What happened
On 15 February 2010, a Boeing 757-204, registration G-BYAT, arrived at Glasgow International Airport from Funchal, Madeira. After the aircraft had docked at stand 28 and passengers had begun disembarking, the cabin crew detected a strong, acrid smell spreading through the aircraft.
Upon noticing the increasing intensity of the odour, the senior cabin crew member notified the flight deck. The co-pilot confirmed the smell was present in the forward galley, though no smoke was visible. To mitigate the issue, the flight crew deactivated the APU and the Utility busbars to isolate electrical power to the galleys.
Concerned by the persistent smell, the senior cabin crew member initiated an emergency evacuation via the rear doors. During the process, 43 passengers exited using the emergency slides, with four passengers sustaining minor injuries. The evacuation was completed via the airbridge at door L2, where airport fire services assisted the passengers.
The investigation
Investigators examined the aircraft's right-hand recirculation fan to identify the source of the burning smell. Maintenance engineers had previously noted the unit was performing poorly. During a technical examination at a UK overhaul facility, investigators found that the unit's rear rotor bearing had failed.
Detailed analysis revealed that the fibre bearing cage had disintegrated. It was determined that the bearing grease shield had likely become loose, allowing grease to escape. This led to a failure of the bearing, causing the rotor and stator to make contact. This friction generated black dust and debris, which produced the burning smell. The investigation also noted that the thermal cut-out on the unit had reset at a temperature of 145ºC, which was higher than the manufacturer's specification of 126ºC.
Findings
- The electrical burning smell was caused by burning grease within the right recirculation fan.
- The failure originated from the disintegration of the fibre bearing cage and the subsequent escape of lubrication.
- Friction between the rotor and stator created the debris and odour that prompted the evacuation.
- The flight crew were unaware that an evacuation had been initiated until after the event had occurred.
- The thermal cut-out reset temperature was higher than the manufacturer's recommended limit.