A “devastating” helicopter crash in Switzerland’s popular Verbier that killed three people may have been caused by a “mechanical error”, according to a well-known local British ski coach with knowledge of the accident.

Warren Smith, who has taught the Duke of Sussex, Claudia Schiffer and James Blunt, told The Telegraph that the Alpine village was in “mourning” after the shocking incident, which saw a helicopter carrying skiers up to a mountain peak above Verbier crash and trigger a 500m avalanche on Tuesday.

Three British skiers miraculously survived after one, Edward Courage, pushed two brothers, Teddy and Guy Hutchings, from the Air Glaciers helicopter as it tumbled from the summit.

Speaking from Verbier, Mr Smith, who runs heliski camps out of Verbier and Canada’s British Columbia, said that it was a “miracle” the three Britons survived.

The other three people in the helicopter all died. They included the pilot, local father of two Jerome Lovey, skier James Goff and their guide, Adam George.

An investigation is ongoing into the cause of the crash, with authorities still working to retrieve the helicopter’s black box.

“It is all a bit raw,” said Mr Smith. “We haven’t seen any technical information so I can’t comment on the cause of the crash but it is believed that it may have been mechanical error.”

“We don’t know what the hell happened. It was a bluebird day – blue skies, sun, fresh powder, low winds. The perfect conditions for heliskiing, usually. But it had been very stormy with very high winds a couple of days before and a lot of fresh snowfall.  It could have been a skier’s or pilot’s worst nightmare.

“It is devastating but I can say that it is a miracle the three survived. In helicopter crashes survivors are rare.”

The brothers have been released from hospital. Mr Courage remains in intensive care, awaiting surgery for various broken bones.

“We know the team,” said Mr Smith. “Adam was an incredible guy. Many of the community are family, friends and colleagues of those injured and who have lost their lives for years and years. These families are at the heart of our community.”

The group was on a heliski day trip aboard an Air Glaciers B3-type helicopter. They were due to be dropped at the top of Petit Combin mountain, a popular heliski route in the Valais region near Verbier.

Mr Smith said that he had worked with the company behind the trip, Air Glaciers, for 20 years and that it was “super safe”.

“I personally have never seen any accidents. You know of them. But we’ve never had one incident in 20 years. That is why I am in shock. Air Glaciers pilots are among some of the most experienced heli pilots in the world.”

“It’s crazy, I have had night frights just thinking about it,” he added. “Verbier is in shock.”

Local police have said they are still investigating.

“Having reached the summit of a mountain culminating at 3,668m above sea level, for a reason that the investigation will have to determine, the aircraft slid down the northern slope,” Valais canton police said in a statement.

Verbier-based Mr Courage, 68, has been hailed as a “hero” for saving the lives of the Hutchings brothers.

The funeral for Mr George is set to take place near Verbier on Monday.

One Verbier skier told The Telegraph: “I have skied with Adam on and off for 20 years, maybe more – and on this exact same route and helicopter landing. I’ve never known a better guide.

“He was as good as they get. The best of the best. That was his reputation far and wide in the Valais. You were lucky to be able to book him.”

An online fundraiser for Mr George has been set up in aid of his widow, Caroline George-Ware, and 12-year-old daughter, Olivia.