TWA Blast Linked to Short Circuit
The center fuel tank explosion that tore TWA Flight 800 apart and hurled it into the sea probably was ignited by a short circuit somewhere else in the plane that transferred excess voltage into the tank, federal officials said Tuesday.
Although the blast and crash off Long Island on July 17, 1996, destroyed most of the direct evidence of exactly what happened, there is plenty of circumstantial evidence that such a short circuit occurred, National Transportation Safety Board officials said.
After four years of painstaking investigation, board experts have ruled out the possibility--still promulgated by some--that a bomb or a missile caused the crash that killed all 230 aboard the Paris-bound Boeing 747.
Two days of hearings on the crash will conclude today with the board’s official conclusions about what caused the disaster. There seemed little doubt Tuesday what those conclusions will be.
Bernard S. Loeb, director of the agency’s Office of Aviation Safety, told an audience of aviation industry representatives, news reporters and relatives of those who died in the crash that the agency’s investigation “leads to the inescapable conclusion that the cause of the in-flight breakup of Flight 800 was a fuel/air explosion inside the center tank.”
The safety board had said five months after the crash that an explosion in the fuel tank was the likely cause of the disaster, although it was unsure what triggered it. Responding to NTSB recommendations, the Federal Aviation Administration has issued 37 directives aimed at increasing the safety of fuel tanks in commercial aircraft. Most required inspections or replacement of wiring systems in aging jetliners. The FAA also is considering proposals to introduce nitrogen into partly filled fuel tanks to replace oxygen, which supports combustion.
Loeb said that exhaustive research and testing have ruled out a number of possible ignition sources aboard the doomed TWA jetliner, including lightning, static electricity and radiation from equipment like radar, cell phones and laptop computers. Also ruled out was a short in the electrical system that measures the amount of fuel in the tank, because it operates at voltages too low to generate a spark that could have touched off the blast.
Much more likely, Loeb said, is a scenario in which a high-voltage wire somewhere else in the plane shorted out one of the low-voltage wires in the fuel-measuring system. He said such a short circuit could have sent high voltage surging through the low-voltage wires to the tank, generating a spark large enough to set off the explosion.
“We cannot be certain that this, in fact, occurred. But of all the ignition scenarios we considered, this scenario is the most likely,” Loeb said.
NTSB engineer Robert Swaim said that a number of factors support this theory.
He noted that inspections of the 25-year-old plane that crashed and several other old aircraft turned up high-voltage wires on which the insulation was cracked and frayed. In many places on all of the planes, high-voltage wires were bundled together with the low-voltage wires leading to the fuel tank.
Cockpit voice recordings show that moments before the explosion Capt. Ralph Kevorkian, referring to a vacillating gauge on his instrument panel, said: “Look at that crazy fuel flow indicator.” The gauge’s wiring was bundled with the fuel sensor wiring, and Swaim said that the vacillations could indicate some kind of short.
Repairs on the plane that crashed had left metal shavings near the fuel tank wires. Swaim said tests had shown that such shavings can cause electrical shorts.
Investigators have not found any fuel tank parts from Flight 800 that show arcing, he said, but some of those parts have never been recovered.
He said some of the recovered fuel tank sensors were covered with a gray sulfide film deposited by jet fuel that turns them into semiconductors. “That stuff burns off with a loud pop and a flash when current is applied,” he said.
But Swaim said he still does not have a smoking gun.
“I would just love to be able to walk in here with a molten piece of wire and say, ‘Here it is.’ ” he said. “But I cannot walk up and say: “This is the piece.’ ”
In announcing the short-circuit theory, safety board officials reviewed the evidence supporting their long-held belief that an explosion of the center fuel tank brought down Flight 800 shortly after it took off from New York.
Loeb said that radar data and undersea wreckage fields, separated into three distinct zones, indicate that the plane broke up at an altitude of about 13,000 feet. About 95% of the wreckage was recovered.
Loeb said that debris from the center fuel tank--located in the belly of the plane near where the wings join the fuselage--fell into the first zone.
Farther along the track of the doomed flight, divers found the wreckage of the plane’s nose, which apparently snapped off in the explosion.
Loeb said that the rest of the plane--the wings, the back three-quarters of the fuselage and the tail--flew on for a short time, climbing before a steep dive into Long Island Sound. This wreckage was the farthest along the flight path.
“We found no evidence that a structural failure and decompression initiated the breakup,” Loeb said.
“We also considered the possibility of a bomb or missile,” he said. “However, [such] high-energy explosions leave distinctive damage signatures, such as severe pitting and cratering. In addition, we found no localized area of severe thermal or fragmentation injuries . . . such as would be expected if a high-energy explosive device had detonated inside the airplane.”
Jim Hall, the safety board chairman, lambasted those who still argue that the crash was an act of terrorism or a Navy error hidden by a government cover-up.
“It is unfortunate that a small number of people, pursuing their own agendas, have persisted in making unfounded charges,” Hall said. “These people do a grave injustice to the many dedicated individuals, civilian and military, who have been involved in this investigation.”