Lauda Air Flight 004 (NG004/LDA004) was a regularly scheduled international passenger flight from Hong Kong, via Bangkok, Thailand, to Vienna, Austria. On 26 May 1991, the Boeing 767-300ER operating the route crashed following an uncommanded deployment of the thrust reverser on the No. 1 engine during the climb phase, causing the aircraft to enter an aerodynamic stall, uncontrolled dive, and in-flight breakup, killing all 213 passengers and ten crew members on board. It is the deadliest aviation accident involving the Boeing 767, and the deadliest aviation accident in Thailand's history as of 2025. The accident marked the 767'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.