Lauda Air Flight 004

Lauda Air Flight 004 was a scheduled international passenger flight from Kai Tak, Hong Kong, China to Wien-Schwechat International Airport, Vienna, Austria via Don Mueang International Airport, Bangkok, Thailand. On 26 May 1991, during it's Bangkok to Vienna leg, the Boeing 767-3Z9ER operating the route suffered from a rare uncommanded thrust reverser deployment while flying over the Burma-Thai border and crashed into wooded terrain about ~94 nautical miles northwest of Bangkok, killing all 213 passengers and 10 crew members on board. It is the first and deadliest loss involving the Boeing 767, and as of 2022, Thailand's worst aviation accident.
The positions of the left engine thrust reverser actuators along with data from the electronic engine control (EEC) and the cockpit voice recorder (CVR) indicate that the left engine thrust reverse system deployed while the airplane was at approximately .78 Mach (478 kn, 550 mph, 885 km/h), climbing through 24,700 feet to flight level 310. The preliminary evidence suggests that the reverse event was recognized by the flight crew, but that the airplane departed controlled flight.
The true cause of the activation of the reverser was never found because all of the wires and the Digital Flight Data Recorder were destroyed in the crash, but it was thought to be caused by a short circuit that opened both valves for a split second, allowing the reverser to activate.
Accident
Lauda Air Flight 004 took off from Runway 21L in Don Mueang at 23:02 PM ICT (4:02 PM UTC). 5 minutes into the flight, the pilots received a master caution "REV ISLN VAL" advisory on the EICAS display, accompanied with the master caution tone. First Officer Thurner replied with an expletive, and Captain Welch replied, "that keeps coming on". The crew discussed the issue as Thurner looked through the quick reference handbook for a solution, but the handbook then quoted "additional system failures may cause in-flight deployment", and to "expect normal reverser operation after landing". There was no further action required.
Thurner asked if he should contact the Lauda maintenance crew in Bangkok, and the captain, reassured, said that it was "just an advisory thing", and that there was "just water, or moisture in there", and moved on; the first officer shortly thereafter tells the captain that the aircraft needs "a little bit of rudder trim to the left".
At 23:17 PM ICT (4:17 PM UTC), some nine minutes after the master caution advisory, while climbing to FL310 as cleared, the left engine thrust reverser activated. Immediately after, the first officer acknowledged this, shouting "Shit, reverser deployed," followed by loud bangs, snaps, and the sound of the overspeed warning. Captain Welch manually disconnects the autopilot and takes manual control, which consisted of continuous sustained elevator nose up inputs. The aerodynamic stresses tore the tail section free of the aircraft, leaving it uncontrollable.
The loss of the tail provides extreme negative loading of the wings and shears them clean of the aircraft, and the burning remains of Flight 004 crashed into wooded terrain in the Dan Chang District of Thailand at speeds of over Mach 1. All 223 passengers and crew died. Shortly after the accident, local villagers began to loot the crash site.
The available recovery time for the crew to rectify the situation was 4 to 6 seconds. The crew never could have reacted fast enough to stop the accident.
Passengers and crew
Josef Thurner, the copilot, once flew as a co-pilot with Niki Lauda on a Lauda Boeing 767 service to Bangkok, a flight that was the subject of a Reader's Digest article in January 1990 that depicted the airline positively. Macarthur Job stated that Thurner was the better known of the crew members. Thomas J. Welch, the captain, lived in Vienna, but originated from Seattle, Washington.