A pilot made seven mayday calls before his plane crashed in Melbourne but anything else uttered in the last moments of the five men onboard remains a mystery because the black box failed.
Max Quartermain was flying four Americans to King Island to play golf when the small plane crashed into the DFO shopping centre and exploded in a fireball moments after take-off from Essendon Airport last month.
The Australian Transport Safety Bureau's preliminary report ruled out an early theory of catastrophic engine failure during take-off.
"Cores of both engines were rotating and there was no evidence of pre-impact failure of either engine's internal components," the report released on Wednesday said.
"However a number of engine components were retained for further examination and testing."
ATSB chief commissioner Greg Hood says the aircraft is so damaged it has not yet been possible to say what caused the crash.
"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," he said.
Air traffic control audio records Mr Quartermain calling 'mayday' seven times but crucially there was no audio from the plane's black box.
Investigators don't know why the Beechcraft King Air's black box did not record on its final flight on February 21 - but it did record a previous trip.
"All the recovered audio was from a previous flight on January 3, 2017," the report says.
Witnesses familiar with the aircraft type reported the take-off roll along the runway was longer than normal.
After becoming airborne it was seen to move left, then perform a shallow climbing left turn while remaining relatively level.
Further investigation will be done on the propellers to determine the blade angles at impact, their pre-impact condition and to assess the impact damage.
Essendon Fields chief executive Chris Cowan said the tragic accident could have happened anywhere in the world and he took aim at people casting aspersions on the airport's safety.
"Much of the speculation to date has been wrong and has not been appropriate, especially to the victims' grieving families," he said.
"It's a reality of modern society that airports operate in close proximity to urban environments."
The Essendon airport is surrounded by shops, houses and freeways, with the plane crash resulting in a huge explosion metres from peak hour traffic.
Texan retirees Greg De Haven, Russell Munsch, Glenn Garland and John Washburn died on impact with Mr Quartermain when the plane hit the DFO.
They had been in Australia on a golfing "trip of a lifetime" with their wives, who were not on the flight.
The ATSB will release a final report in about 12 months.
