Flight and Incident
Prior to departure, the pilot received a weather forecast indicating possible fog at the destination. The aircraft carried adequate fuel for holding or diversion. After a 35-minute flight, the aircraft arrived in the Goulburn area, and the pilot reported an intention to conduct a standard instrument approach. Witnesses observed the aircraft circling over the city several times at a relatively low height. It then rolled and descended steeply, striking two houses. A fierce fire engulfed the aircraft and both residences.
Occupants and Fatalities
The three persons on board the aircraft and one person in a house received fatal injuries.
Investigation Findings
A detailed inspection of the wreckage revealed that the left engine's camshaft had failed in flight due to fatigue cracking from defective manufacture. The pilot had apparently feathered the propeller, and the engine was not operating at impact. No other defects were found. Investigators determined that shallow fog likely obscured part of the aerodrome. The pilot probably used the city lights as a holding point while waiting for conditions to improve. During left-hand orbits, the left engine failed completely.
Single-Engine Performance
To achieve optimum single-engine performance, the pilot needed to feather the propeller, reduce drag, and establish appropriate airspeed. Although the propeller was likely feathered, the landing gear remained lowered, increasing drag. Radar data from Canberra indicated the airspeed was below the optimum figure before radar contact was lost. Witnesses described a final maneuver consistent with loss of control in a twin-engine aircraft when power is supplied by only one engine and speed is below the minimum required for full control.
Probable Cause
The official probable cause was failure of the left engine in flight due to defective manufacture of the camshaft. Contributing factors included fatigue failure of the camshaft, complete loss of power from the left engine, the aircraft not being reconfigured for optimum single-engine performance, airspeed falling below the minimum for effective control, and insufficient height for recovery.