"Weather conditions were difficult, the human factor played its role," said Igor Levitin at a press conference in Moscow on Wednesday.
Tatyana Anodina, head of the Intergovernmental Aviation Committee (IAC) that took part in the enquiry said the pilot had failed to control the airplane.
Facing bad visibility and driving rain, the pilot switched off the aircraft's autopilot as it flew 340m above the Black Sea, causing the crew to lose control of the aircraft, according to the committee's conclusions.
The IAC found that the crew's subsequent attempts to raise the plane's altitude were uncoordinated and insufficient.
Levitin said the families of the 26 Russians who died in the crash would receive payments of about $3,700 on top of $9,300 from regional authorities.
The Airbus A320 crashed into the Black Sea on May 3 amid rainy weather as it was coming in to land in Sochi - a popular coastal resort city in southwest Russia.
It had taken off from the Armenian capital, Yerevan.