Three men who died when a Canadian Coast Guard helicopter plunged into the Arctic Ocean last week were not killed by the crash but died of hypothermia, according to a preliminary post-mortem.

Cathy Menard, Northwest Territories chief coroner, said the results revealed the three men were not seriously injured in the crash.

Menard said it is believed Marc Thibault, the commander of the Amundsen, Daniel Dubé, the helicopter pilot, and Klaus Hochheim, a researcher studying sea ice, were in the water for an hour before rescuers pulled them out. All three were wearing survival suits.

The helicopter, a Messerschmitt BO 105S, was doing a reconnaissance mission on the state of the ice in the area when it crashed in the McClure Strait, about 600 kilometres west of Resolute.

Menard said the helicopter was just minutes away from the Amundsen when the ship lost radio contact.

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The Canadian Coast Guard icebreaker Amundsen arrives at Resolute, Nunavut, last week with the bodies of two crew members and a researcher who were killed in a helicopter crash. (Submitted photo)

"At first they were trying to call them back to see if they could reach them on the radio as well, so it was probably about an hour. But that's part of the investigation that we're trying to work out, is the timeline from when the last contact was made with the helicopter to when they were found."

The McClure Strait is north of Banks Island on the opposite side of the island from Sachs Harbour, N.W.T.

Menard said the bodies of the three men could be returned to their families as soon as Wednesday.

Transportation Safety Board investigators are trying to retrieve the helicopter.