Investigators say frayed wire could have sparked TWA blast Turning up evidence of ignition called search for needle in haystack

December 11, 1997|By Suzanne Wooton | Suzanne Wooton,SUN STAFF

Investigators said yesterday they are still focusing on the possibility that a frayed wire -- possibly in TWA Flight 800's fuel measuring system -- might have short-circuited, touching off an explosion in the jumbo jet's overheated fuel tank.

Testimony during the third day of the National Transportation Safety Board's hearings in Baltimore focused on what event -- or series of events -- might have caused the deadly blast that brought down the Paris-bound Boeing 747 off Long Island, N.Y., shortly after takeoff on July 17, 1996. All 230 people aboard were killed.

But the mystery is complicated because a list of "latent," or dormant, problems -- such as a frayed wire -- could have brought down the airplane only when combined with other things, creating a unique environment for such a catastrophe.

"We have found certain failure conditions could combine to provide a source of ignition," said NTSB technical expert Robert Swaim.

Yet the awesome, if not impossible, task of finding such evidence of a frayed wire, much less determining what produced a spark, became even clearer yesterday as investigators outlined some of the scant discoveries they've made in the 17-month probe.

So far, for instance, they have recovered only a handful of fragments from the seven probes in the center fuel tank.

One of the fragments had a wire that was frayed, but it showed no evidence of an electrical surge or arc.

There are 150 miles of wiring in a Boeing 747, much of which is sitting in bundles in the 6-acre hangar in New York where the plane was reconstructed.

"So if a wire arced, we might be able to find it?" asked NTSB Chairman James E. Hall.

"It's a needle in the haystack," replied Swaim, "but we'll be looking."

Only five of the 355 airline crashes since 1967, when the NTSB was established, remain unsolved.

Without an exact cause, an overriding issue being discussed at the hearings is what aircraft manufacturers and airlines can do to help protect against some strange source of ignition.

In a major policy shift, Boeing Co., which has manufactured more than 1,100 of the 747s, conceded this week that it might have to redesign aircraft fuel systems to guard against a buildup of dangerous fumes in the center fuel tank -- where the explosion in TWA Flight 800 occurred.

Until now, Boeing and other manufacturers had designed planes to keep all possible ignition sources of an explosion -- such as electrical sparks or extreme hot spots -- away from flammable fuel vapors.

But the manufacturer now says it's also looking for ways to reduce the accumulation of dangerous vapors in fuel tanks.

Possible causes discounted

During yesterday's hearing at the Baltimore Convention Center, NTSB investigators officially dismissed a number of possible causes -- including a meteorite, although not before discussing that issue for more than an hour.

They also appeared to rule out a malfunction in the plane's three fuel pumps.

In addition to the possibility of a frayed wire in the fuel system, Swaim said, investigators are still pursuing the possibility that metal shards in the fuel or a copper/silver sulfide buildup found on some of the fuel probes could have conducted a charge from one fuel probe to another.

While investigators will continue looking for the source of the spark, the safety board will focus heavily on reducing flammability of the center fuel tank.

Heat inside and out

Surprise testimony earlier this week by a California Institute of Technology scientist concluded that a cooler fuel tank would have been significantly less likely to explode.

The Boeing 747 had only about 50 gallons of fuel in its room-size center tank, causing the fuel to heat rapidly and filling the tank with a volatile mixture of air and vapors.

In addition, the plane had been sitting on the runway three hours in 86-degree temperatures with the air-conditioning equipment, under the fuel tank, heating up.

TTC Yesterday, the Federal Aviation Administration, which regulates the airline industry, said it will soon direct airlines to conduct thorough inspections of all Boeing 747 fuel tank systems, including the probes.

Fuel probes are not periodically replaced even though many, like the ones in TWA Flight 800, are the original equipment.

Manufactured in 1971, the plane was one of the earliest 747s, one of 205 in the 100 series.

The majority are still in use, according to Boeing.

Today's hearing will focus on aging aircraft and such issues as how often probes and wiring should be inspected and how often they should be replaced.

Pub Date: 12/11/97

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