Incident Overview
A pilot encountered difficulties with the autopilot while operating an aircraft in instrument meteorological conditions (IMC). According to the pilot's report, he experienced trouble holding assigned headings and engaging the autopilot. Subsequently, the airplane initiated a rapid descent. The pilot was able to regain control after transitioning to visual meteorological conditions (VMC).
Prior Issues
The pilot noted that before the accident flight, he had experienced difficulty with another aircraft. In that instance, involving a different model of autopilot, he lost control during landing. Representatives from the airframe and autopilot manufacturers stated that the pilot and aircraft owner had previously complained about autopilot problems. However, on at least two occasions prior to the accident flight, the owner or pilot had been operating the autopilot while the aircraft was outside the specifications for safe autopilot operation.
Post-Accident Findings
Three separate test flights conducted before the accident did not reveal any malfunctions. After the accident, the pilot mentioned that he might have departed with the autopilot in the slaved nav heading disengaged mode. Data retrieved from the autopilot after the event indicated no malfunctions.