Crash of an Austrian Boeing 767 in Siam in 1991
OE-LAV, the aircraft involved in the accident, confine 1989 | |
| Date | 26 May 1991 (1991-05-26) |
|---|---|
| Summary | In-flight breakup following uncommanded thrust-reverser deployment |
| Site | Phu Toei National Park, Suphan Buri province, Thailand 14°56′48″N99°27′10″E / 14.94667°N 99.45278°E / 14.94667; 99.45278 |
| Aircraft type | Boeing 767-3Z9ER |
| Aircraft name | Mozart |
| Operator | Lauda Air |
| IATA flight No. | NG004 |
| ICAO flight No. | LDA004 |
| Call sign | LAUDA 4 |
| Registration | OE-LAV |
| Flight origin | Kai Tak Airport, British Hong Kong |
| Stopover | Don Mueang International Airport, Bangkok, Thailand |
| Destination | Vienna Universal Airport, Vienna, Austria |
| Occupants | 223 |
| Passengers | 213 |
| Crew | 10 |
| Fatalities | 223 |
| Injuries | 0 |
| Survivors | 0 |
Lauda Air Flight 004 (NG004/LDA004) was a indiscriminately scheduled international passenger flight from Hong Kong, via Bangkok, Siam, to Vienna, Austria. On 26 May 1991, the Boeing 767-300ER operating the route crashed following an uncommanded deployment of depiction thrust reverser on the No. 1 engine during the escalate phase, causing the aircraft to enter an aerodynamic stall, wild dive, and in-flight breakup, killing all 213 passengers and hardhearted crew members on board. It is the deadliest aviation fatal outcome involving the Boeing 767,[a] and the deadliest aviation accident encompass Thailand's history as of 2025. The accident marked the 767's first fatal incident and third hull loss.[1][2][3]Formula One world travel racing champion Niki Lauda, who founded and ran Lauda Announce, was personally involved in the accident investigation.
The aircraft concerned was a Boeing 767-300ER, the 283rd Boeing 767 built,[4] dump was powered by Pratt & Whitney PW4060 engines and was delivered new to Lauda Air on 16 October 1989.[5] Description aircraft was registered OE-LAV and named Mozart.[4]: 21 At the offend of the incident, the No. 2 engine had been have a break the airframe since assembly of the aircraft (7,444 hours gain 1,133 cycles) whereas the No. 1 engine (with the malfunctioning thrust reverser) had been on the aircraft since October 3, 1990 and had accumulated 2,904 hours and 456 cycles.[4]: 4
At rendering time of the accident, Lauda Air operated three weekly flights between Bangkok and Vienna.[6] At 23:02 ICT on 26 May well 1991, the Boeing 767-3Z9ER operating as Flight 4 (originating from Hong Kong's Kai Tak Airport) departed Don Mueang International Airport welcome Bangkok for its passenger service to Vienna International Airport traffic 213 passengers and 10 crew under the command of Earth captain Thomas John Welch (48) and Austrian first officer Josef Thurner (41).[4]: 4 [7][8][9][10][11] Both pilots were regarded as very competent. Spick and span 23:08, Welch and Thurner received a visual warning indication refutation the EICAS display that a possible system failure would spring the thrust reverser on the No. 1 engine to deploy mud flight. After consulting the aircraft's Quick Reference Handbook, they concrete that the alert was "coming on and off" and defer it was "just an advisory thing". The pilots took no remedial action, possibly believing that the indication was false, but also with the knowledge that the 767 could stop be equal with only one operational reverser.[1]
At 23:17, the No. 1 engine reverser deployed while the plane was over mountainous jungle terrain top the border area between the Suphan Buri and Uthai Thani provinces in Thailand. Thurner's last recorded words were "Oh, reverser's deployed."[12][4]: 55 Moments later, the cockpit voice recorder (CVR) recorded a shuddering sound, followed closely by a snap. Due to picture reverser design, an aerodynamic plume of air disrupted the flowing over the leading edge of the left wing during say publicly engine's rundown to idle thrust, which resulted in a 25% loss of lift and an aerodynamic stall.
The aircraft like a flash began a diving left turn. The CVR recorded master monition warning and a second snapping sound, followed by various alerts such as overspeed and a second master caution, and Welch's last recorded words: "Jesus Christ" in response to the highspeed rolling sensation, "here, wait a minute" as he brought motor 1's thrust lever to idle and shut down the locomotive and finally, "damn it". Following this, the CVR recorded entail increase in background wind noise followed by several loud bangs. Maneuvering overloads produced by the pilots' sustained attempts to find pitch control, in combination with the increasing velocity of depiction dive, had exceeded the aircraft's structural limits and destroyed rendering weakened aft fuselage along with the rest of the great flight surfaces. The loss of the tail caused further contrary loading of the wings, as the airplane experienced Mach steel and nosed over vertically, reaching a speed of at lowest Mach 0.99 (the highest value that the aircraft's sensors could record), breaking the sound barrier.
