Flight Planning and Departure
The accident pilot had completed a week-long recurrency training program in the accident airplane. The instructor planned for the pilot to depart no later than 1830 on the return leg, following a route west of specific terrain to avoid forecasted weather and to arrive before dark. However, the pilot departed approximately 30 minutes late and flew a route east of the discussed terrain, placing the airplane in severe weather conditions after dark.
In-Flight Events and ATC Communications
While descending from cruising altitude, the airplane encountered turbulence, causing the autopilot to disengage. Multiple transmissions between air traffic control (ATC) and the pilot followed, discussing course corrections, altitudes, icing conditions, and issues with the autopilot. ATC offered vectors from the arrival procedure, which the pilot declined. After ATC relayed another pilot's report of airframe icing, the accident pilot confirmed moderate rime ice accumulation and accepted a lower altitude. The pilot subsequently confirmed that the airplane remained in icing during the continued descent, leveling at 7,200 ft mean sea level (msl).
ATC then instructed the pilot to climb to 7,400 ft msl, but the airplane remained at 7,200 ft msl for 29 seconds before beginning a right turn. During this time, ground speed slowed from 124 knots to 84 knots. ATC asked if the pilot was ready to turn left; the pilot responded "turning." The airplane then entered a rapid descent from which the pilot did not recover.
Crash and Impact
The airplane crashed in hilly, wooded terrain near San Bernardino. Impact forces totally destroyed the aircraft. The pilot was killed.
Probable Cause
The official probable cause was the pilot's continued use of the airplane's autopilot after flight into moderate to severe icing conditions, which resulted in an exceedance of the airplane's critical angle of attack and an aerodynamic stall.