A Russian military plane plunged into the sea killing all 92 people on board after a co-pilot mistakenly pulled a lever to operate the wing flaps, it is thought.
Investigators believe Alexander Rovensky, 33, was partly responsible for the Tupolev Tu-154's horrific crash into the Black Sea soon after take-off from Sochi airport on Christmas Day.
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The airliner was also overloaded on its way to Syria, according to reports in Moscow.
Sixty-four members of the Alexandrov Ensemble - one of the world's most famous military choirs - were among the passengers on board the aircraft when it crashed minutes after leaving for Latakia to provide festive gifts and entertainment for Russian troops.
A search and rescue team recover a body from the sea off Sochi
Co-pilot Alexander Rovensky may have inadvertently pulled a lever to retract the jet's wing flaps
The plane abruptly descended from an altitude of 450m three minutes into the flight due to problems with the wing flaps, Kremlin-loyal news website Life reported.
The two levers are close together in cockpit.
The source added the plight of the aircraft was worsened by overloading, with the luggage compartment filled to the brim, which hampered pilots' fight to stop it plunging into the sea.
Rescue workers take part in a search and rescue operation at the crash site
Wreckage from the doomed Tupolev Tu-154 retrieved from the Black Sea
Black box recordings have revealed panicked exchanges between Major Roman Volkov, the captain of the flight, and Rovensky.
One of them can be heard screaming "we're failing" moments before the doomed jet crashes into waters.
Viktor Sazhenin, a veteran pilot with eight years' experience of flying Tu-154 planes, also told Life be believed the neither pilot in the cockpit had been trained in handling extreme situations.
A diver working to retrieve wreckage from the sea floor
Russian navy ships sail near the crash site on December 26
He suggested the disaster could have been avoided if the pair had received specialist training.
Russian servicemen and nine journalists, including well-known Zvezda TV channel reporter Pavel Obukhov, were also on board the aircraft when it crashed 1.7km off the Sochi coast at 5.40am local time on December 25.
Three days after the tragedy, investigators said they had retrieved 1,547 pieces of wreckage from the ocean floor.
Wreckage recovered from the Black Sea
Roman Volkov, pilot of the crashed Russian plane
A last picture of the doomed plane emerged showing the aircraft sitting on the tarmac at Chkalovsky Airport in Moscow.
The image was posted online by NTV cameraman Evgeny Tolstov - who was among the victims - with the caption: "Travelling to Latakia."
The plane then made a stopover in Sochi for refuelling shortly before the disaster.