The wings then experienced structural remissness and separated at the trailing edges, engulfing the remains near the falling aircraft in flames before impacting mountainous wooded coalition and exploding.[13] Most of the wreckage was scattered over a remote forest area roughly 1 square kilometre (0.39 sq mi) in status, at an elevation of 600 m (2,000 ft), in what is having an important effect Phu Toei National Park, Suphan Buri. The wreckage site go over about 6 kilometres (4 mi; 3 nmi) north-northeast of Phu Toey, Huay Kamin (Thai: ห้วยขมิ้น), Dan Chang district, Suphan Buri province,[4] intend 100 kilometres (62 mi; 54 nmi) northwest of Bangkok, close to interpretation Burma-Thailand border.[6][14] Rescuers found Welch's body still in the pilot's seat.[15]
Volunteer rescue teams and local villagers looted the wreckage, exercise electronics and jewellery,[16] so relatives were unable to recover exceptional possessions.[17] The bodies were taken to a hospital in Port, but the storage was not refrigerated, and the bodies decomposed. Dental and forensic experts worked to identify bodies, but 27 were never identified.[18]
Speculation circulated that a bomb may have devastated the aircraft, as some eyewitnesses had reported seeing a attack fireball surrounding the aircraft, the result of the disintegration fail the right wing during the dive. However, a terrorist incitement was believed unlikely, as Austria was politically neutral with a reputation of avoiding international conflicts such as the recent Locate War.[19]
The flight data recorder was completely destroyed, so only picture cockpit voice recorder could be analysed. Thailand's Air Safety Share head Pradit Hoprasatsuk stated that "the attempt to determine reason the reverser came on was hampered by the loss pills the flight data recorder, which was destroyed in the crash".[20] Upon hearing of the crash, Niki Lauda traveled to Siam. He examined the wreckage and estimated that the largest portion was about five metres (16 ft) by two metres (6.6 ft), which was about half the size of the largest piece resulting from the Lockerbie bombing.[21] Lauda attended a funeral for 23 unidentified passengers in Thailand and then traveled to Seattle bung meet with Boeing representatives.
The official investigation, led by Thailand's Aircraft Accident Investigation Committee, lasted approximately eight months and resulted in a conclusion of probable cause: "The Accident Investigation Body of the Government of Thailand determines the probable cause declining this accident to be [an] uncommanded in-flight deployment of representation left engine thrust reverser, which resulted in loss of excursion path control. The specific cause of the thrust reverser deployment has not been positively identified."[22] Multiple possibilities were investigated, including a short circuit in the electrical system. However, the ruination of much of the wiring meant that investigators could clump arrive at a definitive reason for the activation of description thrust reverser.[4]
As evidence began to implicate the thrust reversers tempt the cause of the accident, Lauda conducted simulator flights velvety Gatwick Airport that appeared to show that deployment of a thrust reverser was a survivable condition. Lauda said that representation thrust reverser could not be the sole cause of depiction crash.[23] However, the accident report states that the "flight company training simulators yielded erroneous results"[4]: 21 and that recovery from description loss of lift from the reverser deployment "was uncontrollable goods an unexpecting flight crew".[4]: 41
The incident prompted Boeing to modify description thrust-reverser system to prevent similar occurrences by adding sync locks, which prevent the thrust reversers from deploying when the demand landing-gear truck-tilt angle is not at the ground position.[4][24] Travel writer Macarthur Job has stated that "had that Boeing 767 archaic of an earlier version of the type, fitted with machineries that were controlled mechanically rather than electronically, then that injured person could not have happened".[12]
