The Pentagon Attack: What the Physical Evidence Shows


 

by
Jim Hoffman
Version 0.9, March 28, 2006

Introduction

The theory that the Pentagon was not hit by a Boeing 757 (the kind of plane that Flight 77 was) is promoted by the most widely distributed books, videos, and other media challenging the official account of the 9/11 attack. The no-Boeing theory forms the central thesis of Thierry Meyssan's books L'effroyable Imposture (The Frightening Fraud), and Le Pentagate; is featured by the videos Painful Deceptions, 9/11 In Plane Site, and Loose Change; and is the subject of the Flash animation 9/11 Pentagon Strike. These pieces have been distributed worldwide in quantities reaching into the millions, thanks to a combination of excellent production values, entertaining and captivating styles of presentation, and expert, well-financed marketing. The work of 9/11 researchers who do not embrace the no-Boeing theory has been eclipsed in every medium except the web.
In late 2004 I wrote The Pentagon No-757-Crash Theory: Booby Trap for 9/11 Skeptics . In it, I examined the no-Boeing theory from several perspectives including analysis of its:
That essay presents a cumulative argument against the no-Boeing theory using each of these perspectives. Critics of this essay failed to acknowledge this and instead zeroed in on one point or another to highlight it as if the entire case against the no-Boeing theory hinged on that point. For example, several critics have misstated my position as relying exclusively on the accounts of eyewitnesses, ignoring my detailed examination of the 'physical evidence case' for the no-Boeing theory.
In this essay I look exclusively at the physical evidence of the Pentagon attack -- post-crash photographs and verifiable information about the building, the Boeing 757-200 aircraft, and the physics of aircraft crashes based on case studies. In some cases I mention elements of eyewitness accounts, but only to frame my analysis of what the photographs show about the crash. I show that the physical evidence is consistent with the crash of a 757, noting flaws in popular arguments to the contrary.
The many eyewitness accounts of the Pentagon attack constitute a rich body of evidence that strongly supports the conclusion that the attack plane was either a Boeing 757 or a very similar aircraft. The physical and eyewitness evidence are thus mutually corroborating, a fact that is obscured by common errors in evaluating the physical evidence. Many researchers have dismissed the body of eyewitness evidence out of hand, primarily for two reasons:
  • Allegations that the body of witness evidence as a whole is plagued by bias, contamination, and unreliability (addressed here) have been widely promoted and have not been effectively countered, apparently because the ponderous volume of the witness reports discourages analysis.
  • Assertions that physical evidence trumps witness evidence in any crime investigation have fostered a reflexive disdain for witness evidence while lending a false sense of infallibility to arguments based on photographs.
Factors such as these have contributed to the creation of a false dialectic, which has eyewitness evidence supporting the Boeing theory and physical evidence supporting the no-Boeing theory. By focusing on the physical evidence here, I hope to sidestep that dialectic and clarify what conclusions the physical evidence actually supports.

Contents


Debris is Consistent with a Jetliner Crash

The Pentagon attack left debris scattered over a wide area. Judging from the dimensions of punctures in the facade the vast majority of debris ended up inside of the building. Nonetheless, the few photographs that show portions of the lawn near the building show an extensive debris field, easily accounting for the portions of a 757 that did not penetrate the building. Although no photographs show large pieces of aircraft, it is not reasonable to expect large pieces to have survived intact given the nature of the crash.

High-Speed Crashes Reduce Aircraft to Small Pieces


It is noteworthy that many crashes that left very little to no large recognizable pieces involved much lower impact speeds than the Pentagon attack. Since the Iranian C-130 was attempting to land, its airspeed was probably less than 150 mph.

Debris from the Attack Plane is Widely Distributed


Photographs show a debris field covering a portion of the lawn directly north of the central impact region of the facade, and extending to the heliport about 120 feet from the facade. Most of the debris in this field is small, but some photographs show pieces as big as four feet across.

