LATER THIS MONTH A TEAM OF FBI agents and government scientists will drive out to a deserted military base two hours north of London. There they'll attach five tiny sophisticated bombs - the kind favored by international terrorists - to a fuel tank taken from a wrecked Boeing 747. Then they'll detonate the charges. If the first four explosions leave anything left to examine, the Feds will add propane to the tank for the grand finale. When it's all over, scientists will scrutinize every twisted shard of metal for some kind of telltale resemblance to the catastrophe that brought down TWA Flight 800.
They don't expect to find it, and with that loud bang, an ocean away from the crash site, the largest criminal investigation in American history is likely to end. The dramatic test is a last concession to those who still think a bomb may have killed 230 people in the sky south of Long Island, a possibility that seems increasingly remote. A year after the crash, investigators still can't tell the victims' families just what caused the plane to explode. But agents looking for killers abroad are now giving way to scientists looking for another kind of killer - a faulty wire, perhaps, or a random charge of static electricity. As horrific as a terrorist act would have been, a malfunction is equally unsettling. Already the two federal agencies charged with air safety are feuding over how to prevent another disaster, with the lead investigator warning that more people will die if changes aren't made. Experts have always been quick to say that 747s don't just tumble from the sky. Apparently, Flight 800 did.
Investigators are testing four mechanical theories to determine what caused the explosion in the plane's center fuel tank, but they're not sure they'll ever have the answer (chart). That contrasts sharply with the bold predictions they made immediately after the crash. Back then it seemed so likely that terrorists were to blame that the National Transportation Safety Board actually offered to cede control of the investigation to the gumshoes. In the months that followed, the investigation was led by James Kallstrom, the FBI's plain-talking point man. Kallstrom piloted a massive investigation involving as many as 700 agents - and became something of a celebrity in the process. (On a shuttle flight from Washington to New York last week, crew members argued in the cockpit over whether Kallstrom was in fact the famed Fed; to settle the dispute, Kallstrom gave them his card.) But even as a new batch of scientists examines the wreckage for clues, the FBI is preparing to close its case. If there is any proof of a bomb or missile, Kallstrom says, it's still sitting on the ocean floor.
The spotlight now shifts to Bernard Loeb, the brainy scientist who heads the NTSB's side of the investigation. Tall and bony with birdlike features, Loeb has investigated every major crash in the last 15 years, and he follows two guiding rules: ""No. 1 is that we be right. No. 2 is that we don't miss anything.'' Edgy and determined, Loeb can be found pacing in his Washington office before 6:30 a.m. At home, he'll read a hundred e-mails and sift through a stack of documents while watching the Orioles on television. This is a big moment for Loeb and his agency; chronically overlooked by the media and the budget makers, the not-so-glamorous NTSB now has a chance to show the world what it can do. It expects to spend some $27 million on Flight 800 - more than half its annual budget. That bill may rise as Loeb chases new theories: he now believes that a small crack in the tank may have caused leaking fuel particles to form a cloud, which then discharged a deadly electric spark. He's been unable to prove it in the lab - so far.
Loeb's doggedness is causing a public rift between the NTSB and its more powerful counterpart, the FAA. The NTSB has been pushing the FAA to mandate costly changes that would prevent the buildup of explosive vapors on 747s and thousands of similar planes. The FAA has resisted, saying there's no proof of a hazard - a response the NTSB has characterized as ""unacceptable.'' Tension peaked this month when Loeb warned publicly that the FAA's recalcitrance could cost more lives. For that, he was upbraided by several members of Congress. Meanwhile, NEWSWEEK has learned that Transportation Secretary Rodney Slater convened a meeting with officials from both agencies last week to try to stop the bickering. It may be futile. The FAA, after all, isn't yet inclined to put cumbersome new restrictions on the powerful airline industry. And nerves are likely to fray as investigators increas- ingly feel they're racing against the clock. They know that what- ever happened on Flight 800 - however improbable - may happen again.
Investigators are still trying to determine what caused TWA 800's nearly empty center fuel tank to explode. The six subjects:
Static electricity: Sloshing or leaking fuel builds up a static charge, causing a deadly spark NTSB's pick.
Fuel-probe residue: Mineral deposits on a fuel-level monitor reach dangerous temperatures, igniting the fuel.
'Shaped charge': A large bomb has been ruled out, but small explosives planted on the center fuel tank could have caused the blast.
Chafing wires: FAA's favorite. Rubbing wires near wing tank start a fire that blows back through vapor vent system to center tank.
Meteors: "Space junk," possible small meteors or missile fragments, hits the jet. The least likely cause.
Scavenge jump: A pump that bails fuel residue from the center tank overheats, touching off hot vapors.