Lauda Air Flight 004 was a regularly scheduled international passenger flight from Bangkok, Thailand, to Vienna, Austria. On May 26, 1991, the Boeing 767-300ER operating the service crashed, following an uncommanded midair deployment of the thrust reverser on the No.1 engine, causing the aircraft to enter an aerodynamic stall, uncontrolled dive, and break up midair, killing all 213 passengers and ten crew members on board. It is the deadliest aviation incident involving the Boeing 767, and the deadliest aviation incident in Thailand's history as of 2023. The crash marked the aircraft type's first fatal incident and third hull loss. Formula One world motor racing champion Niki Lauda, who founded and ran Lauda Air, was personally involved in the accident investigation. Aircraft The aircraft involved was a Boeing 767-300ER that was powered by Pratt & Whitney PW4060 engines and delivered new to Lauda Air on 16 October 1989. The aircraft was registered OE-LAV, was named Mozart and was the 283rd Boeing 767 built. At the time of the incident, the No.2 engine had been on the airframe since assembly of the aircraft (7,444 hours and 1,133 cycles) whereas the No.1 engine (with the faulty thrust reverser) had been on the aircraft since October 3, 1990 and had accumulated 2,904 hours and 456 cycles. Accident At the time of the accident, Lauda Air operated three weekly flights between Bangkok and Vienna. At 23:02 ICT, on 26 May 1991, Flight 4 (originating from Hong Kong's Kai Tak Airport), the Boeing 767-3Z9ER took off from Don Mueang International Airport for its passenger service to Vienna International Airport with 213 passengers and ten crew, under the command of American Captain Thomas J. Welch (48) and Austrian First Officer Josef Thurner (41). Both pilots were regarded as very competent. At 23:08, Welch and Thurner received a visual warning indication on the EICAS display telling them that a possible system failure would cause the thrust reverser on the number one engine to deploy in flight. Having already consulted the aircraft's quick reference handbook, they determined that it was "coming on and off", and that it was "just an advisory thing" and took no action, possibly believing that the indication was false, and because the 767 could stop with only one operational reverser. At 23:17, the number one engine reverser deployed while the plane was over mountainous jungle terrain in the border area between Suphan Buri and Uthai