The Australian Transport Safety Bureau did not conduct an on-scene investigation into this occurrence. The report presented below was derived from information supplied to the Bureau and an ATSB laboratory examination of the engine's electrical wiring harness.
On 27 March 2004, while en route to conduct fire bombing operations south-east of Bunbury, Western Australia, the pilot of the Centrum Naukowo-Produkcyjne-PZL Dromader, registered VH-NIJ, noticed the engine begin to falter. With unsuitable terrain ahead, he elected to carry out a forced landing in a small forest clearing. A short time later the engine stopped completely and during the landing the aircraft was destroyed. The pilot exited the aircraft with minor bruising.
The wreckage was recovered to an engineering facility at Jandakot where the engine and its accessories were dismantled and examined. No faults were detected. During examination of the airframe, electrical continuity checks were conducted on the switch leads for the left and right magnetos1. The right magneto switch lead was found to be shorted or grounded to earth (producing the same effect as if the magneto switch was selected to OFF) and the left magneto switch lead was intermittently shorting to earth.
The electrical wiring harness, which exited the engine bay through a steel pipe in the upper right corner of the firewall, was examined and found to have been exposed to localised heating.
The wiring harness was disassembled and both magneto switch leads, which were positioned adjacent to each other in the harness, were found partially fused, due to the melting of their wiring insulation.
The wires were separated out of the harness and forwarded to the ATSB laboratory for closer inspection in an effort to determine the reason for the melted insulation. The examination confirmed that the heating was from an external source. It was not due to electrical power shorting within the wiring harness.
In the absence of any mechanical malfunction identified within the engine or any of its accessories, it is likely that the loss of engine power was the result of grounding of the right magneto switch lead, which switched that magneto off. The engine then faltered as the left magneto switch lead shorted to earth intermittently, depriving the engine of continuous electrical energy to the spark plugs from the remaining magneto.
Further examination of the aircraft could not determine the source of the localised heating of the wiring harness which melted the magneto switch lead insulation. The Civil Aviation Safety Authority advised that a check of the operator's fleet had not revealed similar damage to any other aircraft.
|Date:||27 March 2004||Investigation status:||Completed|
|Time:||1310 hours WST|
|Location:||15 km SE Bunbury, (ALA)|
|State:||Western Australia||Occurrence type:||Engine failure or malfunction|
|Release date:||29 September 2004||Occurrence class:||Technical|
|Report status:||Final||Occurrence category:||Accident|
|Highest injury level:||Minor|
|Aircraft manufacturer||PZL Warszawa-Okecie|
|Type of operation||Aerial Work|
|Damage to aircraft||Destroyed|
|Departure point||Bunbury, WA|
|Departure time||1310 hours WST|