On July 12, 2018, about 0305 mountain standard time, a Beech C90A King Air airplane, N617MM, was substantially damaged when it was involved in an accident near Tolani Lake, Arizona. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 positioning flight. Instrument meteorological conditions (IMC) were reported along the route of flight about the time of the accident, and the flight was operated on an instrument flight rules flight plan. The flight originated from Flagstaff Pulliam Airport (FLG), Flagstaff, Arizona, about 0250 and was destined for Gallup Municipal Airport (GUP), Gallup, New Mexico. The pilot reported that the airplane was climbing out of 17,000 ft to a cruise altitude of 19,000 ft at 600 ft per minute and at an airspeed of 130 kts, with the autopilot engaged and set to capture 19,000 ft. The conditions were smooth with no turbulence and no known icing, although he had engaged all anti-icing systems, including the engine ice vanes. The pilot reported that he was working on the iPad when it stopped functioning. He was trying to reset it when there was a hard control input to the left as the airplane was at about 17,500 ft. He stated that when he engaged on the controls, the airspeed was increasing rapidly. The airplane was in a steep spiral, rolling left and pitching down as he attempted to regain control. The pilot reported the autopilot was fighting his control inputs during the event, and he disengaged it to affect the recovery. After several attempts, the pilot recovered the airplane, manually flew to the destination airport, and landed without further incident.

Postflight examination of the airplane revealed deformation of the leading edges and wrinkling of the upper wing skins on the left and right outboard wings. Further examination revealed damage to the forward spar on the left outboard wing.

The autopilot system was subjected to on-airplane testing after the accident. Initially, the autopilot modes were not annunciated on the control panel due to a dimmer switch that was on full dim. Contained tests revealed no anomalies with the autopilot system during on-airplane testing. The autopilot computer was removed and examined with no anomalies noted.

Review of data downloaded from the airplane’s Stratus 2 receiver revealed a steady increase in pitch and decrease in airspeed from 16,770 ft through 18,861 ft. About 18,920 ft, the airplane began a left roll and continued through a series of about five-barrel rolls. The airplane recovered from the upset about 13,000 ft, then climbed to 16,000 ft and continued to the destination with no other anomalies.

The pilot reported IMC conditions, with the lowest cloud heights about 14,000 ft msl, a broken layer of clouds at 18,000 ft, and light rain. A weather study showed the airplane was in IMC with light rain at the time of the accident. The weather study showed that light to moderate icing conditions were present and forecast along the airplane’s route of flight with echoes along the flight track indicating the possibility of supercooled large droplets.