Accident Overview
On the return leg of a round trip flight, the pilot was conducting an instrument approach to an alternate airport due to a weather-induced diversion. While descending to the prescribed minimum descent altitude, approximately 1/2 mile from the missed approach point, the pilot failed to maintain flying airspeed. The airplane stalled, rolled left, and entered an uncontrolled descent, colliding with a commercial building 0.96 nautical miles from the runway's displaced threshold.
Meteorological Conditions
Moderate intensity snow showers and freezing fog were present. During the initial approach, the reported visibility was 1 1/2 miles. Around the time the pilot passed the final approach fix, visibility decreased to 1/2 mile. However, the pilot was not informed of this decrease, which fell below his 1-mile minimum requirement.
Aircraft Performance 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 aircraft's speed gradually decreased to approximately 75 knots. After the airplane started vibrating, the pilot increased engine power, but the action was not timely enough to avert the stall.
Aircraft Maintenance and Deice System
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, rendering all empennage deice boots dysfunctional.
Probable Cause and Contributing Factors
The official findings stated that the probable cause was the pilot's inadequate approach airspeed for the existing adverse meteorological conditions, followed by his delayed remedial action to avert stalling and subsequent loss of airplane control. Contributing factors were the pilot's reduced visibility due to the inclement weather and the icing conditions.