A pair of over-spinning propellers is being investigated as the cause of a plane crash that killed 28 people in Papua New Guinea last month.
The PNG Accident Investigation Commission's preliminary report into the October 13 crash near Madang, shows the Airlines PNG Dash 8 went into high speed in the minutes before the crash.
The Sydney Morning Herald says the report said both propellers simultaneously oversped and exceeded their maximum permitted revolutions per minute by in excess of 60 per cent.
Air Crash Investigator Sid O'Toole told reporters it was unusual for both propellers to overspeed at the same time.
Mr O'Toole said the aircraft's propellers will be sent to the USA for analysis, while other parts will be sent to Canada.
He said he expected an update to the report in four months' time.
Australian pilot Bill Spencer, his New Zealand co-pilot Campbell Wagstaff, a crew member and a passenger were the only survivors of the crash.
The airline has resumed flying its Dash 8 fleet after being cleared by PNG's Civil Aviation and Safety Authority last week.
Meanwhile, a proposed merger with national airliner Air Niugini has been scrapped by the PNG government.