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Rescue teams work at the scene of a plane crash near near Imam Khomeini airport out the outskirts of Tehran on Jan. 8, 2020.AKBAR TAVAKOLI/AFP/Getty Images

Ukraine International Airlines Flight 752 roared away from Tehran’s airport at just past 6 a.m. local time on Wednesday, carrying 167 passengers and nine crew members bound for Kyiv. The Boeing 737-800 quickly climbed to more than 7,900 feet, flying at a speed of 312 nautical miles an hour, according to website Flightradar24, which tracks planes by collecting and posting flight data they broadcast.

About three minutes into its ascent, the aircraft stopped emitting all signals and, moments later, slammed into the ground.

The crash killed everyone on board, including at least 63 Canadians.

Iran and Ukraine will lead the search for the cause, an investigation not helped by the dangerous security environment in which the crash occurred.

The plane went down shortly after Iran fired ballistic missiles at Iraqi military bases that house U.S. troops as retaliation for the U.S. strike that killed Iranian General Qassem Soleimani. No evidence has emerged that connects the crash of the passenger jet to the attacks.

Iran said on Wednesday it will not share the plane’s flight-data recorder with U.S.-based Boeing or the United States.

Reuters, citing five people it described as “security sources” in the United States, Europe and Canada, reported on Wednesday that Western intelligence agencies’ early assessment of the cause was a “technical malfunction,” not a missile.

Prime Minister Justin Trudeau said government officials are in touch with their international counterparts and have offered assistance.

The country in which a crash occurs has the responsibility to lead the investigation, with the plane’s manufacturer and countries of origin and registration also playing key roles. But that’s “in a normal environment,” said Larry Vance, a former aviation investigator with the Transportation Safety Board of Canada.

Air safety should never be politicized - but it is

The Canadian government would also seek a role, given the large number of its citizens involved, he said. “The protocol is they would ask, and normally, it would be almost automatic that they could participate,” Mr. Vance said by phone. “Canada would offer expertise in accident investigation. They would send experts from our own [Transportation Safety Board] and perhaps Transport Canada.”

The TSB said it will review the information Iranian investigators release and will be available to provide any technical assistance requested.

A typical plane-crash probe involves two parallel investigations: one criminal and one safety-related.

The criminal investigators look for evidence of sabotage, while the safety investigators look for problems that led to the crash and could be corrected to prevent similar incidents. The information from the flight-data recorder, or black box, “is very important,” Mr. Vance said.

The Boeing 737-800 has a reputation as a reliable aircraft with no history of catastrophic failure. Mr. Vance said it is unusual that a modern, two-engine plane would lose all electronic power and fall from the sky. He noted the plane’s transponder, which sends speed and other data to receivers, stopped transmitting before it plunged.

“A simple engine failure … that’s not what we’re looking at here. That just doesn’t fit the scenario at all,” he said. “Here we had some kind of event that knocked the transponder off the plane. Some kind of event that disabled the electronics to that system. It takes a lot to disable the electronics on a sophisticated aircraft like the 737-800.”

Flightradar24 is a Swedish web-based company that collects and displays flight data – plane speeds, altitudes and other information broadcast by aircraft. The company has three receivers near the Tehran airport, and anyone with a subscription could view the final climb of Flight 752 in real time.

Ian Petchenik, a spokesman for Flightradar24, said the path plotted by Flight 752 ends abruptly at an altitude of 7,925 feet because the plane stopped sending out signals at that point. He said the reason for this is unknown, but is likely due to one of a few events – an electrical failure, a wiring malfunction, physical damage to the transponder that broadcasts data, “or a catastrophic failure of some kind.”

Investigators will be trying to determine what led to this loss of power.

“If there is no electrical power going to the transponder for any wide variety of possible reasons, the transponder signal would stop,” Mr. Petchenik said by phone from Chicago. “It’s impossible to say why the transponder signal stopped other than that it did. ”

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