Russian military officials said on Tuesday they would call on more specialists to help decipher the damaged black box of a warplane shot down by Turkey after a first attempt to read the device failed.
"Reading the memory cards is not yet possible due to internal damage," said Sergei Bainetov, the deputy head of flight safety in the Russian armed forces, RIA Novosti
"The commission is contemplating calling upon specialised Russian research institutions, which have the ability to extract information directly from the microchips' crystals."
Bainetov said further attempts to read the flight recorder would take "quite a long time" but did not provide an estimated timeframe.
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He said 13 of the 16 microchips contained in device had been destroyed, and that the remaining three were damaged.
Moscow and Ankara have been locked in a bitter spat over Turkey's downing of the warplane on the Syrian border last month, which led to the deaths of a pilot and another serviceman who attempted to rescue him.
They were Russia's first combat casualties in its bombing campaign in Syria that was launched on September 30.
Military officials had warned on Friday, when the opening of the black box was broadcast on national television, that its memory cards could have sustained damage.
The Russian air force opened the device in front of specialists from Britain, China and the United States after President Vladimir Putin had ordered that it only be opened in the presence of foreign experts.
Bainetov said today the foreign experts involved had praised the "openness" of the process.
Putin has said an analysis of the black box would help determine the downed jet's flight path and position, which Ankara and Moscow have furiously disagreed upon.
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Turkey says the Russian jet strayed into its airspace and ignored repeated warnings, while Moscow insists it did not cross over from Syria and accused Ankara of a planned provocation.
The November 24 downing triggered the biggest crisis in ties between Moscow and Ankara since the end of the Cold War, with Russia slapping a raft of economic sanctions against