Russian rescuers trawling the Black Sea on Wednesday found the second black box from a Syria-bound military plane that crashed at the weekend with 92 people on board, authorities said.

"The second onboard recorder from the Tu-154 plane has been found and raised from the seabed," the defence ministry said in a statement to Russian news agencies.

The discovery of the black box comes the day after rescuers found the primary inflight recorder and should help provide vital clues as investigators try to work out what caused the fatal crash.

The Soviet-era jet, whose passengers included more than 60 members of an internationally renowned Red Army music troupe, was heading to Russia's military airbase in Syria on Sunday when it went down off the coast of Sochi shortly after take-off from a refuelling stop at the airport.

Russia's FSB security service has said it is looking into four main suspected causes: pilot error, technical failure, faulty fuel and a foreign object in the engine.

The FSB said that so far there were no indications to suggest terrorism was behind the crash, but did not rule it out entirely.

Russian rescue workers told state media Wednesday that the second black box contained the flight parameters, despite contradictory reports over the content of the recorders.

Private news outlet Life published what it said was the panicked exchange between the pilots in the moments ahead of the crash decoded from one of the black boxes, suggesting that a problem with the plane's wingflaps might have been to blame.

According to the transcript one pilot shouted "the flaps, shit. What the fuck!" as an alarm sounds. "Commander, we're falling" are the last words recorded.

The discovery of the second black box comes as searchers scramble to recover bodies and remaining debris from the aircraft in a major operation involving divers, deepwater machines, helicopters and drones.

The defence ministry told Russian news agencies that so far 15 bodies and 239 body parts from those onboard the ill-fated aircraft have been found, with some of the remains transported to Moscow for DNA identification.

The loss of the plane has shocked Russia at a time when the Kremlin was celebrating the recapture of Syria's Aleppo by regime forces, the biggest success since it launched its bombing campaign to support President Bashar al-Assad last year.

The military performers on the plane were set to stage a New Year's concert for Russian troops at the Hmeimim airbase in Syria, Moscow's main staging post in the war-torn country.