What happened
On July 8, 2016, an Airbus A320-200 operating a scheduled flight from Berlin-Schönefeld to Tenerife Sur encountered a serious cabin pressure disturbance. While cruising at FL350 near the Pontoise (PON) radio beacon, the cabin pressure altitude began to rise, reaching approximately 8,800 to 9,000 feet. This triggered a cabin pressure advisory on the Electronic Centralized Aircraft Monitoring (ECAM) system.
The flight crew attempted to follow the relevant ECAM checklist, with the co-pilot attempting to manually adjust the cabin pressure via the control switch. However, the crew was unable to control the cabin pressure altitude manually, which subsequently rose to approximately 11,000 feet. This triggered an "Excessive Cabin Altitude" warning, prompting the crew to declare an emergency and don oxygen masks.
The pilot flying initiated an emergency descent, maneuvering the aircraft northwest to avoid high traffic density in the sector. The crew monitored TCAS alerts on the navigation display while coordinating the descent with air traffic control. After approximately 2.5 minutes, the descent was terminated at FL300, where the crew successfully stabilized the cabin pressure at roughly 6,500 feet. The co-pilot then returned the outflow valve mode selector to the "Auto" position. The flight subsequently diverted to Düsseldorf Airport, where a safe landing was performed on runway 23L.
The investigation
The BFU examined flight data recorder (FDR) and cockpit voice recorder (CVR) data to reconstruct the sequence of events. The investigation also included a technical inspection of the aircraft's engine systems and a review of maintenance records. The investigation confirmed that during the descent, the high-pressure bleed valve of engine number 1 was open.
Findings
Post-flight inspections by the airline's maintenance facility identified the cause of the pressure loss as a damaged solenoid thermostat and a malfunctioning pressure regulating valve within the engine number 1 (left) system. Both components were subsequently replaced.