Explosion over the Atlantic: TWA flight 800

“We just saw an explosion up ahead of us here, about 16,000 feet or something like that; it just went down… in the water”.

These words were pronounced by a pilot, flying near New York, on July 17, 1996, when a Boeing 747 operating as TWA Flight 800 tragically exploded midair off the coast of Long Island, resulting in the loss of all souls on board.

Photograph of flight TWA 800 before the crash. Source: Aviation Safety Network (ASN)

Bound for Rome, Italy, with a scheduled stopover in Paris, France, the flight departed New York’s John F. Kennedy Airport over two hours later than scheduled at 8:19 p.m., due to technical delays while refueling. It carried 212 passengers and 18 crew members on board. Shortly after take-off, as the aircraft was climbing through an altitude of 13,800 feet, the aircraft was suddenly struck by an explosion.

A nearby Eastwind Airlines Boeing 737 reported seeing the explosion followed by what appeared to be a fireball plummeting toward the Atlantic Ocean. Captain David McClain immediately contacted JFK’s ATC to inform them about the explosion of an airplane, “[t]he first officer looked up and then saw the explosion and said what happened, I said it just exploded” he declared. Subsequently, the ATC determined that it had to be flight TWA 800, which had just disappeared from the radars. At the time, it became the third-deadliest Boeing 747 crash in aviation history.

The National Transportation Safety Board (NTSB) quickly launched an investigation, and initial reports speculated the possibility of a bomb on board. At first glance, it seemed to be the most plausible cause, after all, the only previous 747 crashes deadlier than TWA Flight 800 had been the result of terrorist bombings: Air India Flight 182 and Pan Am Flight 103. Even President Bill Clinton, speaking the day after the crash, underscored the gravity of the situation: “[w]hether it was [a] mechanical failure or sabotage… we will find out”, he stated at a press conference. Nevertheless, under mounting public pressure and scrutiny, the NTSB eventually concluded that the breakup had been caused by an explosion in the aircraft’s largest fuel reservoir: the center wing fuel tank (CWT). Still, a question remained, could such a devastating explosion truly have originated from a mostly empty fuel tank?

Reconstructing the final moments of the flight, the NTSB launched tests simulating flight conditions which revealed that a mix of liquid fuel and fuel vapor in the CWT is highly volatile and flammable. A significant factor in this flammability was the heat produced by the plane’s air conditioning packs, which were in operation for about two hours during ground delays to cool the cabin in hot summer weather. These systems, meant to keep passengers comfortable, were located directly beneath the CWT, separated by only five cm–with no thermal insulation between them and the fuel tank. The constant heat from the packs had warmed the fuel to around 51.7°C, well above the minimum ignition temperature of 36.4°C for fuel vapors.

As the plane climbed to 13,800 feet, this heat-induced environment became a ticking time bomb. Investigators determined that an ignition of the fuel-air mixture in the CWT was the immediate cause of the explosion, and the resulting flame front rapidly spread throughout the tank. It caused the internal span-wise beam to collapse and blew out part of the plane's underside. With the interior of the plane now exposed to the outside, structural stress on the fuselage created a large fracture near the nose, which broke away from the rest of the aircraft and led to a rapid sequence of structural failures. Notwithstanding, the exact trigger of the explosion remained elusive. Of all the possible sources analyzed, the most probable cause was a short circuit outside the tank.

Reconstruction of the plane with debris. Source: Aviation Safety Network (ASN)

In their final report, the NTSB concluded: “[t]he probable cause of the TWA Flight 800 accident was an explosion of the center wing fuel tank (CWT), resulting from ignition of the flammable fuel-air mixture in the tank. The source of ignition energy for the explosion could not be determined with certainty, but the most likely was a short circuit…”. Beyond the immediate failure, the NTSB uncovered systemic design flaws in the Boeing 747. The aircraft had been certified under the assumption Reconstruction of the plane with debris Source: Aviation Safety Network (ASN) Source: Aviation Safety Network (ASN) that removing ignition sources alone would prevent fuel tank explosions, overlooking the fact that flammable vapor could still build up during normal operations. Crucially, the air conditioning packs were placed directly beneath the center wing tank, with no insulation to block heat transfer. This oversight created the perfect conditions for ignition without any external threat. TWA Flight 800 wasn’t brought down by terrorism or sabotage, but by a chain of internal vulnerabilities as per the James Reason’s Swiss Cheese model.

In the end, to prevent other plane crashes caused by fuel tank explosions, the United States Head Secretary of Transports Mary E. Peters introduced airlines to a new rule on July 18, 2008. Since then, they have been required to pump inert gas into the tanks to decrease the probability of combustion.

Bibliography:

• Air Disasters UK. TWA Flight 800: Explosion Over the Atlantic. Available online: http://www.airdisasters.co.uk/170796.htm

• National Transportation Safety Board (NTSB). Aircraft Accident Report: TWA Flight 800, Explosion of the Center Wing Fuel Tank, Boeing 747-131, N93119 Near East Moriches, New York, July 17, 1996. Report AAR-00/03, 2000. Available online: https://www.ntsb.gov/investigations/accidentreports/reports/aar0003.pdf

• Aviation Safety Network (ASN). Accident Description for TWA Flight 800. Available online: https://asn.flightsafety.org/asndb/324416

• Tailstrike. TWA Flight 800 Accident Database. Available online: https://tailstrike.com/database/17-july-1996-twa-800/

• Clinton, William J. Statement on the TWA Flight 800 Tragedy. Speech delivered on July 25, 1996. Available on YouTube: https://youtu.be/gX0QW0w3iZg?si=7Gcojnz64qcA4cCL