What happened
During a flight intended to evaluate lateral and directional stability, the crew was conducting a series of maneuvers involving new flap configurations, updated leading edge fairings, and modified stall protection system settings. The flight plan specified that the steady heading sideslip maneuvers should conclude once a stall warning was received or upon reaching a 15° sideslip angle. The crew had agreed to terminate the maneuver at the onset of the stall warning.
However, during the execution of the test, the pilot continued the maneuver beyond the warning threshold, reaching a 21° sideslip with full rudder input. This caused the aircraft type to roll rapidly through a 360-degree rotation and enter a deep stall. In an attempt to recover, the co-pilot tried to activate the anti-spin parachute system. This attempt failed because the cockpit switches for the chute system had not been correctly preset. Rather than aiding in the recovery, the parachute separated from the aircraft.
Findings
Investigations revealed that the three fatalities were the result of the aircraft's inability to recover from the deep stall and the subsequent failure of the emergency recovery system. A critical factor was the improper configuration of the chute system switches. Furthermore, the design of the parachute system was found to be flawed, as it permitted deployment even when the hydraulic lock switch was in the unlocked position and the hooks securing the chute shackle to the airframe were open. Although the system had passed pre-flight testing, it failed to function as intended during the emergency.