherever there was severe structural damage.
In January 2003, FEMA’s team published "The Pentagon Building Performance Report." 2 The Report described the analysis that the BPS conducted between September and April of 2002.
FEMA’s report gives an account of the final approach and crash of the jetliner with the following details.
1. The 757 approached at about 780 ft/s (532 mph)
2. During the approach the plane rolled slightly to the left.
3. The left wing struck a piece of construction equipment that was about 100 feet from the Pentagon’s facade, 0.1 second before impact.
4. The left engine struck the ground at about the time the nose struck the facade.
5. The impact of the fuselage was centered at about column line 14.
6. The left wing passed below the second floor slab, and the right wing crossed the slab at a shallow angle.
7. The impact removed first floor exterior columns from column lines 10 to 14.
8. The impact severely damaged first floor exterior columns on column lines 9, 15, 16, and 17.
9. The impact destroyed the second floor exterior columns on column ine 14 and its adjacent spandrel plate.
10. Facade damage extended to the fourth floor on both sides of the impact area, but did not extend above the third floor over the central impact area.
11. The E-Ring structure deflected downward from an expansion joint on column line 11 south to the exterior column on column line 18.
12. All five levels of Ring E between column line 8 through column line 18 collapsed about 20 minutes after the impact.
It’s not clear why the Pentagon BPS took eight months to publish their study (which contrasts with the World Trade Center BPS publishing promptly in May of 2002). The Report gives a vague account of the the attack plane’s trajectory with unsupported quantitative details, such as the speed of the plane. It makes errors in illustrating damage, such as offsetting the C-Ring punch-out hole by about four feet.
The Pentagon BPS is the only government investigation of the crash of Flight 77 that admits to existing, but it was defined as and limited to an investigation of the performance of the building. There was no investigation into the crash by the National Transportation and Safety Board (NTSB). The Probable Cause document for Flight 77 on the NTSB’s website reads:
The terrorist attacks of September 11, 2001 are under the jurisdiction of the Federal Bureau of Investigation. The Safety Board provided requested technical assistance to the FBI, and any material generated by the NTSB is under the control of the FBI. The Safety Board does not plan to issue a report or open a public docket. 3
The Purdue Study
A group of computer scientists and engineers at Purdue University created a simulation of a 757 crashing into the Pentagon. 4 They noted the existence of a body of literature on collisions of aircraft into reinforced concrete structures such as nuclear reactor containment buildings. A 1992 study by Sugano, et. al. documents the crash of an F-4D Phantom interceptor jet into a 10-foot thick steel-reinforced concrete block at 480 mph. 5 The study shows that most of the jet was reduced to confetti, while producing only a shallow impression in the block.
Although there are limits between the comparison of an F-4 flying into such a block at 480 mph and a 757 flying into the Pentagon’s columnated reinforced masonry wall at 300-450 mph, the Sugano study raised questions for the Purdue scientists as to how the 757 impact broke out as much as it did, and how it destroyed columns deep in the building. To account for the damage they postulated a liquid hammer effect, wherein it was the impact of the jetliner’s fuel that produced most of the damage. 6
Frame 33 of Purdue’s simulation
The Purdue study’s simulation of the plane crash was limited in its realism. The simulation featured on the webpage September 11 Pentagon Attack Simulations Using LS-Dyna is limited to the collision of an engine-less jetliner with the Pentagon’s first-floor columns. 7 It doesn’t account for the facade walls or the second-floor slab or columns. It has the jetliner entering on a level heading with wings inches from the ground. It shows the ends of its wings passing into the building, sliced by columns. Simulating the effects of the walls in deflecting the portions of the wings that could not have fit through the approximately 96-foot-wide span of punctured walls was apparently beyond the scope of Purdue’s study. 8
1. The Pentagon Report, Civil Engineering Magazine, 2/03 [cached]
2. The Pentagon Building Performance Report, ASCE.org, 1/2003 [cached]
3. NTSB Docket DCA01MA064, NTSB.gov, [cached]
4. Producing High-Quality Visualizations of Large-Scale Simulations, [cached]
5. Footage of 1988 rocket-sled test., Sandia.gov, [cached]
6. New simulation shows 9/11 plane crash with scientific detail, Purdue News, 9/10/02 [cached]
7. September 11 Pentagon Attack Simulations Using LS-Dyna, purdue.edu, 9/11/02 [cached]
8. (Pentagon crash simulation video), CS.Purdue.edu, [cached]
page last modified: 2006-07-04