TORONTO – Thirteen years ago next week marks what could have been a grim anniversary: Air Transat Flight 236, bound to Lisbon from Toronto, crash-landed on an island in the Azores off Portugal after running out of fuel over the Atlantic. While all 306 passengers and crew survived the dead-stick landing, those on board had spent a harrowing 30 minutes as the crippled plane glided over the ocean, not knowing whether they would live or die.

Their hair’s-breadth escape on Aug. 24, 2001, not only turned potential tragedy into celebration, it also provided researchers with a unique opportunity to study the effects of trauma and the role that individual memory plays in dealing with such an ordeal.

In a study published online Wednesday in the journal Clinical Psychological Science, researchers had 15 passengers who’d been on the flight relay their memories of the event, as well as those related to the 9-11 terrorist attack in the U.S. that occurred soon after.

Something else about the study was also likely unprecedented: Margaret McKinnon, one of the researchers, was a passenger that day on Flight 236, travelling with her husband to Lisbon for a honeymoon three days after their wedding.

McKinnon, now a psychologist in the mood disorders program at St. Joseph’s Hospital in Hamilton, said she remembers the flight crew’s announcement that the plane was going to have to ditch in the ocean and that passengers should don life-jackets. Shortly after, the oxygen masks above the seats dropped down as the cabin began depressurizing.

“There were countdowns until that would happen,” she said of the excruciating half-hour as occupants inside the darkened plane waited for their expected crash into the water. “We were asked to sit in a braced position.”

Then somebody – she isn’t sure if it was a passenger or crew member – yelled that land had been sighted, “and they sounded quite surprised.”

Pilot Capt. Robert Piche was able to glide the plane into a hard landing on an island airstrip. “The passengers all cheered,” she said, then everyone evacuated the aircraft using emergency chutes and ran, escaping across a field because the plane’s blown-out wheels had caught fire.

“I think for me during those 30 minutes, I sort of imagined that this was likely to be the end. I know not everyone felt that way, but I did,” said McKinnon, then a 26-year-old graduate student at the University of Toronto. “So it sort of gave you time to prepare for that.”

The 15 passengers who took part in the study each had their own set of memories from the horrific event, said senior study author Brian Levine, a senior scientist at Baycrest Health Science’s Rotman Research Institute in Toronto.

Tapping into their recall of events as they unfolded moment to moment, the researchers were able to probe both the quality and accuracy of passengers’ memories along with those of two other events _ Sept. 11, 2001, and a neutral event from the same time period – and relate their findings to the presence or absence of post-traumatic stress disorder, or PTSD.

Compared to 9-11 and the neutral event, the amount of information recalled around Flight 236 “was very rich,” said Levine.

“For example, when we asked these same people to recall 9-11, they produced between 100 and 150 details; when they recalled the Air Transat event, they produced anywhere from 250 to 350 – so more than twice as many details.”

Researchers were not surprised by this finding because emotionally charged events typically produce greater recall.

What was not expected was a finding that passengers who subsequently developed PTSD and those who didn’t showed no difference in the amount of detail they remembered or its accuracy.

“And that was somewhat surprising,” he said. “We thought people with PTSD might have more vivid recall because they have more intrusions, they’re thinking about it more, ruminating about it more. But that was not the case.”

However, those affected by PTSD relayed more “external” details – comments which were not specific to the event, but might involve thoughts or perceptions, such as “Wow, I never thought we were going to make it” or “I’ve never flown Air Transat again,” Levine said.

This pattern was observed across all events tested, suggesting it is not just memories of the trauma itself that’s related to PTSD, but rather how a person processes memory for events in general.

“What our findings show is that it is not what happened but to whom it happened that may determine subsequent onset of PTSD,” said Levine, adding that an inability to shut out external details is related to mental control over memory recall.

“The big question here is why when you’ve got this plane full of people, at least in our sample, half got PTSD and half didn’t? The big question in the (research) literature is why do some people get PTSD and others don’t, when they’re exposed to the same event?

“To me, that’s the most important finding of the study,” he said, noting that the findings add to a growing body of evidence suggesting that altered memory processing may be a vulnerability factor for PTSD.

Dr. Ruth Lanius, a professor of psychiatry at Western University in London, Ont., who specializes in PTSD, said the study shows that memories of a traumatic nature are more vivid than other memories, consistent with other research findings.

“A lot of people who have had traumatic memories experience them in the form of flashbacks, they’re experienced in a timeless form,” said Lanius, who was not involved in the study.

“People will feel like they’re back at the scene of the trauma. They’re often experienced as sensory flashes,” she said, describing how one patient who had been stabbed in the neck kept reliving the experience, “feeling the blood running down his neck over and over again.”

Lanius said in order to help a person heal from a traumatic event, the nature of their memories needs to be changed.

“We don’t want people to be haunted by the memories; we want people to experience them as normal memory of the past that you recall but not relive.”

McKinnon, who was not one of the subjects of the study, said she developed post-traumatic symptoms as a result of her experiences aboard the Air Transat flight.

“I had nightmares. I was very vigilant, I startled easily – you know, typical symptoms of PTSD,” said McKinnon, who was able to address them through treatment, a step she advises others who have been traumatized to pursue.

The research project may also have helped her, as well as some of her fellow passengers.

“The study was a unique opportunity to turn this into something positive.”