PANEL SUMMARY: Ignition Sources - External (Section A)

Every explosion requires an ignition source, and the third day of the NTSB public hearing began with a discussion of the potential sources for the explosion that destroyed TWA 800. This first section of the panel considers external possibilities, and the second (Section B) deals with those from within the Boeing 747’s center wing fuel tank.

NTSB Chairman James Hall pointed out that the Board has received roughly 100 letters addressing the possibility that TWA 800 was felled by an object falling from space. Thomas Haueter, Chief of the agency’s Major Investigations Division, added that numerous telephone calls on the same subject have been received as well. Although, there is no evidence to suggest that Flight 800 was struck by a meteorite. The hearing therefore included testimony from Dr. William Cassidy, Professor of Geology and Planetary Science, University of Pittsburgh.

Responding to a request from NTSB investigators, Cassidy had performed calculations aimed at estimating the likelihood that a meteorite struck TWA 800. As he explained in his presentation at the hearing, the first obstacle in arriving at such a determination is that there has been no reported case of a meteorite impact with an aircraft. But meteorites have struck dwellings and motor vehicles, and the records of those cases, he said, are quite reliable. "If a meteorite hits your house, you’ll want to tell someone. First the police, then a television station."

Using that information for the continental U.S. over 100 years, and factoring in the number and surface area of dwellings, Cassidy arrived at an estimate of the total number of meteorite hits per square foot on dwellings, which turned out to be a range of very small numbers. He also added allowances for vehicles. But aircraft comprise a still smaller total surface area than dwellings and vehicles. With an estimate of that surface area, Cassidy arrived at the following determination: An aircraft-damaging meteorite hit can be expected to occur once in every 59,000 to 77,000 years. He added that an impact capable of causing the kind of damage associated with TWA 800 would be an even more rare event.

The hearing next featured testimony from Edward Kittel, Special Agent with the Federal Aviation Administration (FAA). He and his office are specialists in investigating attacks on aircraft involving explosives.

Kittel reported that he was notified soon after the TWA accident, and he then quickly proceeded to Long Island, remaining there throughout the recovery operation. He said that he and other forensic specialists examined each piece of recovered wreckage – not only the aircraft structure, but also the interior fittings and personal effects. They were looking for any evidence of an explosive device. No such evidence was ever found.

The special agent explained that explosives leave unmistakable signatures on resulting wreckage. He described some of those effects, such as characteristic saw-tooth metal fractures, streaking around holes and melting patterns from hot gases. Nothing he saw from TWA 800 had any of those appearances. Examination was performed not only at the site, but also in forensic laboratories.

Kittel also described explosion tests at a research facility in England, organized by NTSB investigators. To provide comparative data, these tests involved detonating explosive charges near metal samples and also near a replica of the 747 center wing fuel tank.