Dan Harrison, 36, was flying an AS350 Squirrel from Milton to Alexandra to carry out frost protection work early in the morning of September 16 when it went missing about 15 minutes into the flight.
Its wreckage was found about 15km north-east of Lawrence in the Lammerlaw Range a few hours later.
The Transport Accident Investigation Commission’s final report on the accident, released today, said Mr Harrison departed Milton about 5.15am, with no moon, in the darkest part of the night.
He almost certainly encountered increasing cloud, and ‘‘very likely’’ lost a clearly-defined horizon soon after passing Lawrence.
The report said a pilot in such a situation would switch to instrument-only flying to maintain situational awareness and control of the aircraft.
Flight data showed the aircraft made a tight descending right-hand turn, then a left-hand spiral dive that ended in a near vertical nose-down high-speed impact with the ground.
He had about 4200 hours’ flying experience since gaining his commercial helicopter pilot licence in 2008.
However, his restricted night rating barred him from undertaking such a cross-country flight at night.
In a media statement, the Taic chief investigator of accidents Naveen Kozhuppakalam said it was an anomaly that pilots with a night rating like Mr Harrison were not required to practise regularly, despite it being a complex skill.
If a pilot lost sight of visual references, such as on a dark night in thickening cloud, there was more risk of them being unable to rely solely on their instruments, making them more vulnerable to disorientation and losing control of their aircraft, Mr Kozhuppakalam said.
‘‘That's very likely what happened in this accident.''
It had recommended the Civil Aviation Authority (CAA) address the night-flying practice issue, and to review its ‘night Visual Flight Rules’, which were intended to keep pilots within 25 nautical miles of their departure point.
Taic had found the rules could be interpreted to allow pilots to fly at night from one 25-mile zone to the next and so on across country, he said.
``This is much further than intended; it puts pilots at risk of encountering night flying conditions outside their capabilities.''
In response to the Taic recommendations, the CAA has convened an industry helicopter working group to consider the issues raised.
The helicopter’s operator, Alister John Lister, and his company Lister Helicopters Ltd, face a variety of charges before the Dunedin District Court in relation to the crash.
There have been repeated appearances without significant progress, but at the last call, a judge stressed pleas would be expected next month.
