History of the Flight
The aircraft, an ATR 42-300 registered EI-BYO, was operating a scheduled passenger flight from Dublin to Ronaldsway, Isle of Man, on 7 October 2008. On board were 3 crew members and 17 passengers. The flight was uneventful until the aircraft began its initial descent from cruise level, when an AFT SMK warning illuminated on the flight deck.
Response and Landing
The flight crew immediately carried out the ‘AFT SMK’ Quick Reference Handbook (QRH) emergency procedure. The commander informed the cabin crew member at the rear of the aircraft about the warning. The cabin crew member checked the area and found that the cargo bay was clear, but smoke was emanating from the toilet compartment. She discharged one BCF extinguisher into the toilet, closed the door, and reported back to the commander. After approximately two minutes, she rechecked the toilet and found that the smoke had cleared. The AFT SMK warning on the flight deck had also extinguished.
The commander contacted Ronaldsway Air Traffic Control (ATC), advised them that a fire warning had activated in the cabin, and requested a priority landing. ATC declared a full emergency, alerted the Aerodrome Rescue and Fire Fighting Service (RFFS) and external emergency services, and provided vectors for an Instrument Landing System (ILS) approach to Runway 26. The aircraft completed a successful approach and landing, then taxied to the ramp area with the RFFS in attendance. Passengers disembarked normally, and the RFFS inspected the aircraft for signs of fire, finding none.
Examination
Post-flight examination by maintenance personnel revealed that the cover on the illuminated ‘RETURN TO SEAT’ sign in the toilet had overheated and the bulb filaments had failed. Further investigation confirmed that correct bulbs had been fitted, but no cause of overheating could be identified. The troubleshooting documentation and the unit were sent to the manufacturer for examination; as of the report, no apparent reason for the smoke had been determined.
The flight deck smoke warning is triggered by detectors in the aft cargo area and the toilet compartment. The source of activation is not specified on the flight deck, but the Flight Attendant Panel at the rear of the aircraft distinguishes between toilet and cargo smoke detectors.