Although pilots are warned not to allow fuel tank temperatures to reach explosive levels, there is no temperature gauge in the center fuel tank. The NTSB wants gauges installed. Build new planes with insulation between heat sources and the fuel tanks. Flight 800 investigators are still trolling waters off Long Island for a missing fuel pump they say could have overheated in the tank. Design inert gas systems for new planes to force dangerous fumes out of tanks.
Military planes have such systems, but airlines say they are too heavy, costly and hard to maintain.
Monitor the temperature in the tanks closely and avoid flying with a tank that is near-empty. The TWA 747 handbook says the air conditioning system can increase the temperature of the center tank by up to 20 degrees. A test in August by Boeing found air conditioning increased the temperature by 40 degrees, enough to have made the TWA tank explosive. The board wants manuals updated with the new findings. Beginning Monday, the FAA has 90 days to weigh the benefits of the NTSB's recommendations against how much the changes would cost.