The Canadian military is closing the book on the investigation into a training accident that came close to leaving a former army combat medic paralyzed and ended her military career.

Chief of Defence Staff Gen. Jonathan Vance has elected not to conduct a follow-up inquiry into the case of retired master corporal Denise Hepburn, who fractured vertebrae in her neck while jumping from a helicopter into Lake Ontario, near Canadian Forces Base Trenton, during a multinational exercise.

Hepburn filed an internal grievance over the July 21, 2010, accident.

Vance's decision comes despite an acknowledgment that the accident was "preventable" and that the military's investigation into the mishap had "a reasonable apprehension of bias."

Hepburn was informed of Vance's decision just before Christmas in a letter from the chief of defence staff, which has been obtained by CBC News.

It is disheartening. I lost my career because of this. - Denise Hepburn , retired master corporal, Canadian Armed Forces

"I cannot articulate how dumbfounded I am," said the 13-year veteran of the army, who did a tour in Afghanistan. "It is disheartening. I lost my career because of this."

Fractured vertebrae, head injury

Hepburn, who was recently married and went by the last name Gallagher at the time of the accident, was assigned to the exercise as a medic to treat other soldiers should they be injured. She had not been given any specific training for the risky jump.

"It was an opportunity for everyone to just get wet because it was a really hot day, " she said. "It was a morale-booster, and they wanted to include everyone in this manoeuvre. Originally, I declined."

Everyone else took part, and when it came to her turn, Hepburn said, she "received a lot of razzing" and decided it would be fine to jump because she had been a competitive diver years before.

The jump was supposed to take place when the helicopter was 3.5 metres above the surface of the water in light winds.

It didn't turn out that way.

The investigation into the accident estimated the helicopter was flying at more than 12 metres. The wind, which the investigation report said was stronger than anticipated, caused Hepburn to drift sideways before hitting the water.

"I just remember being in the water, opening my eyes and seeing stars," said Hepburn.

She said she was hauled from the lake by the loop of her life vest and initially couldn't speak. In addition to the fractured vertebrae, she suffered a traumatic brain injury.

'It was a specialized manoeuvre for special ops'

After weeks of hospitalization and months of recovery, she was released from the military on medical grounds in November 2014.

An investigation was ordered into the decisions that led to her participation in the exercise and, ultimately, to her injuries, but it was conducted by a subordinate of the officer in charge of the exercise — contrary to military conflict of interest regulations.

When it was completed, the army refused to share the findings with Hepburn, and she ended up filling an access to information request to get a copy of the investigation report.

"That's when I started to piece together that this was a cover-up," she said. "There was an issue. It wasn't a manoeuvre that just anybody should be doing. It was a specialized manoeuvre for special ops and search and rescue for insertion into water for various reasons, but not just for something to do."

Hepburn said the neurosurgeon who treated her told her that only five per cent of patients with the type of injuries she had survive and that most are paralyzed. The surgeon recommended she go buy a lottery ticket, Hepburn said.

Hepburn said those who organized the exercise didn't notify more senior staff of the severity of the accident.

"They just sort of low-balled it, put it under the mat and did their own thing," she said.

Inquiry would be 'unnecessarily excessive': Vance

Vance, in his written decision not to pursue a follow-up inquiry, acknowledged there were problems with the way the case was handled and said the officer in charge of the exercise "should have remained at arm's length from the [investigation]."

"I find, since he did not, there was a reasonable apprehension of bias," Vance wrote.

However, that breach in regulation was "remedied," Vance said, by the intervention of a more senior officer. He said the fact that he personally reviewed the case means "outstanding flaws" in the investigation were being properly addressed.

Chief of Defence Staff Gen. Jonathan Vance has decided there will be no further investigation into the circumstances surrounding the accident. He said he personally reviewed the case and that 'outstanding flaws' in the original investigation were being properly addressed. (Fred Chartrand/Canadian Press)

In addition to compensation for loss of her career, Hepburn had demanded that a board of inquiry be convened into the handling of her case and that the officers involved, at least two of whom have since been promoted, be held accountable.

Vance said in his response that an inquiry would be "unnecessarily excessive and unwarranted" and that he would "consider appropriate steps to ensure this does not reoccur."

He did not explain what action would be taken.

That's not good enough, said Hepburn, who claimed the investigation report mischaracterized the severity of her injuries and that at least one of the soldiers quoted in it made "patently false" statements.