The An-12 transport plane operated on a flight from Andizhan to Semipalatinsk with an en route stop at Novosibirsk. The flight was diverted to Ucharal. The air traffic controller at Ucharal allowed the flight to descend to 600 m in an area where the minimum safe altitude is 2310 m. The airplane collided with a mountain at an altitude of 1269 m.