Coroner Richard McElrea called an inquiry into the deaths of snowboarder Nello Donaggio and skiers Rachel Barrett Swett and Dimity Tomkins, who died within two months of each other at Mt Hutt last year.
A neurosurgeon, Martin MacFarlane, told a hearing in February that the lack of head protection was "very significant in terms of survival" in all three cases.
In written findings released this week, the coroner recommended skiers and snowboarders wear helmets in mountainous terrain, but said it was not a recommendation to make helmet use compulsory.
"It would seem that the wearing of helmets by skiers and snowboarders in New Zealand is now widely accepted," he said. "However, the fact that a significant percentage of skiers and snowboarders in New Zealand do not use protective helmets is a matter of major concern."
In the first incident, American student Swett, 21, suffered severe head injuries after sliding on icy snow and hitting her head on a rock outcrop on June 17 last year.
She never regained consciousness and died in Christchurch Hospital five days later.
Swett's parents, Benjamin and Katherine Swett, had pressed for the mandatory wearing of helmets, but the coroner said it would be difficult to enforce the wearing of helmets in an alpine environment.
Swett had been due to return to New York after a semester studying at Canterbury University and was feeling "happy and confident", her parents said.
"We just wish that she had been able to come home and hope that your inquest will succeed in helping Mt Hutt and other skifields in New Zealand make such progress towards preventing such losses from happening to others," they said.
The coroner also released findings into the death of Donaggio, 30, of Christchurch, who died in Christchurch Hospital on August 6 last year after suffering severe head injuries when he slid about 300 metres on icy snow.
He had not been wearing a helmet and struck his head on an outcrop of rocks beyond the ski area boundary.
The coroner's findings on a third death at Mt Hutt last year were still being finalised, a spokesman said.
Dimity Tomkins, 54, of Christchurch, died on July 12 after sliding more than 800m down the southwest face of Mt Hutt, just outside the skifield boundary.
She was wearing a helmet, but it broke and fell off as she slid.
Reports from Peak Safety Ltd and the Department of Labour after the deaths made recommendations on road improvements, trail ratings and signage, boundary signage and fencing, trail markers, terrain hazard management and access to the triple chair.
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The coroner said the skifield had constructively responded to the recommendations.
Mt Hutt Ski Area manager David Wilson told The Press yesterday that the ski area encouraged people to wear helmets and had bought an extra 350 helmets this season.
Staff on the mountain were required to wear helmets in particular areas. Helmets were always available for staff.
He did not think helmet use should be compulsory, but believed more people were wearing helmets.
"People still have their choices, but I would highly recommend people wear helmets, and I wear a helmet whenever I go skiing."
There had been no fatal accidents at Mt Hutt this year, and to have three deaths on the mountain last year was "odd". "To have even one in a year would be rare."
The ski area had improved signage and boundary fences and was "constantly reviewing" hazard-management practices, he said.