Investigators of the deadly crash of TWA Flight 800 believe the design of the Boeing 747 aircraft and its fuel tanks were at least partly to blame for the tragedy.
They also cite government certification of the safety of the plane and the tanks, sources familiar with the investigation of the crash.
Investigators, on the first day of a two-day NTSB hearing on the crash, Tuesday said an electrical short circuit outside the center fuel tank of Flight 800 likely sent excess voltage through wires into the tank, igniting flammable vapors and causing the jet to explode.
The jet fell, in flaming pieces, into the Atlantic Ocean near New York shortly after taking off from John F. Kennedy airport more than four years ago. All 230 passengers and crew were killed.
The spark most likely occurred in a high-voltage wire outside the tank, investigators believe. They also think the wire short-circuited and the spark then jumped to a low-voltage wire that runs into the fuel tank.
In addition, the investigators believe the design of the jet is in part to blame. They believe placement of air conditioning units under the fuel tank generated heat that led to vapors in the fuel tank being explosive when touched off by the spark, the sources said.
Unanimous Board Approval Today, on the final day of the hearing, NTSB investigators presented their findings, and the five-member NTSB board unanimously agreed with their conclusion that the wing center fuel tank exploded most likely from a short circuit in the wiring outside the tank. The short-circuit then traveled into the tank through low-voltage wires and ignited the flammable vapors, investigators concluded.
The NTSB board also sided with investigators citing design and certification of fuel tanks as a contributing factor to the accident. The board criticized the design philosophy that assumes aircraft fuel tanks will always contain at least some explosive material and approved a series of recommendations for government regulators and airplane manufacturers.
These recommendations include: A massive review of wiring systems on all airplanes to ensure wires for critical systems are adequately protected Better bonding of components in the fuel tank Reducing the sulfite deposits on components of the fuel tank. Sulfite deposits can mix with metals in certain wires and lead to flammability That the FAA seriously address its own review of how to improve safety of systems on aging aircraft.
Boeing Stands By Design Boeing officials Tuesday stood by the aircraft design.
“The design with the air conditioning packs under the center wing tank is a very common design for Boeing and other manufacturers. It is fully certified by the FAA,” Russ Young, a Boeing spokesman, told ABCNEWS.
Both Boeing and the Federal Aviation Administration, which certifies plane and part safety and design, have long held to the philosophy that to prevent explosions, jets had to eliminate ignition sources, but not necessarily tank flammability.
Another Boeing official told ABCNEWS that reduction of ignition sources and flammability went hand-in-hand.
“We think that both ignition source reduction and flammability reduction are really complementary and not mutually exclusive,” said Ron Hinderberger, director of airplane safety for Boeing. “We think that both of them are needed in order to ensure that we can have the most safe system that we can possibly have.”
Other Scenarios RejectedAfter years of speculation and $35 million spent, investigators said the most extensive and expensive probe in aviation history has ruled out two other scenarios in the downing of the Boeing 747-100: structural failure and the impact of a bomb or missile.
Physical evidence “leads to the inescapable conclusion that the cause of the in-flight breakup of TWA Flight 800 was a fuel-air explosion inside the center wing tank,” Bernard S. Loeb, director of aviation safety for the National Transportation Safety Board, said.
The NTSB on Tuesday began the two-day session to discuss the final report on the TWA crash, its causes and possible new safety measures. During the four-year probe, investigators recovered 95 percent of the aircraft, reconstructed a 93-foot segment of the fuselage, and amassed 15,000 pages of documentation.
The investigation into the crash of TWA 800 has already led to almost 40 changes in aviation safety rules and regulations. In December 1996, the NTSB recommended the FAA study design and operational changes based on the preliminary conclusion that heated, flammable vapors in a fuel tank posed a serious risk.
The board’s recommendations included keeping fuel tanks full to prevent vapor buildup and installing temperature gauges in the tanks. The FAA never implemented these proposals, although airplane manufacturer Boeing says its own tests show the moves would have been ineffective.
Thomas McSweeney, head of the FAA’s certification office, said his agency is taking a broad focus, examining factors such as flammability, ignition sources, inert gas and oxygen.
First-Time Disclosure Since the first months of the TWA 800 probe, investigators suspected flammable vapors in the center tank initiated the explosion. But Tuesday marked the first time investigators publicly singled out a short circuit as the most likely ignition source to the exclusion of others they have considered, including a dry, overheated pump and static electricity.
“The crash of Flight 800 graphically demonstrates that even in one of the safest transportation systems in the world, things can go horribly wrong,” said NTSB Chairman Jim Hall.
Investigators were emphatic in their repudiation of speculation in the media that a bomb or missile downed the jet and the government is covering it up.
“It is unfortunate that a small number of people, pursuing their own agendas, have persisted in making unfounded charges of a government cover-up in this investigation,” Hall said.
The damage sustained by the aircraft bore no resemblance to the customary markings of detonated bombs or missiles, Loeb explained.
“High-energy explosions leave distinctive damage signatures such as severe pitting, cratering, hot gas washing, and petaling. No such damage was found on any portion of the recovered airplane structure,” he said.
Eyewitness reports of streaks of light seen nearby on the night of the crash fueled the bomb and missile theories. In efforts to test the theories, the NTSB has studied 736 eyewitness accounts and even test-fired missiles to determine just what witnesses might have been able to see on the night of the crash.
Explanation of ‘Missile Theory’ Tuesday, investigators presented an explanation for what many said they saw the night of the crash: After the initial breakup of the plane, Loeb said, burning fuel from the damaged plane likely appeared as a streak of light.
At the hearing, a victim’s father said the government did a good job eliminating the missile or bomb theory. “That theory undermines what the government is trying to do for the families,” said Jim Hurd, father of 29-year-old James Hurd III. “It only adds to the questions we have.”
Two other commercial airliners have crashed after similar center wing tank explosions: a November 1989 accident involving a Avianca Boeing 727 and a May 1990 accident involving a Philippine Air Lines Boeing 737.
A Boeing official said he didn’t know how the company could take more precautions.
“In the lifetime of a fleet of airplanes catastrophic failure should not occur,” said Charles Higgins, Boeing’s vice president of airplane safety. “We already design it with that in mind. What the NTSB seems to be suggesting is a belt-and-suspenders approach to everything.”
ABCNEWS’ Lisa Stark, ABCNEWS.com’s Ronald Dunsky and Geraldine Sealey contributed to this report.