Because the external load could not be released electrically, the pilot landed on snow to allow an assistant to release the load manually. After the load was released, the assistant had moved to the pilot's window to discuss the next load when the rear of the left skid began to sink into the snow. The pilot attempted to correct the situation but the main rotor struck the ground and the aircraft rolled over. The helicopter was not fitted with any load spreading devices for operations in snow. Although the pilot had tested the load bearing capacity of the snow, the technique did not provide sufficient indication that the snow could not support the aircraft. An intermittent electrical malfunction is believed to have caused the cargo hook failure.
