What happened
During an instrument approach through cloud cover, the pilot observed ice building up on the wings of the aircraft. In response, the pilot activated the deicing boots on two separate occasions. While the deicing boots appeared to be operating correctly on the wings, the pilot could not visually confirm the condition of the tail section. During this period, the elevator began to vibrate, leading to a complete loss of elevator control. To prevent a stall, the pilot applied forward pressure on the yoke and adjusted the trim to a nose-down position.
Prior to the descent, the pilot had disengaged the autopilot. The aircraft continued its descent through the clouds, eventually striking a tree before settling upright in a grassy field. At the time of the impact, the flaps were likely in a position between 0° and 10° extension.
Findings
An investigation of the wreckage and the deicing system components found no evidence of mechanical failure prior to the accident. Meteorological data indicated that the flight path was within an area characterized by moderate to severe structural icing conditions, including the presence of supercooled liquid droplets. Radar analysis showed the aircraft was traveling at an average groundspeed of approximately 82 knots, which translates to an airspeed of roughly 94 knots when accounting for wind.
According to the pilot operating handbook, the minimum required airspeed for flight in icing conditions is 130 knots. The investigation concluded that the pilot's failure to maintain the required minimum airspeed for icing conditions likely caused insufficient airflow over the ice-contaminated elevator, resulting in the loss of control.