What happened
While performing an instrument approach to an alternate airport following a weather diversion, an aircraft entered an uncontrolled descent and struck a commercial structure. The accident occurred approximately 0.96 nautical miles from the runway's displaced threshold. At the time of the incident, the area was experiencing freezing fog and moderate snow showers.
During the approach, the pilot initially operated with a visibility of 1.5 miles. However, as the aircraft passed the final approach fix, visibility dropped to 0.5 miles, a change that was not communicated to the pilot, who required at least 1 mile of visibility for the approach. While the aircraft had maintained a steady 140-knot approach speed until 3.5 miles from the runway, the airspeed began to decay, eventually dropping to approximately 75 knots. As the aircraft reached the minimum descent altitude, roughly half a mile from the missed approach point, the loss of airspeed led to a stall and a left roll. Although the pilot attempted to increase engine power following the onset of vibrations, the intervention was insufficient to prevent the impact.
Findings
Investigation into the mechanical state of the aircraft revealed that the empennage deice boots were non-functional at the time of the crash. It was determined that the deice tube had melted shut. Previous maintenance history indicated that overheating issues had occurred in the aircraft, where heat from melted environmental ducting was transferred to the pneumatic tube responsible for providing deice air to the tail section.