What happened
On 1 August 2003, a BAe 1s46-200, registration G-MANS, was preparing for a scheduled service from Belfast City Airport to Manchester. The aircraft was carrying 53 passengers and 5 crew members. Following pushback from the stand and the commencement of engine starts, the cabin crew noticed the smell of fumes and visible smoke, which appeared most concentrated toward the rear of the aircraft.
While the flight deck remained clear of smoke, the Senior Cabin Crew Member reported that the situation was deteriorating and that passengers were becoming agitated. The commander initially switched off the air-conditioning packs to mitigate the issue, but as the smoke persisted, the decision was made to perform an emergency evacuation. During the evacuation, a passenger opened the rear right door, causing the emergency slide to deploy. All passengers and crew successfully exited the aircraft, though one passenger sustained a minor injury to their back.
The investigation
The investigation focused on the source of the smoke and the mechanical state of the Auxiliary Power Unit (APU). Upon removal, the APU underwent a detailed teardown examination by the manufacturer's agent. This inspection identified oil deposits and staining on the compressor rotor and air intake, suggesting a leak from the compressor carbon seal into the air path.
While minor leakage is not uncommon in such units, investigators found evidence of a recent, significant loss of oil. The examination of the carbon seal and roller bearing showed no signs of overheating or bearing failure, but a missing 'O' ring was noted in the bearing retainer assembly, though this was not deemed the primary cause of the leak.
Findings
- The smoke and fumes in the cabin were caused by an oil leak from the compressor carbon seal into the aircraft's air conditioning packs.
- A compressor surge had caused the rotor assembly to move, leading to the compression and subsequent unseating of the carbon seal bellows, allowing oil to escape.
- The absence of an 'O' ring in the bearing retainer assembly was noted, but it was not found to be the cause of the leak.
- The decision to evacuate was prompted by the increasing density of smoke and the crew's concerns regarding a potential fire.