More details are emerging about the air disaster in the Black Sea involving a famous Russian military choir.
An ageing Tu-154 airliner came down off the Russian coast with the loss of all 92 passengers and crew.
This was no ordinary flight: the plane belonged to the Russian defence ministry and was en route from Moscow to Syria, where the Alexandrov Ensemble was due to perform for soldiers stationed overseas.
As the official investigation gets under way, here are some of the facts and theories.
How did the crash happen?
At 05:23 (02:23 GMT) on Sunday 25 December, the jet took off in good weather from Adler airport near the city of Sochi, where it had been refuelling, for the next leg of its flight to Latakia in western Syria.
A recording of the final conversation between air traffic controllers and the pilot indicates that there was no panic among the crew. All voices were calm before the pilot stopped responding.
Two minutes into the flight the plane disappeared from radar. Wreckage was found about 1.5km (about one mile) from the shore.
Fragments of the plane were found across a radius of about 500m (1640ft), the defence ministry said, after a vast search operation involving a submarine, 45 other vessels, 12 planes, 10 helicopters, three drones and more than 3,500 personnel.
As of 27 December, at least 12 bodies had been recovered.
Who was on the plane?
In addition to the eight crew members, there were:
- Sixty-four men and women of the Alexandrov Ensemble, the official choir of the Russian armed forces
- One of Russia’s best-known humanitarian figures, Yelizaveta Glinka – known popularly as Dr Liza – who was due to deliver medicines to a Syrian hospital
- Nine members of the Russian media including TV crews from Channel One, NTV and the military TV channel Zvezda
- Eight military figures among whom is listed Lt-Gen Valeri Khalilov, the choir’s conductor
- Two civil servants
The victims of the Russian jet crash
Could the disaster have been caused by a bomb or missile?
The plane was flying to an air base in Syria, where Russia has been waging an air campaign on the side of President Bashar al-Assad for more than a year.
So-called Islamic State, one of Russia’s deadliest enemies in Syria, claimed responsibility for the bombing of a Russian airliner returning from Egypt just over a year ago, when 224 people were killed.
However, the Russian authorities have downplayed the possibility of a bomb this time.
“As far as we know the main theories do not involve a terrorist attack,” Russian Transport Minister Maxim Sokolov said.
An unnamed source close to the investigation told Russia’s Interfax news agency on 27 December that human remains recovered from the sea bore no traces of explosives.
Nor, the source added, was there any evidence from the debris or human remains that the plane had been “subjected to external impact”.
That would appear to rule out a missile attack of the kind which downed Flight MH17 over neighbouring Ukraine in July 2014, with the loss of 283 lives.
So what are the likelier causes?
“Investigators were “proceeding on the premise that the causes were pilot error or the plane’s technical condition,” the transport minister said.
In defence of the crew, it was commanded by an experienced pilot, Maj Roman Volkov, who had more than 3,000 flight hours behind him.
He was flying with his regular crew, the Russian Armed Forces flight safety service says, including co-pilot Capt Alexander Rovensky, who had 10 years of aviation service.
The advanced age of the plane may have been a factor – it was 33 years old.
That said, few of the 39 fatal accidents involving this model of the Tupolev have been attributed to technical problems. Many were lost as a result of difficult weather conditions and poor air traffic control.
Another factor in past air crashes in Russia has been overloaded planes.
“Witness accounts and other objective data obtained during the investigation suggest the plane was unable to gain height and for some reason – possibly overloading or a technical fault – crashed into the sea,” an unnamed source close to the investigation told Interfax.
All these theories are speculation, of course, which may be rapidly overtaken by the findings from the plane’s “black boxes”, the first of which has already been recovered and brought to Moscow.