Boeing says alleged cause of fatal crash is impossible

THE US aviation authorities and the Boeing aircraft company were both aware of a potential engine fault that may have caused the Pittsburgh air crash last Friday in which all 132 passengers and crew were killed, according to a report by a US television network.

The main theory being tested by investigators is that the thrust reverser was accidentally or automatically deployed, causing the Boeing 737-300 to crash seven miles from the airport. In May 1991, a Lauda Air Boeing 767 crashed shortly after take-off in Thailand, killing all 223 people on board. That crash was found to have been caused by a computer malfunction which put one engine into reverse. The reverse thrust should be deployed only to help braking after an aircraft lands; deployment during flight is supposed to be impossible.

ABC News said that both the Federal Aviation Administration (FAA) and Boeing were aware of a potential fault on the aircraft with the thrust reversers. USAir had begun modifications on the 737 that crashed last week, but stopped because the new design was not correct. Boeing issued another design in July, but the FAA has not made the modifications mandatory.

Investigators have still not determined conclusively whether the engagement of the thrust reverser was the cause of the crash. They found that half the reverse mechanism on one engine may have been activated, but Boeing says that partial activation is impossible. Two other possible causes might be that the engine came loose, or that the brakes were unevenly deployed. 'We want to examine everything that might have caused the right wing to rise,' a spokesman said.

National Transportation Safety Board investigators are to stage a simulation of in-flight deployment of thrust reversers in an effort to determine the cause. The simulation will then be compared with the flight data-recorder and other information about the aircraft's final turn and its fall from 6,000 feet.

Boeing said last night that the Boeing 737 - of which 2,641 have been delivered, making it the world's most popular commercial airliner - had a safety record well above average, but refused to comment on the likely cause of the crash. Several British airlines including British Airways, British Midland, and Air UK fly Boeing 737s.