Sunday, August 20, 2000 - Page updated at 12:00 AM

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Seattle Times aerospace reporter

THE 1996 MIDAIR EXPLOSION of TWA Flight 800 that killed all 230 people aboard the Boeing 747-100 has brought about profound changes in the way air crashes are investigated and airplanes are designed and maintained.

It doesn't rank in the top 10 in terms of fatalities, but no crash has had as profound an impact in the modern jet age as that of TWA Flight 800.

Airplane design and maintenance have been changed by the tragedy. Airport security was tightened. The credibility of government, and its ability to solve a complex puzzle, were challenged.

Now, after the most extensive and expensive probe in aviation history, the National Transportation Safety Board (NTSB) will close the book this week on the 1996 midair explosion that killed all 230 people aboard the Boeing 747-100.

At a meeting in Washington, D.C., the safety board will likely conclude that a fuel-tank explosion, sparked by an undetermined malfunction, brought the plane down. Flight 800 was en route to Paris when it plunged into the Atlantic Ocean off Long Island just 13 minutes after takeoff from New York.

That conclusion is consistent with what investigators have been saying for years. But the task of documenting it and exploring its implications took far longer than anyone anticipated.

Seattle-based Boeing will essentially lose face in another arcane and circumstantial finding that an aircraft's design was probably deficient. Last year, the safety board concluded that two fatal 737 crashes in the 1990s were probably caused by malfunctions of a rudder mechanism. While findings such as the one expected this week don't directly affect the company's bottom line, they do generate headlines that cast Boeing in a negative light.

The company is still vigorously defending itself in court against lawsuits by families of the victims, although it has settled many of about 200. Because the basic facts and probable conclusions have been known for years, this week's report isn't likely to affect the outcome of legal action against Boeing.

And voluntarily or under orders from the Federal Aviation Administration (FAA) prompted by the TWA investigation, Boeing has in recent years made many design changes to electrical and other systems, intended to decrease the chance of a spark occurring inside a fuel tank. This was costly, and it was inconvenient for airlines flying Boeing planes.

There are numerous other legacies from the Flight 800 investigation, each with global implications:

Having recognized a decade ago that aircraft structures become vulnerable to stress and corrosion over years of use, the aviation industry now knows that mechanical and electrical systems - wiring, in particular - also need to be carefully monitored over time. The plane that was Flight 800 was 25 years old.

The investigation led to a paradigm shift in airplane fuel-tank-design philosophy, with manufacturers now conceding that the fumes inside tanks are in a volatile state most of the time. Research is still under way to lessen this hazard.

Because early speculation focused on a terrorist act, airport security measures were changed.

Through it all, the NTSB and the FBI, which for months considered the possibility that a criminal act led to the crash, had an uneasy relationship, raising questions about the government's ability to manage complicated catastrophic events.

Families of those killed in the crash complained about insensitivity in their treatment - foremost, about how hard it was to get information. The resulting Aviation Disaster Family Assistance acts of 1996 and 1997, which essentially mandate compassion, articulate the obligations of government and airlines in caring for relatives. The NTSB is charged with seeing to it.

Because the World Wide Web emerged during the course of the investigation, ease of access to documents generated by investigators was unprecedented. Previously, one had to inspect factual reports and evidence at the NTSB headquarters in Washington, D.C.

The access to documents and the general connectedness the Web affords also enabled vigorous scrutiny of the investigation by critics. Having examined the NTSB documents, some contend the theory that an internal malfunction sparked the explosion is a sham - that the government is covering up a missile strike or some other nefarious act.

The NTSB says that's nonsense. The FBI ruled out a missile or bomb almost three years ago. Even Boeing engineers concede the explosion was likely caused by something related either to design or maintenance, although the company's lawyers have contended a bomb or missile cannot be ruled out with certainty.

But the skeptics, many of them former or current aviators, have generated their own analyses that nitpick NTSB findings, and they contend the safety board has not been completely forthcoming - Internet access notwithstanding. Boeing, they say, can't afford to upset the government, its biggest single customer.

The Internet-enabled dissent could be one reason the investigation has taken so long.

Sources say the report this week will include a lot of research that ruled out external causes and discuss it in greater detail than the NTSB otherwise might. Besides a missile or bomb, electromagnetic radio interference and even the chances that a meteor caused the explosion will be dealt with.

