Scattered Clues

New shadows darken the TWA Flight 800 probe

The FBI would not allow NTSB investigators near the eyewitnesses in the early days of the investigation, but much later transferred a mountain of witness statements to the NTSB for examination. One member of the NTSB's Witness Group told the Voicethe group began examining the statements last fall and hopes to finish sometime in March or April, after which, he said, the NTSB will put the accounts into its TWA 800 public docket and post them on its Web site. This senior accident investigator said he hopes the group will take a crack at explaining what the witnesses saw, and does not expect to be constrained by the CIA's analysis. "If once it's explained it doesn't make sense, I have no problem going on the record and saying so," the investigator said.

If eyewitnesses really did just imagine they saw a missile, that leaves the NTSB searching for something that could have ignited the vapor above the 50 or so gallons of fuel in the huge center tank. Yet the safety board stated last year that it may never find the ignition source.

That is not surprising, considering the odds it faces. After all, its $30 million investigation was unable to find a single flaw in any of the recovered aircraft components that could have allowed a spark into the tank. That, in turn, is no surprise to the man whose familiarity with 747s is second to none. "When we designed the airplane we did every damn thing we could to make a fuel tank explosion not happen," said Joe Sutter, the retired Boeing chief engineer who more than 30 years ago led the 747 design team. Sutter told the Voice, "There've been thousands of 747s, sitting on the ramp, cooking in violent heat for hours due to delays, and they've taken off with hot empty tanks hundreds of thousands of times, so if it happened this way, that was a real freak accident." (Boeing has built 1200 747s.)

The Flight 800 disaster was truly a freak occurence. As noted in Insight Magazine (February 8), it is one of two unexplained center tank explosions. The other was a new Philippine Air Lines 737 that exploded before takeoff in Manila in 1990— and although a cause for that explosion has never been found, it is known that the airplane had been modified by the owners since it left the factory.

To show it has indeed found the cause of the crash, the NTSB has identified a breakup sequence that it says led in two or three seconds from the center tank explosion to disintegration of the aircraft, specifically when the nose and first-class section fell off. But although its investigators determined which parts of the tank were damaged in the initial explosion, not all those features were included in the scenario developed by the Sequencing Group. In addition, the group made no progress toward identifying where in the tank the explosion may have begun, admitted senior metallurgist James Wildey in his summary to the Sequencing Report. The breakup sequence, then, remains merely a best guess for the order in which things happened.

But one expert who examined the report suggested that the burst of energy that tore the center tank partitions from their rivets, snapped the keel beam beneath the tank, and ripped apart the fuselage skin may not have come from inside the tank at all. "If the tank had 50 gallons of water in it, and you put enough energy into it, it will blow up," said Professor Richard Schile of the University of Bridgeport. Schile, who has degrees in mechanical and aeronautical engineering and has worked on failure analysis at Pratt & Whitney Aircraft, said that in examining combustion in the tank the NTSB may have missed the main event. "This sounds to me like the pressure rise was a hell of a lot higher than we think it was and it occurred so rapidly that it just blew the structure apart," he said. "The fire may have come later and been incidental."

A sudden increase in pressure would be expected to leave its mark on the airplane's black boxes. There is a sonic signature at the very end of TWA 800's cockpit voice recording that investigators have described as a very loud, very abrupt sound. So far, however, the NTSB has barely acknowledged the sound. To electronics engineer James Cash, who as chairman of the Cockpit Voice Recorder Group leads the NTSB's study of the sound, that's as it should be.

"Analysis is never released . . . it's for our internal use," he told the Voice. But one investigator said that the NTSB has turned down offers from outside labs to interpret the CVR sound. (The NTSB did not reply to a query about this.) One member of the CVR group is skeptical that the NTSB has made any real effort to analyze the sound at all. "It certainly should have been investigated thoroughly," he said.

Recently, one investigator said, TWA and the Air Line Pilots Association, two parties to the investigations, have urged the NTSB to say what could have caused the CVR sound, and to release a report on some tests conducted on a retired 747 in Bruntingthorpe, England, in the summer of 1997. In one test the safety board filled the airplane's center tank with propane, exploded it, and recorded the sound on a CVR. "We need to use the Bruntingthorpe data in our analysis. I want the data to be published," said one investigator. The CVR group has not met since the Bruntingthorpe tests, which were finished in August 1997, he said. The NTSB did not respond to a question about the report on its Bruntingthorpe tests.

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