What happened
On September 12, 2013, an Airbus A320-214, registration HB-IJU, operated by Swiss International Airlines, experienced a serious in-flight incident while cruising 60 NM north of Marseille. The aircraft, flying flight SWR 2140, encountered a loss of cabin pressure during its cruise phase. The crew initially issued a PAN-PAN signal and requested a descent to flight level 350. Shortly thereafter, the situation escalated, leading the crew to declare a MAYDAY and initiate an emergency descent. The aircraft descended rapidly through various flight levels, eventually reaching flight level 140, as the crew managed the depressurization.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) conducted an inquiry into the technical and operational aspects of the event. The investigation focused on the state of the aircraft's pneumatic systems and the procedures available to the flight crew. Investigators examined the aircraft's maintenance history, specifically looking at the status of the pneumatic system and any pending manufacturer service bulletins. The investigation also reviewed the airline's Minimum Equipment List (MEL) procedures and the clarity of the flight crew's operational manuals regarding system failures.
Findings
The investigation established that the primary cause of the incident was a loss of cabin pressure necessitated by a failure in the pneumatic system. Several contributing factors were identified:
- The aircraft was operating with only a single functional pneumatic system at the start of the flight.
- The remaining pneumatic system exhibited characteristics that led to overheating, which triggered an automatic shutdown.
- A previously identified improvement recommended via a manufacturer service bulletin had not yet been implemented on the aircraft.
- The airline had not yet received a revised MEL procedure from the manufacturer.
- The flight crew's management of the system was hindered by confusing procedures, as the necessary information for handling such a failure was not presented clearly in the operational documentation.
Safety action
Following the incident, Swiss International Airlines implemented several measures to prevent a recurrence, including:
- A review of the operational risk evaluation regarding cabin decompression.
- The replacement of specific components in accordance with Airbus service bulletins.
- The introduction of new MEL procedures for redundancy checks of the remaining bleed system and packs.
- Upgrades to the Flight Warning Computers to better integrate emergency operating procedures.
- Enhanced training for commanders to address the technical and operational aspects of such incidents.