Aviation experts have so far failed to retrieve information from a flight data recorder on a Russian war plane downed by Turkey last month.
Turkey shot down the Russian Su-24 bomber at the border with Syria on November 24, saying it violated its airspace for 17 seconds despite repeated warnings.
Russia insists the plane never entered Turkish airspace.
Russian Lt Gen Sergei Bainetov, a deputy head of the Russian military’s flight safety service, said an inspection of the recorder has revealed that 13 of 16 microchips on its data board are nearly ruined and the remaining three are damaged.
He said experts will attempt to retrieve information from them, but the effort will take a long time.
The downing of the plane has badly strained ties between Russia and Turkey.
Most microchips of downed Russian bomber's data recorder are damaged — official https://t.co/Rq1vWNbQZ2
— TASS (@tassagency_en) December 21, 2015