The airplane's encounter with severe icing conditions, which resulted in structural icing, and the pilot's increased workload and subsequent disorientation while maneuvering in instrument flight rules (IFR) conditions with malfunctioning flight instruments, which led to the subsequent loss of airplane control. Contributing to the accident was the pilot's decision to takeoff in IFR conditions and fly a single-pilot operation without a functioning autopilot and with malfunctioning flight instruments.