SYDNEY (Reuters) - A seaplane that crashed in Sydney on New Year’s Eve killing six people, including the chief executive of British catering company Compass Group Plc, was off course but the cause of the crash remains undetermined, Australian investigators said on Wednesday.

Richard Cousins, 58, his two sons, his fiancée and her daughter, and the pilot were killed when the plane hit the water shortly after takeoff on December 31.

In its preliminary report, the Australian Transport Safety Bureau (ATSB) said the plane was approximately 1 km (0.6 miles) off the standard course before the pilot turned the plane sharply right. Shortly afterwards, the plan nose-dived into the Hawkesbury River, north of Sydney.

“One of the key lines of enquiry for us is to try and work out exactly what was happening during that time, firstly why the pilot turned and then whether it was an attempt to turn around or a planned turn,” Nat Nagy, executive director of the ATSB, told reporters in Sydney.

The ATSB said there was no evidence of a collision or bird strike and there was no sign of any problem with the controls of the plane.

Nagy said the ATSB will announce its findings should it determine the cause of the crash, but warned it may remain unsolved.

“It is possible that we are not going to find what happened in that cockpit,” said Nagy.