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

Robert Decker, the only passenger to survive when an offshore helicopter crashed earlier this month off the coast of Newfoundland, remains in critical condition but is making substantial progress, a representative of his family said Monday.

David Philpott, a friend who has been asked to speak on the family's behalf, told CBC News that Decker has undergone surgery at the Health Sciences Centre in St. John's to stabilize a fractured vertebra in his spine.

"While Robert's health continues to improve in response to his medical support, it has been a process that can best be described as a roller-coaster," Philpott said.

Decker, who tracked ice conditions for one of the offshore platforms, was hoisted from the Atlantic Ocean on March 12, shortly after a Cougar Helicopters aircraft crashed in the water about 55 kilometres southeast of St. John's. All of the 17 other people aboard were killed, including two helicopter crew.

The Cougar had been ferrying 16 employees to two platforms working in the offshore oil industry, off Newfoundland's east coast.

Philpott said Decker, 27, remained unable to speak until Sunday, and had been both heavily medicated and on a ventilator. However, he said the family is now hoping that the worst is behind them.

"The phrase that we are using is that he has turned the corner and we are very optimistic and relieved," Philpott said in an interview.

It is not yet known how Decker was able to escape the helicopter, which was found on the ocean floor under 178 metres of water. Only one body — that of Allison Maher, a caterer who worked on one of the platforms — was recovered on March 12. Crews working with the RCMP and the Transportation Safety Board were last week able to recover the remaining 16 bodies, as well as most of the wreckage.

Last week, a multi-faith ecumenical service was held at the Roman Catholic Basilica in St. John's, with prayers offered for all those who had been aboard, including Decker.

Philpott said the public outpouring of support and sympathy has been remarkable.

"It is overwhelming, it is wonderful, it is emotional and it's very, very much appreciated," said Philpott.

"His mom and an aunt have slept at the [intensive care unit] every night. It's overwhelming actually to see a group of people come together so fast and stand so strong beside this family, and see the whole city rally behind this mother as she tries to support her son."

The RCMP said late last week their questions about the final minutes of the helicopter's flight will wait as long as necessary for Decker to be well enough to answer them.

On Friday, the Transportation Safety Board of Canada said it had recovered a broken titanium mounting stud on the Sikorsky S-92's gearbox, although the TSB has emphasized that the finding may not be related to the cause of the crash.