Lauda Air

Summary

Lauda Air 004 disintegrated over Thailand when the left engine's thrust reverser deployed in flight at cruise altitude, generating uncontrollable aerodynamic forces. Niki Lauda, the airline's founder and former Formula One champion, personally challenged Boeing's initial denials and demonstrated the reverser deployment in a simulator. Boeing subsequently modified the 767 fleet globally. All 223 aboard were killed.

Cause & Investigation

Timeline & Safety Improvements

1. 1991-05-26

   Flight NG004 disaster

   Boeing 767-300ER operating for Lauda Air. 223 fatalities, 0 survivors.

2. Investigation

   Formal investigation opened

   Conducted by: Thai Department of Aviation with assistance from Boeing, FAA and Austrian authorities.

3. Findings

   Cause determined: Uncommanded thrust reverser deployment in flight

   The left engine's thrust reverser deployed unexpectedly at 24,700 feet. The sudden asymmetric drag caused the aircraft to roll uncontrollably to the left, enter a steep dive, and break apart over the Thai jungle. The specific electrical fault causing the reverser to deploy was never positively identified. Boeing initially denied in-flight reverser deployment was possible, but niki Lauda himself demonstrated it could occur in a simulator.

4. Safety change 1

   Improvement implemented

   Boeing modified the 767 thrust reverser control system to prevent in-flight deployment.

5. Safety change 2

   Improvement implemented

   The FAA issued an Airworthiness Directive grounding 767s until the modification was applied.

6. Safety change 3

   Improvement implemented

   Redundant interlocks were added to thrust reverser systems across all Boeing widebody types.

7. Safety change 4

   Improvement implemented

   Investigation procedures for in-flight reverser deployment scenarios were incorporated into crew training.