An estimated 950 Airbus and 2,327 Boeing aircraft operated by US airlines will be required to reduce the flammability levels of fuel tank vapours under a US Federal Aviation Administration notice of proposed rulemaking (NPRM) issued last week.
The proposal is designed to reduce the likelihood of a repeat of the three fuel tank explosions over the past 14 years – including the 1996 TWA 800 accident – that together have resulted in 346 fatalities.
Because the FAA would require the retrofit of more than 3,200 Airbus and Boeing aircraft with centre wing fuel tanks over seven years, Airbus A320 models and Boeing 737s and 747s would be retrofitted first, says the agency. Airbus A330s, and Boeing 757s, 767s and 777s are included in the NPRM, as are new large aircraft.
The preliminary cost estimate for the US fleet is roughly $808 million over 49 years, including $313 million for retrofitting the existing fleet, says the FAA.
One possible solution allowed by the rule – which the FAA has been avidly promoting – is fuel tank inerting. In May 2002, FAA engineers unveiled a prototype to replace oxygen in the fuel tank with inert gas, which prevents the potential ignition of flammable vapours. Boeing has since developed its own system, which will be installed on new aircraft.
A nitrogen generating system developed by Honeywell for fuel-tank inerting was certificated by Boeing in the 747 earlier this year, while Hamilton Sundstrand is developing the system that will be standard on the 787.
The agency says, however, that it will also consider data supporting other means of compliance.
“This proposed rule is the next step to close the book on fuel tank explosions,” says FAA administrator Marion Blakey. “We’re proposing to increase the level of aircraft safety by reducing the potentially explosive ingredient of flammable fuel vapours.”
Addressing fuel tank vapours has been on the US National Transportation Safety Board’s “Most Wanted Safety Improvements” list of recommended actions to be completed by the FAA.
Blakey points out that the NPRM builds on more than 70 directives during the past nine years designed to eliminate ignition sources and to change fuel tank design and maintenance.
Previous directives have addressed issues such as pump manufacturing discrepancies, wire chafing, and protection of the fuel quantity indication system.
MARY KIRBY/PHILADELPHIA
Source: Flight International
