Background
The pilot filed an IFR flight plan and received a standard weather briefing, which included information about occasional moderate rime or mixed icing below 10,000 feet along the route. During the briefing, the pilot stated: "we got boots, and will be all right."
Flight Progress
Approximately five minutes before the accident, the pilot reported that the airplane was "picking up" rime ice at 10,000 feet and requested 12,000 feet. The pilot also reported that the windshield and wings were covered with ice, and that ice accumulation at 10,000 feet was moderate and steady.
When the airplane started to climb to 12,000 feet, calibrated airspeed (CAS) began to decay. At 11,200 feet, prior to the airplane starting a rapid descent, CAS had dropped to 85 knots. The minimum airspeed for icing conditions was published as 130 knots. Additionally, the stall speed for the airplane was approximately 82 knots.
Examination
The airplane was approved for flight into known icing conditions. Examination of the airframe, engines, and propellers revealed no preimpact failures or malfunctions.