Monday, July 28, 2008
Reducing the Risk of Jetliner Fuel Tank Explosions
The National Transportation Safety Board (NTSB) concluded in 2000 that heated, highly explosive fumes in the Boeing 747's center tank ignited and that most other large jets were vulnerable to such explosions. The NTSB recommended that all large civil transports be equipped with a device to inert fuel tanks.
The nation’s crash-strapped air carriers opposed the plan, arguing it was too expensive. But an FAA scientist in 2002 developed an unexpected scientific breakthrough that replaces oxygen in the fuel tank with inert gas, which effectively prevents the potential ignition of flammable vapors.
“This final rule amends FAA regulations that require operators and manufacturers of transport category airplanes to take steps that, in combination with other required actions, should greatly reduce the chances of a catastrophic fuel tank explosion. The final rule does not direct the adoption of specific inerting technology either by manufacturers or operators, but establishes a performance-based set of requirements that set acceptable flammability exposure values in tanks most prone to explosion or require the installation of an ignition mitigation means in an affected fuel tank. Technology now provides a variety of commercially feasible methods to accomplish these vital safety objectives,” according to the FAA.
“Technology now exists that can prevent ignition of flammable fuel vapors by reducing their oxygen concentration below the level that will support combustion. By making the vapors ‘inert,’ we can significantly reduce the likelihood of an explosion when a fire source is introduced to the fuel tank. FAA-developed prototype onboard fuel tank inerting systems have been successfully flight tested on Airbus A320 and Boeing 747 and 737 airplanes. We have also approved inerting systems for the Boeing 747 and 737 airplanes, and two airplanes of each model type have performed as expected during airline in-service evaluations. Boeing plans to install these systems on all new production airplanes,” the FAA added
Within two years, all new aircraft must include the technology designed to significantly reduce the risk of center fuel tank fires as part of a final rule announced by the U.S. Department of Transportation. In addition, within ten years, large passenger transports built after 1992 must be retrofitted with technology designed to keep center fuel tanks from catching fire.
The cost of installing the new technology is estimated to range from $92,000 to $311,000 per aircraft, depending on its size, a far cry from the estimated $20 billion that an industry group had previously estimated for the overall cost.
The U.S. aircraft that must be retrofitted include: 2,730 aircraft belonging to the A320 family of 900 airplanes, 50 A330s, 965 Boeing 737s, 60 Boeing 747s, 475 Boeing 757s, 150 Boeing 767s and 130 Boeing 777s.
“I recognize that this is a challenging time for commercial aviation,” said DOT Secretary Mary Peters. “But there is no doubt that another crash like TWA 800 would pose a far greater challenge.”
Added Peters: “We want to do everything possible to make sure safety examiners won’t have to investigate another plane shattered by an exploding tank. We can’t change the past, but we can make the future safer for thousands of air travelers, and this rule does just that.”
NTSB Chairman Mark V. Rosenker said "from tragedy we draw knowledge to improve safety and today's announcement represents a significant step toward avoiding future aviation accidents of this nature."
“Today’s rule will add another layer of safety reducing the chance that the vapors in the tank will ignite, even if there is a spark,” said FAA Acting Administrator Robert A. Sturgell.
He called the rulemaking “another step forward on what has been a long journey of investigation, discovery, innovation and cooperation. The NTSB deserves particular recognition for completing one of history’s most challenging and comprehensive aircraft accident investigations, for identifying this critical safety issue and for being steadfast advocates for the safety improvement we are realizing today.”