17th of July 1996
It was on this day in aviation history that TWA 800 exploded in mid-air.
N93119, the accident aircraft
After take-off, the aircraft climbed en route from New York JFK Airport, the USA to Rome, Italy when 12 minutes after takeoff the aircraft exploded, killing all 230 onboard. After an extensive (nearly four year investigation) the NTSB concluded in its report (Published on the 23rd of August 2000) that the probable cause was the explosion of flammable vapours in the centre fuel tank. The vapours probably ignited due to a short circuit in the wiring of the Fuel Quantity Indication System. although this could not be said with 100% certainty. Evidence was found in the recovered wreckage of shorted wiring in this system. The captain of the flight was also heard on the CVR, ~ 2 1/2 minutes before the explosion, remarking that the quantity indication for the centre tank was erratic.
As a result of the investigation results, new requirements were issued for aircraft to prevent fuel tank explosions. These were initially laid down in SAFR 88 (Special Federal Aviation Regulation 88) issued by the FAA. In 2009 EASA ED 2009/007/A and FAA AC 120-97A were issued.
They require that holders of type certificates and supplemental type certificates review the designs of fuel tank systems of large transport category airplanes, and develop design changes and maintenance and inspection programs based on the findings of those reviews.
To reduce the build-up of flammable gasses systems were developed to pump nitrogen in the fuel tanks of aircraft in flight, and so removing oxygen from the fire triangle and preventing explosions. The Nitrogen generation system or O.B.I.G.G.S. (On-Board Inert Gas Generation System) filters air and removes the oxygen using hollow fibres leaving near-pure nitrogen to be pumped in the fuel tanks.
A video of the Honeywell OBIGGS system
Another requirement of the new regulation was the training of maintenance staff and product support staff, Fuel Tank Safety Training Level 1 and Level 2. The purpose of this training can be summarised as providing students with an overview of fuel system safety considerations. That includes. Historical incidents, ignition prevention, theoretical background and practical considerations.
Fuel tank safety training is mandatory for staff that plans, performs, supervises, inspects and certifies the maintenance of large aircraft (as defined in Decision 2003/11/RM) in a Part-145 approved maintenance organisation and personnel involved in the management and review of the continuing airworthiness of large aircraft (as defined in Decision 2003/11/RM) in a M.A. Subpart G organisation.