Event Sequence
Radar data showed the airplane reversing from a southerly to a northerly track. The pilot informed air route traffic control center (ARTCC) that he had just lost manifold pressure in the left engine and requested a lower altitude. The controller cleared the pilot to descend from 16,000 feet mean sea level (msl) to 14,000 feet msl. When asked by the controller if the course reversal was due to the engine problem, the pilot confirmed. The controller then assigned a new frequency, which the pilot acknowledged. No further transmissions were received from the pilot on either frequency, and radar contact was lost when the encoded altitude reached 11,400 feet msl.
Weather Conditions
Radar echoes and satellite data indicated that the accident airplane most likely entered clouds approximately 1010. Based on the current icing potential algorithm, there was a high likelihood of icing and supercooled large water droplets at altitudes between 14,000 and 16,000 feet msl in the accident area. Area forecasts, pilot reports (PIREPS), and weather advisories suggest that the airplane most likely encountered moderate to severe turbulence and moderate to severe mixed icing during the final few minutes before the accident.
Wreckage and Examination
The wreckage was located in mountainous, down sloping, snow covered, forested terrain. The airplane was destroyed. An examination of the airframe, engines, and airplane systems revealed no anomalies.