Synopsis
On 19 July 2024, a Boeing 737-800 operated by Malaysia Airlines Berhad, registration 9M-MXQ, was involved in a serious incident during a scheduled passenger flight from Kuala Lumpur International Airport (WMKK) to Kathmandu Airport (VNKT), Nepal. The aircraft departed WMKK at 1302 UTC with 150 passengers and 7 crew members on board.
Flight History
Operating as flight MH114, the aircraft cruised at Flight Level (FL) 340. After passing waypoint LALAT on airway M770, the Leading Steward reported elevated temperatures in the forward cabin to the Pilot in Command (PIC). The PIC initiated the Cabin Temperature Hot Non-Normal Checklist. Because the high temperature affected both the flight deck and passenger cabin, the PIC proceeded with the flight deck temperature high sequence. The trim air switch was set to OFF, but after one minute the cockpit temperature remained abnormally high, with the supply duct temperature reported at approximately 70°C by the Second in Command (SIC).
While the checklist was being carried out, airflow from the cockpit vents remained hot, and cabin temperature continued to escalate. The cabin altitude rate increased rapidly, peaking at 8,000 feet per minute, resulting in a loss of effective pressurisation at FL340.
Emergency Descent
Off the coast of Myanmar, the aircraft deviated north toward the diversion field and began its descent. While descending through approximately FL200, the flight crew observed the cabin altitude light illuminating and heard the cabin altitude warning horn, signaling a potential pressurisation issue. The crew promptly initiated the emergency descent procedure according to the Non-Normal Checklist for Cabin Altitude Warning or Rapid Depressurisation. Passenger oxygen masks were automatically deployed.
Upon reaching approximately FL100, cabin altitude stabilised, allowing the crew to remove their masks, and the distress condition was cancelled.
Diversion and Landing
The crew selected Yangon International Airport (VYYY) as the nearest suitable diversion airport and prepared for an approach to Runway 21. The SIC attempted to contact the operator via SATCOM and ACARS. A Passenger Address announcement informed passengers of the diversion. Following a performance evaluation, the PIC opted for an overweight landing. The landing distance was calculated using the Operational Performance Tool, and procedures from the Flight Crew Training Manual were reviewed by both pilots. The landing was safely executed on Runway 21 at 1550 UTC with no injuries reported among passengers and crew.
Aircraft Information
The aircraft was a Boeing 737-800, Malaysian registration 9M-MXQ. It was operated by Malaysia Airlines Berhad. The serious incident prompted a Mandatory Occurrence Report to the Civil Aviation Authority of Malaysia and the Air Accident Investigation Bureau, Malaysia.