The coroner has found reduced visibility was a contributing factor in the helicopter crash which killed Whanganui pilot Peter Robb in 2014.

The 56-year-old was carrying out an aerial thistle spraying operation when the Hughes 500 E helicopter he was flying struck two disused electric fence feeder wires on the morning of October 28.

In his findings released this week Coroner Christopher Devonport ruled Mr Robb died from multiple injuries suffered in the crash.

Mr Robb, the sole person on board, died at the scene.

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After a delay due to fog Mr Robb arrived at the Koatanui Rd property managed by Mark Gower-James at about 8am to carry out a spraying operation.

There was more delay for fog to clear before Mr Robb and Mr Gower-James took a short reconnaissance flight to identify hazards.

After landing and filling the helicopter spray tanks Mr Robb began the job.

Shortly after take-off a bang was heard by those nearby when the helicopter struck a pair of electric fence feed wires.

"Contact with the wires resulted in separation of the vertical and horizontal stabiliser assembly and tail rotor from the helicopter," Mr Devonport said.

"Following a climb the helicopter descended and struck the ground [sealed road] initially with the right skid before rapidly rolling over to the left landing heavily on its left side."

The crash was investigated by the Civil Aviation Authority and the resulting report "states that it could not be positively established that the briefing Mr Gower-James provided to Mr Robb specifically included the location of the electric fence feeder wire."

Mr Devonport said the briefing provided to Mr Robb "was not backed up with supporting information such as a hazard map for the farm property".

Also, while much of the fog had cleared by the time of the incident a report by the CAA's senior investigator Colin Grounsell found there was some fog present in the vicinity of the paddock being sprayed.

Mr Grounsell wrote "the reduction in visibility and the grey/white background of the horizon would have made the visual detection of the electric fence feeder wires more challenging to the pilot."

The coroner agreed.

"I accept that reduced visibility to be a contributing factor in Mr Robb not seeing the electric fence feeder wire [whether is had been adequately pointed out to him or not]."

Mr Devonport endorsed CAA campaigns to reduce wire strike and said the provision of detailed hazard maps, a full reconnaissance by the pilot and the removal of electric fence feeder wires "are all steps that can be taken to reduce wire strike occurrences".

"Certainly had the disused electric fence feeder wires been removed prior to the aerial operation undertaken by Mr Robb... then his death would not have occurred as it did," Mr Devonport said.

Along with being an experienced pilot, Mr Robb - or "Rocket Man" as he was sometimes known - was a keen motorsport enthusiast and raced V8 utes for nearly a decade.

In 2014, he won his first UDC V8 utes race at the ITM 500. In 2012, Mr Robb raced at Mt Panorama in Australia, ahead of the 50th anniversary of the Bathurst motorsport celebration.

Nine charges were laid by the CAA against the trust which owned the farm, and against four of the farm's operators, but they were dropped in April last year following a confidential out-of-court settlement.

A statement released by the Tariki Family Trust at the time said the trustees accepted the crash was caused by its failure to bring down the electric feed-out wire.

"The trustees unequivocally lend their support to any campaigns to heighten farmer awareness," the statement said.

"They encourage farmers never to contemplate that such tragedies could not happen to them. They can. These tragedies must be avoided."