Crash
The aircraft performed flight Sh-88 from Leninabad through the Anzob pass to Dushanbe, piloted by a crew led by Captain E. M. Lander. At 13:04, the Yak-40 took off from Leninabad Airport and climbed to a flight level of 7,200 meters. On board were 29 people - 4 crew members and 25 passengers (23 adults and 2 children). [1]
From the pass to Dushanbe, the sky was covered by scattered clouds with a base at 2,500–2,800 meters and a top at 6–7 kilometers. There was moderate turbulence, a fresh westerly wind, and pockets of thunderstorms. This was above the meteorological minimum of the crew commander and did not hinder the flight and landing. There were 73 kilometers left to Dushanbe Airport when at 13:32, the crew deviated 9 kilometers west of the route axis to avoid thunderstorm clouds. However, this was reported to the controller only a minute later when the deviation reached 10 kilometers. The controller allowed thunderstorm avoidance and descent to 6,000 meters at the Pugus NDB. However, the regional center controller did not monitor the flight and did not detect its lateral deviation until the Yak-40 was 67 kilometers from the airport. At 13:36, the crew reported passing the Pugus NDB at 6,000 meters. In reality, they were still 37 kilometers away due to a wind speed error and radio compass failures caused by the aircraft's electrification when passing through dusty haze and nearby thunderstorms. The regional center controller did not monitor flight Sh-88 and did not provide location information. He only passed a bearing of 340° (relative to the airfield control point) and instructed the crew to switch to approach controller. [1]
The Yak-40 was 43 kilometers northwest of Pugus, but the approach controller did not determine its location when he allowed a descent to 4,800 meters at the Dushanbe outer marker, indicating a landing on a magnetic course of 86°. At 13:38, the aircraft turned to a course of 160° toward the outer marker and began descending. During the descent, the crew received a direct bearing of 330° from the approach controller and an instruction: "Hasten the descent to 4,800 meters". Since the aircraft was on a bearing of 330°, it had crossed the limiting bearing of 340° and deviated westward. The controller did not recognize this and did not start monitoring the flight and determining the actual location. In turn, the descending crew in clouds, due to radio compass failures in severe turbulence and icing conditions, could not determine their location correctly. [1]
At 13:40, the pilots erroneously reported passing the outer marker at 4,800 meters, although they were still 43 kilometers away. The approach controller, with the necessary radio technical means, did not check whether the aircraft had actually passed the outer marker, instead allowing a descent to the circuit altitude of 3,600 meters. Flying among mountains up to 4,018 meters high, the crew began a right turn with descent, taking a course of 266° (reverse to the landing course), then descended to the indicated altitude of 3,600 meters. Without determining their position, the approach controller instructed them to switch to the circuit controller. [1]
The sky was now completely covered with clouds. When the crew contacted the circuit controller, he, like his colleagues, did not determine the aircraft's location and allowed descent to 2,100 meters to the third turn according to airfield pressure, ignoring that the aircraft was outside the descent scheme and far right of the 275° limiting bearing. Passing 3,000 meters, the crew reported setting the airfield pressure on the altimeters at 694 mm Hg. The pilots also determined they were far north of the landing scheme, leveled off at 2,840 meters, stopped descending, and turned south to rejoin the landing scheme. When the controller asked: "What course are you holding?", the crew replied: "Holding course 180 degrees", although they were still turning and actually on course 217°. Then the pilots requested a bearing and reported unreliable radio compass operation, asking for their position. The circuit controller gave them an azimuth of 300°, not paying attention to the significant excess of the 275° limit, and responded to their position request that he could not provide it since the radar was off (due to equipment change), although an ARP-75 direction finder was available. [1]
The Yak-40, in clouds at 2,840 meters, continued turning left to a course of 180° when at 13:44:00, flying on course 208° at a speed of 380 km/h, it crashed into a mountain slope and was completely destroyed. All 29 people on board died. [1]
Investigation
Conclusions of the investigations: [1]
- In the final phase of the flight, while avoiding thunderstorm cells, due to unstable radio compass operation and wind speed discrepancies, the crew could not accurately determine the passage of the Pugus NDB and the Dushanbe outer marker, complicating path control and position determination.
- The aircraft's flight while avoiding thunderstorm cells with route and approach scheme deviations was not monitored by Dushanbe airport air traffic controllers. The aircraft's position was never determined and communicated to the crew, despite the flight being in special conditions and outside the limiting bearings. The flight operations manager did not take necessary measures to prevent violations by ATC and did not organize proper shift work.
The following violations of NPP GA-78 were committed by controllers and the crew:
- The regional center controller did not monitor the flight and did not inform the crew of the aircraft's position while avoiding thunderstorms;
- The approach controller did not determine and inform the crew of the aircraft's position, did not clarify the location when transferring control to the circuit controller, and allowed descent to 3,600 meters - below the height of mountains in the aircraft's actual location;
- The circuit controller did not ensure aircraft identification, did not monitor the crew's compliance with the descent and landing scheme, and allowed descent to 2,100 meters when the aircraft was outside the scheme and beyond the limiting bearings;
- The crew, while avoiding thunderstorms, did not account for radio compass indication distortions due to thunderstorms and mountain effect, provided incorrect NDB passage data, and did not use rational navigation methods to reach the NDB.
These violations led to the aircraft deviating 32 kilometers off the route towards mountains up to 4,764 meters high, and further descent to 2,100 meters resulted in the aircraft colliding with a mountain slope in controlled flight configuration.
The cause of the crash was ATC service violations at Dushanbe airport, failing to meet NPP GA-78 requirements in managing the flight and crew errors in determining the aircraft's position while avoiding thunderstorms in mountainous terrain. [1]
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