Photographs of Interior Wreckage Are Sparse

Given the extent and shape of punctures in the Pentagon's facade, it is reasonable to expect that well over 90 percent of the mass of a 757 would have ended up inside the building. Unfortunately, there are relatively few public photographs of the interior of the Pentagon after the crash, and there are very few photographs showing the interior before the rescue and recovery operations had removed debris.
Skeptics of the crash of Flight 77 into the Pentagon have argued that the lack of public photographs showing airliner seats, bodies, and luggage is evidence against the crash of Flight 77. This argument is based on several assumptions, none of which are supported.
  • The seats, passengers, and luggage would have survived the over 500-mph crash and subsequent fires in a form yielding to easy identification in photographs.
  • Remains of the seats, passengers, and luggage would have been photographed and the photographs would have been made public.
The baselessness of the second assumption becomes particularly apparent when one notes that nearly the entire fuselage (containing the seats, passengers, and luggage) probably entered the Pentagon, where we know that 125 Pentagon workers were killed. Yet there are no photographs in public circulation of the remains of these victims.

Summary

Proponents of the no-Boeing theory have made the following claims about the debris from the crash:
  1. There was no aircraft debris.
  2. There was insufficient aircraft debris for a jetliner crash.
  3. There was an absence of aircraft wreckage that should have survived a jetliner crash, such as pieces of wings and tail.
  4. The absence of signs of bodies, seats, and luggage in photographs of the crash site prove that the attack plane wasn't Flight 77.
Claim 1 is disproved by numerous post-attack photographs of the Pentagon.
Claim 2 is based on the unfounded assumptions that the quantities of debris can be established from public evidence.
Claim 3 is invalidated by a review of the debris fields of any number of jetliner crashes.
Claim 4 supposes that bodies, seats, and luggage should have survived in easily recognized forms, and that they would have ended up in places that were photographed. However, the impact holes would have admitted an entire fuselage of 757 into the building, and there is no complete photographic record of the interior wreckage available to the public.
Crash Test
The Sandia crash test of an F-4 into a concrete barrier reduced the plane to rubble. ( source)
Crash Examples
This photograph shows the crash site of a DC-8, a jetliner of about the same size as a B-757
Fire Damage Example
This photograph shows what fire can do to an aircraft. This was all that was left of a Boeing 747 after it caught fire while landing.
Pentagon Debris Fields
This photograph shows a portion of the lawn near the heliport. This photograph by Steve Riskus shows a foreshortened portion of the debris field in front of the Pentagon's facade. The far end of the heliport is about 100 feet from the facade.
Debris Inside Pentagon
This photograph of the C-Ring punch-out hole shows a significant quantity of aircraft debris. This photograph shows scraps of metal, some with green aircraft primer paint, piled wrapped around a damaged column.
Debris in Yard
This photograph shows one of the larger pieces of debris on the lawn in front of the facade.

Pentagon Facade Damage Fits a 757

The Pentagon attack resulted in extensive damage to the facade corresponding roughly to the frontal profile of a 757. The damaged area included extensive punctures on the first floor and much smaller punctures on the second floor.

Punctured Walls Admitted Most of a 757


The portions of the Pentagon's facade punctured by the crash are easily measured by combining data from several different photographs, both before and after the collapse of the section. Several photographs by Jason Ingersoll provide detailed views of right portions of the impact zone. Other photographs show the left portions of the impact zone. Together, these photographs show that the facade was punctured over a wide swath on the first floor and a much smaller extent on the second floor.
Measuring the punctured regions shows that the facade was completely punctured for a width of 96 feet on the first floor and 18 feet on the second floor. Punctured areas were bounded by columns and floor slabs. This is natural since the columns and floor slabs were constructed of steel-reinforced concrete, whereas the window bays spanning them were brick walls reinforced with steel window frames and Kevlar mesh as part of the renovation program.
On the first floor, the primary puncture extended from column 8 to column 18. Three leaning objects in the first floor space left of the hole center are often assumed to be displaced remains of columns 15, 16, and 17. However, this analysis shows that those objects are more likely to be fallen pieces of the second floor slab than columns. Thus, it appears that the crash initially left a first floor hole that extended unobstructed for 96 feet. Surviving column 18 marked the rightmost extent of the hole, but to the right of it is another hole extending to column 19. Thus the total width of punctured walls on the first floor was at least 105 feet.
On the second floor, the puncture extended from column 13 to column 15. Photographs show a hanging object in the position of column 14. This appears to consist in part of remains of the steel reinforcements that were part of column 14.

