Since Thursday morning a team of 35 rescuers has been combing the taiga area where the helicopter is presumed to have disappeared, their search complicated by strong winds and heavy snowfall.
Poor weather conditions have so far prevented the use of aircraft, but there are two Mi-2 helicopters and an An-2 plane at the ready.
"We are investigating a possible air crash," the official said, adding that the chances of a successful rescue were high because the helicopter was being flown by an experienced test pilot.
The president and vice president of the small aircraft association Flag were the other two people on board.
The helicopter was last spotted Tuesday evening. Officials said it may have made an emergency landing in bad weather. Local witnesses confirmed seeing an Mi-2 flying at low altitude over the trees Tuesday.
The Mi-2 is an eight-passenger utility helicopter with a flight range of about 600 kilometers (370 miles).
