It is expected that airlines must retrofit existing aircraft in the U.S. commercial fleet, which now number more than 3000, within 7 years after the rule takes effect.

This technology, developed under NASA's Aviation Safety Program (ASP), is intended to reduce flammability and explosion risk within an airplane's heated center wing tank, which is located under the passenger cabin between the wings. Dr. Clarence Chang of Glenn's Combustion Branch leads the team that is conducting studies to improve aircraft fuel tank safety.

Reducing the oxygen concentration from 21 to 10 to 12 percent will prevent fuel tank ignition. Dr. Marty Rabinowitz, Combustion Branch, is working on the fuel reformulations to make the fuel harder to ignite to reduce the inerting requirement,

and Dr. Gary Hunter, Sensors and Electronics Technology Branch, rounds out the team with research on sensors that detect the levels of gases in a tank.

"We know that in order to initiate combustion, three ingredients are needed: oxygen, fuel vapor, and an ignition source," said Chang. "We can't remove the fuel from the tank and we've already removed just about all the known ignition sources. Since we can't remove the ignition sources we don't know about, decreasing the oxygen level is currently the easiest way to avoid fuel tank explosion."

The explosion of TWA 800 over Long Island Sound in 1996, killing all 230 people aboard, spurred NASA's research on a workable solution for neutralizing fuel tank potential for fire and explosion. A number of other initially unexplainable explosions later determined to be fuel tank explosions, led to National Transportation Safety Board recommendations on the need for an On Board Inert Gas Generation System (OBIGGS).

The events of September 11, 2001, however, were the catalyst for the FAA and NASA's effort to apply this technology, previously limited to use in military aircraft, to develop a more affordable safety device for commercial aircraft.

"The military already uses nitrogen or halon to inert their tanks. They began testing this concept near the end of WWII," said Chang. "In later years, very expensive and large safety devices were installed on combat planes. We're working on something smaller and more affordable, but equally efficient for commercial planes, although the threat levels are very different."

Researchers have been working since September 2003 under four NASA contracts to determine the feasibility of the next-generation hardware, with Creare Engineering, Inc., of Hanover, NH; Essex Cryogenics, Inc., of St. Louis, MO; Honeywell Environmental Controls Systems of Torrance, CA; and Valcor Engineering of Springfield, NJ. Valcor and Honeywell were retained to develop the high-temperature air separation modules (ASM) for the nextgeneration OBIGGS.

The next step is to determine that the hardware works onboard an airliner. Hardware and technology demonstrations of the current-generation ASM OBIGGS developed by the FAA were conducted in October 2003, and more demonstrations are planned for mid-May of this year. Arrangements have been made with the NASA Johnson Space Center to fly the inerting hardware on the Boeing 747 used for transporting the space shuttle.

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