The pilot of a seaplane that plunged into water near Sydney after flying into a bay off the authorised route would have known he was too low to escape the dead-end, an investigator has said.
Gareth Morgan, who had more than 10,000 hours of flying experience, is thought to have turned into Jerusalem Bay after taking off from Cottage Point on New Year's Eve.
The de Havilland Canada DHC-2 Beaver was then seen turning steeply to the right before smashing into the water at a near-vertical angle.
Mr Morgan and his five passengers - British businessman Richard Cousins, the chief executive of FTSE 100 company Compass Group, his two sons, his fiancee Emma Bowden and her 11-year-old daughter - were all killed.
Aaron Shaw, chief executive of operator Sydney Seaplanes, said the aircraft "simply should not have been where it was" and that the manoeuvres prior to the crash were "inexplicable".
Nat Nagy, an executive director of transport safety at the Australian Transport Safety Bureau (ATSB), said Mr Morgan, 44, had flown from Cottage Point, the location of an exclusive restaurant, a "significant number of times and was very familiar with the area".
"The initial input we have been given is that in terms of the standard climb-out rate you wouldn't normally climb out in that direction," Mr Nagy said.
When asked if Mr Morgan would have know that he could not have escaped from Jerusalem Bay, he said: "Yes."
The ATSB's preliminary investigation, released in a report on Wednesday, had found nothing to indicate any issues with the structure of the seaplane, its flight controls or engine.
Mr Nagy said his team was attempting to ascertain exactly why Mr Morgan turned into the bay, adding that they "do not have a preferred theory at this stage as to why he went off-course".
The investigator said he had "no information at all" to suspect that the crash had been deliberate and the ATSB had received no information to suggest concern about Mr Morgan's mental health.
The pilot had been employed by Sydney Seaplanes from 2011 to 2014 before relocating overseas, returning to Australia in May 2017 when he undertook a number of checks.
His commercial pilot licence was last reissued by the Civil Aviation Safety Authority (CASA) on March 21 2017, after he had undertaken a flight review and proficiency check.
He also held an Aviation Medical Certificate valid until March 6 2018 and was reported to have a "high standard of health".
As to whether a medical episode involving someone else on board could have played a part, Mr Nagy said this possibility would be considered, as is routine.
"We will look at any health aspects that may have occurred," he said.
"The post-mortem results may shed some light on that."
Results of post-mortems and toxicology tests have not been released, and form part of a police investigation that will be handed to the New South Wales Coroner in due course.
An inquest into the deaths is not expected until after the ATSB publishes its final report in about 12 months.
Mr Shaw said the key question arising from the preliminary report was why the seaplane crashed in Jerusalem Bay, which is surrounded by steep terrain and has no exit.
"It is not a route we authorise in our landing and take-off area register and the plane simply should not have been where it was," he said.
"Further, the aircraft is then reported to have entered in to an 80 to 90-degree bank angle turn.
"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."
The ATSB is hoping witness accounts will help to piece together what happened from the moment the plane took off at 3.01pm on January 31.
The bodies of Mr Cousins, 58, his sons, Will and Edward, aged 25 and 23, Ms Bowden, 48, and her 11-year-old daughter Heather were recovered from the water the same day.
Tributes to the victims flooded in after their identities emerged on New Year's Day.
Friends and colleagues said Mr Cousins was a "well-known and respected" businessman who helped transform Compass's fortunes upon becoming the catering firm's boss in 2006.
Ms Bowden, a former arts editor at OK! Magazine, was described as the "Grace Kelly" of their office by Lisa Byrne, its ex-editor-in-chief.
Mr Cousins's son Will was head of press for pro-European Union campaign group Open Britain, and was described by the group's chairman, Roland Rudd, as an "extraordinary young man" who would be "missed beyond words".
The wreckage of the seaplane was pulled from approximately 15 metres of water on January 4, in an operation by police divers and the ATSB.