The Australian Transport Safety Bureau (ATSB) has released the investigation report into a fatal crash near Tumut, NSW, in 2013.
Amateur-built Rand Robinson VH-CTE crashed on private property at Adelong on 5 October 2013, killing the pilot. No-one else was on board the aircraft.
The ATSB concluded that the crash was the result of a stall as the pilot tried to return to the airstrip following a partial engine failure.
Tracking data retrieved from a hand-held GPS on board the aircraft showed the pilot aborted a flight to Holbrook and instead returned to the runway, flying a closer downwind leg than usual. The data showed a ground speed of only 29 kts and a bank angle of 42o as the aircraft turned onto base leg.
Investigations later showed the engine lost power because a spark plug was ejected from a cylinder hole. This happened because a spark plug thread insert was installed wrong.
"There were reports and evidence that the pilot maintained and modified the aircraft, despite not being qualified or authorised to do so," the investigation report states.
"As well, in the previous two years, an authorised maintainer had not completed the required regular aircraft maintenance.
"The pilot’s decision not to have proper maintenance performed on the aircraft most likely contributed to the ejection of the spark plug, resulting in the accident."
However, the ATSB also stressed the importance of maintaining airspeed in the event of a loss of engine power.
"Managing airspeed and bank angle is critical to preventing an aerodynamic stall following partial engine failure after take-off. Research shows partial engine power loss is more complex and more frequent than a complete engine power loss.
"These accidents are typically a result of the aircraft entering an aerodynamic stall from a height where recovery is not possible."
The full investigation into the crash of VH-CTE is available on the ATSB website.