A helicopter pilot was told to turn around because a "wall of cloud" was approaching, minutes before the aircraft crashed north of Melbourne, a preliminary report into the accident says.
Pilot Dean Neal, 32, was killed along with four passengers when the Microflite helicopter he was flying crashed at Mt Disappointment 60 kilometres north of Melbourne on March 31.
The Australian Transport Safety Bureau's preliminary report into the crash, published on Thursday, said Mr Neal's helicopter was following a second aircraft as they approached the mountain that morning.
They were initially flying between a layer of scattered cloud at about 3500 feet, but the pilot of the leading helicopter reported seeing a "wall of cloud" begin to surround the aircraft.
They initially broadcast to Mr Neal they would turn around, before repeating again, "U-turn, U-turn, U-turn", as they performed a sharp left-hand turn about 7.56am.
The pilot saw Mr Neal's helicopter pass below them and continue towards the mountain about 30 seconds later.
The ATSB report said the helicopter hit a large tree before crashing to the ground through the tree canopy and catching fire.
Mr Neal, First AG Capital co-founder Nicholas Vasudeva, AXIchain founder Linda Woodford, finance consultant Ian Perry, and meat industry boss Paul Troja were all killed.
ATSB chief commissioner Angus Mitchell said investigations into the fatal crash would continue, with weather data, the helicopter's maintenance history, and the operator's management systems among the areas still to be analysed.
Helicopter operator Microflite said it would continue to work with the ATSB over the ongoing investigation.
