Potential explosion danger from fuel vapour in Boeing 737 fuel tanks is to be addressed in a new US Federal Aviation Administration airworthiness directive (AD).
The proposed AD, affecting 1,140 US-registered and about 1,600 other 737s, specifies all models from the -100 to the -500. It calls for protection of the fuel quantity indication system against transient electrical voltage spikes or short circuits, and will require installation of electrical suppressors and/or shielding, and separation of the fuel system wiring from adjacent wiring.
Installation of fuel vent system flame arrestors and pressure relief valves designed to prevent external flames from entering through the wing tip vents, will also be ordered.
The agency issued a similar AD late last year covering Boeing 747 Classics, following the Trans World Airlines crash in July 1996 blamed on a centre fuel tank explosion for which no ignition cause has yet been established.
A Philippine Air Lines 737-300 fuel tank exploded in May 1990, but the ignition source also remains a mystery. The FAA is considering similar rules for Boeing 707s and 727s.
Source: Flight International
