The operator of the seaplane that crashed into a river north of Sydney on New Year's Eve, killing all six people on board, says the aircraft "should not have been where it was".
The DHC-2 Beaver, piloted by Canadian Gareth Morgan, slammed into Jerusalem Bay on the Hawkesbury River with high-profile UK businessman Richard Cousins and his family on board on December 31.
Sydney Seaplanes chief executive Aaron Shaw says the key question coming out of an initial Australian Transport Safety Bureau report - released on Wednesday - is why the plane crashed in an area surrounded by steep terrain and with 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 in a statement on Wednesday.
"The aircraft is then reported to have entered into 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 preliminary ATSB report found "no evidence of a bird strike or collision with an object prior to take-off or in-flight".
There was also no evidence of flight control issues, an in-flight break-up or pre-impact structural damage.
The damage to the plane's wings when it crashed was consistent with witness statements that it hit the water while banking right, the ATSB said.
Pilot Gareth Morgan, left, and Richard Cousins, were among the people that died when a Sydney Seaplanes' single-engine DHC-2 Beaver crashed into the river. Source: AAP
Numerous witnesses reported seeing the plane suddenly enter a steep right turn and its nose drop before hitting the water almost head-first.
Sydney Seaplanes hopes the ATSB's call for more witness accounts will help shed light on the cause of the crash.
"While the precise cause of the accident remains unknown, the preliminary report reflects the excellent flying conditions on the day and suggests no evidence of airframe, fuel or engine issues," Mr Shaw said.
Sources have suggested it's possible the pilot or one of the passengers may have experienced a medical episode before the crash.
The ATSB notes the seaplane had no cockpit voice or flight data recorder fitted as there was no legal requirement for a plane of that size to have the equipment.
There were also no video recorders fitted to the plane.
The investigation is ongoing.
