What happened
On 18 August 1999, a Fokker F28 Mark 0100, registration G-UKFA, was conducting a scheduled public transport service from Belfast to Amsterdam. While cruising at FL330, cabin crew alerted the flight deck to a burning odor and identified a warm area on the cabin floor located behind the left forward main passenger door. The First Officer was able to confirm the presence of this heat.
In response to the potential fire risk, the commander declared a PAN-PAN call to facilitate a rapid descent and diverted the aircraft to Leeds-Bradford Airport. The commander selected this destination due to his familiarity with the airfield. The aircraft performed a standard ILS approach and landed safely on Runway 32. Upon arrival, the airport fire service met the aircraft and utilized thermal imaging cameras to inspect the area. Their inspection revealed no active fire, only warmth concentrated around the avionics bay. After the avionics bay was opened and found to be clear of fire, passengers remained on board while the fire service completed a thorough inspection before the aircraft taxied to the stand for disembarkation.
The investigation
Following the incident, company engineers performed a detailed inspection of the aircraft, specifically examining ducting and potential leaks. The investigation focused on the area of the cabin floor that had felt warm, which sat directly above the electronics bay where electrical wiring is routed under the carpet. No damage to the wiring or any leaks were identified during this check, and the aircraft was cleared for service following a successful ground run.
However, during a subsequent flight to Amsterdam, the cabin crew reported the return of the oily, burning smell after requesting increased heating. The smell dissipated once the air conditioning output was reduced. A follow-up examination of the air conditioning system identified oily contamination within the coalescer (water separator) bags. These components were subsequently replaced, which prevented any further recurrence of the issue.
Findings
- The perceived heat on the cabin floor was likely a subjective sensation influenced by the presence of the strong odor.
- The source of the smell was identified as oily contamination within the air conditioning system's water separator bags.
- The incident occurred during the first flight of the season where the air conditioning temperature was increased from a fully cold setting, coinciding with warmer ambient weather.