Investigators on Wednesday found the second flight data recorder of the Russian military aircraft that crashed into the Black Sea on Sunday, AP reported. The first flight recorder was found around 1,600 m away from the shore on Tuesday.

So far, 15 bodies and 239 body parts had been recovered, the Defence Ministry told Russian news agencies, according to AFP. Investigators are still looking to establish what caused the crash – it could have been caused by fuel, pilot error, foreign objects in the engine or a technical failure.

Russia, however, had ruled out a possible terror strike behind the mishap, even though a few aviation experts had highlighted that the crew did not report any technical problem, which they said suggested an explosion.

The Tu-154 aircraft with 92 people on board had crashed into the Black Sea on Christmas Day minutes after taking off from Sochi. Musicians from the Alexandrov Ensemble and an Russia’s Army choir were among the passengers.

The Soviet-era plane was built in 1983 and had last been serviced in September. While Russian commercial airlines have replaced it with Western-built planes, government ministries continue to use the model. In 2010, Tu-154 – a Polish jet – carrying then-president Lech Kaczynski and others went down in Russia, killing everyone on board.