Aircraft Stall and Collision During Instrument Approach in Icing Conditions (N948CC)

Accident Overview and Flight Context The accident occurred during the return portion of a round-trip flight while the aircraft was on final approach to the pilot's alternate airport due to a weather-induced diversion. Moderate-intensity snow showers and freezing fog were present. During the initial approach, the reported visibility was 1 1/2 miles. About the time the pilot passed the final approach fix, the visibility decreased to 1/2 mile, but the pilot was not informed of the decrease below his 1-mile minimum requirement. ## Approach and Loss of Control During an instrument approach, upon descending to the prescribed minimum descent altitude, about 1/2 mile from the missed approach point, the pilot failed to maintain flying airspeed. The airplane stalled, rolled left, and in an uncontrolled descent collided with a commercial building 0.96 nm from the runway's displaced threshold. ## Airspeed and Pilot Actions The pilot had maintained the recommended 140-knot approach speed in the icing conditions until about 3 1/2 miles from the runway. Thereafter, the airplane's speed gradually decreased until reaching about 75 knots. After the airplane started vibrating, the pilot increased engine power, but his action was not timely enough to avert stalling. ## Maintenance and Deice System Findings Company mechanics maintained the airplane. On previous occasions, overheat conditions had occurred wherein the environmental ducting melted and heat was conducted to the adjacent pneumatic tube that provides deice air to the empennage boots. During the accident investigation, the deice tube was found completely melted closed, thus rendering all of the empennage deice boots dysfunctional.