The memory card in the flight recorder of a Russian fighter plane downed by Turkey on the Syrian border last month is damaged, Russian investigators say.
The "black box" of the Su-24 jet was officially opened in Moscow on Friday in front of journalists and diplomats.
Nikolai Primak, head of the Russian investigation, said flight information appeared to be missing.
Data from the box could help resolve the dispute over the jet's location when it was hit.
An analysis is expected to be released next week.
The downing of the jet plunged relations between Russia and Turkey into crisis, with Moscow imposing sanctions in response.
Turkey insists that the jet, from the Russian air contingent deployed in Syria in support of President Bashar al-Assad, ignored warnings to leave its airspace.
Russia says it was shot down within Syrian airspace and President Vladimir Putin vented his anger at Turkey's government again on Thursday, accusing it of subservience to the US and of "creeping Islamisation".