What happened
While maintaining a cruising altitude of 10,000 meters over the Voronezh area, the aircraft entered a region of cumulonimbus clouds. The flight initially encountered upward currents that pushed the plane to 10,700 meters, followed by intense downdrafts that forced a descent to 7,000 meters. During these severe atmospheric disturbances, the propellers on both the first and fourth engines automatically feathered.
The aircraft continued to lose altitude, reaching 2,800 meters before the crew successfully regained control of the plane. After establishing contact with Air Traffic Control, the crew received authorization to perform an emergency landing at Vnukovo. Upon arrival, all 56 occupants were evacuated from the plane; while most were unharmed, some individuals sustained injuries. The aircraft was subsequently determined to be a total loss because the structural damage was too extensive for repair.
Findings
Investigations revealed that a leak of chemical fluid from the lavatory compartment had spread to various electrical components. This leakage resulted in multiple short-circuits, affecting several connectors and disabling the VHF communication system. The primary driver of the incident was severe turbulence and downdrafts encountered within thunderstorm activity.