Investigation Summary
The flight was the final leg of a multi-stop route originating in Kazan, with Chelyabinsk serving as the intermediate stop and the immediate point of departure for the accident leg to Alma Ata. During the approach to Alma Ata, the air traffic controller provided an erroneous instruction to turn, and the crew compounded this by selecting an incorrect heading of 199 degrees instead of 140. Although ATC later corrected the heading, the controller instructed the aircraft to descend to 600 meters (approximately 2,000 feet). This was significantly below the minimum safe altitude for the surrounding mountainous terrain, which was 4,620 meters (15,160 feet). Under Soviet flight regulations, the crew had the authority to ignore ATC instructions that compromised safety, yet they continued the descent. The Ground Proximity Warning System (GPWS) sounded for 23 seconds, but the crew did not initiate an urgent climb until 1 to 2 seconds before the aircraft struck the mountain at an altitude of 690 meters above airfield elevation.
Final Conclusions
The investigation attributed the crash to a violation of the approved approach scheme and the failure of the flight manager to monitor the situation effectively. A primary factor was the crew's violation of the flight operations manual by following a controller's instruction to descend below the minimum safe altitude. The delayed response to the GPWS alarm further ensured the catastrophic outcome.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Responsible for the final decision to follow the unsafe ATC descent instruction.
Navigator
Responsible for monitoring terrain and approach path.
Systems & Failure Modes
GPWS
The Ground Proximity Warning System alerted the crew for 23 seconds, but the warning was ignored until it was too late to clear the terrain.
ATC Radar/Communications
Air traffic control provided erroneous turn instructions and cleared the flight to an unsafe altitude.
Interesting Facts
- 01The aircraft was a Tupolev Tu-134A manufactured in 1978.
- 02The minimum safe altitude for the terrain in the approach area was 4,620 meters (15,160 feet).
- 03The aircraft struck the mountain at an altitude of 690 meters above airfield elevation (1,365 meters above sea level).
- 04Visibility at the time of the accident was 10 kilometers with cumulo-nimbus cloud cover.
- 05The GPWS alarm sounded for 23 seconds before the crew took any action.
Safety Actions & Advisories
Crew Authority Reinforcement
The investigation emphasized that crews must exercise their right to ignore ATC instructions that violate minimum safe altitudes, as per Soviet flight regulations.