Breached Limestone Marks Profile of 757's Wings


Photographs also show extensive damage to the south of the impact punctures, with most of the damage to the south of column line 19 being above the first floor.
Although the damage beyond the impact punctures appears to be consistent with the impact of the outer portions a 757's wings in both degree and extent, many observers think that the impact should have left a clear imprint of a 757's profile on the facade, much as the impacts of 767s left their profiles in the Twin Towers. This is not a persuasive argument against the crash of a 757:


Lateral Displacement of Tail Damage Suggests Explosion


The above argument is based on at least three assumptions:
  1. The vertical tail section would have made an imprint in or otherwise visibly damaged the limestone facade.
  2. The impact of the plane would not have deflected the tail section and caused it to impact some other part of the facade.
  3. Some other event would not have deflected the tail section and caused it to impact some other part of the facade.
Assumption 1 is intuitive, but there appears to be no experiment or rigorous argument that establishes its validity. The vertical tail sections of most jetliners are constructed of lightweight materials, and do not have to support the kinds of loads that the wing ends or elevators do. There are even cases of vertical stabilizers breaking off due to wake turbulence, as was reported to happen in the crash of American Airlines Flight 587 on November 12, 2001.
Assumption 2 is also intuitive, because the tail section would have had to undergo high accelerations perpendicular to the flight path in order to deflect far from the region above the impact hole center. Whether the impact was insufficient to impart those accelerations, however, has yet to be established.
Assumption 3 appears to have been overlooked by most no-757-crash theorists. Any of a number of events consistent with the available evidence could have altered the trajectory of the vertical tail section before or at the moment of impact. Three possibilities are:
  1. Stresses to the aircraft on its final approach caused the vertical tail section to separate. For example, the impacts of the engines with the generator trailer and retaining wall might have sufficiently jolted the airframe to break off the vertical stabilizer.
  2. A bomb in the luggage hold exploded just as the front of the fuselage was beginning to impact the facade.
  3. A surface-to-air missile exploded on the aft starboard side of the jetliner just as the nose was beginning to impact the facade.

Summary

Proponents of the no-Boeing theory have made the following claims about the damage to the Pentagon's facade:
  1. There was only one impact hole measuring no more than 18 feet across.
  2. The impact hole was at most 65 feet across.
  3. Standing columns remained where heavy 757 parts should have obliterated them.
  4. The hole was too small to accommodate wing ends and tail.
Claim 1 is based on the selective presentation of photographs in which fire retardant spray obscures the entire first floor. Claim 2 is based on the fallacy that the distance between the expansion joints bounding the collapsed region of the facade marked the maximum extent of impact punctures. Post-crash photographs clearly show impact punctures extending over twenty feet to the right and to the left of the expansion joints.
Claim 3 is based on the confusion of hanging sections of the second floor for columns. Claim 4 is true, but consistent with the crash of a 757 whose wing ends and tail are too light to puncture the Pentagon's walls.
Facade Impact Punctures
This photograph by Jason Ingersoll shows the impact hole center extending to the second floor and punctured walls to its right. Punctured walls to the left of the hole center are obscured by smoke. The cluster of three spools which appears close to the facade is actually about 80 feet away from it, to its right. This study of facade damage builds a profile of the region of breached walls by assembling information from four different photographs. This simulation shows a 757-200 colliding with the Pentagon's facade, where the damage to the facade documented by photographs is indicated by colors.
Damage Dimensions
This study measures the extent of punctured walls (outlined in red) and breached limestone (outlined in green).
Breached Limestone
This photograph from the FEMA Report (Figure 3.8) shows missing limestone around and above windows to the left of the impact punctures. This photograph from the FEMA Report (Figure 5.12) shows impact damage to the steel reinforced columns and brick walls to the right of the impact center following the removal of some of the limestone facing. This photograph shows a larger view of damage to the south of the impact center.
Tail Damage
This photograph shows scoring of the limestone on the facade of the fourth floor.
Missile Batteries?
These photographs all show concrete structures with open metal doors. Do these structures contain some kind of defensive system?
757-200 Dimensions
These drawings depict a Boeing 757-200F, a freighter. It has the same dimensions and shape as the passenger version of the 757-200.
wing span 124 ft 10 in
length 155 ft 3 in
tail height
(above ground)		 44 ft 6 in
fuselage width 12 ft 4 in

