The public hearing on the 1996 Trans World Airlines flight 800 fatal crash ended in Baltimore on 12 December without the US National Transportation Safety Board (NTSB) coming any nearer to discovering the cause, although it can claim to have clarified potential safety policies.
Measures to reduce the risk of in-tank fuel-vapour ignition have been spelled out, and the US Federal Aviation Administration has been forced to review long-standing aircraft fuel-system certification standards.
Much of the hearing involved discussion of mechanical or electrical problems which might have sparked the Boeing 747-100's centre-fuel-tank explosion. NTSB investigators are still trying to determine whether electrical faults in the fuel-measuring probes were involved. This, however, remains a theory.
Safety measures advanced at the hearing include:
to change from Jet-A to JP-5 fuel. JP-5's flash point is higher; to reduce or eliminate explosive fuel-air vapours in fuel tanks, possibly by filling empty tanks with nitrogen instead of air; to reduce heat-sources near fuel tanks, keeping fuel-vapour temperature low; Periodic inspection of fuel tanks for potential ignition sources. Manufacturers and airlines must develop fuel-tank maintenance/ inspection programmes for FAA approval; The FAA has issued an airworthiness directive requiring checks of the Teflon coating in all wiring conduits associated with 747 fuel pumps. The original airworthiness directive (AD) issued a year ago only covered aluminum conduits, but now stainless-steel ducts have been found vulnerable to arcing damage also.The FAA had based its certification principles on the elimination of ignition sources, assuming that purging potentially explosive fuel vapours from tanks is impossible. NTSB chairman Jim Hall insists that purging explosive vapours is "a more attainable goal".
Source: Flight International
