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<p>Beech Model B200 King Air</p>
<p>Disconnect Failure</p>
<p>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.</p>
<p>Part total time: Unknown</p>
<p>Cessna 421C Golden Eagle</p>
<p>Rapid Descent</p>
<p>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.</p>
<p>Part total time: Unknown</p>
<p>Lancair LC40-550FG Columbia 300</p>
<p>Abrupt Climbs And Descents</p>
<p>“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.”</p>
<p>Part total time: Unknown</p>
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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 aircrafts 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.
Key Takeaways:
- Multiple aircraft experienced critical autopilot malfunctions, including uncommanded rapid descents or abrupt altitude changes, leading to hazardous flight conditions.
- In several instances, pilots were unable to disengage the faulty autopilots using standard disconnect switches, necessitating emergency actions like pulling circuit breakers or shutting off master avionics.
- Other reported issues include an autopilot mode controller failure causing smoke in the cockpit and a separate incident of jammed flight controls after an autopilot unexpectedly tripped off.
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