de Havilland Canada DHC-6-320, VH-FNU

The crew of the DHC-6-320 aircraft reported that during descent to Cairns they smelt smoke in the cockpit. They then noticed the battery load meter was at maximum discharge and the right generator light was illuminated. The left generator switch was moved to the OFF position, however, the generator remained on-line.

Subsequent in-flight inspection revealed that the smoke was coming from behind the right cabin roof panel, which had begun to melt and bubble. The pilot in command then contacted Cairns approach control reporting a fire in the cabin and the aircraft was cleared to track direct to Cairns. The co-pilot accessed the cabin fire extinguisher and extinguished the fire. At approximately 4NM from the airport, the co-pilot reported that the fire was an electrical fire and had been extinguished. After landing, the crew stopped the aircraft on the runway and shut down the right engine to allow the fire fighters access to the cabin. Following confirmation that the fire was extinguished the aircraft was taxied to the terminal.

Investigation by the owner's maintenance organisation found that the left reverse current relay had severe heat damage. Other components and wiring near the left reverse current relay were also heat damaged. The reverse current relay was disassembled by the maintenance organisation's engineers, but they were unable to determine the reason for the failure due to the severity of the heat damage.

The Bureau did not conduct an on-site investigation of this occurrence.