Accident of An-12 near Surgut on January 22, 1971

An-12B with tail number 11000 (serial number 5343610, serial number 36-10) was launched by the Tashkent Aircraft Plant on December 3, 1965, and by February 2, 1966 was transferred to the Main Directorate of the Civil Air Fleet . The last place of work of the aircraft was the Syktyvkar squadron of the Komi Territorial Administration of the Civil Air Fleet. In total, at the time of the disaster, the 11000 aircraft had 5626 flying hours and 2578 landings ^{[1] [2]} .

In the first half of January, 2 An-12s and 3 crews from the 75th flight detachment were temporarily based at the Omsk Airport, which from there carried out custom-made cargo transportation. But on January 22, an order was received to overtake board 11000 to the base airfield - Syktyvkar , where he was scheduled to undergo maintenance. It was also decided to make a passing flight to Surgut , during which 12 tons of cargo were to be transported. The cargo was mainly a net in rolls, PVC tiles and various other household products, as well as one S-955 construction pile . There were two crews on the plane: pilot and interchangeable. The pilot consisted of a commander (FAC)S. A. Bakharev , co-pilot A.P. Dekhtyarenko , navigator V.K. Bakhin , flight instructor M. I. Kazachkova , flight attendant A. A. Tychenko and flight attendant V. M. Malinina . The shift consisted of a commander (FAC) L. A. Butov , co-pilot A.M. Shamy , navigator P.S. Azarenkova , flight engineer A. M. Yudaev , flight attendant N.I.Soklakov and the flight attendant I.I. Pushnikova . Also on board was an engineer of the 75th detachment N.P. Kayakin and accompanying cargo E.R. Kramar . According to the forecast available to the crew, in Surgut, layered cumulus clouds with a height of 500-700 meters, visibility of 3-4 kilometers, snow, icing in the clouds were expected. At 18:09 Moscow time, the Airliner took off from the Omsk airport and after climbing climbed to the given level of 6,600 meters ^[1] .

In Surgut, it was overcast 450 meters high, visibility was 5.5 kilometers, a fresh north wind was blowing, and air temperature was -9 ° C. At 19:20, the radar control officer at Surgut Airport allowed the An-12 crew to drop to an altitude of 4,500 meters, and then to 1,200 meters. When the crew reported the occupation of a height of 1200 meters, they were instructed to switch to communication with the landing controller. Carrying out a landing approach at a magnetic course of 180 °, the aircraft entered the area of ​​the second turn with a decrease to a height of 400 meters, while the distance to the airport was 11 kilometers. At 19:34, Moscow time, from an airplane, they reported on the flight of the DPRM beam at an altitude of 400 meters. At 19:36 Moscow time (21:36 local time), when the lateral distance was 11 kilometers with a radial distance of 16 kilometers, the crew was instructed to complete the third turn. The answer was: " Got it . " After that, the crew no longer got in touch and did not answer calls ^[1] .

When the An-12, 18 kilometers north-east of Surgut Airport, performed a left turn at a speed of 330 km / h, the flow was interrupted on the wing , as a result of which the An-12 began to enter the progressive left bank and lose altitude. Deviating from the initial course by 110 °, the airliner at an angle of 40 ° and with a left bank of about 90 ° crashed into the ground, in the vicinity of the Pochekuyka River, completely collapsed and burned ^[1] .

According to a synoptic analysis of meteorological conditions, strong icing was found at heights of 400–1300 meters. Also about the icing at an altitude of 1200 meters and reported the crew of the An-12 aboard the USSR-12996 ^[1] .

Commission conclusions : Stalling during the third turn due to a sharp deterioration in aerodynamics due to icing of the wing during flight under intensive icing, as well as due to the mismatch between the speeds provided for the third and fourth turns with a landing weight of more than 55 tons with an icy wing. The wing icing occurred due to insufficient heating of the leading edge of the wing due to incomplete opening of the air intake taps from the engines.

Other factors:

1. The absence of flight tests on the behavior of the aircraft during icing of the wing and recommendations to the crew when flying in similar conditions.
2. Lack of data on the effectiveness of PIC wing with intensive icing.

- ^[1]

With a difference of 9 days (January 22 and 31, 1971 ), two An-12 crashed at the Surgut airport - USSR-11000 and USSR-12996 . At the same time, both disasters occurred according to a similar pattern - during the third turn, the aircraft began to spontaneously enter the roll due to the stall of the flow on the wing caused by the deterioration of aerodynamics due to icing, which in turn was caused by the insufficient efficiency of the anti-icing system , since the hot air taps from the engines were not fully open. To prevent such disasters from happening again, significant improvements were made to the air sampling control system, including the addition of an alarm for the complete opening of the taps. We also conducted special tests, according to the results of which we were able to clarify the aerodynamic characteristics of the An-12 aircraft during icing. This has also led to changes in many civil aviation guidelines ^[1] .

Similar disasters

• Accident An-8 in Kirovabad
• Accident An-8 in Lakhta
• Accidents of An-10 in Lviv:
  • November 16, 1959
  • February 26, 1960
• Accident of An-12 near Surgut on January 31, 1971
• Accident An-12 in Nalchik