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| Date: | Friday 19 July 2024 |
| Time: | 14:53 UTC |
| Type: |  Boeing 737-8H6 (WL) |
| Owner/operator: | Malaysia Airlines |
| Registration: | 9M-MXQ |
| MSN: | 40154/4749 |
| Year of manufacture: | 2014 |
| Engine model: | CFMI CFM56-7B |
| Fatalities: | Fatalities: 0 / Occupants: 157 |
| Other fatalities: | 0 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | over Andaman Sea, south of Yangon -
 Indian Ocean
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Kuala Lumpur International Airport (KUL/WMKK) |
| Kathmandu-Tribhuvan Airport (KTM/VNKT) | |
| Investigating agency: | AAIB Malaysia |
| Confidence Rating: |  Accident investigation report completed and information captured |
Malaysia Airlines flight MH114, a Boeing 737-8H6, suffered a loss of cabin pressure while en route over the Andaman Sea at FL340. The flight made an emergency descent to FL100 and diverted to Yangon Airport (RGN), Myanmar.
While cruising at Flight Level (FL) 340 and after passing waypoint LALAT on airway M770, the Leading Steward (LS) reported elevated temperatures in the forward cabin to the PIC. The PIC initiated the Cabin Temperature Hot Non-Normal Checklist (NNC).
Since the high temperature anomaly affected both the flight deck and passenger cabin, the PIC proceeded with the flight deck temperature high sequence to prevent
potential crew incapacitation. The trim air switch was set to OFF; however, after one minute, the cockpit temperature remained abnormally high, with the supply duct temperature reported at approximately 70°C by the SIC.
While the non-normal checklist was being carried out the 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 cruising altitude FL340.
Off the coast of Myanmar, the aircraft deviated north toward the diversion field and began its descent. While descending from FL340 and approximately passing through 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 (NNC) 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. The crew selected Yangon International Airport (VYYY) as the nearest suitable diversion airport and prepared for an approach to Runway 21.
Causes/Contributing Factor
The incident was caused by the rupture of the RH Flexible Pressure Sleeve, located downstream of the Air Cycle Machine (ACM) and High Pressure Water Separator (HPWS). This failure resulted in a significant loss of conditioned air from the right Environmental Control System (ECS) Pack, reducing the system’s ability to cool and pressurize the cabin at high altitude. The compromised airflow contributed to inadequate cabin temperature control and degraded pressurisation during descent The RH Flexible Pressure Sleeve failure is categorised as a System/Component Failure or Malfunction – Non-Powerplant (SCF-NP) under ICAO accident classification standards and represents a critical technical factor in the incident sequence.
Accident investigation:
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|
Sources:
https://www.flightradar24.com/data/aircraft/9m-mxq#36399d95
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 19-Sep-2024 16:53 | ASN | Added |
| 19-Sep-2024 16:53 | ASN | Updated [Damage, ] |
| 25-Aug-2025 18:59 | ASN | Updated [Total occupants, Narrative, Accident report, ] |
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