A two-seater plane that crashed south of Sydney, killing its occupants, was built from a kit, crash investigators say.

Investigators from the Australian Transport Safety Bureau were expected to pore over the wreckage in coming days after arriving at the crash site in Appin on Tuesday afternoon.

The doomed plane collided with terrain and sparked a grass fire about 3pm on Monday.

Two bodies were later found in the wreckage of the Subaru-powered Glasair Super II.

The plane had earlier been near Goulburn. But where it took off from and whether it was to land at a small airstrip in Appin was undetermined, the ATSB said.

“We do know that it was a small two-seater, single engine, kit-built experimental aircraft initially coming out of the US,” Chief Commissioner Angus Mitchell said.

Mr Mitchell said his team was trying to determine whether the amateur-built aircraft was under power when it crashed and whether it was undergoing any sort of practice run, including a landing and takeoff manoeuvre called a touch-and-go.

Small aircraft often don’t have many recording devices, but the plane would be searched for mobile phones in case usable data could be retrieved.

Eyewitness accounts could also provide valuable information.

“There were a number of planes in the area, there are a number of people who have seen the plane in its final phases of flight and then lost sight of it as it’s gone behind the trees,” Mr Mitchell said.

“Exactly what it was doing at the time, how low it was – we have to piece together.”

He said it was too early to speculate based on witness accounts until they have been verified with other sources.

The initial ATSB safety investigation will include an assessment of aircraft and pilot records, the aircraft’s maintenance history and weather information.

A preliminary report is expected to be delivered within eight weeks.

The ATSB is also at the scene of a fatal light plane crash in the Northern Territory after a Cessna 210 crashed during a flight from Nhulunbuy to Katherine.

Mr Mitchell said 2022 had been one of the worst years on record for light plane fatalities, with 23 deadly crashes across Australia.

“We’re certainly hoping … we can start next year with much safer skies than we’ve had in these past 12 months,” he said.

Like a coroner, the ATSB conducts “no-blame” investigations to prevent similar incidents from occurring. Police and other authorities are responsible for taking appropriate administrative, regulatory or criminal action.

-AAP