A seaplane was not following an authorised route when it plunged into a river north of Sydney killing six people, according to its operator.
Five members of a British family and a Canadian pilot died in the incident on new year’s eve.
A preliminary report, released today, did not draw any conclusions about why the seaplane had crashed.
But Sydney Seaplanes described events moments before the crash as “totally inexplicable,” the BBC reported.
The Australian Transport Safety Bureau report said the DHC-2 Beaver had made a steep right turn before diving nose-first into the Hawkesbury River at Jerusalem Bay, about 30 miles from the city.
“The key question arising from the report is why the plane crashed approximately half way down Jerusalem Bay… the plane simply should not have been where it was,” said Sydney Seaplanes chief executive Aaron Shaw.
Among the victims was Richard Cousins, chief executive of FTSE 100 catering company Compass Group.
He died alongside his 48-year-old fiancée, magazine editor Emma Bowden, her 11-year-old daughter Heather and his sons, Edward, 23, and William, 25, and pilot Gareth Morgan, 44.
The pilot had flown the authorised route “hundreds of times before”, Shaw said.
“A turn of this nature at low altitude by a pilot with Gareth’s skills, experience and intimate knowledge of the location is totally inexplicable,” he said.
The ATSB said it was investigating why the pilot had flown in that direction.
“We don’t have a preferred theory at this stage as to why he went off course,” transport safety director Nat Nagy said.
Investigators were exploring whether the sudden turn was “an attempt to turn around or whether it was a planned turn”.
The pilot had more than 10,000 hours of flying experience – including about 9,000 hours on floatplanes. He had appeared to be in a “high standard of health”, the report said.
Morgan and the family from Tooting, in south-west London, had been flying back to Sydney from a waterfront restaurant near the crash site.