What happened
On November 7, 2016, an Airbus A319, registration F-GRHS, was conducting a ferry flight from Bologna to Paris. The aircraft was operating under the Minimum Equipment List (MEL) following a previous failure of the engine number 1 pressure regulating valve on the preceding day, which had left the aircraft relying solely on the second pneumatic system.
While cruising at flight level 380 over the Alps, near the PUNSA navigation point, the aircraft experienced a second failure. The Bleed Monitoring Computers (BMC) detected a hot air leak, which triggered the automatic closure of the engine number 2 pressure regulating valve. This secondary failure resulted in the total loss of all pneumatic sources for cabin pressurization.
As the cabin altitude began to rise, the crew declared a 'Pan Pan' and requested a rapid descent. Shortly after, the cabin altitude exceeded 9,550 feet, triggering the 'CAB PR EXCESS CAB ALT' alarm. The crew immediately donned oxygen masks and initiated an emergency descent, declaring a 'Mayday' to air traffic control. The aircraft descended to below 10,000 feet, where the crew removed their masks. Due to the loss of wing anti-ice capabilities, the crew requested a long approach to manage speeds in potential icing conditions. The flight concluded with a safe landing at Geneva Cointrin Airport.
The investigation
The investigation focused on the cause of the secondary pneumatic failure and the loss of pressurization capability. Investigators examined the pneumatic system architecture, specifically how the aircraft was configured to operate with a single pneumatic source under the MEL. The investigation also looked into the sequence of events leading from the initial engine 1 valve failure to the subsequent loss of the engine 2 system.
Findings
- The primary cause of the loss of pneumatic pressure was a defective seal on the first manifold located in the right wing, near the engine number 2 pylon.
- This leak caused the Bleed Monitoring Computers to detect high-temperature air, which automatically closed the engine 2 pressure regulating valve to protect the system.
- The aircraft was operating under the MEL, which allowed for flight with only one pneumatic system but left no redundancy for pressurization in the event of a second failure.
- The crew followed established emergency procedures, including the use of oxygen masks and the declaration of an emergency, to manage the rapid increase in cabin altitude.