What happened
On June 5, 2009, an Airbus A310-325, registration OK-YAD, operating for ČSA, was en route from Hurghada to Prague at flight level 380. During the flight within the Belgrade FIR, the crew identified a malfunction in the cabin air supply system. The failure progressed as the first bleed valve failed, followed by the failure of the second bleed valve.
As the aircraft descended, the cabin altitude increased significantly, triggering the activation of oxygen masks for both the flight crew and the passengers at flight level 280. The crew initiated a descent to flight level 100 to stabilize the cabin environment. Following the descent, the crew evaluated fuel levels and determined that while they could reach Prague, they did not have sufficient fuel to divert to an alternative airport such as Budapest or Vienna. The aircraft landed safely in Prague with no injuries to the 88 passengers or the 8 crew members.
The investigation
The ÚZPLN investigation utilized data from the Cockpit Voice Recorder (CVR) and the Quick Access Recorder (QAR) to reconstruct the sequence of events. The investigation examined the technical state of the aircraft's bleed air system and the crew's adherence to established operating procedures. Maintenance records were reviewed, revealing that subsequent inspections and repairs identified various components of the bleed system as having suffered from operational wear, including a corroded connector and a cracked supply pipe.
Findings
- The primary cause of the incident was a technical failure of the engine bleed air system components.
- The failure was characterized by the sequential loss of both bleed valves.
- The crew's response to the emergency was assessed as uncertain, as they did not immediately follow the Quick Reference Handbook (QRH) checklist for a dual bleed fault, which mandates an immediate descent.
- The descent was initiated only after an ECAM warning for excess cabin altitude was triggered.
- The crew's descent speed was lower than the speeds permitted by emergency procedures.
- Standard procedures for workload distribution between the Pilot Flying (PF) and Pilot Not Flying (PNF) were not strictly maintained.
- Communication between the flight crew and the cabin crew was inadequate, leading to a delay in informing passengers of the situation.
- The operator's maintenance findings attributed the component failures to operational wear and tear.
Safety action
Following the preliminary report, the operator conducted retraining for the crew involved, focusing on emergency procedures during cabin depressurization and the commander's ability to manage undesirable aircraft states. The investigator recommended that the operator familiarize all A310 flight crews and maintenance personnel with the findings of this investigation.