New York Times

Print Media Edition: Late Edition (East Coast)
New York, N.Y.
Aug 15, 2000

Authors: Matthew L. Wald
Dateline: WASHINGTON, Aug. 13

Copyright New York Times Company Aug 15, 2000

Four years after Trans World Airlines Flight 800 exploded off the coast
of Long Island, the National Transportation Safety Board is preparing to
approve an unusual final report on the crash, one that will identify only
the penultimate cause.

The agency is working on a 700-page report, far longer than typical for
a major crash, that investigators say contains unusual detail, documenting
an ambitious foray into basic science.

But the report does not tell what the public most wants to know: the source
of ignition for the explosion in the center fuel tank, when the Boeing
747 was about 11 minutes out of Kennedy International Airport on its way
to Paris on July 17, 1996. As the plane climbed to 13,700 feet the fuel
tank explosion ripped it apart, chopping off the front of the plane as
if with a guillotine. All 230 people aboard were killed.

The investigation has been mammoth. Searchers retrieved 95 percent of the
170-ton aircraft from the ocean floor and reconstructed a 90-foot-long
section. ''It's the most intensely investigated accident in aviation history,''
said Beth Erickson, director of aircraft certification at the Federal Aviation
Administration, which has been deeply involved.

Even with no certainty about the source of ignition, the accident has set
off a wide review of airplane design and operating practices. That review
found troubling conditions on several varieties of jets, which fly about
30 percent of the time with an atmosphere in their center tanks that will
support combustion. The findings seem likely to result in major changes,
aviation regulators say, that will reduce the amount of time that fuel
tanks have an atmosphere that will support fire or explosion.

After analysis of the damage and the pattern in which debris fell convinced
researchers that the cause was the explosion of the center fuel tank, they
desperately tried to figure out where in the tank the blast originated.
They built a quarter-scale model of the tank, complete with baffles and
girders, and filled it with propane gas. Then they tried igniting the gas
from various parts of the tank to see whether they could create a pressure
wave like the one they deduced, from the damage pattern, must have occurred
on the plane.

They could not. ''There were just too many variables,'' one investigator
said. Some people involved said that effort was doomed from the start,
and that it needlessly delayed the safety board's effort to reach a conclusion.

The board spent months on other possibilities. One was that a pipe inside
the tank, filled with fuel under pressure, sprang a leak and created a
spray, which built up a static charge. But the investigators did not find
evidence of a failure of the parts that prevent static buildup.

A scavenge pump that sucks out the last dregs of fuel from the center tank
remains a suspect, even though it is designed to avoid introducing a spark,
but it was never found. Likewise, suspect parts of the fuel quantity indicating
system are missing.

Investigators have also delved deep into fuel chemistry, including how
sulfur in the fuel can combine with copper or silver from wiring to form
deposits on electrical connectors that can cause short circuits and sparks.
And they have conducted experiments with an airplane in flight to measure
the amount of time that the air space above the fuel in a tank has air
and fuel vapors in a proportion that will allow combustion.

Some safety experts are saying that the work to identify a variety of potential
problems and to make improvements in many systems will be more vital to
safety than finding the one cause of the Flight 800 explosion. ''How important
is it whether it was the fuel gauge wiring, the scavenge pump or some other
wiring?'' one former board official asked. ''If we knew it was one, would
we exclude the other two? No.''

An investigator still with the board, in a separate conversation, said
fixing one specific source of ignition would not do enough to prevent future
explosions.

''The whole drift of our work now is that this is the wrong tack to take,''
he said. ''Even if we found five or six ignition sources, there could be
more; we've got to go toward making the tank less explosive. When this
is done, we will have extracted the safety value from this crash.''

At the Boeing Company, officials also said that failure to zero in on one
cause was not a detriment to safety.

''We've thrown a blanket over everything,'' said Ron Hinderberger, the
director of airplane safety at Boeing's Commercial Airplanes Group unit,
''and we've found other opportunities in the design, other opportunities
in the maintenance, to enhance the safety of the fuel system.''

The report is different for another reason: it is concerned not only with
what caused the crash, but also what didn't. It dwells heavily on ruling
out a bomb or missile, both subjects of fevered speculation in the weeks
following the crash.

As part of the effort to create an airtight case for a mechanical failure,
the Pentagon test-fired Stinger missiles off the coast of Florida so investigators
could see exactly what those would look like from shore, to compare the
results with witness reports. Boeing has told the board that there was
no evidence of a bomb or missile damage.

The board is scheduled to meet on Aug. 22 and 23, in a new multimedia hearing
room built partly in anticipation of this event, to discuss the staff report
on the crash, probably haggle over some details and then approve it and
make some additional recommendations. Those may include advice to the F.A.A.
and aircraft manufacturers, notably Boeing, to review the design of their
jets, people familiar with the report said. The board plans to broadcast
the meeting live on its Web site, www.ntsb.gov, and will post the report
there in a few months.

Even if no ultimate cause is determined, the report, combined with recommendations
that the safety board issued in April 1998 and actions recommended by Boeing
or ordered by the F.A.A., are a sort of a cure, aviation experts say.

''The actions we've taken are the most sweeping and unprecedented, and
broadest in scope, that we've ever engaged in at the F.A.A.,'' Ms. Erickson
said. Her agency has issued 37 directives to aircraft operators, and is
developing three more. One requires a flame arrestor on the scavenge pump.
Other orders focus on wiring changes in the plane.

Boeing has recommended that airplanes sitting for long periods on hot days
use portable carts that pump cool air instead of their air-conditioners,
which are next to the center tanks.

A more ambitious idea, injecting nitrogen gas into the tanks when the planes
are on the ground, to reduce the amount of oxygen, is under development.
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