Investigation Summary
Flight 4 was operating a domestic service from Khabarovsk to Irkutsk under the Moscow Civil Aviation Directorate of Aeroflot when it encountered a massive storm front. The weather forecast had warned of cumulonimbus and stratiform clouds in the Birobidzhan, Arkhara, and Magdagachi regions, but the conditions deteriorated significantly during a three-hour departure delay. To avoid the weather, the crew requested successive climbs, eventually reaching 12,000 meters (39,000 feet). At this altitude and weight (66 tons), the Tu-104A was operating at the very edge of its flight envelope. Powerful updrafts within the cumulonimbus clouds, which reached heights exceeding 12,000 meters, pushed the aircraft into a stall. The resulting aerodynamic forces caused the engines to flame out and the landing gear to inadvertently extend, further increasing drag. The crew suffered spatial disorientation as the aircraft's artificial horizons failed during the upset, making recovery impossible in the dark, turbulent conditions.
Final Conclusions
The investigation concluded that the aircraft stalled due to a combination of severe weather (updrafts) and the crew's decision to climb to an altitude that was unsafe for the aircraft's current weight. The crash highlighted critical design flaws in the Tu-104, including longitudinal instability in certain atmospheric conditions and a lack of stall recovery procedures. Secondary factors included poor weather forecasting that failed to identify the height of the cloud tops and inadequate flight manual guidance regarding maximum safe altitudes.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Mikulin AM-3M Engines
Both engines suffered flameouts during the stall, depriving the crew of thrust and electrical power for instruments.
Artificial Horizon
The attitude indicators failed during the upset, contributing to the crew's spatial disorientation.
Landing Gear
The gear extended during the stall, likely due to high G-loads or aerodynamic forces, increasing drag and worsening the stall.
Interesting Facts
- 01The aircraft was a Tu-104A, the world's first successful jet airliner, which was known for high stall speeds.
- 02At 66 tons, the maximum safe altitude for the aircraft was 11,700 meters, yet it was flown to 12,000 meters.
- 03Nearby Tu-16 bombers reported strong updrafts in the area at similar altitudes.
- 04The crash site was a dense forest 215 kilometers northwest of Khabarovsk.
- 05The debris field was approximately 450 meters wide.
- 06The aircraft was re-registered as CCCP-42349 on May 9, 1958, but the new registration had not yet been applied to the airframe at the time of the crash.
Safety Actions & Advisories
Operational Altitude Restrictions
The investigation led to a better understanding of the Tu-104's maximum safe altitudes relative to takeoff weight and atmospheric conditions.
Stall Recovery Procedures
The accident highlighted the lack of defined stall recovery procedures for the Tu-104, leading to updates in flight manuals and pilot training.
Known Controversies & Unanswered Questions
Undisclosed Design Flaws
Reference ↗At the time of the accident, the Tu-104's propensity for losing longitudinal stability in certain atmospheric conditions—leading to uncommanded landing gear extension and engine failure—was not well-documented in flight manuals. The investigation revealed that the aircraft's high stall speed and weak wing mechanization were critical factors that were not adequately communicated to flight crews.