Story highlights The second black box -- a cockpit voice recorder -- is still missing

There are likely no survivors, the Defense Ministry says

(CNN) One of the two black boxes on a Russian military jet that crashed into the Black Sea with 92 people on board has been found, the country's Defense Ministry said Tuesday, according to the state-run Sputnik news agency.

The flight data recorder will be sent to a central research institute in Lyubertsy, where officials hope to get some insight into why the Tupolev Tu-154 plunged into the sea shortly after takeoff from Sochi on Sunday morning.

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But it could take two weeks or more just to extract data from the recorder, aviation expert Col. Gen. Pyotr Belonozhko told Russia's state-run RIA Novosti.

"It all depends on the state of the black boxes," he said.

The flight data recorder was found 1,600 meters from the shore at a depth of 17 meters, the ministry said in a statement, as rescuers carry out a massive search operation in the sea.

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