Industry Steps Forward on Fuel Tank Inerting

Air Safety Week, August 4, 2008

Twelve years after TWA Flight 800 exploded off Long Island on July 17, 1996, killing all 230 people aboard the Boeing 747, the Federal Aviation Administration (FAA) has issued a final rule aimed at reducing the threat of fuel tank explosions aboard commercial passenger transports.

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.

"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.

It said technology now exists that can prevent ignition of flammable fuel vapors by reducing their oxygen concentration below the level that will support combustion. The likelihood of an explosion when a fire source is introduced to the fuel tank is reduced by making the vapors 'inert'.

FAA-developed prototype onboard fuel tank inerting systems have been successfully flight tested on Airbus A320 and Boeing 747 and 737 airplanes. The FAA has approved inerting systems for the Boeing 747 and 737, with two aircraft of each model type performing as expected during airline in-service evaluations. Boeing plans to install these systems on all new production airplanes.

Within two years, all new aircraft must include the technology designed to significantly reduce the risk of center fuel tank fires as part of the final rule. 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 2,730 U.S. aircraft that must be retrofitted include: 900 A-320s, 50 A-330s, 965 Boeing 737s, 60 Boeing 747s, 475 Boeing 757s, 150 Boeing 767s and 130 Boeing 777s.

Industry officials believe the safety modifications will cost an estimated $1 billion just for US-registered jetliners. Many foreign air carriers voluntarily adhere to U.S. air safety directives and further nitrogen generation system sales outside the United States can be expected.

There are at least two companies claiming to have developed nitrogen generation systems that comply with the new federal safety directive.

Honeywell says it has now delivered Nitrogen Generation Systems (NGS) for the Boeing Next-Generation 737 aircraft, which delivers nitrogen-enriched air to the aircraft center fuel tank, significantly reducing flammability and increasing commercial aircraft safety.

Honeywell claims that its NGS is the first fully FAA-certified fuel tank inerting solution for commercial transport aircraft. Honeywell is developing additional systems for the Boeing 737-300/400/500, 777-200/300, 747-400, and the 747-800 aircraft.

Honeywell in 2004 was selected by Boeing to develop a Nitrogen Generation System for Boeing 737, 747, 767 and 777 aircraft. "We have applied our expertise in thermal management and systems integration to provide a solution that can be adapted for new production aircraft or for retrofit onto existing aircraft," according to a company statement.

That year Honeywell delivered an NGS test bed to Boeing for ground and flight testing on a 737 aircraft. In mid-2003, Honeywell provided a NGS test bed that was used on a to Boeing 747.

Parker Aerospace is providing Honeywell with the air separation module for the system.

Honeywell's NGS is an on-board inert gas generation system (OBIGGS). The OBIGGS process starts with processed air, which is conditioned to optimum pressure and temperature and then passed through a series of Air Separation Modules (ASM). The ASMs separate the oxygen from the process air through a permeable gas separation membrane, producing primarily nitrogen-enriched air (NEA). The NEA is delivered to the fuel tank where it displaces the flammable fuel/air mixture to reduce the risk of an explosion or fire.

Boeing has reportedly developed its own NGS system for the 787 Dreamliner. Honeywell is reportedly working to put a deal together with Airbus.