July 10, 1997. Copyright, 1997, Graphic News. All rights reserved

Investigators are close to ruling out definitively a missile as the cause of last yearÕs crash of Flight 800. The Paris-bound Boeing 747, operated by Trans World Airlines, exploded shortly after take-off from New YorkÕs Kennedy Airport on July 17, 1996, killing all 230 people aboard.

Experts have completed their study of a photograph that allegedly showed a missile heading toward TWA Flight 800 and concluded it was simply another jet, probably flying at cruise altitude. Reports of other ÔmissileÕ sightings before the crash, including a mysterious streak of light seen by some 30 witnesses, may actually have been a stream of burning fuel.

Crash investigators have concluded that the disaster was caused by an explosion in the centre fuel tank but have not determined why.

Like many 747s flying transatlantic routes, TWA 800 took off with only residual fuel in the centre tank, relying on fuel in its wing tanks to make the crossing. In addition there had been a delay before take-off and the planeÕs air conditioning units, situated directly beneath the fuel tank, had been in operation for over two hours.

The investigators believe the heat from those machines combined with the effects of a hot day outside increased the temperature by some 40 degrees, until the entire tank was filled with explosive vapour.

As the aircraft gained altitude, lower air pressure allowed oxygen dissolved in the remaining fuel to come out of solution, enriching the deadly mixture.

Eleven and a half minutes into the flight, as the aircraft passed 13,700 feet (4,175 metres), a spark from static, faulty wiring or possibly a terrorist device ignited the vapour.

The first blast stripped a ring of fuselage from the plane, causing the nose section to break off and fall 13,000 feet (3,962 metres) to the sea, according to the new theory.

The remainder of the plane, still powered by four running engines, continued to ascend at a sharp angle until acute stress on the damaged right wing fuel tank caused the final explosion and fireball.

The National Transportation Safety Board (NTSB), which is heading the Flight 800 investigation, has called for centre fuel tank improvements and recommended that to reduce the risk of a fuel-air explosion aircraft should always carry enough fuel to inhibit the build-up of explosive vapours. 

Investigators have now identified 26 fuel tank explosions since 1959. Four years ago a U.S. military KC-135R, also built by Boeing, was destroyed by a centre wing tank explosion while on the ground at Mitchell Field, Milwaukee. Six maintenance engineers were killed. In 1990 a Philippine Airlines Boeing 737 suffered an empty centre wing fuel tank explosion while on the ground at Manila, killing eight. The outside temperature was 95 degrees.

The NTSB has urged the Federal Aviation Administration (FAA) to look at requiring airlines to refuel the centre fuel tank from cooler ground-fuel tanks and suggested close monitoring and management of fuel temperatures in the centre tank.

As far back as 1974 the FAA was advised to fill empty fuel tanks with inert nitrogen gas, which will not sustain a flame, or use polyurethane safety foam as a fire screen, but have taken no action. These design changes have been in use by the military since the Vietnam War but opposed by the commercial airline industry because of the high costs involved.

NTSB officials complain that the FAA knew about centre fuel tank problems prior to July 17, 1996, but had taken no action to prevent them. Commercial operators complain that the extra weight of foam required to inert the tanks of a jumbo would displace as many as eight passengers and baggage on each flight. At a meeting in Seattle on Tuesday (July 8), airline representatives decided to oppose requirements that inert gas be added to fuel tanks to reduce the risk of explosion. To install such a tank on a Boeing 747 could cost $500,000 per aircraft.

NTSB Director of Aviation Safety, Bernard Loeb, says the fuel tank explosion that brought down TWA 800 need not have happened. ÔI think itÕs very important for the public to understand that this accident, or any accident that is similar, does not have to occur...Õ

Loeb confirms that this summer could see other planes take off with vapour in their centre fuel tanks.

ÔI personally hope Ð I know our board feels the same way Ð that the public doesnÕt stand for that. That the public lets the FAA know that this is unacceptable.Õ

/ENDS
Sources: Reuter, Aviation Week and Space Technology