Thai 737 explosion prompts FAA rule on fuel pumps
WASHINGTON (CNN) -- The Federal Aviation Administration is ordering U.S. airlines not to use fuel pumps on Boeing 737s when the fuel tanks are mostly empty.
The order was prompted by the explosion of a Thai Airways International jetliner in Bangkok two months ago.
While the cause of the Thai explosion is still not known, investigators say it appears that the Boeing 737-400's center wing fuel tank's pumps were operating dry -- meaning no fuel was passing through them -- at the time of the explosion. That could result in overheating and excessive wear on bearings, and could ultimately lead to a fuel tank explosion, the FAA said.
The FAA rule is expected to have little impact on U.S. airlines, which already follow the manufacturer's recommendation not to run pumps for extended periods when tanks are dry. But it is expected to prompt authorities overseas to more diligently adhere to Boeing's guidance. Overseas aviation authorities typically adopt FAA rules.
The Thai Airways plane -- a 9-year-old Boeing 737-400 -- exploded March 3 as it was sitting at a gate at Don Muang International Airport in Bangkok. A flight attendant aboard the plane was killed and seven people were injured.
The plane exploded just 35 minutes before it was to depart with the prime minister of Thailand, prompting speculation that a bomb had been planted in an attempt to assassinate the leader. But investigators say initial tests have shown no signs of a bomb.
In 1990, a Boeing 737-300 had a similar center wing tank explosion, the FAA said. The ignition source was never determined, but the center wing tanks were operating dry at the time of the explosion, the FAA said.
Earlier this month, after investigators learned details of the Bangkok explosion, the Boeing Co. notified operators of 737s worldwide that it was reiterating its recommendation not to use fuel pumps when there is less than 1,000 pounds of fuel in the center wing tank.
The FAA rule gives that recommendation the force of law in the United States. It requires airlines to modify their 737 flight manuals by May 17 to ensure the center tank fuel pumps are not run dry.
Investigators are also looking at any role heat-generating air conditioning units may have played in the Thai blast. The cooling units, located directly under the center wing fuel tank, had been operating for at least 40 minutes while the plane was at the airport gate.
Air conditioners were deemed a "contributing factor" to the explosion of TWA Flight 800 off the coast of Long Island, New York, in the summer of 1996. All 230 people aboard died.
The source of ignition was never determined in that incident, but investigators said a short circuit probably occurred outside the center wing tank, allowing voltage to enter the tank through a wire connected to a fuel gauge.
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