AS THE US Federal Bureau of Investigation (FBI) works to discover, whether the 17 July crash of a Trans World Airlines (TWA) Boeing 747-100 was caused by a bomb or missile, investigators from the US National Transportation Safety Board (NTSB), are examining a theory that fuel in the centre tank might have ignited, causing the fatal explosion.

Only about 25% of the aircraft has been recovered from the ocean floor, but no explosive residue has been detected (Flight International, 24-30 July, P4). The US Navy has salvaged a severely damaged 1t section of the cockpit, and almost the entire right wing has been found.

One theory being examined by the NTSB is that vapour in the aircraft's empty centre fuel-tank ignited - possibly following an electrical short-circuit - which could then have blown away the aircraft's front section. The cockpit and forward passenger section crashed into the sea some 2.4km (1.5nm) behind the wings and rear cabin. A second theory being considered by investigators is that fuel was ignited by high-velocity particles from an engine explosion, but no evidence to support that idea has yet been discovered.

Four aircraft fires are known to have started in 747 centre fuel-tanks, but without disastrous consequences.

No pieces of the centre fuel-tank have been found, but two complete engines, which appear to be the outboard power plants, have been located. Parts of a third engine have been found, but one of the inboard engines remains missing.

The flight-data recorder shows that the four engines operated normally to the end of the recording, and the cockpit-voice recorder offers no evidence of mechanical or other problems before the crash. Investigators continue to try and identify a split-second loud sound recorded at the flight's end.

Meanwhile, the USA's review of aviation security has begun, with a "baseline working group" set up to define what the Commission, headed by US vice-president Al Gore, will cover.

Governments meeting in Paris, France, for a conference on terrorism have urged nations to accelerate the adoption of security measures already recommended by the International Civil Aviation Organisation (ICAO), but not widely used in practice. Following the meeting, ICAO Council president Dr Assad Kotaite has emphasised the Ministers' call for more states to ratify the 1991 Convention on the Marking of Plastic Explosives at manufacture, which allows such materials not only to be detected while hidden, but their origin to be identified during the investigation of blast damage.

Source: Flight International