Four years after TWA Flight 800 exploded and plunged into the ocean, federal investigators ruled out any sabotage or missile as the cause of the explosion that brought down the Boeing 747 and killed the 230 people on board.
The National Transportation Safety Board said Tuesday during the opening of a two-day public meeting to release its final report that evidence confirms what they've long suspected: the jumbo jet was blown apart in flight on July 17, 1996, by a catastrophic explosion of the plane's center-wing fuel tank shortly after takeoff.
Bernard Loeb, director of the NTSB's office of aviation safety, said the most likely cause of the crash involved electrical wiring leading to the center-wing fuel tank.
"Although the voltage in the fuel quantity indication system wiring is limited by design to a very low level, a short circuit from higher-voltage wires, could allow excessive voltage to be transferred to fuel quantity indication system wires and enter the tank," Loeb said. "We cannot be certain that this, in fact, occurred but of all the ignition scenarios we considered, this scenario is the most likely."
Jim Hall, chairman of the NTSB, officially ruled out any chance that the jet was brought down by a missile or a bomb.
"After conducting an extensive investigation, the FBI suspended its investigation in November 1997 indicating that no evidence had been found to indicate that a criminal act was the cause of the tragedy of TWA Flight 800," he said.
Hall said the investigation, which has now become the most expensive and far-reaching probe four years at $35 million in U.S. aviation history, has led to many changes in the construction of the 747 jumbo jet.
"The crash of Flight 800 graphically demonstrated that, even in one of the safest transportation systems in the world, things can go horribly wrong," Hall said during his opening statement at the hearing. "It should stand as a reminder to us all of the need for diligence and aggressive action in identifying and eliminating potential safety problems."
Ninety-five percent of the shattered jet has been recovered more than 100,000 pieces. Investigators have rebuilt the fuselage around the center fuel tank and they've checked more than 100 miles of the plane's wiring.
Although investigators think they know how the fatal spark found its way into the plane's fuel tank, they have not isolated the precise spot where it originated on the New York to Paris flight.
They believe a charge from a high voltage wire jumped onto an adjacent low voltage wire leading to a fuel-measuring device inside the tank. The spark, they said, then could have traveled down that low voltage wire into the tank, touching off explosive vapors.
Wires in Boeing 747s are now shielded just one of more than four dozen changes ordered for the jumbo jets since the crash. The FAA and Boeing hope the changes will greatly reduce thrisk of a catastrophic fuel tank blast ever happening again.
Since the focus shifted toward the fuel tank, the FAA has ordered 37 corrective actions for commercial airliners. Among them are replacing sharp-edged fuel probes that might damage wires, keeping pumps idle unless they are submerged in fuel, installing protective sleeves on wiring in tanks and developing electronic devices to suppress power surges in wiring.
Beth Erickson, head of aircraft certification for the FAA, said the agency has reviewed the history of fuel tanks on 10,000 commercial and noncombat military planes and found few problems.
Industry also participated, reporting a week ago that a three-year study concluded airline fuel tanks are safe.
The Air Transport Association, the airline industry's trade association, said more than 100,000 work hours were spent inspecting 990 aircraft operated by 160 airlines as part of the program.
Erickson said the FAA determined that three factors are needed for a fuel-tank explosion: flammable vapors, oxygen and an ignition source.
Changes are being made in all three areas: eliminating sparks; inerting, or filling the empty area of fuel tanks with nitrogen rather than allowing in air that contains potentially flammable oxygen; reducing vapors by keeping tanks fuller; cooling fuel tanks; and changing fuel formulas.
Investigators can't fully prove that their internal explosion theory may have caused the Flight 800 crash, and that leaves room for conspiracy theorists to continue to challenge the government's crash findings.
"One of the problems is that accidents such as this are enormously rare and random at this point," Robert Francis, former NTSB investigator who lead part of the Flight 800 inquiry, said Tuesday on The Early Show. "The system is very, very safe, and when you have an accident like this, it is becoming a lot harder to figure out why it happened."
Some skeptics still believe federal investigators are covering up evidence of a missile strike. So, while the TWA 800 investigation comes to a close, some doubts will endure.
This month a group of disbelievers in Springfield, Mass., sued the government seeking details of its inquiry into the crash, including radar data and information on material found with some of the victims' bodies.
Retired Navy pilot William Donaldson, a vocal critic of the investigation, issued a statement Monday contending that the government is determined to cover up the cause of the crash.
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