LAUDA AIR FLIGHT 004
On May 26, 1991, Lauda Air Flight 004 crashed in Thailand, while en route from Bangkok, Thailand to Vienna, Austria. The aircraft involved was a Boeing 767-3Z9ER, registered as OE-LAV. The aircraft was delivered new to Lauda Air on October 16, 1989. The captain on the flight was American Thomas J. Welch, and the first officer was Austrian Josef Thurner.
The flight departed Don Mueang International Airport, Bangkok at 23:02 hours. At 23:08, Welch and Thurner received a visual warning, indicating that a possible system failure would cause the thrust reverser on the number one engine to deploy in flight. No action was taken, since the aircraft's quick reference handbook indicated, that no action was required. At 23:17, the number one engine reversed thrust, while the plane was over mountainous jungle terrain, in the border area between Suphanburi and Uthai Thani provinces. The lift on the aircraft's left side was disrupted due to the reverser deployment, and the aircraft was placed in an immediate diving left turn. The aircraft stalled, and entered an uncontrolled descent. The aircraft broke up in mid-air, and crashed into the jungle. All 223 people on board were killed.
The probable cause of this accident was uncommanded in-flight deployment of the left engine thrust reverser, which resulted in loss of flight path control. The specific cause of the thrust reverser deployment has not been positively identified. Different possibilities were investigated, including a short circuit in the system. Due in part to the destruction of much of the wiring, no definitive reason for the activation of the thrust reverser could be found.
The incident led Boeing to modify the thrust reverser system to prevent similar occurrences by adding sync-locks, which prevent the thrust reversers from deploying, when the main landing gear truck tilt angle is not at the ground position.
With 223 fatalities, Flight 004 remains the deadliest accident involving the Boeing 767 aircraft.
NOTABLE AVIATION ACCIDENTS AND INCIDENTS