An "engine failure" became an "unintentional" missile strike. Here's how a moment in the Ukranian jet's flight path baffled so many.
At 6.12am local time on Wednesday, January 8 2020, Ukraine International Airlines Flight 752 departed Tehran's Imam Khomeini International Airport on a scheduled to the Ukrainian capital of Kyiv.
Carrying 167 passengers and nine crew on board, the three year old Boeing 737-800 reached around 5000 feet after two minutes in the air. There was nothing unusual about the plane's takeoff, until the third minute of its ascent. Abruptly, and without warning, all signals to the ground stopped. The aircraft's broadcast system failed, and within moments, Flight 752 slammed into the ground, killing everyone on board.
Before smouldering debris had been extinguished and the bodies recovered and identified, speculation boiled around what caused the horror crash near Shahedshahr, a town on Tehran's western outskirts.
Iran stood firm, blaming technical problems as a cause over any other theory. Armed forces diffused any accusation they were involved, ruling out accusations of a possible terrorist attack or missile strike.
But now, the cause of the tragedy appears to be the result of what the world feared. According to reports, Iranian armed forces say the Ukrainian plane that crashed killed 176 people was in fact shot down due to an "unintentional" human error.
THE BLAME GAME BEGINS
Iranian investigators' initial finding claimed there was a "technical fault" that brought down the aircraft, elaborating that a fire had broken out in one of the engines and the plane was trying to return to the airport when it crashed.
Ukraine's embassy in Iran quickly issued a statement ruling out terrorism or a missile strike, also blaming a fault of the Boeing aircraft.
"According to preliminary information," the statement had read. "The plane crashed as a result of a technical failure of the engine. The possibility of a terrorist attack or missile strike are currently ruled out."
But the statement was removed from the embassy's website within 24 hours, and instead replaced with a Revised Version saying it was "too early" to draw any conclusions on what caused the crash.
Ukraine International Airlines's president Yevgen Dykhne added more confusion, insisting there was "nothing wrong" with the three-year-old aircraft as previously suggested, and that crew experience was second-to-none and also not to blame for the tragedy.
"Given the crew's experience, error probability is minimal," Dykhne said.
"We do not even consider such a chance."
In the aftermath, blame became more and more confused and contradictory. Theories began to swirl as world leaders and aviation experts raised their suspicions over what brought down the Boeing.
The timing, for one, couldn't have been worse. In the hours before the tragedy, Iran fired at Americans forces in Baghdad in retaliation for a United States air strike that killed a top Iranian general and the leader of Iran-backed Iraqi militias.
Now, the final minutes in the air that baffled aviation experts about what brought down the Boeing have been put to rest, with reports Iran had in fact "unintentionally" shot down the passenger plane.
"If there is no electrical power going to the transponder for any wide variety of possible reasons, the transponder signal would stop," Petchenik told the publication. "It's impossible to say why the transponder signal stopped other than that it did."
It was this abrupt end after six minutes in the air, along with debris fragments and sudden loss of the fail-safe systems that experts say point to a missile strike.
In a report prepared by OpsGroup, an aviation safety information website which was set up immediately after MH17 was downed in 2014,the sudden and catastrophic nature of the crash, including the loss of both communications and tracking systems, as well the aircraft appearing to be on fire, points to a missile.
According to The Guardian, the fail-safe system which would have allowed the aircraft to land safely in the event of an engine failure at that altitude appeared to have been compromised.
In an interview with Canada's Globe and Mail newspaper, Larry Vance – a former aviation investigator with the Transportation Safety Board of Canada – said that "simple engine failure" at an altitude of less than 8000 feet could not explain the crash.
"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."
In an opinion piece for CNN, former American Airlines captain Les Abend, who has flown Boeing aircraft for 34 years, said while there are "all kinds of possible explanations for the crash" the impact of the plane will play a key role in the investigation.
"Judging by the relatively small pieces seen dispersed widely over the well-defined debris field of the accident site, the aeroplane's impact with the earth was at high speed and with great force," Abend said.
"In other words, the aircraft didn't skid across the ground striking immovable barriers, i.e. trees, rocks, etc., in an apparent effort at emergency landing. It plunged dramatically and crashed. This implies that the aeroplane was not in the direct control of the pilots."
But the question still remains over how the passenger plane could have been mistaken for a hostile aircraft.
In an interview with Business Insider, Justin Bronk, a research fellow in combat airpower and technology at London's Royal United Services Institute, said the tragedy could be down to human error.
Doomed Flight 752 followed 10 other successful departures following the same path out of Tehran on the morning it crashed.
But Bronk says that while the plane would have been following a regular flight plan and emitting a transponder signal showing the aircraft's identity and position, determining a civilian flight from military ones can require skill.