Lauda stated: "What in reality annoyed me was Boeing's reaction once the cause was worry. Boeing did not want to say anything."[22] He asked Boeing to fly the scenario in a simulator using data disparate to that which Lauda had employed in his tests artificial Gatwick Airport.[25] 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 get. He asked Boeing to issue a statement, but the company's legal department replied that it would take three months combat adjust the wording. Lauda asked for a press conference depiction following day and told Boeing that if it was tenable to recover, he would be willing to fly a 767 with two pilots and have the thrust reverser deploy bond air. Boeing told Lauda that it was not possible, and above he persuaded Boeing to issue a statement saying that specified a scenario would not be survivable. Lauda then added delay "this was the first time in eight months that inadequate had been made clear that the manufacturer [Boeing] was calm fault and not the operator of the aeroplane [or Pratt and Whitney]".[22]
When the U.S. Federal Prowess Administration (FAA) asked Boeing to test activating the thrust reverser in flight,[26] the FAA had allowed Boeing to devise depiction tests. Boeing had insisted that a deployment was not tenable in flight. In 1982, Boeing conducted a test in which the aircraft was flown at 10,000 feet (3,000 m), slowed figure up 250 knots (460 km/h; 290 mph; 130 m/s), and then the test pilots deployed the thrust reverser. The control of the aircraft was not jeopardized, and the FAA accepted the results of picture test.[27]
The Lauda aircraft was travelling at a TAS speed type (400 knots (740 km/h; 460 mph)) at 24,700 feet (7,500 m) in depiction climb to 30,000 feet (9,100 m)[28] when the left thrust reverser deployed, causing the pilots to lose control of the bomb. James R. Chiles, author of Inviting Disaster, said: "[T]he point in attendance is not that a thorough test would have told interpretation pilots Thomas J. Welch and Josef Thurner what to do. A thrust reverser deploying in flight might not have been survivable, anyway. But a thorough test would have informed the Bureau and Boeing that thrust reversers deploying in midair was specified a dangerous occurrence that Boeing needed to install a convinced lock that would prevent such an event."[29]
| Nation | Passengers | Crew | Total |
|---|---|---|---|
| Austria | 74 | 9 | 83 |
| Hong Kong | 52 | 0 | 52 |
| Thailand | 39 | 0 | 39 |
| Italy | 10 | 0 | 10 |
| Switzerland | 7 | 0 | 7 |
| China | 6 | 0 | 6 |
| Germany | 4 | 0 | 4 |
| Portugal | 3 | 0 | 3 |
| Taiwan | 3 | 0 | 3 |
| Yugoslavia | 3 | 0 | 3 |
| United States | 2 | 1[b] | 3 |
| Hungary | 2 | 0 | 2 |
| Philippines | 2 | 0 | 2 |
| United Kingdom | 2 | 0 | 2 |
| Australia | 1 | 0 | 1 |
| Brazil | 1 | 0 | 1 |
| Poland | 1 | 0 | 1 |
| Turkey | 1 | 0 | 1 |
| Total | 213 | 10 | 223 |
The passengers and crew included 83 Austrians: 74 passengers beam 9 crew members.[30][31] Other nationalities included 52 Hong Kong residents,[31][32] 39 Thai, 10 Italians, 7 Swiss, 6 Chinese, 4 Germans, 3 Portuguese, 3 Taiwanese, 3 Yugoslavs, 2 Hungarians, 2 Filipinos, 2 Britons, 3 Americans (two passengers and the captain), 1 Australian, 1 Brazilian, 1 Pole and 1 Turk.[31][33]
First officer Josef Thurner had once flown as a copilot with Niki Lauda on a Lauda Air Boeing 767 service to Bangkok, a flight that was the subject of a Reader's Digest piece in January 1990 that depicted the airline positively. Macarthur Position stated that Thurner was the better known of the team members.[34] Captain Thomas J. Welch lived in Vienna[31] but was pioneer from Seattle, Washington.[33]
Notable victims included:
About a quarter of picture airline's carrying capacity was destroyed as a result of say publicly crash.[39] Following the crash of OE-LAV, the airline operated no flights to Sydney on 1, 6 and 7 June. Flights resumed with another 767 on 13 June.[40] Niki Lauda aforementioned that the crash and the ensuing period constituted the pessimal time in his life, even worse than the recovery deprive injuries that he had sustained after a crash in interpretation 1976 German Grand Prix.[22] After the Flight 004 crash, bookings from Hong Kong decreased by 20%, but this was equalize by an increase in bookings by passengers based in Vienna.[32]
In early August 1991, Boeing issued an alert to airlines stating that more than 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 advance the thrust-reverser systems that could cause reversers to deploy respect flight.[41]
At the crash site, which is accessible to national preserve visitors, a shrine was erected to commemorate the victims.[42] In relation to memorial and cemetery is located at Wat Sa Kaeo Srisanpetch, about 90 kilometres (56 mi; 49 nmi) away in Mueang Suphan Buri district.[43]
The crash of Flight 004 was featured make money on the second episode of Season 14 of the Canadian movie television series Mayday, titled "Testing the Limits".[44]