Accident Details
Before departure, the pilot received a weather briefing and filed an IFR flight plan to Idaho Falls, Idaho, with an intended cruising altitude of 13,000 feet. The aircraft departed at 1804 Pacific Standard Time. At 1814, just before reporting level at 13,000 feet, the pilot advised of light turbulence and light rime ice.
Approximately four minutes later, the pilot reported experiencing heavy vibrations and requested and received clearance to return to Portland and descend to 7,000 feet. Shortly thereafter, the aircraft entered a tight descending turn, which the pilot reported difficulty arresting. The pilot stated that directional control was regained at 6,000 feet and that the aircraft had a heavy load of ice. Soon after, the aircraft crashed in mountainous terrain at an elevation of 3,130 feet.
Icing and Certification
The aircraft was not certified for flight in known icing conditions. The forecast called for moderate mixed icing and moderate turbulence. The pilot had been briefed that there were reports of moderate icing throughout the area. Due to impact damage and wreckage retrieval, the preimpact condition of all deicing components could not be verified.
Investigation
The investigation noted the weather briefing and the pilot's reports of icing and vibrations. The aircraft's lack of certification for known icing conditions was a central element. The exact sequence of events leading to the loss of control and impact could not be fully determined due to the inability to examine the deicing system's preimpact state.