Lauda Air Flight 004
Lauda Air Flight 004 was a regularly scheduled international passenger flight from Bangkok, Thailand, to Vienna, Austria. On 26 May 1991, the thrust reverser on the No.1 engine of the Boeing 767-300ER operating the flight deployed in flight uncommanded, causing the aircraft to enter an uncontrolled dive, break up, and crash, killing all 213 passengers and the 10 crew members on board. It was the deadliest aviation incident involving a Boeing 767 at the time and the deadliest aviation incident in Thailand's history as of 2022. 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. On 26 May 1991, at 23:02 ICT, flight NG004 (originating from Hong Kong's Kai Tak Airport), a Boeing 767-3Z9ER, took off from Don Mueang International Airport for its flight 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). 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. Having consulted the aircraft's quick reference handbook, they determined that it was "just an advisory thing" and took no action. 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 Thani Provinces in Thailand. Thurner's last recorded words were, "Oh, reverser's deployed". Just after, the cockpit voice recorder (CVR) recorded a shuddering sound, followed closely by a snap . Lift on the aircraft's left side was disrupted as a cause of reverser deployed, and the aircraft immediately began a diving left turn. The CVR recorded a second snapping sound, followed by various alerts such as overspeed and master caution, and Welch's last recorded words, which were, "Jesus Christ!" followed by "here, wait a minute", and then, "damn it!" Following this, the CVR recorded an increase in background noise, followed by several loud bangs, and then stopped recording. The extreme stress of the dive caused sections of the rudder and right elevator to fail and break off as  the crew attempted to arrest the descent. This was followed by the complete separation of the right horizontal stabilizer, and then moments later the rear section of the fuselage failed and broke off, taking the rest of the tail with it. With the loss of the tailfin, the aircraft went into a vertical nose down attitude. It reached a speed of Mach 0.99, breaking the sound barrier. At that point, the entire right wing failed and detached, igniting a fireball according to eyewitness accounts. What remained of the aircraft disintegrated at before impacting the ground and exploding violently. Most of  the wreckage was scattered over a remote forest area roughly one square kilometre in size, at an elevation of , in what is now Phu Toei National Park, Suphan Buri. The wreckage site is about north-northeast of Phu Toey, Huay Kamin (), Dan Chang District, Suphan Buri Province, about northwest of Bangkok, close to the Burma-Thailand border. Rescuers found Welch's body still in the pilot's seat. Recovery. Volunteer rescue teams and local villagers looted the wreckage, taking electronics and jewellery, so relatives were unable to recover personal possessions. The bodies were taken to a hospital in Bangkok. The  storage was not refrigerated and the bodies decomposed. Dental and forensic experts worked to identify bodies, but twenty-seven were never identified. Speculation circulated that a bomb may have destroyed the aircraft. "The Philadelphia Inquirer", citing wire services it did not identify, stated that "the search for a motive is difficult because politically neutral Austria has generally stayed out of most international conflicts – such as the Persian Gulf War – that have made other countries' airlines the targets of terrorist attacks." Investigation. The flight data recorder was completely destroyed, so only the cockpit voice recorder was of use. Pradit Hoprasatsuk, the  head of the Air Safety Division of the Thailand Department of Aviation, stated, "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". Upon hearing of the crash, Niki Lauda traveled to Thailand. He examined the wreckage and estimated that the largest fragment was about by , which was about half the size of the largest piece in the Lockerbie crash. In Thailand, Lauda attended a funeral for 23 unidentified passengers, and then traveled to Seattle to meet with Boeing representatives. The official investigation, led by  Thailand's Aircraft Accident investigation Committee, took about eight months, and was released with the "probable cause" stating: "The Accident Investigation Committee of the Government of Thailand determines the probable cause of this accident to be [an] 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. As evidence started to point towards the thrust reversers as the cause of the accident, Lauda made simulator flights at Gatwick Airport which appeared to show that deployment of a thrust reverser was a survivable incident. Lauda said that the thrust reverser could not be the sole cause of the crash. However the accident report states that the "flight crew training simulators yielded erroneous results" and stated that recovery from the loss of lift from the reverser deployment "was uncontrollable for an unexpecting flight crew". 