BURLINGTON - Railway officials grappled Monday with the deaths of three of their own in a "rare" deadly passenger train derailment as investigators focused on a black box that captured the crew's final moments -- crucial evidence in the case.

Three locomotive engineers were killed in Sunday's devastating crash in Burlington, Ont., west of Toronto. It was the first time in more than a decade that Via Rail employees were killed aboard one of the company's trains in a derailment.

Two of the engineers, Peter Snarr, 52, and Ken Simmonds, 56, both of Toronto, were experienced drivers, each with more than 30 years in the industry, Via said. A trainee, Patrick Robinson, 40, of Cornwall, Ont., joined them in the cab to observe, though investigators haven't ruled out the possibility that he was driving at some point.

As investigators pored over the wreckage, the head of Via Rail said the derailment that killed the men and injured 45 passengers has sent shockwaves through the close-knit company.

In an afternoon visit to the site, Via president and CEO Marc Laliberte called the collision "tragic," but stressed it was a rare occurrence.

"Despite this very tragic accident, I can assure you that rail travel is still a very safe way to travel," he said.

Hundreds of non-fatal derailments are reported each year, the majority of them involving freight trains on secondary lines. Fatalities on passenger trains from derailments are not common.

The most recent deaths recorded aboard a Via Rail train were in 1999, when two engineers were killed after a train jumped the tracks and plowed into parked freight cars in Thamesville, Ont.

A team sent by the Transportation Safety Board began Monday combing through data recorded in the train's black box for clues into what caused the crash, which occurred while the train changed tracks.

Transportation Safety Board investigator Tom Griffith said it's too early to speculate on what sent the train careening off the tracks, but promised the board will look into every possible factor, including speed.

The speed limit for a passenger train along that corridor is about 130 kilometres per hour, but would be restricted considerably while a train switches tracks, he said.

"The download (from the box) will tell us exactly what was happening, what the crew was doing on that locomotive," he said at the scene.

"It will tell us the speed, it will tell us the brake pressure, tell us when the brakes were applied, whether he was blowing the whistle," he said.

The Ministry of Transportation and CN, which owns the track, were also on the scene Monday.

Although Robinson was said to be observing "as part of his familiarization program" when the accident happened, "it's possible" he was driving at some point, Griffith said.

"It would have been under strict supervision from the other two locomotive engineers," he added.

Earlier Monday, Via said Robinson was taking part in "observation training, he was looking."

But spokeswoman Michelle Lamarche added later she couldn't confirm who was driving, saying the company will have to wait for the board's report to know exactly what happened.

CN says it investigated the tracks before the crash and found no signs of deterioration or wear.

"It was last inspected on Sunday morning, before the incident, and no issues were found," said CN spokesman Jim Feeny said, noting that particular stretch is given a once-over at least twice a week.

In-depth tests that would reveal hard-to-see flaws are performed several times a year, including the morning of the crash, he said.

Train 92 was travelling from Niagara Falls, Ont., when it left the tracks around 3:30 p.m. on Sunday in Burlington -- about 100 metres from where a freight train derailed some four years ago.

The train's manifest listed 75 passengers but emergency officials have said they couldn't confirm whether it was accurate.

The locomotive and one passenger car flipped onto their sides and crashed into a small building next to the tracks. Another passenger car was leaning precariously.

In all, 45 people were admitted to hospitals to be treated for injuries ranging from minor to a broken leg, a back injury and a heart attack, Via officials said.

All but eight people had been released from hospital by Monday afternoon.

Trains were being detoured or replaced by chartered bus service on the Toronto-Niagara Falls and Toronto-London-Windsor routes.

Ontario Premier Dalton McGuinty offered condolences to the families of the victims.

"It's going to be very important, of course, that we work together with the federal government now to pursue whatever inquiries, investigations are necessary to ensure we better understand what exactly happened here so we can take steps to ensure it's not repeated," McGuinty said.