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Summary

Summary

In cruise at 10,000 ft the pilot noticed the left alternator light had illuminated, and that the right alternator was now taking all electrical loads. The left engine power then reduced from 31hg to 23hg, suggesting to the pilot that the turbo-charger was malfunctioning. As the aircraft was now unable to maintain its cruise altitude the pilot requested a descent to 7,000 ft. He also requested an airways clearance to return to Parafield. He changed the left fuel tank selection from the main to auxiliary, and turned the left fuel boost pump on. This restored engine power for a short period of time before it suffered a complete failure, followed by a complete loss of electrical power and smoke entering the cabin. The pilot feathered the left propeller, and turned the fuel selector and all electrical switches off. He maintained communications with Adelaide FIS using a mobile telephone. A successful single engine landing was made after the pilot manually extended the landing gear. An investigation indicated that the alternator field wire had chaffed on the engine fuel supply line, wearing through its insulation which allowed the bared wire to then arc on the line, eventually burning a hole through it. The ensuing loss of fuel supply through the hole, with associated loss in fuel pressure, contributed to the reduction of engine power. Activation of the fuel boost pump assisted in restoring some pressure, and power. Fuel spraying from the holed line was ignited by the arcing alternator field wire, causing fire damage to the wing leading edge skin, wing structure rear of the firewall, oil pressure, hydraulic and fuel supply lines, and the nacelle fuel tank and vent lines. The electric loom between the engine and cabin had the insulation burnt off, allowing it to short circuit and cause the electrical failure. The magneto earth wires, being part of this loom, and also bared of insulation, grounded both magnetos, shutting down the engine. The engine failing due to the grounded magnetos, and the pilots action of turning the fuel off, probably deprived the fire of fuel before it became established, and self extinguished.
 
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