Boeing 737s Get Fuel Tank AD

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The aftereffects of the NTSB's conclusions about TWA Flight 800 live on, as Boeing continues to address the board's suspicion of an exploding fuel tank. This week, the FAA issued a final rule for Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. The FAA claims that the actions specified by this Airworthiness Directive are intended to prevent fluid contamination inside the fueling float switch or chafing of the wiring to the in-tank conduit, which could generate an ignition source and consequent fire and explosion in the fuel tank. The amendment requires replacement of the existing fueling float switch and conduit assemblies in the main and center fuel tanks with new, improved assemblies. Of course, this is not the first measure taken to combat this fuel-vapor issue, as the FAA and NTSB have met with Boeing and other industry groups to work on various remedies. Just last month, the feds unveiled a 160-pound onboard nitrogen generator intended to pump the inert gas into emptying fuel tanks. The new system takes ambient air and reduces the oxygen content from 21 percent to 12 percent. The oxygen-reduced air makes a much less combustible mixture in the tank. Earlier proposals for this type of system, dating as far back as 1997, were criticized for high cost and weight, but the new system apparently alleviates those concerns.