The accident occurred at 11:45 a.m. Moscow time [08:45 GMT] on Tuesday near Pugachyov airfield in the Saratov Region and killed all three crewmembers.
"The results of a preliminary investigation show that the helicopter's rotor got jammed, which caused the destruction of the blades. The aircraft fell like a stone to the ground from an altitude of 1.5 kilometers [about 5,000 feet]," Vladimir Belykh of the Saratov garrison said.
"Voice recordings [from black boxes] revealed that everything happened so fast that the crew members did not have time to react," he said.
He added that investigators had located three eyewitnesses, who confirmed that the helicopter's rotor had fallen apart before it plummeted to the ground.