The Australian Transport Safety Bureau (ATSB) on Wednesday released its report into the September 6 2019 crash that cost five lives.

Queensland men Jamie Ogden and Grant Kuhnemann, married Sydney couple Jocelyn Villanueva and Gregory Miller, and the chopper's pilot and owner David Kerr - also a Queensland man - died in the crash.

The safety body had previously flagged weather as a major area of its examination in the crash of the Bell UH-1H. Its final report, though, pointed to the fading light as a major factor.

"Published last light for Anna Bay was 6:01pm, with recorded data showing that the helicopter made a rapidly descending left turn and collided with water at about 6.13pm," the authority said in a statement.

The wreckage and human remains were found in about 30 metres of water about five kilometres southwest of Anna Bay after weeks of searching.

The ATSB report said Mr Kerr was only qualified to fly by day under visual flight rules (VFR) "and so was not trained or experienced in maintaining control of the helicopter with sole reference to the flight instruments".

"The ATSB found that the pilot continued to fly after last light without the appropriate training and qualifications, and then into dark night conditions that provided no visual cues," ATSB Chief Commissioner Greg Hood said.

"That significantly reduced the pilot's ability to maintain control of the helicopter, which was not equipped for night flight.

"Once visual references were lost, the pilot likely became spatially disorientated and lost control of the helicopter, resulting in a collision with water."

The helicopter had left Brisbane on its way to Bankstown, stopping to refuel at Coffs Harbour before taking off at 4.48pm.

The inquiry found that departing so late in the day would have left insufficient time to reach Sydney before dark.

"As the flight passed the halfway point and progressed closer to the destination, the pilot may have become increasingly committed to continuing with the original plan," it notes.

"Recognising that the pilot could have identified prior to departing Coffs Harbour that the flight could not be completed in daylight, given the inherent utility of a helicopter, there were also opportunities to land at a beach, or other suitable areas, prior to reaching Broughton Island."

Air traffic control from Williamtown RAAF base made several radio calls to the aircraft before it crashed, assisting the pilot with altitude changes. Mr Kerr mentioned turbulence in those calls, prompting the controller to offer further assistance.

At 6.11pm the helicopter commenced a left turn and departed its coastal route, tracking offshore "on what appeared to be a direct track to Bankstown".

That left it flying over "a featureless sea with overcast conditions blocking out celestial lighting", giving Mr Kerr few visual cues to navigate.

Radar contact with the helicopter was lost about two minutes later.

"Research has shown that pilots not proficient in maintaining control of a helicopter with sole reference to flight instruments will become spatially disorientated and lose control within one to three minutes after visual cues are lost," Mr Hood said.

"A VFR flight in dark night conditions should only be conducted by a pilot with instrument flying proficiency as there is a significant risk of losing control if attempting to fly visually in such conditions.

"If day VFR-rated pilots find themselves in a situation where last light is likely to occur before the planned destination is reached, a diversion or precautionary landing is almost certainly the safest option, or air traffic control may be able to provide assistance with available landing options."

The investigation also found Mr Kerr had failed to disclose ongoing medical treatment for "significant health issues" to the Civil Aviation Safety Authority, with his treatment coming from a "non-aviation medical specialist".

"While not considered to be a contributing factor to the accident, this non-disclosure prevented specialist consideration and management of the ongoing flight safety risk the medical conditions and prescribed medications posed," the report notes.

Mr Hood said there were pathways for pilots to manage certain conditions to keep their aviation medical certificates.

In 2019 the bureau noted 101 cases of pilots qualified to fly under visual flight rules entering instrument meteorological conditions were reported in Australia airspace in the decade to June 30.

Nine were accidents that included 21 deaths.

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