What happened
On 21 October 2025, a Malaysia Airlines Berhad flight, MH2742, was operating a scheduled domestic service from Kuala Lumpur International Airport to Bintually Airport. The aircraft, a Boeing 737-800 with registration 9M-MXR, was cruising at Flight Level 350 when the crew identified an abnormal cabin pressurization event.
During the cruise phase, approximately 40 nautical miles before the top of descent, the cabin altitude began to rise rapidly, with the cabin rate of climb reaching about 1,200 feet per minute. In an attempt to stabilize the pressure, the pilot in command switched the pressurization mode to manual and closed the outflow valve; however, the cabin altitude continued to climb. During this period, the crew noted a "BLEED TRIP OFF (2)" indication, signaling that the No. 2 engine bleed air supply had been isolated due to high temperature or pressure conditions.
As the cabin altitude surpassed 10,000 feet, the cabin altitude warning was triggered. The crew initiated an emergency descent to 10,000 feet. During the descent, the cabin altitude peaked at approximately 15,000 feet, necessitating the manual deployment of passenger oxygen masks by the safety co-pilot. The aircraft eventually stabilized at 10,000 feet, allowing the crew to reset the bleed system. The flight proceeded to Bintulu, where all 117 occupants landed safely without injury.
The investigation
The Air Accident Investigation Bureau (AAIB) Malaysia conducted an investigation into the incident. The inquiry examined the aircraft's maintenance history, which showed the 9M-MXR was in airworthy condition with valid certificates of airworthiness and registration. The investigation also reviewed the flight recorders, including the Flight Data Recorder and Cockpit Voice Recorder, and confirmed that the flight crew members held valid licenses and had undergone negative drug and alcohol screenings.
Findings
- The aircraft experienced a rapid rise in cabin altitude following a pressurization abnormality.
- The No. 2 engine bleed air supply was isolated due to a high-temperature or high-pressure condition.
- The crew successfully managed the emergency descent and stabilized the cabin altitude at 10,000 feet.
- There was no structural damage to the aircraft identified during post-flight inspections.
Safety action
Following the incident, the operator has taken several immediate steps:
- The engineering department, in coordination with Boeing, has implemented enhanced monitoring and inspections of the B737NG pressurization and pack systems.
- Flight Operations has issued internal safety communications to all crews to increase awareness of such events and to emphasize clear communication protocols during the use of oxygen masks.