page_title: TWA Flight 800
section_title: Fuel-air explosion in the center wing fuel tank
hierarchical_section_title: TWA Flight 800 / Further investigation and analysis / Possible causes of the in-flight breakup / Fuel-air explosion in the center wing fuel tank
caption_attribution_description: Schematic/location of center wing fuel tank of a 747
context_page_description: Trans World Airlines Flight 800 was a Boeing 747-100 that exploded and crashed into the Atlantic Ocean near East Moriches, New York, on July 17, 1996, at about 8:31 p.m. EDT, 12 minutes after takeoff from John F. Kennedy International Airport on a scheduled international passenger flight to Rome, with a stopover in Paris. All 230 people on board died in the crash; it is the third-deadliest aviation accident in U.S. history.
  Accident investigators from the National Transportation Safety Board traveled to the scene, arriving the following morning amid speculation that a terrorist attack was the cause of the crash. Consequently, the Federal Bureau of Investigation and New York Police Department Joint Terrorism Task Force initiated a parallel criminal investigation. Sixteen months later, the JTTF announced that no evidence of a criminal act had been found and closed its active investigation.
  The four-year NTSB investigation concluded with the approval of the Aircraft Accident Report on August 23, 2000, ending the most extensive, complex and costly air disaster investigation in U.S. history to that time.
context_section_description: In order to evaluate the sequence of structural breakup of the airplane, the NTSB formed the Sequencing Group, which examined individual pieces of the recovered structure, two-dimensional reconstructions or layouts of sections of the airplane, and various-sized three-dimensional reconstructions of portions of the airplane. In addition, the locations of pieces of wreckage at the time of recovery and differences in fire effects on pieces that are normally adjacent to each other were evaluated. The Sequencing Group concluded that the first event in the breakup sequence was a fracture in the wing center section of the aircraft, caused by an "overpressure event" in the center wing fuel tank (CWT). An overpressure event was defined as a rapid increase in pressure resulting in failure of the structure of the CWT.
  Because there was no evidence that an explosive device detonated in this (or any other) area of the airplane, this overpressure event could only have been caused by a fuel/air explosion in the CWT. There were 50 US gal (190 L) of fuel in the CWT of TWA 800; tests recreating the conditions of the flight showed the combination of liquid fuel and fuel/air vapor to be flammable. A major reason for the flammability of the fuel/air vapor in the CWT of the 747 was the large amount of heat generated and transferred to the CWT by air conditioning packs located directly below the tank; with the CWT temperature raised to a sufficient level, a single ignition source could cause an explosion.
  Computer modeling and scale-model testing were used to predict and demonstrate how an explosion would progress in a 747 CWT. During this time, quenching was identified as an issue, where the explosion would extinguish itself as it passed through the complex structure of the CWT. Because the research data regarding quenching was limited, a complete understanding of quenching behavior was not possible, and the issue of quenching remained unresolved.
  In order to better determine whether a fuel/air vapor explosion in the CWT would generate sufficient pressure to break apart the fuel tank and lead to the destruction of the airplane, tests were conducted in July and August 1997, using a retired Air France 747 at Bruntingthorpe Airfield, England. These tests simulated a fuel/air explosion in the CWT by igniting a propane/air mixture; this resulted in the failure of the tank structure due to overpressure. While the NTSB acknowledged that the test conditions at Bruntingthorpe were not fully comparable to the conditions that existed on TWA 800 at the time of the accident, previous fuel explosions in the CWTs of commercial airliners such as Avianca Flight 203 and Philippine Airlines Flight 143 confirmed that a CWT explosion could break apart the fuel tank and lead to the destruction of an airplane.
  Ultimately, based on "the accident airplane's breakup sequence; wreckage damage characteristics; scientific tests and research on fuels, fuel tank explosions, and the conditions in the CWT at the time of the accident; and analysis of witness information," the NTSB concluded that "the TWA flight 800 in-flight breakup was initiated by a fuel/air explosion in the CWT."
caption: The wing center section of a Boeing 747-100, including the CWT.[1](fig. 4a, p. 13)
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