What happened
During a scheduled flight test at Kiev-Gostomel Airport, an Antonov AN-8RU was undergoing evaluations of a JATO (Jet-Assisted Take-Off) propulsion system. The mission was designed to simulate engine failure scenarios using this supplemental thrust system. The crew, consisting of pilots, engineers, and technicians, initiated the test by igniting the JATO units approximately twenty seconds after departure while the aircraft was climbing toward 220 km/h.
As part of the procedure, the left engine was intentionally deactivated once the airspeed reached 264 km/h. Following this shutdown, the propeller entered an auto-rotation state, but the crew was unable to feather the blades. This loss of control led to a steep left bank of approximately 70 to 80 degrees. The aircraft subsequently entered a dive and impacted the ground in a field situated 1,850 meters beyond the runway threshold.
Findings
While investigators could not reach a definitive conclusion regarding the exact cause, evidence suggests that the failure to feather the propeller on the deactivated left engine was the primary factor. This resulted in significant asymmetric thrust and excessive drag, rendering the aircraft uncontrollable during the critical phase of the test.