Interior Damage is Consistent With a 757 Crash

Impact damage to the interior of the Pentagon was primarily on the first floor, and extended in a tapering swath from the first-floor facade puncture to the vicinity of the C-Ring punch-out hole.

Floor Space Between Facade and C-Ring is Mostly Unobstructed


A figure on the left shows a path from the center of the facade impact puncture to the center of the C-Ring punch-out hole. That path could describe the path of fuselage debris from the facade to the C-Ring wall, where it could have produced the punch-out hole. It shows that there was a narrow path for that debris between the columns left standing by the crash.

C-Ring Punch-Out Hole Is in Path of Most Aircraft Mass

Many observers find the size of the punch-out hole peculiar because it is small relative to a 757. Measuring about 9 feet in diameter, it is much less than the 12.5-foot diameter of a 757's fuselage.
However, the mass of a jetliner is not uniformly distributed throughout its shape. The fuselage of a 757 comprises only about a quarter of the area of its frontal profile, but makes up well over half of its mass. The distribution of the mass within the fuselage is far from uniform. Most of the structure is located in the lower third of the fuselage, as are the heavy components such as the landing gear.
In a high-speed collision with a building, only the parts of the aircraft with the greatest density and total mass, such as the lower third of the fuselage, could be expected to penetrate far into the building. That part also has a small frontal profile -- approximately the size of the punch-out hole.

Column Damage Is What a Jetliner Would Produce

The last photograph in the right column shows a portion of the first floor interior just north of the collapse zone. Portions of the jet's left wing would have passed from right to left in this area. We can see the remains of several columns, which originally had a square cross-section. The impact apparently stripped away the concrete, in several cases exposing the spiral steel reinforcement, and in one case leaving only four strands of vertical rebar anchored in the ceiling. The photograph shows that all of the columns are bent in the same direction, the same as throughout the crash zone. The fact that the columns are bent in the same direction, even 40 feet away from the impact center, is indicative of the crash of an aircraft with large wings.

Summary

Proponents of the no-Boeing theory have made the following claims about damage to the Pentagon's interior:
  1. The C-Ring punchout hole could not have been made by a jetliner's nose
  2. The C-Ring punchout hole could not have been made by a jetliner
Claim 1 may be true but is entirely irrelevant because the nose of a jetliner is just the front end of the fuselage. The fuselage, and particularly its lower half, is the most massive part of a jetliner, and in a collision its force would be concentrated in a small frontal profile, much like a battering ram.
Most variants of Claim 2 incorrectly assume that there are ground level masonry walls between the C- and D-Rings, and D- and E-Rings.
Crash Trajectory
This illustration from FEMA's Report summarizes the path of aircraft remains through the first-floor space between the facade and the B-to-C-Ring courtyard.
Lack of Obstructions
This photograph shows the size and spacing of the columns in the first-floor interior space between the facade and the C-Ring This photograph from outside of the C-Ring punch-out hole gives a sense of the lack of obstructions between the facade and the C-Ring exterior wall. One can see clear through the C-, D-, and E- Rings to a pair of windows in the facade on the right and the northmost end of the entry impact punctures on the left.
Debris Path
In this illustration, a gray line marks the path from the center of the facade impact hole to the center of the C-Ring punchout hole. The path is unobstructed by columns that remained standing.
Interior Damage
This photograph was taken in the E Ring at the north end of the crash zone looking south toward the collapsed section.

Damage to Surroundings Fits a 757

Eyewitness reports of the attack aircraft describe it as clipping lamp-poles and a generator trailer on its approach to the Pentagon. Post-attack photographs corroborate these reports, and show a pattern of damage fitting a Boeing 757.

