Beech Model B200 King Air
Disconnect Failure
While in IFR cruise at 4000 feet, the pilot observed the flight director command bars move out of view as the airplane started a gradual descent. When the pilot corrected, the electric trim started to run nose down and the aircraft’s descent rate increased. The pilot attempted to disconnect the autopilot and trim with the control switches and the red disconnect switch. None of this had any effect. With the turbulence and conditions, the pilot was unable to reach the autopilot and electric trim circuit breakers. After all other remedial procedures had failed, he shut off the avionics master switch at about 1000 feet and recovered the airplane at about 500 feet.
Part total time: Unknown
Cessna 421C Golden Eagle
Rapid Descent
Passing through 8000 feet msl, the autopilot entered an uncommanded rapid. The pilot tried the autopilot disconnect switch while trying to slow the descent with elevator back pressure. The disconnect switch did not disengage the autopilot; neither did the go-around or electric trim switches. Pulling the autopilot circuit breaker finally shut off the autopilot and relieved the yoke pressure. The pilot landed without further incident.
Part total time: Unknown
Lancair LC40-550FG Columbia 300
Abrupt Climbs And Descents
“For about three years my autopilot will abruptly climb and descend up to 300 feet in altitude hold and will climb and descend in a set vertical rate climb or descent. I have found that if I keep an Allen hex key in the airplane so that if the autopilot starts to climb and descend in altitude hold, I tighten up the Allen hex screw so the autopilot will stop the deviation from altitude for a while. This autopilot flying is uncomfortable and dangerous [in] IFR.”
Part total time: Unknown
Pilatus PC-12/45
Mode Controller Failure
On descent, the autopilot disconnected, followed by an electrical odor and smoke in cockpit. Troubleshooting revealed the autopilot mode controller was faulty and was the source of the electrical odor. The mode controller/glareshield wiring harness was inspected with no defects found. The mode controller was replaced and no further defects were found.
Part total time: 2230.0 hours
Pilatus PC-12/47
Autopilot Tripped Off
While in IMC at FL230, the autopilot tripped off. Ailerons were jammed. Pitch control normal. Much higher control wheel pressure required to roll. Partial jam remained until reaching about 2500 feet msl.
Part total time: Unknown
