Hamilton-Ravalli County

The airline transport pilot was repositioning the airplane to an airport near the owner's summer home. The airplane was not maintained for instrument flight, and the pilot had diverted the day before the accident due to weather. On the day of the accident, the pilot departed for the destination, but returned shortly after due to weather. After waiting for the weather conditions to improve, the pilot departed again that afternoon, and refueled the airplane at an intermediate airport before continuing toward the destination. The route of flight followed a highway that traversed a mountain pass. A witness located along the highway stated that he saw the accident airplane traveling northbound toward the mountain pass, below the overcast cloud layer. He also stated that the mountain pass was obscured, and he could see a thunderstorm developing toward the west, which was moving east toward the pass. A second witness, located near the accident site, saw the airplane descend vertically from the base of the clouds while spinning in a level attitude and impact the ground. The second witness reported that it was snowing and that the visibility was about ¼ mile at the time of the accident. The airplane impacted terrain in a level attitude, and was consumed by a postcrash fire. Examination of the flight controls, airframe, and engine revealed no mechanical malfunctions or anomalies that would have precluded normal operation. It is likely that the pilot experienced spatial disorientation and a subsequent loss of aircraft control upon encountering instrument meteorological conditions. The airplane exceeded its critical angle of attack and entered a flat spin at low altitude, resulting in an uncontrolled descent and impact with terrain.

During the initial climb after takeoff, just after the aircraft passed 400 feet above ground level (agl), the pilot shut off the fuel boost pumps in preparation for the en route climb. Soon thereafter, one of the engines lost power without warning, and because he was carrying a heavy load, he immediately feathered the propeller and started looking for a place to put the aircraft down. Because there was rising terrain and scattered houses south of the airport, he had to maneuver to get to an open area. During the forced landing on the uneven terrain, one of the landing gear legs collapsed, and the aircraft impacted the terrain and slid into a power pole. A post-accident teardown inspection of the engine and the aircraft systems did not reveal any anomalies that would have resulted in the failure of the engine that lost power.

Immediately after taking off and raising the landing gear, the pilot noticed the left engine began to lose power. The airplane subsequently veered to the left before impacting up slopping terrain in a left wing low attitude, resulting in a fire breaking out which consumed the left side of the airplane. A postaccident examination revealed that the left engine had sustained thermal but no impact damage, and that the engine's right hand turbocharger had no thermal or impact damage. A further examination indicated that no restrictions were found in the center section of the turbocharger and there was no damage to the housing or the impeller; however, the impeller was frozen in the center section and would not turn. Indications of grooving and scraping from a lack of lubrication to the bearings and drive shaft was observed. No mechanical anomalies with the aircraft were noted by the pilot prior to takeoff which would have prevented normal operations.