September 19, 1996, Thursday, Late Edition - Final 

SECTION: Section A;   Page 1;   Column 5;   Metropolitan Desk 

New Focus on Malfunctions In Inquiry on T.W.A. Crash 

BYLINE:  By MATTHEW L. WALD 

DATELINE: WASHINGTON, Sept. 18 

BODY: 
Investigators from the National Transportation Safety Board, saying they are convinced that none of the physical evidence recovered from T.W.A. Flight 800 proves that a bomb brought down the plane, plan tests intended to show that the explosion could have been caused by a mechanical failure alone. 

The investigators acknowledge that they have no evidence pointing to a mechanical malfunction. Rather, they say, the failure to find proof of a bombing, after more than two months, lends indirect credence to another theory, that an explosion in the Boeing 747's center fuel tank might have been been sufficient to destroy the plane. "If you get a fuel-air explosion in that tank, how does it vent itself?" said a senior investigator who insisted he not be named. "How does the airplane open up? That's what we have to come to grips with." 

Boeing, on the basis of its own calculations, has contended that there would not be sufficient energy in such an explosion to bring the plane down. 

But safety board officials say they are unpersuaded. They plan computer simulations and lab tests, and they may even try putting fuel in the center tank of a scrapped 747 and blowing it up. 

James K. Kallstrom, the deputy director in charge of the Federal Bureau of Investigation's New York office, said yesterday that the safety board tests of the center fuel tank do not reflect any new consensus among law enforcement investigators that a malfunction destroyed the plane. 

"They should do all the tests in the world to try to ascertain what caused this," Mr. Kallstrom said. "Just as we should do, from the standpoint of our bomb technicians and forensic people. Those procedures are complimentary to each other, and they have been done simultaneously." 

All the investigators have their own "private hunches" about the most likely cause of the crash, he added. And Mr. Kallstrom acknowledged that N.T.S.B. investigators, unlike most Federal law enforcement officials, place more credence in the malfunction theory. 

Behind the different approaches is a growing sense of surprise and frustration that proof of the cause of the crash still has not been found, even though more than 100 divers have been in the water nearly every day since the crash on July 17. 

The F.B.I and the safety board have different missions that lead them to favor different theories. On the F.B.I. side, there is a grim determination to catch the criminals responsible, presuming they exist, for a crash that killed all 230 passengers and crew. Meanwhile, the aviation experts want to make sure they are not overlooking a mechanical flaw that, if it exists, could threaten hundreds of other Boeing 747's. 

And they are anxious to keep control of the investigation. The safety board remains in charge unless the F.B.I. declares the crash to be a criminal act. 

At the safety board, a senior official said that "it would be incorrect to imply that there is conflict" between his agency and the F.B.I. over this approach. The safety board's investigators say they believe that not even the metal parts that bear microscopic traces of explosive residue prove that a bomb was involved. 

In fact, a senior N.T.S.B. official said, if there was a bomb, investigators probably would have seen "classic signs" of it by now, including metal that is pitted and bent by high-energy shock waves. Likewise, he said, the fact that they have not found any parts of a missile puts that theory in more doubt. 

As a result, several safety board officials said, the board plans to run tests on other Boeing 747's in commercial service to see if investigators can find levels of plastic explosive similar to the tiny samples the F.B.I. found in the Flight 800 wreckage. Explosives experts say traces are common in public spaces where people who work with explosives have been present. 

But the N.T.S.B.'s central question is whether the 50 to 100 gallons of jet fuel sloshing around in the 12,800-gallon center tank, located in the lower part of the fuselage where the wings come together, would have enough energy to do all the damage they have observed on parts now in hangars in Calverton, L.I. 

The F.B.I.'s strong belief that a bomb caused the crash is based on these pieces of circumstantial evidence: The plane's flight data recorder did not contain even a hint of an impending mechanical calamity, the jetliner split in two in a pattern remarkably similar to that of other 747's that were bombed out of the sky and forensic tests of the wreckage confirmed traces of two chemical ingredients of Semtex, a favorite explosive of terrorists. 

The safety board officials acknowledge all of that. Some even say that it still looks, on a circumstantial basis, like a bomb. But the agency's top officials say that on the basis of their experience the center fuel tank explosion could produce the same set of facts. 

The new analysis is a sign that an understanding of the crash is still evolving. A month ago, some investigators thought that because parts of the tank showed no blast damage, it had not exploded. The thinking now is that an explosion in the tank would punch a hole in it somewhere, rather than blowing the tank apart, and engineers will need to know how big a hole, and where, and what consequences would follow. 

The safety board intends to continue working closely with the F.B.I. and the Navy retrieving wreckage from the ocean floor for the remaining weeks of the dive season, probably until the end of October. 

Between now and then, they are considering seeking second opinions from underwater experts on the scanning work done so far. This could include using outside experts to review sonar logs, to assure that there are no objects on the bottom that were missed in the first searches, and might include new scans. 

Demonstrating that the crash could have occurred simply from a fuel tank explosion would not prove that that happened; in fact, it would leave open the major question of what could ignite the tank. Investigators have several theories but no evidence for a mechanical ignition source. 

According to safety board experts, the vapor in the tank could be set off by a spark so small that it would not be visible to the human eye in daylight. A possible source is the wiring in the fuel-monitoring system. 

But getting such a spark requires two separate failures: a break in the insulation of the wiring, and a failure in a part that is supposed to limit the energy in those wires to a quantity 10 times too small to make the necessary spark. 

The tank also has three fuel pumps, but their wiring is outside the tank. Engineers are studying whether the pumps could somehow conduct current into the tank where it could cause a spark. So far, they have found only two pumps. 

The safety board investigators stress that they still do not know what made the plane crash. They add that their planned analysis, which will probably last into midwinter, could end up showing the opposite -- that burned, bent parts already in hand could not have been produced by a fuel tank explosion alone. 

It is also possible, they say, that a diver could raise a part tomorrow that would unambiguously show bomb damage. 

According to executives in the aviation industry, the safety board has already begun asking around about the availability of a scrapped, but intact, 747 fuselage for an experimental explosion of the center fuel tank. 

A spokesman for Boeing, Russell D. Young, said that if tests were planned to see if the center fuel tank could cause all the damage, it would be an effort by the safety board to advance the investigation "to the level where you don't leave anything to the imagination." 

LOAD-DATE: September 19, 1996