This article from NYTimes.com has been sent to you by psa188@juno.com. F.A.A. Tests System to Avoid Fuel Explosions December 13, 2002 By MATTHEW L. WALD EGG HARBOR, N.J., Dec. 12 - The Federal Aviation Administration said today that it had developed a simple lightweight system for preventing fuel tank explosions like the one that destroyed T.W.A. Flight 800 in 1996. The system uses a combination of equipment already on the aircraft and parts that are in common use in the chemical industry. Since it became clear in late 1996 that the cause of the Flight 800 disaster was a center fuel tank explosion, safety experts have made tank improvements a top priority. Some flaws that could introduce a spark have been addressed on Boeing 747's, like Flight 800, and in other models, notably Boeing 737's. But there has been no overall solution to the problem of the potentially explosive mix of fuel and air in near-empty tanks. The new system, installed on an old 747 at the aviation agency's Technical Center at Atlantic City Airport here, separates air into oxygen and nitrogen, and pumps the nitrogen into the air space in the tanks, to assure an inert condition that could not support fire or explosion even if fuel and a spark were present. "This is a major milestone for us," Nicholas Sabatini, the agency's associate administrator for regulation and certification, said. Some industry experts were more cautious, noting that the agency had no estimate of what the system would cost. But Boeing hopes to fly the system for testing next year. The fumes in the almost-empty center tank on Flight 800 exploded. Safety investigators later determined that the mixture of air and fuel in such tanks is frequently capable of supporting combustion. The spark's source was never found. Officials said today that if oxygen could be excluded from the tanks, some potential sources of ignition would be irrelevant. At one point the agency focused on changing the fuel so it is harder to ignite, and later on "inerting" the tanks by pumping nitrogen into them while planes are on the ground. It backed away from both ideas when the industries involved said they would be too expensive. But on-board "inerting" shows some promise, experts say. Boeing recently applied for permission to install such a system on planes it builds. A Boeing spokeswoman, Liz Verdier, said, "There are a lot of hurdles." Among the problems, Ms. Verdier said, is that the agency has not stated in any detail what requirements such a system would have to meet. And it would have to be "reliable, maintainable and practical," she said. The agency's device has evident attractions; it weighs only 160 pounds and has hardly any moving parts. At the National Transportation Safety Board, Carol Carmody, the acting chairwoman, said, "We are most encouraged that the F.A.A. had taken this on and made such progress." She said that in December 1996, five months after the T.W.A. accident, the board recommended to the agency that it consider "inerting" but that three and a half years later the agency said it would be too expensive. In the last few months, however, the agency has made two revisions that led to its change of heart. The first was to relax the goal for reducing oxygen in the air space in the tank. At first, the agency convened an industry committee to work on the problem and told the committee that the amount of oxygen should be reduced to 10 percent. (Ordinary air has about 21 percent oxygen and about 78 percent nitrogen.) This year the agency decided that it could permit 12 percent oxygen and still eliminate most of the threat of explosion. The difference seems small, but a system that will achieve 12 percent is far smaller and lighter than a system that must achieve 10 percent, experts say. The second change was in making use of on-board equipment, specifically compressed air ducts. The engines on big jets compress air to use in the engine itself, but the planes bleed off some of that to pressurize the cabin. The agency's system takes some of that compressed air to power the system that makes nitrogen. The heart of the system is a three-foot cylinder filled with a polymer membrane that allows oxygen to pass through more readily than nitrogen. The oxygen is allowed out through vents on the side of the cylinder and is dumped overboard; the nitrogen comes out the base and is routed to the fuel tank. The system produces nitrogen of varying purity, depending on how much gas it is called upon to produce. In cruise flight, it can produce a mixture that is 99 percent nitrogen, and can gradually raise the nitrogen level in the tanks very high. As the plane descends into denser air, the tank has a tendency to "inhale," and the system must put out more gas to prevent the empty space in the tank from filling with regular air; at that point, the system puts out a mixture that is only 88 percent nitrogen. But that is high enough to keep the tank inert on landing, and it is still inert on the next takeoff, said Ivor Thomas, the aviation agency's chief scientific and technical adviser for fuel systems. Agency officials said that military planes carry inerting systems that can push the oxygen content down to 8 percent or 10 percent but that these weigh thousands of pounds. A reason for stricter limits in military planes is that they may face much higher-energy sources of ignition; rather than stray sparks from frayed wires, they may face enemy fire. http://www.nytimes.com/2002/12/13/national/13PLAN.html?ex=1040798358&ei=1&en=0e33768c746b7722 HOW TO ADVERTISE --------------------------------- For information on advertising in e-mail newsletters or other creative advertising opportunities with The New York Times on the Web, please contact onlinesales@nytimes.com or visit our online media kit at http://www.nytimes.com/adinfo For general information about NYTimes.com, write to help@nytimes.com. Copyright 2002 The New York Times Company