What happened
On 13 February 2024, a Batik Air Malaysia Boeing 737-800, registration 9M-LCM, was operating a scheduled passenger service from Kuala Lumpur International Airport to Sibu Airport. The flight, carrying 92 passengers and crew, began experiencing technical difficulties during the initial climb. At approximately 5,000 feet, the crew noted the illumination of the Engine No. 2 Bleed Trip light and subsequently deactivated Pack No. 2 following standard procedures.
As the aircraft climbed to 29,000 feet, the crew activated the engine anti-ice systems due to icing conditions. This triggered a secondary issue where the Engine No. 1 Thermal Anti-Ice (TAI) annunciator illuminated, indicating a valve stuck in the open position. To mitigate icing risks, the crew climbed to 35,000 feet. However, during the descent toward Kuching International Airport, the aircraft experienced an uncontrolled change in cabin pressure. The cabin altitude warning triggered at 20,000 feet, leading the crew to initiate an emergency descent. During the descent, passenger oxygen masks were deployed. The aircraft eventually stabilized the cabin altitude at 10,000 feet and landed safely at Kuching after a brief hold due to weather.
The investigation
The AAIB Malaysia examined the flight history, maintenance records, and technical components of the aircraft. The investigation reviewed the sequence of engine bleed trip events and the maintenance performed on the aircraft's anti-ice and pressurization systems. Investigators also analyzed the flight data and cockpit voice recorder to reconstruct the timeline of the depressurization event and the crew's response to the emergency.