Swath of Downed Lamp Poles Fits a 757's Wingspan


Of the downed lamp poles whose condition was documented by photographs, all appear to exhibit similar types of damage: each was severed some distance from its base, and is bent in an arc in the direction of the shear over a much shorter distance. This pattern of damage appears to be consistent with the high-speed impact by the leading edges of wings.
Assuming that the downed lamp poles were clipped and toppled by an aircraft, their pattern indicates that the aircraft had a wingspan of at least 100 feet. The pattern of unmolested lamp poles and other objects, such as the overhead sign, indicates that the aircraft had a wingspan of not more than 130 feet. (Since poles are probably designed to survive hurricane-force winds, it is reasonable to exclude the idea that turbulence downed any lamp poles.) Given a 757's 125-foot wingspan, it fits the swath of damaged lamp poles.

Damage to Generator and Retaining Wall Fits a 757's Profile

Witnesses who observed the final moments of the crash stated that the plane banked left (some saying that the left wing hit the heliport) and that its low-hanging engines hit objects on the way in: the right engine hitting a generator trailer and the left engine hitting a low retaining wall. Post-crash photographs of the yard fit these accounts and show a pattern of damage consistent with the paths of the engines of a 757 based on the other data such as the light-pole path.
A trailer containing a generator stood at the northwest corner of the construction yard at the time of the attack. In the attack, it was severely damaged, sustaining a broad gouge on its northern end and a narrow gouge on its top. The generator was apparently pushed off its front stand, leaving the front (north end) resting on the ground.
The narrow gouge appears to be slightly less than 45 degrees away from the normal direction of the trailer's face. Assuming that the trailer was oriented parallel to the fence prior to the crash, the angle of the narrow gouge is consistent with damage from a part of the same aircraft that clipped the lamp-poles. The relative positions and shapes of the broad and narrow gouges suggests they were caused by a 757's right engine, and the first flap canoe beyond the right engine. The distance between centerline of the narrow gouge and the parallel line intersecting the center of the arc of the broad gouge appears to be about the same as the distance between the centerline of a 757's engine and the next flap canoe beyond the engine: about 10 feet.
A low retaining wall surrounded a structure with a rectangular footprint lying about 50 to 90 feet from the Pentagon's facade. The structure has been described as part of a ventilation system. Post-crash photographs show that the southwest corner of the concrete retaining wall was gouged away. The location of the gouge lies on the path of the left engine of a 757 on a trajectory whose centerline intersects the facade between column lines 13 and 14 and is 38 degrees from normal.

Positions of Cable Spools are Consistent With a 757 Crash

Post-crash photographs show five large cable spools in front of the impact region of the Pentagon's facade. One of the spools is toppled, while four are standing on their edges. In most of these photographs, the spools appear very close to the facade, making them appear to be obstacles in the low-angled flight path of a jetliner into the Pentagon. Since these photographs were taken from the highway about 500 feet west of the facade, the ground near the facade is highly foreshortened in them. An analysis of the spool positions using photographs from different vantage points shows that the spool nearest the facade was about 30 feet from it. The other standing spools were about 80 feet away from the facade.

I estimate below that the wings impacted the facade at an average elevation of about 8 feet, and that the plane was losing about a foot of altitude for each 20 feet traveled. The four standing spools appear to lie between the paths of the two engines. Assuming that the larger spools were 6 feet in diameter, the flight path would have taken the bottom of the wings and fuselage about two or three feet over the tops of the larger spools. The spool lying on its side is damaged, and may have been hit by debris from the engine that hit the retaining wall.

Summary

Proponents of the no-Boeing theory have made the following claims about the damage to the Pentagon's surroundings:
  1. Lamp-poles on the highway overpass were pulled out or toppled the wrong way.
  2. The damage to the generator could not have been produced by a 757's engine and wing.
  3. Spools standing in the yard should have been toppled by a 757.
Claim 1 is often repeated, but I have yet to find a single coherent exposition of it.
One variant of Claim 2 holds that the engine could not have made the broad gouge because the engine housing is too weak compared to the generator trailer. However, given the high speed of the impact, it would not be surprising for an aluminum engine housing to carve a hole through the trailer. By way of analogy, consider that a soft lead bullet can puncture a hole in a 1/8-inch-thick steel sign, given enough speed.
Most variants of Claim 3 appear to assume, incorrectly, that the cable spools were very close to the facade, or that they would be toppled by turbulence from the fly-over of a 757.

