Meanwhile, the NTSB says that earlier fixes aimed at preventing sparks from igniting vapors in aircraft fuel tanks don't work. In a news release last week, the board said the wing tank of a Transmile Boeing 727 exploded even though it had been properly fitted with electrical shields designed to prevent the electrical arcing that most likely ignited the vapors. An airworthiness directive required the wiring harness in question to be inspected, repaired and then wrapped in plastic before being returned to the conduit in the wing tank. "This accident illustrates that ignition sources continue to exist and fuel tank explosions continue to occur in both wing and center wing fuel tanks despite the corrective efforts of government regulators and industry," the board concluded. The accident happened while the plane was on the ground at Bangalore, India, and no one was hurt. But the blast wrecked the wing and the plane would have crashed had it been airborne, the NTSB said. The board continues to press the FAA to require systems that displace the explosive vapors in fuel tanks with inert gases, such as nitrogen. Boeing has already designed and installed systems on several aircraft and can retrofit airliners for between $100,000 and $300,000 each, depending on the size.
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