Accident Overview
On July 12, 2018, about 0305 mountain standard time, a Beech C90A King Air airplane, registration N617MM, sustained substantial damage during an inflight upset near Tolani Lake, Arizona. The pilot and two passengers were not injured. The aircraft was operated as a Title 14 Code of Federal Regulations Part 91 positioning flight.
Flight Details
The flight originated from Flagstaff Pulliam Airport (FLG), Flagstaff, Arizona, about 0250, and was destined for Gallup Municipal Airport (GUP), Gallup, New Mexico. Instrument meteorological conditions (IMC) were reported along the route of flight, and the flight was operated on an instrument flight rules flight plan.
Pilot Report
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. Conditions were smooth with no turbulence and no known icing, although the pilot had engaged all anti-icing systems, including the engine ice vanes. The pilot stated he was working on an iPad when it stopped functioning. While trying to reset it, there was a hard control input to the left as the airplane reached about 17,500 ft. The airspeed increased rapidly, and the airplane entered a steep spiral, rolling left and pitching down. The pilot reported that the autopilot was fighting his control inputs, so he disengaged it to recover. After several attempts, the pilot recovered the airplane, manually flew to the destination, and landed without further incident.
Postflight Examination
A postflight examination revealed deformation of the leading edges and wrinkling of the upper wing skins on the left and right outboard wings. Further examination identified damage to the forward spar on the left outboard wing.
Autopilot Testing
The autopilot system underwent 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.
Data Analysis
Review of data downloaded from the airplane’s Stratus 2 receiver indicated a steady increase in pitch and decrease in airspeed from 16,770 ft through 18,861 ft. At 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.
Weather Conditions
The pilot reported IMC 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 indicated the airplane was in IMC with light rain at the time of the accident. The study showed that light to moderate icing conditions were present and forecast along the route, with echoes along the flight track suggesting the possibility of supercooled large droplets.