Most of the dead were Iranian.
"An operator had forgotten to re-adjust the direction on the radar system after moving to a new position, an error that contributed to misreading the radar's data", an interim report on the Civil Aviation Organisation (CAO) website said.
The shootdown happened at Tehran's main airport the same night Iran launched a ballistic-missile attack targeting USA soldiers in Iraq, its response to the American drone strike that killed Guard Gen. Qassem Soleimani in Baghdad on January 3. The Iranian government later admitted that its forces mistakenly fired a missile at the plane.
Iranian President Hassan Rouhani described the downing of the plane as an "unforgivable mistake".More news: Coronavirus: Aishwarya Rai Bachchan, daughter Aaradhya test positive
The report also noted that the first of the two missiles launched at the aircraft was sacked by a defence unit operator who had acted "without receiving any response from the Coordination Centre" on which he depended.
The report did not say why the Guard moved the air defence system, but noted the Ukrainian flight had done nothing out of the ordinary up until the missile launch, with its transponder and other data being broadcast.
The second missile was sacked 30 seconds later, "by observing the continuity of (the) trajectory of the detected target", the report added.
An Iranian general had said in January that many communications had been jammed the night of the disaster. Hours earlier, the country had fired ballistic missiles at two U.S. bases in Iraq in retaliation for the killing of top Iranian general Qasem Soleimani by a United States drone strike in Baghdad.More news: China's SinoVac starts late stage trials for its Covid-19 vaccine
This mistake "initiated a hazard chain" that caused further errors in the minutes before the plane was shot down. The downing came days after the USA killing of Iran's General Qassem Soleimani.
Last month, Iran said the black boxes of the Boeing 737-800 airliner will be sent to France, to be analysed starting July 20.
The recording is allegedly a conversation between the family of one of the accident victims and Hassan Rezaeifar, who at the time was leading Iran's investigation into the incident.More news: Russia's Sechenov University Successfully Completes Trials of World's 1st COVID-19 Vaccine