A light plane that crashed in northern NSW killing its pilot did five hours of spraying before the fatal incident, the transport safety investigator says.
But the ATSB says the cause of the crash is still not known.
The plane - built primarily for agricultural purposes and known as an air tractor - plummeted to the ground and burst into flames on a farm at Rowena, about 140km west of Moree, on December 4 last year.
Neighbours tried to help the pilot, who has not been named, prior to the arrival of emergency services but he died at the scene.
On Wednesday, the Australian Transport Safety Bureau said that the pilot took off from, and landed at, an airstrip on a property 80km from Moree for five hours before the deadly crash.
"The pilot sprayed ten hopper loads of chemical on designated areas of the property. These were sprayed using a racetrack pattern," the ATSB said in the preliminary report.
At around 11.30am, the plane made its final doomed flight with its 11th load of chemicals to spray the property's eastern boundary, the ATSB said.
"During this flight the pilot used a back-to-back pattern, conducting a 'procedure turn' to reposition the aircraft on the reciprocal heading for the next spray run," it said.
"After the aircraft had completed the fourth parallel run, a witness located in the neighbouring paddock observed the aircraft enter a right procedure turn above trees."
During the turn, the plane plummeted then disappeared behind trees, shortly before witnesses saw plumes of dark smoke from the crash site.
The ATSB said its probe so far indicated that powerlines, bird strike or a failed engine were not to blame for the downing of the plane.
It said it would continue to hunt for the cause of the fatal crash.
"The ATSB will examine electronic components recovered from the accident site, and review the pilot's qualifications and experience, weather conditions, operational documentation and relevant regulations, and accident survivability aspects," ATSB's Stuart Godley said in a statement.
