Investigators recovered the flight-data recorder from a crashed Russian military plane Tuesday and began reviewing its contents to learn why the jet went down moments after takeoff, killing all 92 people aboard, including members of a famous choir.
The Tu-154 crashed into the Black Sea early Sunday two minutes after departing in good weather from the city of Sochi. The plane was carrying members of the Alexandrov Ensemble, widely known as the Red Army Choir, to a New Year's concert at a Russian military base in Syria.
Meanwhile, rescue workers raced to wrap up their efforts to recover bodies and wreckage ahead of predicted bad weather. The work has involved 3,500 people, including about 200 navy divers flown to the site from all over Russia. Aided by drones and submersibles, teams have recovered 12 bodies and numerous body fragments about a mile away from the shore.
The main flight recorder was quickly flown to Moscow, where experts started analyzing it, Transport Minister Maxim Sokolov said. Preliminary findings could be available as early as Wednesday, according to some aviation experts.
Investigators were looking into whether the crash might have been caused by bad fuel, pilot error, equipment failure or objects stuck in the engines. The top Russian investigative agency, known as the Investigative Committee, said it had taken samples from a fuel tank used to fill the plane, which flew from Moscow's Chkalovsky military airport and stopped in Sochi for refueling.
The committee also said it found a witness who filmed the crash but offered no details.
Online publication Life.ru published what it described as a script of cockpit conversation, with one pilot yelling about a problem with the plane's flaps and then shouting: "Commander, we are falling!" It was impossible to verify the report, but Life.ru is known to have good connections with Russian security agencies.
Flaps are moveable panels mounted on the edge of the wings to increase lift.
The Interfax news agency reported that the flaps were not functioning in sync, causing the jet to lose speed and triggering an aerodynamic stall. It also said that the preliminary analysis of the flight recorder pointed at pilot error.
The government has sought to quell speculation that the crash might have been caused by a bomb planted on board or a portable air-defense missile. A terrorist attack on a Syria-bound military flight would badly embarrass the Kremlin at a time when it boasts about the success of its campaign in Syria after Aleppo fell into President Bashar Assad's hands.
Russia's main domestic security and counter-terrorism agency, the FSB, said it found "no indications or facts pointing at the possibility of a terror attack or an act of sabotage" on the plane.
However, some aviation experts have noted that the crew's failure to report any technical problem and the large area over which fragments of the plane were scattered point to a possible explosion on board.
The Tu-154 is a Soviet-built three-engine airliner designed in the late 1960s. Russian airlines decommissioned the noisy, fuel-guzzling aircraft years ago, but the military and other government agencies continue using the plane, which is still loved by crews for its maneuverability and sturdiness.
The plane that crashed Sunday was built in 1983 and underwent factory checkups and maintenance in 2014 as well as earlier this year. Investigators have taken relevant documents from the plant that did the job.