So after nearly 10 weeks of relentless effort, one of the largest investigative task forces in U.S. history is essentially back at square one. Though the bomb theory is by no means dead, the possibility of a catastrophic mechanical malfunction is getting a deeper look. More than 70 percent of the shattered plane has been recovered, but not a single piece of debris shows the characteristic signs of pitting or scarring that would confirm a bomb explosion–and none of the 213 corpses recovered so far bears the kind of mutilating injury that a bomb would have caused.
Meanwhile, there are suggestions the investigation has been inherently slanted toward the bomb theory all along and that the FBI, with its obvious bias toward detecting crime and catching bad guys, is largely responsible for that. There also are rumors of tension between the FBI and the National Transportation Safety Board, which is nominally in charge of the probe but which, because it is outmanned and outgunned by the G-men, has always been a junior partner in the quest. When the FBI crime lab found the residue of PETN and RDX, for example, NTSB vice chairman Robert Francis wasn’t even told about the results. But in a case like TWA 800 you cannot rule anything out–and the NTSB techno-sleuths are better equipped to consider the chances of a random mechanical glitch than their colleagues at the FBI.
One thing everyone agrees on is that the first ““event’’ in Flight 800’s demise was a blast in the plane’s midsection, somewhere between rows 17 and 22 in coach. That has led the FBI to theorize, quite plausibly, that a terrorist bomb was placed in or under a seat in that area and that the bomb then touched off a secondary explosion in the center fuel tank below the cabin floor. This tank (chart) was nearly empty–no more than 100 gallons of jet fuel were sloshing around inside. Jet fuel is mostly kerosene, which is not particularly explosive. But if the kerosene had vaporized–and there was plenty of air in the tank to allow this to happen–an exploding bomb could have touched off the fuel-air mixture and ripped the plane apart.
Arcane techno-glitch: But there is a no-bomb theory as well–and even if it’s a million-to-one chance, it is the kind of arcane techno-glitch the NTSB loves to solve. That is the possibility that a stray electrical spark set off the jet-fuel mixture. By this hypothesis, a short circuit in one of the tank’s three fuel pumps could have produced an electrical arc that caused the blast. Since the pumps are outside the tank itself, this theory also implies that the tank must have been leaking at least some fuel. To support this scenario, investigators note that in 1989 Boeing Corp. warned that in some cases center fuel tanks on 747s could leak, and the FAA ordered inspections.
Take it one more step. Investigators are now re-examining a little-noticed airline disaster that occurred in 1990. This accident, in Manila, involved a Boeing 737–a different and much smaller plane–and it has never been solved. The plane was on the ground when it suddenly burst into flames, killing eight and injuring 30. No evidence was found of a bomb or an incendiary device. But Filipino government investigators, assisted by NTSB officials and Boeing Corp. experts, found a possible manufacturing defect in a fuel-tank switch that, combined with damaged wiring, could have caused a spark. And Boeing acknowledges getting a report of a minor fire on a 747 in which a faulty fuel pump was the suspected cause. Not long after TWA 800, the Federal Aviation Administration announced that it may order testing and possible replacement of fuel pumps on all 747s and Boeing 757s. (The FAA has not yet ordered the tests.) Two of the three fuel pumps from the center fuel tank on TWA 800 have been recovered, with no evidence of malfunction. Navy divers are still searching for the third.
None of this rises to the level of probable cause–but it is a fact that both the NTSB and the Boeing Corp. are looking hard at the possibilities. Boeing engineers have already performed a computer simulation to see if accidentally ignited fuel vapor could have caused an explosion powerful enough to blow Flight 800 apart–and concluded that such a blast would not have created enough pressure, measured in pounds per square inch, to cause such awesome damage. But investigative sources also say that NTSB officials are not satisfied with some of the assumptions behind Boeing’s computer run–which is why, for the past several weeks, NTSB officials have been talking about conducting a real-world test explosion on an obsolete 747.
This falls under the heading of ““check everything, no matter how unlikely.’’ But the theory is complicated and the stakes are huge. Boeing and its subcontractors face liability suits worth hundreds of millions of dollars if some manufacturing defect is found to be the cause of the explosion. The fuel-tank hypothesis assumes leaking fuel, an electrical spark and that less than 100 gallons of kerosene could produce enough explosive vapor to blow the 747 apart–for as investigators have re-created the terrifying last seconds of Flight 800, the plane was effectively decapitated by the explosion. Finally, as Boeing spokesman Brian Ames observes, there is no evidence whatsoever that a faulty fuel pump or any other mechanical defect contributed to the disaster.
Against all this is another powerful fact. On radar and in reconstruction, the last moments of Flight 800 were uncannily similar to those of Pan Am 103. So the crucial piece of evidence may yet emerge to confirm that a bomb was indeed aboard the TWA plane. But given the enormous difficulties of the underwater search, pessimists are increasingly apt to say we may never know for sure what happened.
Fuselage fractures: Whatever the cause, the front of the plane blew off first. Boeing has argued that a fuel-tank blast alone would not have been strong enough to blow the plane apart. But the 747 reportedly split open behind section 42, an area prone to cracking. Vapors build up: Fuel vapors, normally released through the wing, are not properly vented, allowing them to heat up to flashpoint–about 100 degrees for commercial-jet fuel A spark sets it off: A central-tank fuel pump (one is still missing) or one of the tank’s seven fuel gauges malfunctions, generating a spark that ignites the trapped fuel vapors Sources: Boeing Commerical Airplane Group, Newsweek Research
