What happened
On 8 September 2003, a BAe 146-200, registration G-MIMA, arrived at Gatwick Airport for a scheduled passenger flight. Following a routine landing and engine shutdown, passengers had begun disembarking when an unusual odour was detected in the flight deck. Shortly thereafter, smoke was observed emerging from beneath the commander's seat.
In response, the commander initiated an emergency evacuation via the aircraft's public address system. During the process, approximately 18 passengers exited the aircraft via the front left door and the rear slide, with 2 passengers sustaining minor injuries. To mitigate the perceived risk, the crew opted to de-power the aircraft entirely, though they did not discharge the APU fire extinguisher as they believed the smoke originated in the avion and electronics bay.
The investigation
The AAIB investigation focused on the source of the smoke and the crew's response to the emergency. Technical examination of the aircraft's Auxiliary Power Unit (APU) revealed that the unit had been recently replaced. While the APU had only been in service for a few flight sectors, investigators found that the main rotor bearing had suffered a cage failure. This mechanical breakdown caused the shaft to move against a carbon oil seal, allowing hot engine oil to leak into the bleed air stream and enter the passenger cabin.
Engineers also noted that the flight deck door design contributed to the difficulty in monitoring the cabin during disembarkation. The bulkiness of the existing door made it difficult for the crew to observe the aisle effectively while the door remained closed.
Findings
- The primary cause of the smoke was a failure of the APU main rotor bearing cage.
- This failure led to the degradation of a carbon oil seal, allowing oil to contaminate the air supply.
- The crew lacked a specific checklist for managing smoke/fumes during the post-shutdown phase of operations.
- The physical design of the flight deck door limited the crew's ability to monitor the cabin's status during passenger disembarkation.