Robert Decker was the only passenger to survive a helicopter crash about 55 kilometres off Newfoundland's east coast. (CBC)

The sole survivor of an offshore helicopter crash that killed 17 people near Newfoundland and Labrador last March will testify at a safety inquiry Thursday.

Robert Decker, 28, was pulled from the North Atlantic about 55 kilometres southeast of St. John's on March 12.

He will be the fifth witness to speak at the inquiry into offshore helicopter safety that was set up by the Canada Newfoundland and Labrador Offshore Petroleum Board after the crash. The board regulates the province’s oil industry.

Cougar Helicopters flight 491 went down on a routine morning trip ferrying offshore workers to two offshore oil production platforms.

The helicopter crashed after it turned back toward St. John's and its flight crew reported mechanical problems.

Decker was working as a weather observer for an oil company operating hundreds of kilometres offshore.

Sank into ocean

Still recovering, he has never spoken publicly about what happened to him last March when the Sikorsky S-92A chopper plummeted into the ocean and sank.

Decker was hoisted out of frigid three-metre waves by a Cougar search-and-rescue crew and was flown to the Health Sciences Centre in St. John's with serious injuries. He stayed there for more than two weeks.

Only one other person, Alison Maher, 26, made it to the surface that day, but she did not survive.

Sixteen other people, flight crew and passengers, dropped 178 metres to the ocean floor inside the wrecked chopper.

Their bodies were later recovered by Transportation Safety Board of Canada investigators using a remotely operated underwater vehicle.

The wreckage was also raised from the ocean floor for an ongoing TSB investigation. The board is trying to understand what went wrong and how to prevent it from happening again.

Speaking at the inquiry in late October, TSB official Wendy Tadros said the investigation is months away from completion.

On Oct. 19, inquiry lawyer Anne Fagan gave an overview of what Decker is expected to talk about at the inquiry Thursday.

"He will describe the flight back towards land, the crash of the helicopter into the ocean, his escape and ascent to the surface. Mr. Decker will explain how the cold water affected his ability to access features of the survival suit," said Fagan.

Decker is scheduled to begin testifying at 9:30 a.m. NT. Inquiry officials say it's the only time he'll speak publicly about his ordeal.