Spark of Static Electricity May Have Caused TWA Jet to Crash

Believing that a spark generated by static electricity may have set off the fuel tank blast that destroyed TWA Flight 800 last July, the National Transportation Safety Board recommended urgent center fuel tank design changes Friday in hundreds of jetliners, including all Boeing 747s.

All 230 people aboard the TWA jumbo jet perished on July 17 when the Paris-bound plane plunged into the Atlantic Ocean shortly after takeoff from New York, prompting one of the most intensive investigations in the NTSB’s history.

“We wouldn’t have issued that [recommendation] if we didn’t think a spark couldn’t have gotten into that tank,” a source close to the investigation said. “The most probable source of that spark would be static electricity.”

The NTSB stressed, however, that it was not putting forth a definitive cause of the crash, a stance also taken by the FBI, which has not ruled out any of three possibilities advanced for the crash.

“The FBI’s position is that all three theories are still under active investigation, and the report issued tonight specifically does not state what the cause was,” said an FBI spokesman. “There is still a significant amount of work being done along all three lines of inquiry--a bomb, a missile or mechanical failure.”

Nevertheless, attention is now focused on the 747’s cross-feed manifold--a fuel line running through the center tank that connects the two other fuel tanks in the wings.

One theory is that the line’s O-rings--which connect the segments of pipe that form the line--had become old and distorted. This, in turn, might have caused grounding problems that could have allowed static electricity traveling along the manifold to discharge into the tank, which apparently contained a highly volatile mixture of fuel vapor and air at a temperature conducive to ignition.

Blast evidence found on recovered wreckage convinced investigators months ago that the tragedy aboard Flight 800 began with a center fuel tank explosion. The unanswered question was: What touched it off?

The explanation offered Friday came less from evidence than from the elimination of other scenarios, one by one. Divers still combing the floor of the Atlantic and experts assembling the shattered wreckage in a hangar in Long Island hope to come up with the few critical fragments that might verify the theory.

That so many critical conditions--warm tank temperatures, a dangerous fuel mixture and a static-electricity spark--would have to come together for an explosion to occur could explain why there is no precedent for the disaster.

In the recommendations offered Friday, the Safety Board asked the Federal Aviation Administration to order a series of “urgent” changes that would preclude the buildup of volatile fuel/air mixtures at temperatures warm enough to permit ignition.

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The NTSB urged the FAA to require airlines to add insulation between heat-generating equipment, such as air conditioners, and fuel tanks. The board suggested that center tanks be filled shortly before takeoff with fuel that has been kept cool before loading and that tanks be kept full enough to preclude substantial vapor buildup.

In the long term, the board said, the FAA should consider design changes such as systems that would pump an inert gas like nitrogen into the tank as the fuel is being expended. The NTSB noted that the military prevents the risk of fuel tank ignition by inserting nitrogen into tanks of its planes to create “an oxygen-deficient fuel-air mixture that will not ignite.”

The NTSB also proposed the installation of sensing devices that would warn the cockpit crew if fuel tank temperatures reached dangerous levels.

The recommendations apply to the approximately 1,000 Boeing 747s in service, along with hundreds of other airliners that have center fuel tanks.

Aviation sources said most of these proposals should be relatively easy and relatively inexpensive to implement. Much of the work probably could be done during routine maintenance breaks, so most planes could remain on the line and there would be relatively little inconvenience to the airlines and the flying public.

Because of intense White House and Capitol Hill interest in the Flight 800 investigation, a prompt response is expected from the FAA.

The FAA said the board’s letter had not been received by Friday night, but said the recommendations would be reviewed carefully.

“The FAA has been working closely with the NTSB in the course of that agency’s investigation,” the agency said. “FAA takes the board’s recommendations very seriously, and it will respond to today’s proposals in a timely fashion.”

The FAA added that in the past it has “responded positively” to 90% of the urgent recommendations put forth by the Safety Board.

In a statement from its headquarters in Seattle, Boeing said its “position where safety is concerned is to err on the side of caution. We will take action and support any directives from the FAA.”

The 747 is one of the most widely used passenger aircraft in the world. Many of the planes have been in operation for decades and issues of wear and tear have been under examination as the cause of the disaster is being sought. TWA Flight 800 was one of the oldest 747s in the airline’s fleet, but was reported to have been well-maintained.

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Like the bomb theory, the possibility that a missile brought down Flight 800 remains under scrutiny. Numerous people on the shore of Long Island reported seeing a streak of light in the sky about the same time the plane exploded as it climbed above 13,000 feet.

On Thursday, a Saudi airline pilot reported a green “flare” in the sky near New York’s Kennedy International Airport. Federal officials, including the FBI are investigating. Some government officials believe, however, the pilot witnessed a meteor shower.

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A Potentially Deadly Spark

Investigators believe a buildup of static electricity on a fuel line could have caused the tank of TWA Flight 800 to explode last July off Long Island, killing 230. As a result, the National Transportation Safety Board has “urgently” recommended modifications on commercial aircraft of similar design.

* The Design

Fuel is stored in the wings and in a center wing fuel tank beneath passenger seats. A pipe is used to move fuel from the wing tanks on one side of the plane to the engines.

* What Investigators Believe

1. A fuel pipe was in use at the top of the center fuel tank, where vapors are formed. Static electricity tends to form on the outside of the pipe.

2. O-rings between aluminum sections of that pipe may have come loose. If the static charge has no ground, an electrical spark can result.

3. Fumes in the nearly empty center tank--at a volatile temperature and concentration--exploded violently.

* The Recommendations

Short-term changes could be made to prevent buildup of explosive vapors and heat in the center fuel tank. In the long run, design changes are suggested. There are about 1,000 747s operating worldwide with center tanks.