Lamp-Pole Path
This illustration shows the positions of intact lamp poles on and around the highway overpass, indicating which ones were downed (yellow dots) which were not (turquoise dots), and the path of a Boeing 757 that would account for the downed poles. This illustration from PentagonResearch.com estimates the positions of lamp poles after they fell.
Lamp-Pole Damage
These photographs show the kind of damage that was inflicted on some of the lamp poles.
Generator Damage
These photographs show the generator-trailer at the northeast corner of the construction yard. This illustration by Pierre Desmoulins shows a 757 approaching the Pentagon at 38 degrees from normal. This path takes the right engine over the north end of the generator.
Retaining Wall Damage
These two photographs both show damage to the southwest corner of the retaining wall surrounding the structure seen from above in the following photograph. ( source)
Cable Spools
In most photographs, the cable spools appear deceptively close to the building.

Specific Debris Matches a 757

Although most of the debris in photographs of the Pentagon attack aftermath is too small to be identifiable, as is typical of high-speed aircraft crashes, some pieces are large enough to compare to known 757 components. Of those pieces, all plausibly match parts of a 757, and none fail to match 757 parts while matching parts of some other aircraft.

Engine Parts Match a 757's Engines


The shape and dimensions of the rotor in the photographs match those of several of the high-pressure rotors in a 757 engine. (Boeing 757s are equipped either with the Rolls-Royce RB 211-535E4, or the Pratt & Whitney PW 2037 or PW 2040.) While the largest rotor in such an engine -- the bypass fan -- is about 9 feet in diameter, the high pressure compressor and turbine rotors are a fraction of that dimension.
A photograph from inside of the Pentagon shows a scrap that appears to be part of a jet engine's combustion chamber assembly. The size, arrangement, and screw holes in the circular fuel nozzle ports appear to match those of an RB211-535 -- a type of engine used by Boeing 757s.


Landing Gear Parts Match a 757


A photograph of the Pentagon's interior shows a metal object with a cylindrical shaft and structures on its end that were apparently formed connections to other parts. The part in the photograph has the same kinds of features as the main rear landing gear strut on similar Boeing jets such as 767s, and it may be an exact match for the strut of a 757.

Hull Piece Matches a 757 With American Airlines Colors

A scrap of aircraft photographed by Mark Faram on the lawn just north of the crash site has a color scheme matching an American Airlines jet: silver, white, and red.
Closer examination of the scrap and comparison of its decorations and rivet pattern with that of an American Airlines 757-200 suggests that it matches a section of the fuselage just aft of the starboard forward cabin door. If the red marking is a part of the 'n' in 'American', then the smooth edge on the rightmost end of the scrap appears to be in the correct position for the door opening -- four rivet lines from the end of the 'n'.
Based on this argument, implying that the piece could only have come from the forward right (starboard) side of a 757, some observers have noted peculiarities about the piece. How did it end up far to the left of the flight path? Why does it show no signs of abrasion or burning? Perhaps the argument is wrong, and the piece came from the aft left (port) side of a 757.

