sat, october 30, 1999
FAA alters fuel-tank rules
Changes aim to cut chance of explosion
By Sylvia Adcock
Newsday
The Federal Aviation Administration will 'require design changes in aircraft built in the future to minimize buildup of flammable vapors in the fuel tanks, a measure that stems from the 1996 explosion of TWA Flight 800.
And in a plan that will affect 6,000 commercial aircraft, the agency will tell manufacturers to spend a year revalidating the designs of the fuel-tank systems and developing mandatory inspection and maintenance procedures to prevent fuel-tank explosions.
"This action represents a ftindamental change in how fuel tanks are designed, maintained and operated," FAA Administrator Jane Garvey said Thursday.
The proposed rules, which are expected to take effect next year, will affect 36 models of aircraft made by a dozen manufacturers, including most models of Boeing and Airbus planes - the most popular commercial aircraft in the world. Manufacturers will have 12 months to do design reviews and come up with new inspection and maintenance plans, and all new aircraft - either on, the drawing table or the assembly line - will have to comply with new standards to minimize fuel vapors.
On new planes, manufacturers will need to change long-standing designs to keep air-conditioning packs - often located beneath the center fuel tanks - from heating up the vapors to an explosive level. Alternatively, manufacturers could provide ways to prevent catastrophic damage to the plane if a fuel-tank explosion did occur.
The actions come almost three years after the National Transportation Safety Board issued recommendations to keep flammable vapors out of new and existing aircraft. For years, the FAA and the industry have assumed that they could prevent any sparks from entering fuel tanks, making them safe even though they almost always contain flammable vapors during flight. But the Flight 800 explosion killed 230 people,
The new maintenance and inspection procedures are designed to catch such problems as frayed wiring, worn pumps and broken grounding straps that allow a spark to get into the tank.
In its documentation, the FAA listed 29 ways that sparks could enter the tank - all of them scenarios that have been found on in-service airliners "contrary to policies intended to preclude the development of ignition sources within airplane fuel-tank systems."
The new rules will cost $170 million over 10 years, including costs to manufacturers and costs to airlines for new maintenance procedures. The FAA seldom asks manufacturers to revalidate a design on this scale.
"It is unusual in this magnitude," Elizabeth Erickson, the FAA's director of aircraft certification, said. "I don't know that we've done something quite so in-depth."
The regulation on new aircraft means that most of the jet planes flying today would not pass muster if they were being certified next year, when the rule is expected to take effect. In documents submitted to the Federal Register, the FAA said that reviews of the Boeing 747 design after the crash of Flight 800 showed that certain failure modes had not been given enough consideration.
But Erickson insisted that the FAA was not applying different standards to existing airplanes and those built in the future. As a practical matter, she. said, it's more feasible to make-certain changes in aircraft before they are built than after they are finished:
"The existing fleet issues are very significant," Erickson said.
"We're requiring an in-depth design review and significant new maintenance tasks. . . . . . But for existing airplanes, there isn't, right now anyway, a feasible solution to addressing fuel vapors."
The agency is studying a system to pump nitrogen into fuel tanks on the ground, which would render the fuel vapors not flammable.
In the meantime, the commercial fleet-of airliners will be getting new maintenance and inspection procedures to keep ignition sources out as the plane ages.