OTTAWA—Investigators know the “how” of the devastating crash of Ukraine International Airlines Flight 752. Now the issue facing accident investigators from Canada and other nations is “why?” And what lessons must be learned to prevent such a tragedy in the future?

Any doubt about the cause was removed Saturday with Iran’s surprise admission that it made a “disastrous mistake” when it thought the Boeing 737-800 was a hostile target and launched a missile to shoot it down soon after it took off from Tehran’s airport, bound for Kyiv.

“Yes, we know what has happened. What we don’t know is why. So the investigation is going to try to understand why it happened,” said Natacha Van Themsche, the director of air investigations for the Transportation Safety Board of Canada.

The Boeing jet crashed into a Tehran suburb Wednesday, killing all 176 people on board, including 57 Canadians. Among the passengers, 138 were scheduled to fly to Canada on a connecting flight from Kyiv.

The crash happened hours after Iran unleashed missiles at Iraqi military sites housing U.S. and coalition forces, as its own military was on high alert.

Prime Minister Justin Trudeau in part blamed the loss of life on heightened tensions between Iran and the U.S. following Washington’s targeted killing of a prominent Iranian general.

“I think if there were no tensions, if there was no escalation recently in the region, those Canadians would be right now home with their families. This is something that happens when you have conflict and war. Innocents bear the brunt of it,” he said in an interview with Global News.

Trudeau said he has spoken with U.S. President Donald Trump on the need to de-escalate tensions in the region and noted that Washington gave Canada no advance notice of its strike against Gen. Qassem Soleimani, which set in motion Iran’s missile strikes against coalition forces in Iraq, including Canadian personnel.

Asked if he would have wanted a heads-up, Trudeau replied, “obviously.”

The circumstances around the crash are prompting questions about military procedures, why the airspace had not been closed given the tension and why commercial aircraft continued to operate even after the Ukrainian aircraft had been shot down.

“We need to establish a sequence of events. We need to understand how everything happened,” Van Themsche said.

Investigators will even look at Iran’s assertion that the missile strike was accidental.

“When accident investigators approach an accident scene, everything is on the table, notwithstanding what people have said publicly. We don’t take that just at face value. We need to corroborate that, validate that information,” said Kathy Fox, chair of the safety board, adding it’s normal for investigators to look at the sequence of events that led up to a crash.

If it was unintentional, she said, “what was the context that led someone to make such a tragic mistake?”

She cautioned that the investigation will not be short, but the outcome could help avoid a similar disaster in the future.

Fox noted the fate of Malaysian Airlines Flight 17, which was shot down over Ukraine in 2014, killing 298 people on board, as evidence that the lessons of that air disaster were not fully learned.

She pointedly quoted from the conclusion of a Dutch safety board report into that disaster, saying: “Practice shows that states in which there is ongoing armed conflict will not implement restriction on their airspace on their own initiative.”

The downing of the Ukrainian airlines flight is “clear evidence that more needs to be done when you’re dealing with military activities versus civilian operations,” Fox said.

She acknowledged that the upcoming probe will put a spotlight on the actions of the Iranians.

“Clearly some of these questions are going to very uncomfortable for the country to answer but we hope that the purpose of safety investigations will override those,” Fox said.

Nevertheless, safety board officials said the access granted by Iran to Canada has gone beyond what is required under international protocols.

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Two board investigators are in Tehran and are expected to be allowed access to the crash site and the wreckage on Tuesday. As well, Canada has been asked to help download the data recorders. Safety board experts skilled at analyzing voice and flight data recorders are ready to deploy, once they know where that work will be done.

“Everything we’re seeing so far is giving us optimism,” she told a news conference Monday.

Because Iran is leading the investigation, Fox cautioned that Canada will be restricted in what information it can release about the investigation. But she said that the Canadian team would speak out if it had concerns about the transparency of the investigation or its findings.

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