"A mix of oversights, poor training and confirmation bias in a tense situation is the best explanation I can see at this point," he said.
Pieter van Huis, a senior researcher at the open-source investigations organisation Bellingcat, added that "panic" could have played a role in the error.
"It normally is very easy for trained anti-aircraft units to distinguish civilian airliners from military jets," he said. "Panic among soldiers and/or miscommunication must have played a role."
'HIGHLY LIKELY' PLANE WAS SHOT DOWN BY IRAN
Canadian and U.S. officials began pointing fingers, believing it to be "highly likely" Ukrainian Flight 752 was shot down by Iran.
Canada's prime minister Justin Trudeau said his country had received "intelligence from multiple sources" that indicates "the plane was shot down by an Iranian surface-to-air missile."
He added that while it "may well have been unintentional", he has called for a thorough investigation that includes Canadian participation.
"The evidence indicates that the plane was shot down by an Iranian surface-to-air missile," Trudeau said.
"This may well have been unintentional.
"The news will undoubtedly come as a further shock to the families who are already grieving … (and) reinforces the need for a thorough investigation into this matter."
Trudeau's comments follow the publication of video, obtained by the New York Times, that appears to show a missile soaring across the night sky over Tehran and then exploding on contact with a plane. About 10 seconds later a loud explosion is heard on the ground as the plane, while ablaze, continues to fly.
President Donald Trump speculated that somebody "could have made a mistake" and shot down the plane, expressing doubt the crash was caused by a technical fault.
"Somebody could have made a mistake on the other side … not our system. It has nothing to do with us," he said.
"It was flying in a pretty rough neighbourhood. They could've made a mistake. Some people say it was mechanical. I personally don't think that's even a question."
Oleksiy Danylov, secretary of Ukraine's National Security and Defence Council, followed suit, saying a missile attack or terrorism made up two of the four scenarios Ukrainian investigators are exploring. Ukrainian President Volodymyr Zelensky supported the urge for a transparent investigation, saying their country welcomes any intelligence from its international allies.
Peter Goelz, a former managing director of the National Transportation Safety Board in the United States, told the New York Times investigators will probe a potential aircraft attack "at the top of their agenda".
CNN reported Iran's Foreign Affairs spokesperson Abbas Mousavi tweeted that the investigation into the cause behind the crash of Ukrainian Airlines flight has officially launched based on international guidelines set forth by the International Civil Aviation Organisation.
Mousavi added that representatives from Ukraine and aircraft manufacturer Boeing have been invited to take part in the investigation.
He ended the tweet by saying, "We appreciate any country who can provide information to the committee in charge."
But Iran's civil aviation chief, however, said he was "certain" that the plane was not hit by a missile.
"The thing that is clear to us and that we can say with certainty is that this plane was not hit by a missile," Ali Abedzadeh told reporters, with Iranian government spokesman, Ali Rabiei, accusing the US and its allies of "lying and engaging in psychological warfare" in their speculation over the cause of the accident.
Now, however, Iranian state TV, citing the military, says the country 'unintentionally' shot down a Ukrainian jetliner because of human error.
HOW WILL THE INVESTIGATION PLAY OUT?
Amid tensions between Iran and the US, local investigators initially said it would not hand over the recovered black box flight recorders to Boeing, the plane's manufacturer, or to the US.
Now, Iran has gone back on their word, promising a full investigation along with the assistance of the National Transportation Safety Board, the U.S. accident investigation agency, to participate in the probe of the downed Ukrainian Boeing.
Iran also invited Boeing, the U.S. manufacturer of the plane, and the Ukraine to be a part of the investigation team. It is not, however, immediately clear what level of participation the two U.S.
But alarming TV images from the crash site on Thursday showed a mechanical digger helping to clear debris away, raising concerns that important evidence could have been removed.
Ukrainian experts have been given access to the black box flight recorders of the plane that crashed in Iran, Foreign Minister Vadym Prystaiko said, adding that they were receiving "full co-operation" from the Iranian authorities.
"Our team has now got access to the black boxes," Prystaiko told a briefing. The Ukrainian experts had also been given access to the plane's fragments and the crash site, as well as recordings of the radio exchange between the pilots and traffic control, according to Prystaiko.
"Conclusions — as soon as they are made — will be presented to the public," he said.
He said the plane's fragments had been scattered over a wide area including "certain settlements".
Speaking to reporters, Prystaiko also stressed that all possibilities were under consideration.
"We are not rejecting any of the leads, all leads are being considered," he said.
"Our main task is to find the reasons of this tragedy in an absolutely just and unbiased manner.
"To find who is guilty if someone is guilty.
"But of course if we prove that this plane has been shot down we will of course demand that the guilty be brought to justice but also compensation."
Ukraine's top diplomat refused to say what kind of information Kiev had received from the West.
"This is secret information," he said.