A 757 airliner has about 200 seats, which are designed to support
and protect the passengers in a crash that generates deceleration
forces of up to 16 times the force of gravity (16Gs) -- 4800 pounds
for a 300 lb passenger. They have heavy metal frames under the
upholstery.

These seats are mounted throughout nearly the entire length of the
fuselage. Yet not one single passenger seat was photographed either
inside or outside the Pentagon after the event. They could not have
melted, because there was not a great deal of fire -- the photos
show intact books and other burnable objects that would have been
destroyed at temperatures far lower than those required to melt
aluminum alloy or steel seat frames. In fact, there was not nearly
enough metal debris in general, inside or outside the building,
to account for a 100,000 lb airplane.

Also, the neat round exit hole that the government said was punched
by the nose of the 757 could not possibly have been. The nose is made
of fiberglass to permit transmission and reception of the waves from
the radar apparatus inside it. The diagram of the Pentagon damage
made by the American Society of Civil Engineers shows many intact
steel-reinforced concrete columns between the impact area and the
exit hole. The plastic nose could not have passed through or around
these columns. When this was pointed out, the government changed its
story and said that the hole was made by a backhoe. As the hole is
perfectly round, this is also impossible. One or more loops of explosive
detcord (primacord) fastened to the inside of the wall would probably
have made a nice round hole.