Aeroflot flight 5143, a Tupolev Tu-154, departed Karshi (KSQ) on a flight to Leningrad (LED) via Ufa (UFA). The flight climbed to the cruising altitude of 11.600 m and maintained an airspeed of 400 km/h, which was close to stall speed under the given conditions. During cruise flight vibrations started because of the low airspeed. The crew assumed that the vibrations were caused by engine surges. They reduced power to flight idle, causing the airspeed to drop to 290 km/h. Trying to maintain altitude, the angle of attack increased until the airplane eventually stalled. The Tu-154 went into a flat spin and crashed. Cause (translated from Russian): The cause of the accident was the aircraft entering a flat spin during the flight at a jet stream altitude with a high aircraft weight, influenced by high non-standard outside air temperature, low margin of angle of attack, and engine thrust. In these flight conditions and rapidly developing catastrophic situation, the crew deviated from the requirements of the flight manual, lost speed, and failed to maintain control of the aircraft.