Lauda Air Flight 004

Crash of an Austrian Boeing 767 in Thailand in 1991

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, the Boeing 767-3Z9ER operating the flight under the callsign NG004 (LAUDA 4, LDA004) suffered an uncommanded thrust reverser deployment midair while flying over 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 accident and the deadliest loss involving the Boeing 767, and as of 2022, Thailand's worst aviation accident.

Lauda Air Flight 004
Lauda Boeing 767-3Z9ER OE-LAV (Cropped).jpg
OE-LAV, the Lauda Air Boeing 767-3Z9ER involved in the accident
Date26 May 1991 (1991-05-26)
SummaryIn-flight break-up caused by uncommanded thrust reverser deployment
SitePhu Toei National Park, Suphan Buri, Thailand
14°56′48″N 99°27′10″E / 14.94667°N 99.45278°E / 14.94667; 99.45278Coordinates: 14°56′48″N 99°27′10″E / 14.94667°N 99.45278°E / 14.94667; 99.45278
Aircraft typeBoeing 767-3Z9ER
Aircraft nameMozart
OperatorLauda Air
Flight originKai Tak Airport, Hong Kong
StopoverDon Mueang Int'l Airport, Bangkok, Thailand
DestinationVienna International Airport, Vienna, Austria
Fatalities223 (all)

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, accelerated past the maximum operating velocity, and experienced an in-flight structural breakup at a low altitude. Indications of an in-flight fire prior to the breakup have not been found. However, during the breakup, a large explosion was witnessed and burning debris fell to the ground. The explosion was most likely the ignition of discharged fuel from the aircraft's wings during the breakup.

The true cause of the reverser deployment 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.


Lauda Air Flight 004 took off from Runway 21L in Don Mueang at 23:02 ICT. 5 minutes and 45 seconds into the flight, where the pilots received a "REV ISLN VAL" warning on the EICAS, to which Captain Welch replied, "that keeps coming on", indicating that the warning would come on, then extinguish. This probably made the Captain think that this warning was not true. The crew discussed the issue for approximately 5 minutes, looking through the aircraft's quick reference handbook, to which they found no action was needed, but the handbook then quoted "additional system failures may cause in-flight deployment", and to "expect normal reverser operation after landing". 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 claiming that the captain needs "a little bit of rudder trim to the left", in response to the ailerons being slightly out of trim.

At 23:17 PM ICT (local time, 4:17Z PM), nine minutes after the first warning, while climbing past 24,500 feet, the left engine thrust reverser activated, the reverser plume causing asymmetrical lift that took away 25 percent of the original lift away from the left wing. Almost immediately, the aircraft assumed a hard left yaw, bank, and descent, with a value that peaked at -28 degrees per second. Immediately after reverser activation, the first officer noticed the discrepancy, shouting, "Shit, reverser deployed". The Captain disconnected the autopilot and inputted maximum right rudder and aileron, soon after shutting down the left engine. The airplane experienced massive negative G-forces during the descent. Contrary to existing procedures, the flight crew proceeded to pull back on their flight controls before regaining a wings level attitude. This put massive stress on the airframe as it accelerated past its maximum operating speed (Vmo), to which parts of the tail began to disintegrate. Parts of the rudder and massive areas of the right elevator began to disintegrate from the aircraft, followed by the complete separation of the right tailplane, and the breaking of the aircraft's skin.

The aircraft's tail section broke completely free of the main assembly, causing the rest of the aircraft to assume a near vertical nose down position, as the aircraft exceeded 660 knots (Mach 1). The wings then broke free of the aircraft, and the remaining fuel inside the fuel tanks ignited into a massive fireball, and the aircraft crashed into wooded terrain in the Dan Chang District of Thailand. All 223 passengers and crew died. Shortly after the accident, local villagers began to loot the crash site, uncontrolled by the local police.

Passengers and crewEdit

Nationality Passengers Crew Total
  Argentina 1 0 1
  Australia 1 0 1
  Austria 74 9 83
  Belgium 1 0 1
  Bolivia 1 0 1
  Brazil 1 0 1
  Canada 2 0 2
  China 6 0 6
  Croatia 1 0 1
  Denmark 1 0 1
  Dominican Republic 1 0 1
  France 5 0 5
  Germany 4 0 4
  Hong Kong 52 0 52
  Hungary 2 0 2
  India 8 0 8
  Ireland 3 0 3
  Israel 4 0 4
  Italy 10 0 10
  Jamaica 1 0 1
  Japan 1 0 1
  Mexico 7 0 7
  Netherlands 3 0 3
  Norway 1 0 1
  New Zealand 1 0 1
  Philippines 2 0 2
  Poland 1 0 1
  Portugal 3 0 3
  Russia 1 0 1
  South Africa 2 0 2
  Spain 1 0 1
  Sweden 2 0 2
   Switzerland 7 0 7
  Taiwan 3 0 3
  Thailand 39 0 39
  Trinidad and Tobago 1 0 1
  Turkey 1 0 1
  United Kingdom 2 0 2
  United States 2 1 3
  Yugoslavia 3 0 3
Total 213 10 223

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.[1] Thomas J. Welch, the captain, lived in Vienna,[2] but originated from Seattle, Washington.[3]

Other websitesEdit


  1. Job, p. 204. "Of all the crew, Josef Thurner was perhaps the better known thanks to having been copilot to Niki Lauda himself on a Boeing 737 service to Bangkok which became the subject of a highly affirmative article on the airline and its history in the January 1990 issue of Reader's Digest [...]"
  2. Wallace, Charles P. "'All Evidence' in Thai Air Crash Points to Bomb". Los Angeles Times. 28 May 1991. 2. Retrieved 15 February 2013.
  3. "Pilots' Final Words". Associated Press]. The Seattle Times. 6 June 1991. Retrieved 15 February 2013.