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. Aviation writer Macarthur Job has said that "had that Boeing 767 been of an earlier version of the type, fitted with engines that were controlled mechanically rather than electronically, then that accident could not have happened". Lauda's visit with Boeing. Lauda stated, "what really annoyed me was Boeing's reaction once the cause was clear. Boeing did not want to say anything." Lauda asked Boeing to fly the scenario in a simulator  that used different data as compared to the one that Lauda had performed tests on at Gatwick Airport. Boeing initially refused, but Lauda insisted, so Boeing granted permission. Lauda attempted the flight in the simulator 15 times, and in every instance he was unable to recover. He asked Boeing to issue a statement, but the legal department said it could not be issued because it would take three months to adjust the wording. Lauda asked for a press conference the following day, and told Boeing that if it was possible to recover, he would be willing to fly on a  767 with two pilots and have the thrust reverser deploy in air. Boeing told Lauda that it was not possible, so he asked Boeing to issue a statement saying that it would not be survivable, and Boeing issued it. Lauda then added, "this was the first time in eight months that it had been made clear that the manufacturer [Boeing] was at fault and not the operator of the aeroplane [or Pratt and Whitney]." Previous testing of thrust reversers. When the US Federal Aviation Administration (FAA) asked Boeing to test activating the thrust reverser in flight, the FAA had allowed  Boeing to devise the tests. Boeing had insisted that a deployment was not possible in flight. In 1982 Boeing conducted a test wherein the aircraft was flown at , then slowed to , and the test pilots then deployed the thrust reverser. The control of the aircraft was not jeopardized. The FAA accepted the results of the test. The Lauda aircraft was traveling at a high speed () and at almost when the left thrust reverser deployed, causing the pilots to lose control of the aircraft. James R. Chiles, author of "Inviting Disaster", said, "the point here is not that a thorough test  would have told the pilots Thomas J. Welch and Josef Thumer what to do. A thrust reverser deploying in flight might not have been survivable, anyway. But a thorough test would have informed the FAA and Boeing that thrust reversers deploying in midair was such a dangerous occurrence that Boeing needed to install a positive lock that would prevent such an event." As a result of their findings during the investigation of Lauda Flight 004, additional safety features such as mechanical positive locks were mandated to prevent thrust reverser deployment in flight. Passengers and crew. The passengers and crew included  83 Austrians: 74 passengers and nine crew members. Other nationalities included 52 Hong Kong residents, 39 Thai, 10 Italians, seven Swiss, six Chinese, four Germans, three Portuguese, three Taiwanese, three Yugoslavs, two Hungarians, two Filipinos, two Britons, three Americans (two passengers and the captain), one Australian, one Brazilian, one Pole, and one Turk. 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. Notable victims include: Aftermath. About a quarter of the airline's carrying capacity was destroyed as a result of the crash. Following the crash of OE-LAV, the airline had no flights to Sydney, on 1, 6, and 7 June. Flights resumed with another 767 on 13 June. Niki Lauda said that the crash in 1991 and the period after was the worst time in his life, even worse than the recovery from his injuries after his crash in the  1976 German Grand Prix. After the crash, bookings from Hong Kong decreased by 20% but additional passengers from Vienna began booking flights, so there were no significant changes in overall bookings. In early August 1991, Boeing issued an alert to airlines stating that over 1,600 late model 737s, 747s, 757s, and 767s had thrust reverser systems similar to that of OE-LAV. Two months later, customers were asked to replace potentially faulty valves in the thrust reverser systems that could cause reversers to deploy in flight. At the crash site, which is accessible to national park visitors, a shrine was  later erected to commemorate the victims. Another memorial and cemetery is located at Wat Sa Kaeo Srisanpetch, about away in Mueang Suphan Buri District. In popular culture. The crash of Flight 004 was featured on second episode of fourteenth season of the Canadian documentary television series Mayday, in the episode titled "Testing the Limits".