Hunt for Cause of Flight 800 Crash Leads Experts Back to Square One

It’s been almost four months since the crash of Trans World Airlines Flight 800, and investigators are virtually back where they started.

The revelation that residue from explosives may have come from an earlier training exercise has cast serious doubts on the theory that a bomb brought down the jumbo jet.

Lack of a telltale track on radar screens damages the theory that a missile was to blame for the 230 deaths on the Paris-bound plane.

The failure of engineering experts to figure out what might have generated a spark that could have caused the Boeing 747’s center fuel tank to explode seems to undercut the mechanical malfunction theory.

And those, federal investigators say, are still the only plausible theories that have been proposed.

They are the same theories that officials announced a week after the crash. Each has enjoyed popularity only to fade because of a lack of corroborating evidence.

Now, winter is approaching, and with it the stormy weather that could postpone for months further searches for wreckage. About 95% of the debris from Flight 800 has been recovered from the ocean floor south of Long Island, N.Y., but investigators keep hoping the final 5% will be found--and with it the conclusive evidence they have been seeking.

Robert Francis, the National Transportation Safety Board vice chairman in charge of the investigation, and James K. Kallstrom, the FBI assistant director in charge of the probe’s possible criminal aspects, insist they are optimistic of finding the cause.

If they are wrong--if a cause is never found--that raises the possibility that millions of passengers every year will fly in a widely used jetliner that could have an undiagnosed, and fatal, flaw.

That happened with another Boeing plane--the smaller, shorter-range 737--after two crashes, one in Colorado Springs, Colo., in 1989 and the other near Pittsburgh in 1994. Experts have never figured out what caused either crash, but some suspect an unexplained malfunction in the 737’s rudder system. Boeing has acknowledged a rudder-jamming problem that some think could be linked to the crashes, and the NTSB has recommended a rudder retrofit on the more than 2,800 Boeing 737’s currently in service.

“I think it’s premature to say we have another Pittsburgh,” Francis said recently during a telephone interview. “I think we’ll find the answer.”

Weather permitting, the undersea search for evidence in the Flight 800 crash continues. Francis said visibility in the murky, 120-foot-deep water at times is “down to a few inches,” but subsurface dredging equipment is still able to collect small bits of wreckage.

“We’ll be here as long as it takes,” Francis said.

In the crash of Flight 800, investigators have come to one firm conclusion: The center fuel tank, located directly under a midsection of the passenger cabin, exploded in flames as the jumbo jet climbed after taking off from New York’s John F. Kennedy International Airport.

The question is: What triggered the explosion?

Within a day of the disaster, investigators said they were looking at the possibility of a bomb. They pointed to the terrorist bombings of Pan Am Flight 103 and other airliners, noting that Flight 800 went down on the eve of the Atlanta Olympic Games, an event that might attract the machinations of terrorists.

For weeks, investigators had little but speculation to support the bomb theory. Field tests showed indications of tiny bits of explosive residue on some of the recovered wreckage, but lab tests in Washington failed to back up the findings. Then, on Aug. 23, the FBI announced that lab tests finally had confirmed the discovery of “microscopic” traces of an explosive on some debris.

Federal officials described the residue as PETN, a component of the bomb that tore apart Flight 103 over Lockerbie, Scotland.

The officials said the “speckle” of PETN was found on a seat from the midsection passenger compartment, at a point over the center fuel tank. In the days that followed, a tiny trace of RDX, another explosive component of the Lockerbie bomb, also was found in the rear of the plane.

To many outsiders, it seemed the bomb theory had won out. But FBI investigators urged caution.

For one thing, they said, a bomb would have been expected to produce a lot more than a speckle or two of residue. For another, other common evidence of a bomb--blast marks, pitting and bulging, shattered fragments of metal--was missing. And why was the RDX in the back of the plane?

Four weeks later, the bomb theory suffered a stunning blow: The FAA announced that the plane had carried test packages of PETN, RDX and other explosives during exercises to train bomb-detection dogs a month before the crash. The residue, several officials said, probably came from leaking packages.

The explanation for the PETN and RDX residues hurt the missile theory too. If the residues came from the training exercise, then they didn’t come from the explosion of a missile warhead. No debris from a missile has been found in the search area.

Weapon experts said any missile big enough to bring down a 747 almost certainly would have left a track on radar. Careful studies of the air-traffic control radar images of Flight 800 showed no such track.

Some witnesses said they saw a streak of light ascending toward the jet just before it exploded. And an amateur’s photograph taken moments before the crash shows something that looks a bit like a missile in the sky.

But investigators said the photographer was facing in the wrong direction to have captured any missile that could have struck Flight 800. The streak of light, some national security experts suggested, might have come from a hobbyist’s rocket--far too small to have brought down the plane.

There was even talk on the Internet of “friendly fire”--rumors spread by onetime John F. Kennedy Press Secretary Pierre Salinger and others that a Navy ship, or perhaps an Air National Guard plane, had mistakenly shot down the jet and that the government was involved in a cover-up. Kallstrom, whose agents reportedly checked out every tip, calls that one “nonsense.”

A meteorite also has been considered, but the odds against that one are, literally, astronomical.

“And there’s the same problem with that one that there is with all the missile theories,” a source said. “No evidence of an entry wound.”

That leaves the mechanical malfunction theory, which--by process of elimination--has been garnering increasing attention.

The center fuel tank was almost empty when Flight 800 took off, but it contained kerosene fumes at a temperature and concentration that engineers believe were right for explosive combustion. Experts have said that even a tiny spark could have touched off the blast that tore through the tank as the plane climbed to 13,700 feet. The only requirement would be voltage high enough to generate that spark.

Boeing said the electrical components within the tank are deliberately designed with voltage too low to pose a threat. Investigators have recovered and studied two of the three submersible fuel pumps from within the tank, and both appear normal. They said parts of what may be several of the seven probes that measure the amount of fuel in the tank have been recovered.

Blast damage has been noted on at least one part, but engineers said that could have been caused by the explosion of the tank and does not necessarily implicate the probe.

Boeing has ruled out static electricity, and no other possible source of a spark has been suggested. Engineers are looking at the possibility of a flame entering the tank through the venting system, but no workable scenario has been offered.

Last month, New York attorney Lee Kreindler, who plans to sue TWA and Boeing on behalf of the families of 23 victims, claimed that computer simulations and tests on spare parts showed a mechanical failure “of some kind” caused the fuel tank explosion. An investigative source said there is skepticism about Kreindler’s information, but it will be reviewed.

Boeing has argued that the explosion in the center tank was--by itself--probably not powerful enough to cripple the jetliner and plunge it into the dive that was punctuated seconds later by a massive fireball apparently fueled by kerosene spewing from the ruptured wing tanks.

If Boeing’s arguments prove correct, that even casts doubt on the significance of the center fuel tank explosion.

“There still are lots of unanswered questions,” a source close to the probe said. “Too many unanswered questions.”