The Federal Aviation Administration has proposed regulations intended to make jetliner fuel systems less vulnerable to fire and explosion.
The unusual move raises the standards for new designs and, to a lesser degree, affects 6,000 U.S.-registered planes ranging from Boeing jumbo jets to De Havilland Dash 7 turboprops. The regulations come four years after the explosion and crash of a TWA Boeing 747 prompted an ongoing examination of fuel and wiring hazards.
If adopted, the regulations would create a new flammability standard for new plane designs, which the FAA said would minimize the volatility of vapors in jet fuel tanks.
Manufacturers also would have to take steps to ensure that, if ignition of vapors does occur, it would not cause catastrophic damage.
And the new regulations would require manufacturers to review the designs of existing airplane models to ensure system failures could not create ignition sources in fuel tanks.
The proposed regulations are the first comprehensive action taken by the FAA to remedy what is believed to be an extremely remote hazard–the ignition of fuel vapors by spark or fire inside tanks, pumps and pipes.
“The existing regulations provide a high level of safety in fuel tanks,” said Beth Erickson, director of the FAA’s Aircraft Certification Service, last month in Washington, D.C. “But during the course of the accident investigation, we found that there are unanticipated failures that could lead to an ignition source.”
The 1995 explosion of the center fuel tank of TWA Flight 800, a 25-year-old 747-100, killed 230 people off Long Island, N.Y. Investigators may never be able to determine what sparked the explosion, but the accident awakened the industry to the fact that jet fuel-tank fumes are more volatile than thought.
Before that the only known passenger-aircraft fuel-tank explosion attributed to an internal source involved a Philippine Airlines Boeing 737-300, which blew up on the ground in Manila in 1990. The precise ignition source in that accident was never determined with certainty.
The proposed new FAA rules would:
– Require a review of fuel-tank systems on existing models to ensure that fires and explosions will not occur. That requirement would apply to manufacturers such as Boeing and companies that modify airplane systems after they leave the factory.
– Require new inspection and maintenance procedures to spot and fix potential problems in old and new aircraft. Debris in fuel tanks and worn electrical components have been determined to be potentially hazardous.
– Impose standards on new aircraft designs, requiring that fuel tanks minimize the development of flammable vapors or that alternate means be proposed to limit the effects if fuel vapors are ignited.
The FAA estimates that the cost over 10 years of the assessment and maintenance of the present fleet would be about $170 million. The benefits, the agency said, would be the prevention of an estimated 75 to 90 percent of fuel-tank explosions.
The cost of the requirements for new airplane designs could not be determined, the agency said.
The proposed design and maintenance requirements answer a 3-year-old National Transportation Safety Board call for design or operational changes to reduce the flammability of fuel-air mixtures in airliner fuel tanks.
Last month, in formal correspondence, the NTSB chastised the FAA for not acting on the recommendations it issued in 1996 after the TWA crash.
The aviation industry has participated in the FAA study of fuel-system dangers but resisted a number of suggested ways of making fuel vapors inert, citing their high cost.
Airworthiness directives of recent years, covering wiring in and near tanks and fuel pumps, address at least some of the issues raised by the new design requirements.
It was not immediately clear how the new requirements, if adopted, might affect manufacturers such as Boeing and Airbus Industrie. Those companies are certain to submit detailed feedback to the FAA before it adopts the new rules. The public-comment period closes Jan. 27.
The NTSB continues to investigate the crash of Flight 800 into the Atlantic Ocean near Long Island. Official findings are expected next year.
Government and the aviation industry, including Boeing, agree that the plane’s center wing fuel tank exploded.
There is no consensus, however, as to what might have caused a spark to ignite fumes in the nearly empty tank. The plane was at 13,500 feet and had just departed New York for Paris.
A leading theory in the crash probe holds that a high level of energy, perhaps induced by electromagnetic interference or a short circuit from other wiring, could have entered the tank through fuel-measuring system wires.
The presence of debris on a fuel-measuring probe could have created an arc of electricity, igniting fumes that had been heated for hours while the plane sat on the hot ramp at John F. Kennedy International Airport. The 747 fuel-measuring system normally uses very low energy to send information from submerged probes to the flight deck.
High-energy electricity from high-voltage lines, the FAA has said, could be introduced into adjacent low-voltage fuel-measuring wires outside a tank, through a short circuit involving damaged wires or by electromagnetic interference.