Summary

Proponents of the no-Boeing theory have made the following claims about the identification of aircraft parts in the rubble:
  1. The rotor photographed north of the impact zone is too small to be from a 757.
  2. The rotor photographed north of the impact zone is from an APU, SkyHawk A-3 engine, or other origin.
  3. Only one engine was found.
  4. Parts actually from or made to look like they were from a 757 were planted as part of the cover-up.
Claim 1 is based on the misapprehension that all the rotors in a turbofan engine have the same diameter as the fan.
Variants of Claim 2 have been circulated by stories from sources such as TomFlocco.com which usually take the form of an alleged aeronautical engineer claiming to have confirmed a match between one of the parts in Pentagon photographs and a part of an aircraft other than an Boeing 757. I have yet to find such a story which meets even the most basic journalistic standards.
Claim 3 is without basis since we have no way of knowing how many or what engine pieces were found.
The best-known example of Claim 4 is the idea that the hull piece described above had to be moved because its position and condition were unnatural for the crash. That may or may not have been true, but even if it was, it could have been moved for reasons having nothing to do with covering up the absence of a jetliner crash.
Engine Parts
The rotor in this photograph appears to be about 2.5 feet in diameter. The object in the photograph with multiple round holes appears to be the crumpled fragment of a jet engine's combustion chamber casing. The pattern of holes is similar to that of the combustion chamber casing of a RB211-535.
Landing Gear Parts
A wheel hub in Pentagon crash debris photographs matches the hubs of a 757's rear landing gear. This piece of landing gear found in the C-Ring near the exit hole has matching structures and a similar shape to a 767's landing gear's main shaft (right), the 767 having larger parts than a 757. (Source of 767 part photograph: PentagonResearch.com)
Hull Piece
A piece of debris photographed in the yard north of the crash site appears to match the portion of an American Airlines 757 just aft of the front starboard cabin door.
Debris in C-Ring Courtyard
In this photograph showing debris outside the C-Ring punchout hole, an apparent piece of aircraft debris that does not appear to have been greatly distorted shows a curvature corresponding to the 12-foot diameter of a 757.

The Attack Plane's Approach Is Consistent With a 757


The approach maneuver was, in several ways, extreme and unusual for a jetliner. According to reports the plane descended seven thousand feet and turned over 270 degrees in the last three minutes and then approached the west side of the Pentagon at a very low altitude, clipping some obstacles and narrowly avoiding others on its low-angle approach that ended with its careening primarily into the Pentagon's first floor.
Many people have pointed out that the alleged pilot of Flight 77 -- Hani Hanjour -- did not have the requisite skills to perform the maneuvers. Others have alleged that a Boeing 757 could not have flown the maneuvers.

Spiral Dive Is Well Within a 757's Capabilities


Radar shows that Flight 77 did a downward spiral, turning almost a complete circle and dropping the last 7000 feet in two-and-a-half minutes.
Air traffic controller Danielle O'Brien told ABC News:
The speed, the maneuverability, the way that he turned, we all thought in the radar room, all of us experienced air-traffic controllers, that that was a military plane. ... You don't fly a 757 in that manner. It's unsafe.
Such a maneuver is not normal for jetliners, but is it within the capabilities of a 757? I will calculate the G force that the turning component of the described maneuver would have imparted on the aircraft. The G force produced by travel along a circular arc can be calculated using the following formula: 
RCF = 0.001118 * r * N^2
where
RCF = Relative Centrifugal Force (gravities)
r = rotation radius (meters)
N = rotation speed (revolutions per minute)

If the plane were traveling at 400 miles per hour it would travel 16.666 miles, or 26,821 meters, in 2.5 minutes. Assuming it was traveling in a circular arc, it would trace out 3/4ths of a circle with a 35,761-meter circumference, giving a rotation radius of 5,691 meters and rotation speed of 0.3 rotations per minute. Plugging those values into the above equation, I obtain a centrifugal force of 0.5726 Gs.

Jetliners such as 757s are rated for accelerations of around two Gs, but they may be able to survive much greater accelerations. An IcelandAir 757-200 logged an incident in which it experienced pitch accelerations of +3.95 Gs.

Final Approach Is Consistent With an Autopiloted 757


By all accounts the Pentagon attack plane approached the building's west side from the southwest flying in a descending trajectory that took it primarily into the Pentagon's first floor. Details of the approach path can be inferred from damaged objects such as the highway lamp poles and generator trailer.

The downed lamp poles indicate that the aircraft passed directly over the highway overpass and cloverleaf intersection southwest of the impact zone. Two of the clipped lamp poles were on the northeast side of the cloverleaf, about 600 feet from the impact zone center. Assuming that the ground at the base of the poles was elevated 18 feet relative to the Pentagon's foundation, and that the poles were clipped at a height of 20 feet, the aircraft's wings were 38 feet higher than the foundation at 600 feet before impact. Assuming that the plane's wings were at an average elevation of 8 feet upon impact, the plane would have lost 30 feet of altitude in 600 feet of travel, averaging one foot of altitude for each 20 feet traveled.

