The small plane that crashed at Appin on Boxing Day, leaving two people dead, is understood to have been an "experimental" aircraft built from a kit.
Initial investigations by the Transport Safety Bureau revealed the plane was not a mass-produced aircraft, but a Glasair Super II, a small, two-seater plane from the United States with a Subaru engine, the bureau understands.
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 bureau said.
Transport Safety Bureau chief commissioner Angus Mitchell said the plane may have been on its way to Wedderburn Airstrip, a small airstrip in Campbelltown.
While the plane was originally registered in the United States, authorities are yet to determine how long it has been in Australia.
Police are yet to confirm the identities of the two passengers. However it is understood that emergency services may complete the recovery of the pilots involved later on Tuesday.
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 Transport Safety Bureau will attempt to map the exact flight path of the plane and other details of the crash as investigations continue.
"It will be a painstaking process for investigators to piece together what they can from the site," Mr Mitchell said.
Police, investigators from the ATSB and Rural Fire Service personnel remain at the Appin crash site.
RFS Firefighters are continuing to manage parts of the bush where fires were sparked by Monday's crash to ensure the areas do not reignite.
- with AAP
