Investigation Summary
The flight was a cargo operation transporting 12,515 kg of coins from Saint Petersburg to Nalchik with a stopover in Volgograd. During the final approach to Nalchik, the aircraft was operating in conditions conducive to icing, but the crew had not been briefed on these specific hazards by the local controllers. Consequently, the airframe de-icing systems remained off. As the aircraft intercepted the glide path and the crew increased flap deflection from 15 to 35 degrees, the aerodynamic profile of the tailplane was compromised by ice accumulation. The aircraft initially experienced pitch oscillations and nosed up to 15 degrees before a spontaneous elevator deflection of 15 degrees occurred. This caused the aircraft to pitch down violently between 50 and 55 degrees. Despite the pilots' attempts to recover by pulling back on the control columns, the low altitude of approximately 320 metres left insufficient room for recovery.
Final Conclusions
The investigation concluded that the primary cause was the accumulation of ice on the horizontal stabilizers, which led to a loss of pitch control when flaps were extended. Contributing factors included the airport's failure to provide an updated weather report regarding icing conditions, the crew's resulting failure to activate de-icing systems, and deficiencies in the aircraft flight manual regarding approach recommendations in such weather.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
De-icing System
The aircraft was equipped with a system to prevent ice buildup on critical surfaces, but it was not activated because the crew was unaware of the icing hazard.
Flaps
Extension of flaps to 35 degrees changed the airflow over the tailplane, triggering the stall of the iced horizontal stabilizer.
Elevators
The elevators experienced a spontaneous deflection to 15 degrees, forcing the aircraft into an unrecoverable dive.
Interesting Facts
- 01The aircraft was manufactured in 1971 (MSN 01348002).
- 02The aircraft was carrying 12,515 kg of coins minted in Saint Petersburg.
- 03The elevator deflection spontaneously increased from 5 to 15 degrees due to aerodynamic forces on the iced stabilizer.
- 04The aircraft struck the ground at a nose-down angle of 55 degrees.
- 05The crash occurred approximately 4.5 kilometres short of the runway threshold.
Safety Actions & Advisories
Flight Manual Revision
The investigation highlighted that the aircraft flight manual contained incorrect recommendations for executing approaches in icing conditions, necessitating updates to pilot procedures.