Aeroflot Flight E-35D. Aeroflot Flight E-35D was an aviation disaster that occurred on Wednesday, August 1, 1990, in the vicinity of Stepanakert with a Yak-40 aircraft operated by Aeroflot, resulting in the deaths of 46 people.

Aircraft 
The Yak-40 with tail number 87453 (manufacturer's number 9431036, serial number 36-10) was manufactured by the Saratov Aviation Plant on September 9, 1974, and was handed over to the Ministry of Civil Aviation, which, by October 7, had directed it to the 2nd Yerevan Aviation Detachment of the Armenian Civil Aviation Directorate.

Disaster 
The aircraft was operating flight E-35D from Yerevan to Stepanakert. It was piloted by a crew consisting of Captain Ararat L. Dallakyan, co-pilot Alexander Ovanisyan, and flight engineer Zhora Davtyan. Initially, 30 passengers with tickets were seated in the cabin; then, the captain, in violation of the rules, took on board 13 more unauthorized passengers who were without tickets. At 09:41, the Yak-40 took off from Yerevan's Erebuni airport. The established flight levels on the Yerevan-Stepanakert route were in the region of 5100-6600 meters, but the crew obtained permission from the air traffic controller to fly at an altitude of 4500 meters, which they occupied after passing the OPRS Andranik, although the minimum safe altitude on the route was set at 4516 meters.

At 09:47, the dispatcher at Erebuni airport instructed the crew to switch to communication with the approach controller, mistakenly stating that the distance between the aircraft and the departure airport was 20 kilometers, whereas it was actually 35 kilometers. The crew then contacted the approach controller, who provided the correct distance to the airport—35 kilometers. However, the crew disregarded the corrected data and continued to operate with the initial incorrect data, which led to an incorrect calculation of their track speed. As a result, this error in distance gradually increased, compounded by a tailwind. At 09:50, the crew reported passing Andranik, although they were already 17 kilometers beyond it, and at 09:57, they reported passing Azizbekov, when they were actually 21 kilometers beyond it. In fact, the crew was not performing comprehensive aircraft navigation. The ADF-9 radio compass had been set to the beacon of Stepanakert airport since the departure from Erebuni, with the flight to Stepanakert being conducted using a passive method. The crew made four left turns during the flight along the route: at 09:50:10 to a course of 110°, at 09:53:10 to a course of 90°, and then to courses of 81° and 75°. Given the incorrect determination of distance from the airport, this led to the crew passing Andranik 2 kilometers to the left at 09:49, and Azizbekov 4 kilometers to the left at 09:55.

It is worth noting that the flight trajectory differed from the established route as it was straightened. This was due to the fact that the long-brewing Nagorno-Karabakh conflict had by 1990 escalated into armed clashes between Azerbaijanis and Armenians, causing Armenian crews to avoid flying over Azerbaijani territory for fear of being shot down. The approach scheme for Stepanakert airport included a maneuver near the OPRS Aghdam, located 20 kilometers to the northwest in the territory of the Azerbaijan SSR. By straightening the route, the captain aimed to reach the transition level of 2400 meters on the final approach, then head towards the Stepanakert OPRS with a course of 75°, allowing for the quickest approach maneuver.

At 09:59, when the crew reported passing the OPRS Azizbekov, they were actually 21 kilometers beyond it. They were instructed to contact the dispatcher at Kafan airport. When the crew contacted him, the dispatcher instructed them to maintain an altitude of 4500 meters until reaching the traverse of Lachin, which was the descent boundary, although it was somewhat arbitrary, as it was neither marked nor included in the Kafan and Stepanakert aerodrome flight instructions. Moreover, the dispatcher did not monitor the aircraft and did not inform the crew of the distance and azimuth relative to the airport, and the crew, in turn, did not report the estimated time of passing the Lachin traverse, nor did they clarify their location.

By that moment, the captain had already started doubting the calculations for determining the aircraft's location, but the ground was obscured by a continuous cloud layer with an upper boundary of 3000-3300 meters. Then, to the left on the traverse, he thought he saw the height of 2823 meters and reported at 10:03:00 the estimated time for descent. The dispatcher, checking the aircraft's location by radar, gave permission to descend at the Lachin traverse from the safe altitude to 3900 meters. In reality, the mountain seen was at an altitude of 3616 meters, so the crew, having incorrectly determined their location, began an early descent (before reaching the traverse). Since the Kafan airport dispatcher was not controlling the aircraft's flight, the crew, having reached the level of 3900 meters at 10:07, did not report this and continued the descent without delay. At 10:08, the crew, deliberately giving the dispatcher an incorrect altitude of 3900 meters, requested to switch communication to Stepanakert airport. The Kafan dispatcher was not observing the aircraft and did not know its actual altitude; moreover, he lacked direct communication with the Stepanakert dispatcher, but nonetheless gave permission for the crew to switch to communication with the landing airport.

When at 10:08 the crew contacted the Stepanakert airport dispatcher, the error in determining the flight's location had already reached 24 kilometers. The crew intended to land with the shortest maneuver, so the aircraft descended on a course of 75°, as the crew believed, towards the outer marker. The captain informed the dispatcher about entering the zone at an altitude of 3900 meters and passing the Lysogorsky pass, requesting permission to descend to 2400 meters at the outer marker. There was no radar at Stepanakert airport, but the dispatcher, unaware of the aircraft's actual location, allowed descent to 3000 meters at the inner marker.

At 10:09:57, the Yak-40 descending in the clouds collided with a mountain of the Karabakh Ridge at an altitude of 2520 meters, 22 kilometers west of Stepanakert airport, and was completely destroyed. All 46 people on board died. At the time of the incident, this was the deadliest Yak-40 disaster, and as of 2013, it is the third deadliest (after the crashes in Khorog and near Makhachkala).

Causes 
Conclusion: The disaster occurred due to a combination of the following factors: 
 Violations by the Captain of the established flight rules, resulting in inadequate navigation, route straightening, and premature unauthorized descent to an unsafe altitude, leading to a collision with a mountain.
 Violations by air traffic controllers at Erebuni, Kafan, and Stepanakert airports of air traffic control rules in their respective zones, manifested in failure to adhere to flight monitoring rules and lack of intervention in the crew's actions, which violated navigation rules and flight mode, preventing timely prevention of the aircraft's collision with an obstacle. These violations were possible due to shortcomings in the organization of flight operations and air traffic management on the Yerevan–Stepanakert route by the Armenian and Azerbaijani UGA.

References 

E-35D
Accidents and incidents involving the Yakovlev Yak-40
Aviation accidents and incidents involving controlled flight into terrain
Aviation accidents and incidents caused by air traffic controller error