The FAA did not consider lightweight inerting systems for commercial jets until the 1996 crash of TWA Flight 800 . The crash was blamed on an explosion in the center wing fuel tank of the Boeing 747 used in the flight . This tank is normally used only on very long flights , and little fuel was present in the tank at the time of the explosion . A small amount of fuel in a tank is more dangerous than a large amount , since heat entering the fuel tank with residual fuel causes the fuel to increase in temperature faster and evaporate . This causes the ullage fuel-to-air ratio to increase rapidly and exceed the lower flammability limit . A large quantity of fuel ( high mass loading ) in the fuel tank can retain the heat energy and slow the fuel evaporation rate . The explosion of a Thai Airways International Boeing 737 in 2001 and a Philippine Airlines 737 in 1990 also occurred in a tank that had residual fuel . The above three explosions occurred on a warm day , in the center wing tank ( CWT ) that is within the contours of the fuselage . These fuel tanks are located in the vicinity of external equipment that inadvertently heats the fuel tanks . The National Transportation Safety Board 's ( NTSB ) final report on the crash of the TWA 747 concluded “ The fuel air vapor in the ullage of the TWA flight 800 CWT was flammable at the time of the accident . ” NTSB identified “ Elimination of Explosive Mixture in Fuel tanks in Transport Category Aircraft ” as Number 1 item on its Most Wanted List in 1997
Philippine Airlines 737 in 1990
Philippine Airlines Flight 143
Inerting system