The Tupolev plane crashed early on December 25, minutes after it took off from the resort of Sochi. Journalists and a well-known charity activist were among the dead and there were no survivors.
In the first findings from an expert investigation, the defence ministry said late Wednesday "the reason for the incident could have been problems with the plane captain's spatial orientation."
These "led to his mistaken actions with the plane's flight controls," the ministry said in a statement to Russian news agencies.
President Vladimir Putin's spokesman refused to comment on the findings to journalists on Thursday, saying it was a matter for the defence ministry.
In its statement, the ministry said the plane was not overloaded and there were no "outside factors" identified as causes.
But the Kommersant business daily published a far more detailed report citing experts in the investigation.
The pilot lost his orientation after leaving a well-lit airstrip and finding himself over the sea at night and he stopped following the plane's instruments and began to take "chaotic" actions.
It reported that seconds after take-off the pilot Roman Volkov "became emotional, using swear words" and questioned other crew members over the course they had taken.
The plane took off correctly but Volkov then made errors, slowing the speed at which the plane gained altitude and retracting the flaps on the wings at too low a height.
At a height of 231 metres, it started to descend and then plunged "intensively", Kommersant reported, citing experts.
"The pilot's actions became not just strange but basically suicidal," it wrote. He pulled the plane into a sharp leftward roll, which speeded up its descent.
Seventy seconds into the flight, "the plane and all its passengers were doomed" as it was just 90 metres above the sea, and even an experienced test pilot would not have been able to save it, the daily reported.
Russia's Investigative Committee which probes serious crimes is already probing if the accident was caused by breaches of safety rules and could add a charge of negligence, Kommersant reported.
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