Cause of TWA Blast Unknown, Boeing Concludes

WASHINGTON —  Boeing Co. said Thursday that a four-year, $32-million in-house investigation had failed to pinpoint even so much as the possible spark of the 1996 midair explosion of TWA Flight 800, one of its jumbo jets, that killed all 230 people on board.

But the wreckage showed no signs of the Boeing 747-100’s having been bombed or hit by a missile, contrary to conspiracy theories that have circulated widely, company officials said in summarizing their part of the largest transportation accident probe in history.

The Paris-bound aircraft exploded and fell into the Atlantic off Long Island on July 17, 1996, 14 minutes after takeoff from New York’s John F. Kennedy International Airport.

In an April 28 submission to the National Transportation Safety Board, which heads the federal investigation, Boeing attributed the crash to “an ignition of flammable vapors in the center wing tank, resulting in a loss of structural integrity of the aircraft.”

Briefing reporters in suburban Arlington, Va., company officials said Thursday they had been unable to determine the ignition source and declined to name any likely candidates.

“There would be nothing that would please us more than to say, ‘We found it,’ ” said Ron Hinderberger, director of aircraft safety for Boeing’s commercial airplane group, referring to whatever sparked the explosion.

But he said the hunt had identified ways to enhance fuel tank system safety, including a recommendation that airplane operators use air-conditioning carts when on the ground to lower fuel-tank temperatures when the thermometer tops 60 degrees.

Dennis Floyd, the Seattle-based company’s chief engineer for airplane safety, said the investigation has prompted 48 service bulletins recommending design, maintenance and/or inspection improvements across the Boeing fleet, the most to result from any accident by far. Eleven others are in the works.