What happened
On 19 July 2024, a Boeing 737-800, registration 9M-MXQ, was operating a scheduled service from Kuala Lumpur to Kathmandu with 150 passengers and 7 crew members. While cruising at 34,000 feet, the crew was alerted to rising temperatures in the forward cabin. As the flight crew attempted to manage the heat, the cabin altitude began to rise rapidly, reaching a rate of 8,000 feet per minute. This sudden loss of effective pressurization triggered the cabin altitude warning and the automatic deployment of passenger oxygen masks.
The crew initiated an emergency descent, leveling off at 10,000 feet. The aircraft subsequently diverted to Yangon International Airport in Myanmar. Due to the necessity of the diversion, the aircraft performed an overweight landing on Runway 21. There were no injuries reported among the passengers or crew.
The investigation
AAIB Malaysia examined the technical failures of the aircraft's environmental control systems. The investigation focused on the right-hand side of the aircraft's air conditioning infrastructure. Investigators analyzed maintenance records and the physical condition of the components involved in the temperature and pressure fluctuations.
Findings
- The primary cause of the incident was the rupture of the right-hand flexible pressure sleeve, located downstream of the Air Cycle Machine and High Pressure Water Separator.
- This rupture led to a significant loss of conditioned air from the right Environmental Control System (ECS) pack.
- The failure of this component directly resulted in the inability to maintain adequate cabin temperature and caused the uncontrolled cabin pressurization during the cruise phase.
Safety action
Following the preliminary report, the operator issued a Flight Safety Memo to increase awareness of technical failures. The final investigation has recommended that the aircraft operator improve its strategy for the availability of non-critical components. Specifically, the report suggests enhancing spare parts inventory management and streamlining procurement processes to ensure that even non-critical items, which can have significant operational impacts, are readily available to maintain fleet serviceability.