Aeroflot Flight 136 was an aviation disaster involving an Ilyushin Il-12P passenger aircraft operated by Aeroflot, which occurred on Thursday, October 28, 1954, in Krasnoyarsk Krai on the slope of Mount Sivukha. The crash resulted in the deaths of 19 people (unofficially 20).
The Il-12P with factory number 93013206 and serial number 32-06 was produced by the aviation plant No. 30 "Znamya Truda" (Moscow) in 1949. The airliner received the registration number USSR-L1789 and was transferred to the Main Directorate of Civil Air Fleet under the Council of Ministers of the USSR, which assigned it to the 64th (Vnukovo) aviation squad of the Moscow territorial administration of the civil air fleet.[1]
On October 27, while operating a passenger flight from Moscow, aircraft L1789 arrived in Novosibirsk, where the crew changed. The new crew was to operate passenger flights 135/136 from Novosibirsk to Irkutsk and back. These flights were considered international as they connected with flights 03/04 on the route Irkutsk—Ulaanbaatar—Beijing—Ulaanbaatar—Irkutsk, operated by the Soviet-Chinese airline SKOGA (Sino-Soviet Joint Stock Company). At 14:28[* 1] flight 135 took off from Novosibirsk and landed safely in Irkutsk at 18:52. The return flight 136 to Novosibirsk was planned, but due to adverse weather conditions, the flight was redirected to Krasnoyarsk at an altitude of 2,700 meters. The crew received the weather forecast only for the route to Krasnoyarsk. According to this forecast, the route expected variable (6-9 points) stratocumulus and ragged-rain clouds with a lower limit of 600 to 1,000 meters, while on the section Taishet-Kansk—clouds with a lower limit of 300 to 600 meters, medium, upper, precipitation, visibility from 4 to 10 kilometers, icing in the clouds, and mountains covered with clouds. In Krasnoyarsk itself, variable upper stratocumulus clouds with a lower limit of 600 to 1,000 meters, occasional snow, northwest wind 6–9m/s, gusts up to 12m/s, visibility from 4 to 10 kilometers were expected. At an altitude of 1,000 meters, wind was expected at 200° 40km/h, at 1,500 meters—240° 40km/h, at 2,000 meters—250° 50km/h, and at 3,000 meters—260° 60km/h. At 21:09 with 13 passengers (9 foreigners from the connecting flight and 4 Soviets from Irkutsk) and 6 crew members on board, the Il-12 took off from Irkutsk.[2][3]
At 22:55, with a ground speed of 275km/h, Nizhneudinsk was passed. The flight had been above the clouds and without deviations until then. However, the plane then flew into clouds, where icing from light to moderate was observed. Likely relying on the weather forecast received in Irkutsk, the crew believed the wind was southwest at 40km/h. However, at 23:50, the AMS in Krasnoyarsk received data that the wind was northwest and at 2,000 meters reached a speed of 130km/h, meaning the plane was drifting not to the north but to the south. However, this information was not transmitted to the flight supervisor at the Krasnoyarsk airport or to the aircraft crew. At 23:26, the crew received bearing data—a back bearing of 282° from the Krasnoyarsk-Severny Airport and a true bearing of 147° from the Yeniseysk Airport. This data indicated that since passing Nizhneudinsk, the airliner had traveled 132 kilometers in 31 minutes and was 18-20 kilometers south of the route. At 23:43, the crew reported passing Kansk, although due to the slowness of the senior dispatcher at the Krasnoyarsk area control service, the radio beacon at the Kansk airport was turned off at that time. But at 23:54, the crew received new bearings—a back bearing of "about 280°" from Krasnoyarsk airport and a true bearing of 158° from Yeniseysk airport, meaning the plane was actually 73 kilometers from Krasnoyarsk, and based on the previously received bearings, its ground speed was 435km/h. This shows that the crew reported passing Taishet and Kansk based only on calculations. The "approximate" back bearing of 280° given to the crew was incorrect, which the radio operator reported to the ground. This error occurred because trainees were sitting behind the radio direction finders in Krasnoyarsk, as the regular staff of 11 people had been sent to serve in the Soviet Army.[2]
