The Russian military says it has been unable to retrieve information from the flight data recorder recovered from a warplane shot down by Turkey last month.
The head of Russia's military flight safety service, Sergei Bainetov, said an inspection of the recorder shows 13 of 16 microchips are nearly ruined and the remaining three are damaged.
He said experts will attempt to retrieve information from them, but that it will take a long time.
Turkey shot down the Russian SU-24 bomber on November 24 near the country's border with Syria, saying it violated Turkish airspace.
The downing led to the death of the pilot and a Russian service member who tried to rescue him.
