Accident Sequence
The airplane was climbing from 5,000 to 10,000 feet but reached a maximum altitude of only 6,300 feet before beginning to lose altitude and deviate off course. The pilot declared a mayday and reported that the airplane was in a spin. Multiple witnesses near the accident site reported hearing engine noises and seeing the airplane descend from the clouds in a nose-down spiral to the ground.
Weather Conditions
At the time of the accident, two AIRMETs were in effect covering the accident location. AIRMET TANGO update 3 forecast occasional moderate turbulence below 18,000 feet due to wind shear. AIRMET ZULU update 2 indicated occasional moderate rime and/or mixed icing in clouds and precipitation below 8,000 feet. Two pilots who departed in separate Beech 200 airplanes around the same time reported encountering moderate rime icing between 5,000 and 6,000 feet, and one of them reported instrument meteorological conditions and light turbulence between 1,800 and 6,000 feet.
Examination
Post-accident examination of the airplane revealed no evidence of airframe or engine malfunction. The de-ice ejector flow control valves for the left wing, right wing, and empennage pneumatic boots were removed and tested; all valves functioned when power was supplied.
Probable Cause
The official probable cause was the pilot's failure to maintain adequate airspeed during climb in icing conditions, which resulted in an inadvertent stall/spin of the airplane and subsequent uncontrolled descent and collision with terrain. A factor was the accumulation of airframe ice.