What happened
On 18 August 2005, an A330-301, registration EI-CRK, was operating a scheduled flight from Shannon to New York (JFK). The flight was preceded by a flight from Dublin to Shannon, during which the crew noted a pressurization issue and a low-temperature engine bleed warning. Although the aircraft landed safely in Shannon, the crew was unable to maintain the desired cabin altitude during the subsequent flight to the United States.
While cruising at FL350 near position 53N 15W, the crew observed that the cabin pressure altitude was rising unexpectedly. As the cabin altitude climbed toward 10,000 ft, the crew activated the master warning, donned oxygen masks, and declared a PAN. To manage the loss of pressure, the captain initiated an emergency descent to 10,000 ft. The aircraft then diverted back to Shannon, performing an overweight landing. There were no injuries to the 225 passengers or the 2 crew members on board.
The investigation
The AAIU investigation focused on the cause of the depressurization. While initial troubleshooting in Shannon had addressed engine bleed issues, it had not identified a leak in the pressurization system. Subsequent inspection of the aircraft revealed that the aft cargo door seal had been incorrectly installed during maintenance performed in Dublin.
Maintenance records showed that a replacement seal had been fitted by a crew that had no prior experience with A330 cargo door seals. The installation took place late at night under challenging conditions, including darkness and the need to move the aircraft between stands. The investigation found that the seal was installed both upside down and inside out, which prevented the inflation holes from properly sealing the gap between the door and the airframe.
Findings
- The loss of cabin pressure was caused by the incorrect installation of the aft cargo door seal.
- The maintenance crew, led by a relatively new deputy crew leader, lacked specific experience with this safety-critical task.
- Environmental factors, such as darkness and the pressure to complete the task after delays in part delivery, contributed to the error.
- The manufacturer's instructions and the seal's physical markings were not sufficiently clear to prevent the orientation error.
Safety action
Following the investigation, several safety improvements were implemented:
- The aircraft manufacturer updated the Aircraft Maintenance Manual (AMM) to include a specific caution regarding the orientation of the seal's inflation holes.
- The manufacturer improved the visibility of the 'UP' and 'DOWN' markings on the seal itself.
- Recommendations were made to enhance the maintenance contractor's training regarding safety-critical tasks.