The dispatchers should have understood that the data from the crew about their ground speed contradicted the data obtained from the bearings. Nevertheless, they did not determine the exact location of the aircraft and did not give any instructions to the crew. The flight supervisor and the senior dispatcher of the area control service did not carry out any calculations and did not supervise the flight. After 23:26, neither the crew, the flight supervisor, nor the senior dispatcher knew the exact location of board L1789. The fact that the previous two Il-12 flights from Irkutsk to Krasnoyarsk veered south of the route and arrived late did not raise concerns. Although entering the Krasnoyarsk airport zone was supposed to be done at an altitude of 2,100 meters according to the instructions, the dispatcher gave flight 136 the instruction to descend to an altitude of 1,500 meters. However, the crew, being confident that their ground speed was 275km/h, decided to head to Novosibirsk as per schedule. They contacted Novosibirsk to request weather information, and at 23:48 received a response that Novosibirsk was overcast with a lower limit of 290 meters, visibility 10 kilometers, and southwest wind 5m/s. Then, around 00:02–00:04, the aircraft reported to Krasnoyarsk: approaching, 2,700 meters, fuel 2,600 liters, enough, Novosibirsk will accept me, I will fly over. However, the dispatcher stated: Novosibirsk is closed due to weather conditions. Landing here. The crew then acknowledged the instruction and began descending to the previously indicated altitude of 1,500 meters. At 00:10 (04:10 local time), the crew called Krasnoyarsk airport for contact. The Krasnoyarsk airport command and control center dispatcher then began calling board L1789, but there was no response. After several unsuccessful attempts to contact the crew, a search for the aircraft began. However, board L1789 disappeared without a trace.[2]
In June 1955, seven months later, a hunter on Mount Sivukha (elevation 1,807 meters, 54°30′25″N94°41′10″E / 54.50694°N 94.68611°E / 54.50694; 94.68611) and in the upper reaches of the Mana River accidentally discovered the wreckage of the aircraft. On June 12, an investigative commission arrived at the crash site. Investigators determined that the airliner, flying on a magnetic course of 280° at an altitude of 1,725 meters, 132 kilometers south of the route and 204 kilometers from the Krasnoyarsk airport, crashed into the rocky eastern slope of the mountain at an angle of 40-45°, resulting in total destruction. All people on board died, including the Polish UN delegation returning from Vietnam.[2][3] Officially, 19 people died; however, other sources indicate 20 deaths, as the co-pilot was not listed in the crew's names.[4][5]
Causes
According to the investigative commission, the following factors led to the crash:[2]
Gross neglect of their duties by Krasnoyarsk air traffic controllers: the airport flight supervisor and the senior dispatcher of the area control service. They did not manage the flight, instructed the crew to descend to an altitude of 1,500 meters instead of the established 2,100 meters, and did not take measures to turn on the radio beacon at Kansk airport. Because of this, the aircraft began to deviate from the route and soon found itself in a mountainous area with elevations over 1,500 meters.
Duty meteorologists at AMS in Irkutsk and Krasnoyarsk provided inaccurate and unfulfilled forecasts for winds at altitudes. Also, the duty meteorologist in Krasnoyarsk, after receiving data on the actual wind direction and speed at 23:50, did not relay this information to the flight supervisor and aircraft crews.
The Krasnoyarsk territorial administration of the civil air fleet poorly monitored the service of the Krasnoyarsk airport, including failing to address deficiencies in airport services, especially in the control service.
The Krasnoyarsk radio direction finder unit performed poorly.
The crew made incorrect calculations of wind speed and direction, causing them to take a 10° deviation to the south. Since the wind was not southwest but northwest, the chosen deviation only increased the southward drift from the route.
Aftermath
Despite the death of foreign nationals, all data about the crash was classified. In the summer of 2010, an expedition of 10 people arrived at Mount Sivukha in GAZ off-road vehicles and installed a memorial cross at the crash site.[3] In the summer of 2013, a memorial plaque was installed at the crash site.[4][5]
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