Flight AK-139 | Registration: 9M-DAE
Date: 6 April 2025 | Location: Near Kuala Lumpur, Malaysia
Flight Details
• Aircraft Type: Airbus A320-216
• Engines: 2 × CFM56-5B6/3
• Operator: AirAsia
• Registration: 9M-DAE
• Flight Number: AK-139
• Callsign: AXM139
• Route: Hong Kong International (VHHH), China to Kuala Lumpur International (WMKK), Malaysia
• Date of Incident: 6 April 2025
• Total Occupants: 186 (178 passengers, 8 crew)
• Weather Conditions: VMC conditions reported over Malaysian airspace
Introduction
On 6 April 2025, an AirAsia Airbus A320-200 operating flight AK-139 from Hong Kong to Kuala Lumpur experienced a cabin pressurisation failure during descent into Kuala Lumpur airspace. The incident resulted in automatic deployment of passenger oxygen masks and a precautionary continuation of the approach. The aircraft landed safely without further complication. No injuries were reported, but the aircraft was subsequently removed from service pending maintenance.
Sequence of Events
Flight AK-139 was nearing its destination and descending through the lower flight levels when a loss of cabin pressure was detected. This triggered the automatic deployment of passenger oxygen masks in accordance with the A320’s cabin altitude control system design.
The crew promptly donned oxygen masks, initiated the appropriate ECAM checklists, and began managing the descent in a controlled manner. A rapid descent was not required, indicating that the cabin altitude remained within manageable limits below the emergency threshold.
There was no declaration of a PAN or MAYDAY, and the flight continued on a stabilised approach to Kuala Lumpur’s runway, landing safely without delay or deviation.
Following landing, the aircraft was directed to a remote stand where engineers began fault diagnosis procedures. The aircraft remained grounded for over 28 hours after the event.
Crew & Communication
The flight crew acted in accordance with Airbus standard operating procedures for pressurisation anomalies. Upon receiving the ECAM warning for abnormal cabin pressure, the crew:
• Donned oxygen masks
• Initiated the pressurisation system checklist
• Monitored cabin altitude trends
• Managed descent profile within ATC guidance
There was no immediate emergency declared, which suggests the rate of depressurisation was either slow or plateaued at an altitude where oxygen masks were triggered as a precaution.
Cabin crew coordinated with the cockpit crew and reassured passengers once the oxygen deployment occurred. Communication between cockpit and air traffic control remained standard, with no requests for expedited approach, indicating the situation was stabilised.
Aircraft Systems & Technical Analysis
The Airbus A320’s pressurisation system is managed by a digital Cabin Pressure Control System (CPCS), which includes:
• Outflow valve
• Safety valve
• Cabin pressure controllers
• Manual and automatic modes
A cabin pressure anomaly during descent can result from several factors, including:
• Outflow valve malfunction or uncommanded opening
• Faulty cabin pressure controller
• Bleed air failure or inconsistent pressure from the engines
• Seal leakage around cabin doors or service panels
• Incorrect mode selection (manual vs. automatic)
The deployment of passenger oxygen masks occurs automatically when the cabin altitude exceeds 14,000 feet. In this case, the system responded as designed, indicating a cabin altitude threshold was breached temporarily.
Post-flight inspection would involve:
• BITE data analysis from the CPCS
• Inspection of the outflow valve and pressure controller
• Evaluation of engine bleed air flow and air conditioning packs
• Cabin seal integrity checks
Given the extended grounding, engineers likely required deeper systems checks or part replacements to confirm full integrity of the pressurisation system before return to service.
Passenger Experience & Cabin Conditions
Passengers experienced the deployment of overhead oxygen masks during descent, which can be unsettling even in a controlled situation. Cabin crew instructed passengers to remain seated and use the masks as required.
No physical injuries or reports of decompression effects were recorded. Cabin pressurisation loss was not violent, and there was no need for emergency descent or diversion.
Some passengers posted images and brief videos of the deployed oxygen masks on social media, though no reports indicated panic or disorganisation.
Passengers disembarked normally in Kuala Lumpur, and most were unaware of the technical specifics until later announcements or news coverage.
Emergency Response & Aftermath
Ground services at Kuala Lumpur International Airport were notified in advance of the issue and positioned equipment on standby, although no emergency landing procedure was triggered.
The aircraft was inspected on arrival and taken out of service for detailed engineering review. Passengers were accommodated on onward connections or transfers.
AirAsia issued a statement confirming the pressurisation issue, stating that the aircraft’s systems functioned correctly, masks deployed automatically, and that the crew responded according to standard safety protocols.
At the time of reporting, 9M-DAE remains out of service more than 28 hours post-landing.
Investigation Status
No formal air safety investigation has been initiated, as the event falls under operational safety management rather than a reportable serious incident. However, internal reports will be filed with Malaysia’s Civil Aviation Authority and Airbus for trend monitoring.
AirAsia’s engineering team will coordinate with Airbus to determine if any components require replacement or further analysis.
Flight data from the FDR and ECAM fault logs will be cross-referenced with cabin altitude data to determine:
• Peak altitude
• Rate of pressurisation loss
• Specific fault codes or manual intervention
Root Cause & Contributing Factors
The root cause remains under investigation, but likely candidates include:
• Faulty pressure controller or sensor
• Malfunctioning outflow valve logic
• Uncommanded switch to manual pressurisation mode
• Bleed air inconsistency due to duct or valve issues
Contributing factors may include:
• System redundancy delays in triggering corrections
• Altitude crossover during descent coinciding with system degradation
• Possible historical maintenance deferral on ECS components
Safety Recommendations & Industry Impact
While not classified as a serious incident, this pressurisation event highlights several key areas of safety focus:
• Importance of cabin pressurisation system integrity checks before descent
• Crew training on handling slow depressurisation scenarios
• Need for rapid fault diagnosis tools post-flight
• Emphasis on clear passenger communication during mask deployment events
AirAsia and other A320 operators may review existing maintenance procedures and system fault history to identify any recurring patterns or components with elevated failure rates.
Conclusion
The cabin pressurisation loss experienced by AirAsia flight AK-139 was safely managed thanks to rapid crew response, onboard system protections, and stable atmospheric conditions. The automatic deployment of oxygen masks served its intended function without escalation, and the flight concluded without injury or incident.
Nonetheless, the occurrence serves as a reminder of the critical role of cabin pressure control systems, especially during high workload phases like descent. Preventative maintenance, robust system diagnostics, and effective communication remain central to ensuring flight safety across global operations.
Disclaimer
This article is based on publicly available information and reports at the time of writing. While every effort has been made to ensure accuracy, we cannot guarantee the completeness of the information provided.
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