PANEL SUMMARY: Wreckage Examination and Sequence of Breakup

A senior NTSB investigator told the NTSB’s Board of Inquiry that a reconstruction of the wreckage of TWA flight 800 showed the breakup of the jet was touched off by an explosion of the wing center section fuel tank, an event that triggered the destruction of the craft and its plunge into the ocean.

Jim Wildey, a senior NTSB metallurgist and National Resource Specialist, said the explosion in the fuel tank led to the 747’s breakup.

He said the effort of the Metallurgy and Structures Sequencing Group began with the recovered pieces of wreckage assembled into two- and three-dimensional mockups of the fuselage.

He said the NTSB decided to reconstruct 94 feet of the fuselage in an unused hangar at Calverton, N.Y., in order to find out, if possible, where and how the breakup of the plane began so that the investigation could begin to focus on why it broke up. He said no evidence of a criminal act was found.

He said that investigators also rejected scenarios that the explosion and subsequent breakup of the plane was caused by a large scale structural fault, pre-existing weakness, or a faulty cargo door or nose landing gear doors.

He said his group studied fire effects on the wreckage as well as deformations and fracture surfaces to determine the sequence of the breakup. In some cases, he said, the specialists used magnifying glasses to see where cracks began and how they developed.

Center Wing Tank (18K)

The examination, Wildey said, concentrated on the center fuel tank, a box-like structure about 21 feet wide, 20 feet long and 4½ to 6 feet tall – comparable to a two-car garage up to about eye level. Buttressed by cross beams, it carries some wing loads and, helped by a keel beam, supports the fuselage during flight.

Most of the wing center section, he said, is the center wing fuel tank, with a capacity of about 13,000 gallons of fuel, weighing about 87,000 pounds. At the time it was carrying about 50 gallons of fuel. The tank is interlaced with cutouts for various tubing as well as holes to allow the fuel to move between the various bays inside the tank structure.

The fuel tank structure is designed to withstand pressure of up to 20 PSI (pounds per square inch).

Following the explosion, he said, the initial breakup occurred very rapidly, likely in less than one second. The explosion in the tank caused the front spar of the tank to break forward, the belly structure forward of the tank to separate and the keel beam to break, allowing the nose of the aircraft to break away. The aft fuselage, tail and wings remained relatively intact for many seconds after the explosion, until just before impact with the ocean.