What happened
On January 26, 2004, an Airbus 321-200, registration EI-CPD, was operating a scheduled flight from London Heathrow to Dublin. Earlier that morning, during a landing at Heathrow, the flight crew had noted a noise in the forward hold area. A ground inspection revealed an open blow-out panel, but because no other issues were identified, the panel was reset and the aircraft was cleared for its return leg.
Twelve minutes after departing London, while climbing through Flight Level 2/66, the crew observed the cabin altitude climbing rapidly. The Electronic Centralised Aircraft Monitoring (ECAM) system issued warnings for excessive cabin altitude and low differential pressure. The pilots donned oxygen masks and initiated an emergency descent to 10,000 feet. The aircraft subsequently diverted to Cardiff Airport, where the crew performed an assessment and landed without further incident. There were no fatalities or injuries among the 8 crew members and 155 passengers.
The investigation
The investigation focused on the mechanical failure within the left-hand air conditioning system. Post-flight inspections at Cardiff revealed that a metal clamp holding the air conditioning bellows to the condenser unit had broken, causing the bellows to rupture. This failure allowed cabin air to escape through the Pack Outlet Check Valve (POCV) flap, which had also fractured.
Technical analysis by the aircraft manufacturer suggested that the clamp had been incorrectly installed during a previous maintenance check, leading to increased stress and eventual rupture. Furthermore, examination of the broken POCV flap by a subcontractor revealed material inclusions and surface scratches from the casting process, which likely contributed to the valve's failure under the oscillating airflow caused by the bellows rupture.
Findings
- The primary cause of the depressurization was the fracture of the clamp on the left-hand air conditioning condenser, which led to a rupture of the bellows unit.
- The resulting airflow instability caused the POCV flap to oscillate violently against its stops, leading to the valve's failure.
- Material inclusions within the valve flap casting acted as a contributing factor to the metal fatigue and fracture.
- The initial ground inspection at London Heathrow failed to identify the damaged bellows, as the crew did not follow the specific troubleshooting tasks required when a blow-out panel is found open.