travelled to Thailand to assist in the investigation. The
flight data recorder was completely destroyed, so only the
cockpit voice recorder could be analysed. Thailand's Air Safety Division head Pradit Hoprasatsuk stated that "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 resulting from the
Lockerbie bombing. Lauda attended a funeral for 23 unidentified passengers in Thailand and then traveled to
Seattle to 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 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." Multiple possibilities were investigated, including a short circuit in the electrical system. However, the destruction of much of the wiring meant that investigators could not arrive at a definitive reason for the activation of the thrust reverser. However, the accident report states that the "flight crew training simulators yielded erroneous results" Aviation writer
Macarthur Job has stated 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". 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 in which the aircraft was flown at , slowed to , and then the test pilots deployed the thrust reverser. The control of the aircraft was not jeopardized, and the FAA accepted the results of the test. The Lauda aircraft was travelling at a
TAS of at in the climb to when the left thrust reverser deployed, causing the pilots to lose control of the aircraft. James R. Chiles, author of
Inviting Disaster, said: "[T]he point here is not that a thorough test would have told the 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 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."
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." 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 company's legal department replied that 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 a 767 with two pilots and have the thrust reverser deploy in air. Boeing told Lauda that it was not possible, so he persuaded Boeing to issue a statement saying that such a scenario would not be survivable. Lauda then added that "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]". ==Passengers and crew==