Flight recorders have revealed no evidence of an explosion on board a Russian plane that crashed, killing all 92 on board, but investigators haven't ruled out a deliberate mechanical impact to down the plane, a military official says.
The Russian air force said on Thursday that a cockpit conversation recorder contained the captain's words that indicated a "special situation" that began unfolding on board the plane.
They wouldn't elaborate on what may have led to the crash, but noted that it likely had been caused by several factors.
The Tu-154 of the Russian Defence Ministry crashed into the sea early on Sunday, moments after taking off in good weather from the city of Sochi.
It 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.
Bainetov said that the plane crashed 70 seconds after takeoff from an altitude of 250 metres while it was traveling at a speed of 370 kilometres per hour.
"After deciphering the first flight recorder we have made a conclusion that there was no explosion on board," the air force's Sergei Bainetov said.
But asked if that means that investigators have ruled out a terror attack, Bainetov said "we aren't ruling that version yet."
"A terror attack doesn't always involve an explosion," he said. "Along with an explosion on board, there could have been some mechanical impact."
He wouldn't offer any details, saying that Russian law-enforcement agencies are working on the case.
Bainetov's words appeared to contradict a previous statement from Russia's top domestic security and counter-terrorism agency, the FSB, which has said it found "no indications or facts pointing at the possibility of a terror attack or an act of sabotage."
It said investigators were looking into whether the crash might have been caused by bad fuel, pilot error, equipment failure or objects stuck in the engines.
