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Probe Fails to Resolve Cause of 1991 Air Disaster

August 31, 1993

BANGKOK, Thailand (AP) _ A two-year investigation has failed to determine why a jetliner’s engine reversed in flight and sent the plane plunging at nearly the speed of sound, an official said Tuesday.

Thai and U.S. experts determined the May 26, 1991, crash occurred when engine thrust reverser of the Boeing 767-300 was activated. The jet lost 25 percent to 30 percent of its lift and plunged out of control into the ground, killing all 223 people aboard. The plane was operated by Lauda Air of Austria.

But the attempt to determine why the reverser came on was hampered by the loss of the flight data recorder, which was destroyed in the crash, said Pradit Hoprasatsuk, head of the Department of Aviation’s Air Safety Division.

The cockpit voice recorder was recovered, and the last words on the tape said the reverser was open.

After a year of testing, investigators concluded the control system for the reversers needed improvement. Boeing’s main change was to use a motor rather than hydraulic power to control a valve, Pradit said.

Boeing made the modification in early 1992 to the approximately 80 767s then in operation and the problem has not arisen again, Pradit said.

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