The Australian Transport Safety Bureau has released the preliminary report into its investigations into the aircrash that killed pilot David Black, of Trangie.

The 43-year-old father-of-three was waterbombing a bushfire in rugged terrain when his fixed-wing plane crashed on October 24.

According to the report, the PZL-Mielec M18A Dromader, registered VH-TZJ, was approaching the target point when its left wing separated. The aircraft immediately rolled left and descended, crashing into the ground in the Charleys Forest area of Wirritin National Park. 

For several days the accident site was inaccessible due to rugged terrain, high winds, low cloud, and nearby bushfires. On October 30, due to the efforts of the Rural Fire Service, the NSW National Parks and Wildlife Service, and the NSW Police, a team of five ATSB investigators, including a materials specialist, examined the aircraft wreckage on site.

Preliminary investigations indicate that the left outboard wing lower attachment lug had fractured through an area of pre-existing fatigue cracking in the lug lower ligament.

The investigation is continuing however a final report is not expected until October next year.

It is the fourth fatal accident in Australia involving an M18 Dromader aircraft since 2006. Of those four, it is the second to have crashed while fighting bushfires.

The M18 Dromader involved in the Ulladulla crash was operated by Rebel Ag in Trangie, and had been contracted to the Rural Fire Service for firefighting efforts.

Dromader planes are commonly used for crop-dusting but are often pressed into fighting bushfires during summer.