These calculations suggest that the plane was flying within a wingspan of the ground for at least its last thousand feet, but not "inches from the ground" as some have stated. Flying so close to the ground means the plane would have been experiencing ground effect -- an increase in lift and decrease in drag produced by proximity to the ground. These effects result from the fact that the ground partially blocks the trailing vortices produced by the wing, decreasing the downwash and increasing the wing's effective angle of attack.

The influence of ground effect may have required the plane to adjust its attitude in order to maintain a course toward the Pentagon's first floor. Since lift is proportional to angle of attack up to the critical angle of attack (at which the wing stalls), compensating for the increased lift due to ground effect is simply a matter of adjusting the pitch downward to cancel out the increased lift. Although the adjustments required to maintain the shallow angle of descent may have challenged a human pilot, they would seem an easy task for a 757's autopilot, with its ability to read instruments and adjust control surfaces accordingly with great speed and accuracy.

Summary


Proponents of the no-Boeing theory have made the following claims about the approach of the attack aircraft:

  1. The spiral dive maneuver could not have been made by a jetliner.

  2. The final approach was impossible due to ground effect.


Claim 1 is contradicted by the demonstrated performance capabilities of a Boeing 757, and Claim 2 fails to acknowledge that the increased lift due to ground effect can be negated by lowering the angle of attack.


Spiral Dive Maneuver
This illustration from the NTSB's Flight Path Study - American Airlines Flight 77 shows the ground path of the attack plane for about the last five minutes of its flight.
Final Approach Elevation
This illustration from Pierre Desmoulins' website estimates the slope of the aircraft's approach using based on the positions of the clipped lamp-poles and the heights at which they were clipped.
Ground Effect
This graph shows the reduction of induced drag as a function of the proximity of an aircraft to the ground.
Lift Function
This graph shows the relationship of lift to angle of attack.

Suppressing Evidence of the Crash Serves the Cover-up







Evidence from the Pentagon crash that would decisively resolve the question of whether Flight 77 was the attack plane has been systematically suppressed by authorities, such as the FBI. Actions have included the following:


  • The seizure of security videos from the nearby Citgo gas station and Sheraton hotel within minutes of the attack, and their refusal to release those videos.

    Update and correction
    Videos were released in 2004  to Judicial Watch





  • A failure to release recordings of security video cameras thought to ring the Pentagon or traffic monitoring video cameras along the nearby highways maintained by the Virginia Department of Transportation.

  • A failure to release photographs of the Pentagon's interior prior to removal of debris.


  • A failure to disclose the fate of aircraft debris collected at the Pentagon, and their failure to document or disclose the results of any attempts to identify the aircraft parts.

  • An implausible insistence that the recovered black boxes yielded "nothing useful."


This behavior is consistent with three different motives on the parts of the those responsible for suppression and destruction of evidence.


  1. An institutional penchant for secrecy, amplified by the atmosphere of national emergency produced by the attack

  2. A desire to suppress evidence that would disprove the crash of Flight 77

  3. A desire to suppress evidence that would prove the crash of Flight 77

People who fail to grasp the role of disinformation in the cover-up will tend to overlook Motive 3 and attribute the suspicious actions to Motive 2. However, as I point out in the Booby Trap article, an analysis of the history of the 9/11 Truth Movement demonstrates the value of the no-jetliner theories in sidelining challenges to the official story as the product of lunatic conspiracy theorists.

Conclusion


In this essay I asked what conclusions about the Pentagon attack were supported by physical evidence -- primarily post-crash photographs of the site. I found that, in every aspect I considered, this evidence comports with the crash of a Boeing 757. At the same time, the evidence does not conclusively prove that the aircraft was a 757, much less that it was Flight 77. However, that lack of conclusiveness should not be surprising given the systematic suppression of evidence by authorities.

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