PC Version
I have experienced this issue. I identified what caused it for me:
DESCRIPTION OF INCIDENT:
While climbing to altitude in my P-38, I set for cruise power instead of climb power. During my introspective investigation into the incident, “it was discovered that” I had failed to complete the After Takeoff Checklist. I gradually lost all my energy. The autopilot continually compensated with nose up trim until I ultimately began to stall.
The incident was ultimately addressed by disengaging the Autopilot for the remainder of the flight. It did not result in a virtual fatal mishap.
RESULTING AFFECT ON AUTOPILOT:
After recovering from stall and returning to level flight, I engaged autopilot. It remained in full nose up trim and caused me to nearly depart controlled flight again. This condition remained and cycling the autopilot several times did not correct the issue.
UNSUCCESSFUL CORRECTIVE ACTIONS TAKEN:
- While re-engaging autopilot, I compensated for the full trim deflection of autopilot to stay in controlled flight - hoping that the autopilot just needed time to slowly return to normal control input levels and expected behavior. I made several attempts, but this corrective action was ultimately unsuccessful.
- Resetting the horizontal stabilizer trim to 0 after returning to level flight and prior to re-engaging the Autopilot did not resolve the problem.
- Setting a lower altitude capture and -1700 vertical speed appeared to bring AP back to expected behavior quickly. It followed the command until reaching the lower altitude. Once reaching the set altitude, AP appeared to want to return to full nose up deflection and began pulling me up and out of controlled flight.
INITIAL THEORY OF SUSPECTED CAUSE:
The subsequent malfunction of the Autopilot’s logic by being operated to its limit was initiated as a result of Pilot error in failing to complete and follow the after take off checklist. This resulted in the continued inability of the Autopilot to maintain a desired flight path.
Since I typically fly with no failures, Modern FM, and no Flight Assists, I chalked it up as as a simulated in flight failure of my Autopilot - initiated by pilot error. I disengaged autopilot and I continued to hand fly the rest of the flight without further incident.
ADDITIONAL OBSERVATION / CONFIRMATION:
As mentioned by N6722C, engaging autopilot on the ground appears to cause issues.
I use the Logitech Multipanel. I used to be able to pre-arm Alt and VS without the autopilot engaging itself while still on the ramp after getting IFR Clearance. I observed the issue in my following flight in a Cessna 172 Classic - right after my incident in the P-38.
Lately, if I try to pre-arm Alt or VS, the Logitech Multipanel will automatically engage the Autopilot while I’m still on the ramp until I disengage it. The result is that when I engage AP after takeoff, the autopilot behaves as if it was already at a high trim deflection setting and begins to pitch or dive me out of my intended flight path and controlled flight. The autopilot appeared to return to normal functionality later after troubleshooting it at a higher altitude.
Maybe we’ll get relief in SU VII
