What happened
On May 26, 1991, a scheduled passenger service operated by Lauda Air departed Bangkok, Thailand, bound for Vienna, Austria. The flight, involving a Boeing 767-300ER with registration NG004, proceeded normally during the initial stages of its departure. Approximately five minutes after takeoff, the crew engaged in a discussion regarding a cockpit alert related to a thrust reverser isolation valve. For roughly four and a half minutes, the crew consulted the Quick Reference Handbook (QRH) to evaluate the notification, ultimately determining that no specific corrective actions were necessary.
Ten minutes into the flight, the co-pilot noted the necessity for left rudder trim, which the pilot-in-command acknowledged. However, fifteen minutes after departure, the co-pilot reported that a reverser had deployed. This was immediately followed by sounds of airframe vibration recorded on the cockpit voice recorder. Shortly thereafter, the recording captured noises consistent with a structural failure. The aircraft's electronic engine control data indicated the plane was climbing at Mach 0.78 and an altitude of approximately 24,700 feet when the event occurred.
The aircraft subsequently crashed into mountainous jungle terrain in Thailand at approximately 16:17 hours. All 223 fatalities were recorded, with no survivors. The accident took place under night-time visual meteorological conditions.
Findings
Investigations focused on the sudden deployment of engine components during the climb phase. While the exact mechanism that triggered the event remained unconfirmed, the investigation concluded that the uncommanded in-flight deployment of the left engine thrust reverser led to a total loss of control over the flight path.