The US Federal Aviation Administration is proposing a new regulation that will have an impact on airliner manufacturers.

Under the new rule, they will have to conduct design reviews and develop new, compulsory maintenance programmes for fuel tank systems on existing aircraft to ensure that mechanical failures could not create ignition sources within the fuel tanks.

The US aviation agency also intends to set new flammability certification standards and maintenance requirements on the fuel systems for newly designed aircraft which minimises the development of combustible vapours in fuel tanks. Airlines will be required to develop and implement an FAA-approved maintenance and inspection programme for fuel tanks on their affected aircraft.

The FAA's notice of proposed rule making (NPRM) results from the mid-air explosion of a Trans World Airlines Boeing 747-100 on 17 July, 1996. Accident investigators have yet to pinpoint the source of the ignition, which caused a blast in the aircraft's centre fuel tank, but they believe that fuel vapours inside the tank were ignited as the result of a mechanical failure.

The US National Transportation Safety Board (NTSB) has recommended costly measures to reduce the risk of future explosions, including potential installation of nitrogen-inerting systems. Last year, an aviation industry advisory group led by Boeing and Airbus Industrie recommended that the FAA continue investigating cost-effective ways to solve the problem while ordering changes for new aircraft designs.

The NPRM represents a fundamental shift in the FAA's thinking. Longstanding certification standards are designed simply to ensure that the ignition of fuel vapour is precluded. FAA Administrator Jane Garvey says: "This action represents a fundamental change in how fuel tanks are designed, maintained and operated."

The special federal aviation regulation affects 6,000 aircraft, including all Airbus Industrie and Boeing transport-category aircraft product lines, the Lockheed L-1011, and regional aircraft. The regulation proposes for manufacturers a 12-month deadline from the effective date of the final rule. Airlines must comply within 18 months. The FAA says the initiatives will cost $170 million over 10 years, an estimate the US Air Transport Association believes is too low.

Source: Flight International