On 17 July 1996, TWA flight 800 exploded twelve minutes after leaving New York for Paris and fell into the Atlantic off Long Island. All 230 people aboard died. Hundreds of witnesses on the ground reported seeing a streak of light rising towards the aircraft, and the missile theory took hold immediately and has never entirely gone away.
What the investigation did
The NTSB ran a four-year investigation, one of the longest and most expensive in its history. More than 95% of the aircraft was recovered from the seabed and reassembled in a hangar in Calverton, New York — a physical reconstruction of a 747 that became the template for how large-scale wreckage analysis is done.
The reconstruction showed the break-up sequence beginning at the centre wing fuel tank, from the inside out. There was no penetration from outside consistent with a missile or a bomb, and no explosive residue pattern consistent with either. The FBI conducted a parallel criminal investigation and closed it in 1997, finding no evidence of a criminal act.
What actually happened
The centre wing tank was nearly empty, but an empty fuel tank is not empty — it contains fuel vapour and air. On this aircraft the tank sat above the air conditioning packs, which had been running on the ground for hours in July heat, warming the tank and its vapour to a temperature where the mixture became flammable.
The ignition source could not be identified with certainty. The probable cause was determined to be a short circuit outside the tank transferring excess voltage into the fuel quantity indication system wiring inside it — a spark in a place where a spark had never been considered credible, because the design assumption had been that the tank would not contain a flammable mixture in the first place.
The witness accounts
The streak of light many people saw was examined at length. The investigation concluded it was consistent with the aircraft itself after the initial explosion: the nose separated, the remaining airframe with engines still running pitched up and climbed briefly while burning, before falling. Investigators reconstructed sightlines and timing, and the reported observations matched that sequence rather than an ascending missile. The explanation has not persuaded everyone.
What changed
The consequences were substantial and are on every aircraft flying today. The FAA required fuel tank inerting systems on new transport aircraft and retrofits on much of the existing fleet — nitrogen-enriched air is pumped into the tank ullage to keep oxygen below the level that supports combustion. Wiring inspection and separation requirements around fuel systems were tightened significantly.
The underlying shift was conceptual: the industry stopped treating an empty fuel tank as a benign space and started managing the flammability of the vapour inside it.