What happened
On 30 October 2005, an Airbus A319-131, registration G-EUPF, was conducting a public transport flight from Aberdeen, Scotland. Shortly after departing the airfield, the cabin crew reported a peculiar odour in the forward section of the aircraft. While the flight crew initially believed the smell might originate from galley ovens, the scent soon intensified, spreading to the flight deck and accompanied by a rise in cabin temperature.
During the flight, several system alerts were triggered, including messages related to the Ground Proximity Warning System (GPWS) and the Instrument Landing System (ILS). Due to the developing situation, the crew donned oxygen masks and declared an emergency, subsequently performing an uneventful return to Aberdeen. Following the landing, the unusual smell dissipated. The aircraft was taxied to a stand where, after an inspection by the fire service, passengers were allowed to disembark normally.
The investigation
Engineers conducted a comprehensive inspection of the aircraft's engines, air conditioning system, pressurisation system, and the auxiliary power unit. This investigation found no issues within those primary systems. However, an 'AVIONICS VENT SYS FAULT' message had appeared on the engine and warning display during the flight.
Because of the combination of the ILS and GPWS faults alongside the ventilation error, investigators focused on the avionics cooling system. The avionics vent fan and its associated filter were replaced. Subsequent inspections of the removed fan revealed that the steel ball bearings were worn and noisy. This component was sent for repair, and no further issues were reported on later flight sectors.
Findings
- The primary cause of the smoke-like smell and temperature increase was a failing bearing within the avionics vent fan.
- The failure of the bearing produced a low rumbling noise and a burning odour.
- The degradation of the bearing reduced the efficiency of the avionics cooling system, triggering the ventilation fault message.
- The manufacturer had previously issued service information regarding improvements to these fans, moving from steel to ceramic ball bearings to prevent similar occurrences.