The doomed two-seater plane hit the ground, sparking a small bushfire and killing the pilot and passenger, who co-owned the aircraft.
A report by the Australian Transport Safety Bureau said earlier on the day of the accident the pilot and passenger had conducted the aircraft's first flight since its assembly after importing it from the US in 2021.
The plane took off from Bankstown to Temora, then on to Wedderburn in its first test flight on Australian soil, ATSB director Stuart Macleod said in a preliminary report published on Wednesday.
On arrival at Wedderburn, a private airfield catering for recreational aircraft owners, the plane landed shortly before 3pm.
"For unknown reasons, the aircraft then became airborne again, and was observed by eyewitnesses and recorded by CCTV to have been in a shallow climb – enough to just clear rising terrain and trees at the end of the runway," Mr Macleod said.
"About two minutes after disappearing from view, the aircraft collided with terrain, about 150 metres from Appin Road."
Two bodies were later found in the wreckage of the Subaru-powered Glasair Super II, which was consumed by a post-impact blaze.
"To the extent possible due to the condition of the wreckage, on-site examination of the aircraft's flight controls and structure did not identify any pre-existing faults or failures," Mr Macleod said.
The federal transport body conducts "no-blame" investigations to prevent similar incidents from occurring.
The ongoing investigation will examine the aircraft's maintenance history, its weight and balance and performance characteristics, as well as the weather conditions at the time of the accident.
A final report, detailing the ATSB's findings and analysis, will be released at the conclusion of the investigation.
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