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.
1 A magneto is a
component driven by the engine to produce electrical power for the
ignition system spark plugs independent of the aircraft electrical
system.