Essendon crash pilot Max Quartermain radioed Mayday seven times before the B200 Super King Air he was operating struck the DFO building adjacent to the airfield and burst into flames.
A preliminary report by the Australian Transport Safety Bureau has shed little light on the cause of the tragedy that claimed the lives of Mr Quartermain and his four American passengers Glenn Garland, Greg DeHaven, John Washburn and Russell Munsch on February 21, according to news.com.au.
The report said Mr Quartermain's "mayday" call provided no further information and no audio from the flight was obtained from the cockpit voice recorder.
The on-site examination of the wreckage "did not identify any pre-existing faults with the aircraft that could have contributed to the accident".
"Cores of both engines were rotating and there was no evidence of pre-impact failure of either engine's internal components," the report said.
"However a number of engine components were retained for further examination and testing."
Witnesses to the crash told investigators the takeoff from the runway took longer than normal and after becoming airborne the King Air was observed to veer to the left.
It then performed a "shallow climbing left turn" at a maximum height of 160 feet (50m) above ground level.
"The aircraft subsequently collided with a building in the Essendon Airport retail precinct," the report said.
The group was heading for King Island off Tasmania, a trip Mr Quartermain had done countless times before in the B200 Super King Air.
ATSB Chief Commissioner Greg Hood said investigators had done an extensive amount of work to date but the considerable damage to the aircraft was presenting challenges.
"The extensive damage caused by the collision and post-impact fire has meant investigators are yet to determine a clear picture of the causal factors behind the accident and loss of life," said Commissioner Hood.
"I offer my deepest sympathies to the families and loved ones of those on board the aircraft.
"Every effort is being made to determine the cause of this tragic accident."
Engine failure had previously been thought to have occurred during takeoff prompting the mayday calls from the pilot.
As well as a number of engine components, investigators have retained several airframe parts, documents and electronic devices for further examination.
Built in the US in 1996 and first registered in Australia in 2013, the turboprop was considered a very safe aircraft and capable of flying on one engine.
The investigation is continuing with the assistance of US regulatory bodies and the engine manufacturer.