TWA crash forces Boeing rethink

It is an assumption that has survived decades of aircraft-building: keep ignition sources away from fuel tanks and never mind how flammable their contents become. But, as David Usborne in New York explains, now is the time for second thoughts.

A year and a half after the fiery crash of TWA 800 off the coast of Long Island, the Boeing Company has conceded that it may have radically to rethink the design of the fuel tanks inside all the aircraft it builds.

The remarkable change of tack, offered at hearings on the TWA 800 tragedy under way in Baltimore, may affect not just aeroplanes now on the drawing board. It could force costly modifications on thousands of aircraft already in the sky, whether made by Boeing or by its main rival, Airbus.

"I don't know when the last time was that we had a shift like this," said Douglas Webb, a spokesman for Boeing which manufactured the 747 Jumbo Jet which crashed on 17 July last year killing all 230 people on board.

Investigators with the National Transport Safety Board, which convened the hearings, are confident that the crash followed a devastating explosion in the Boeing's huge central fuel tank which tore the plane's fuselage apart.

The blast apparently occurred after temperatures in the tank rose sufficiently to cause the small amount of fuel it contained to vaporise. What ignited the vapour is a mystery, however. One expert noted that dropping a 10 cent coin half an inch would produce sufficient energy for ignition.

Yesterday, a safety board expert testified that special attention was being paid to the probes that measured the fuel level in the plane's tank. Investigators consider it just possible that excess current in a probe, perhaps caused by a short circuit, might have triggered a fatal spark.

Both Boeing and the Federal Aviation Administration were until recently sticking by a four-decade-old principle that it was enough simply to ensure the insulation of such tanks from all potential sources of ignition. But in Baltimore both have acknowledged that a parallel effort is now needed also to combat the build-up of flammable vapours inside tanks.

"It has become clear to us throughout this investigation that tank maintenance hasn't been a high-priority issue fleet-wide," said Daniel Cheney of the FAA. "It's something we plan to take action on and it's going to apply to more than just the Boeing 747 and more than just the Boeing fleet."

The implications for the industry could be enormous. Changing the configuration of the fuel tanks could be extremely expensive and might lead to temporary groundings of thousands of planes.

Jim Hall, the safety board chairman, was angered that six months after he issued a directive asking airlines to inspect all 747 fuel tanks, only 52 of the jets out of a world fleet of 970 have been checked.

The possible options being considered by Boeing engineers include insulating central fuel tanks from the heat-generating air condition units that often lie directly beneath them by introducing a thin current of cool air between them. Alternatively, it might be possible to vent fuel vapours from tanks.