Latent problems pose risk

What the NTSB thinks really happened supports the notion that modern air crashes are products of latent problems no one thought of before - the most-obvious flaws in airplane design having been figured out long ago.

On July 17, 1996, at 8:18 p.m., Flight 800 took off from John F. Kennedy International Airport for Paris. It was a clear evening, so there were many eyewitnesses on the south shore of Long Island who saw or heard something. Eight miles south of the island, while climbing through 13,700 feet, Flight 800 suddenly exploded and broke apart.

Investigators later learned that the plane's center wing tank, which is in the fuselage where the wings join, was virtually empty - it usually is except for the longest flights - and it had been baking in the summer heat over a period of hours while the plane sat at the gate at the airport.

Moreover, the air-conditioning units on most Boeing planes are located directly below the tank. Their motors radiate heat. It makes sense that this heat would increase the volatility of the fuel-air mixture in the empty tank, but it took years of testing to fully document the phenomenon.

So what sparked the explosion?

Malfunction suspected

Besides exploring and ruling out fire, static electricity and pump problems, investigators came up with a number of scenarios involving short circuits or other electrical malfunctions that could have introduced an errant surge of high energy into the tank. Those scenarios involve the surge of power entering through a low-energy circuit that electrically measures fuel level.

Further, ignition of the warmed fuel vapor would have required an electrical arc inside the tank - electricity jumping across a gap - perhaps enabled by debris or worn wire.

In other words, a series of astronomically unlikely things would have had to go wrong at precisely the same moment for an explosion to occur.

Because that area of the plane was blown to bits, there is no physical evidence of a malfunction on Flight 800 that could have caused the spark. The NTSB settled on an electrically caused spark as a likely cause after ruling everything else out, analyzing the breakup of the wreckage and demonstrating in tests that it could have happened that way.

Conventional wisdom once held that errant ignition sources such as sparks could be eliminated through smart design. Boeing says that's still a safe standard. But if an electrical malfunction blew up Flight 800, it's obviously not a fail-safe design philosophy.

So the FAA has directed a committee of industry representatives to study ways to lessen the hazard of fumes in tanks. Take away the spark or take away the fumes it ignites: Either way, disaster is averted. "Inerting" tanks by replacing the fuel-air mixture with nitrogen gas is a possibility.

Probe breaks records

The NTSB estimates the cost of the Flight 800 investigation was about $35 million, which includes the unprecedented reconstruction of much of the plane's fuselage in a Long Island hangar. Boeing says it has spent $32 million in its role as an official party to the investigation.

Besides the record time it took and the unprecedented cost, the investigation of TWA Flight 800 was the first crash probe involving extensive underwater recovery of human remains and wreckage. The lessons learned by the NTSB, the Navy and the Coast Guard from Flight 800 were applied in similar recovery efforts after the crashes into the sea of Swissair Flight 111 in 1998, EgyptAir Flight 990 last year and Alaska Airlines Flight 261 this year.

The five members of the safety board - Chairman Jim Hall, John Hammerschmidt, John Goglia, George Black and Carol Carmody - will consider a draft report written by the NTSB staff, discuss changes, and either request a rewrite or adopt the report's findings. The draft reportedly is about 600 pages, double-spaced.

Copies of the draft, which safety board members have been studying for about a month, will not be available during the proceedings, and at the end only a summary report will be issued. The full report will be published and made public later.

Besides a formal finding of probable cause, the report will likely include new recommendations to the FAA and possibly other parties to prevent future accidents. Over the years of the investigation, the NTSB has issued such recommendations, which helped inspire some of the design changes the FAA has ordered.

The two-day meeting will be held in the NTSB's new boardroom, a 300-seat former movie theater in the L'Enfant Plaza government-office complex where the safety board is headquartered.

Proceedings begin at 6:30 a.m. Seattle time on Tuesday and will be broadcast live on the safety board's Web site at

Chuck Taylor's phone number is 206-464-2465. His e-mail address is


NTSB meeting

The NTSB on Tuesday begins a two-day meeting to consider the final report on TWA Flight 800. The Seattle Times will report from the meeting in Washington, D.C.

Copyright (c) 2000 Seattle Times Company, All Rights Reserved.


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