Narrative:

Twenty minutes into the flight; ATC told me to go to 8;000 feet. I was on autopilot - a G1000 glass cockpit with a GFC700 autopilot. I set us up for 8;000 feet and we simply blew straight through it. I evaluated and couldn't figure out why this happened; so I disengaged the autopilot to fly by hand and re-establish; but it wouldn't disengage; and I was still climbing. I attempted to disengage using the ap disc switch; ap button; met; and I pulled the circuit breaker but the autopilot would not disengage. I pushed with all my might against the yoke; and my copilot had her knees buried in the yoke just to get the aircraft to stop climbing. We reduced power and I came left as I called 'mayday'. ATC asked if I wanted to declare an emergency; and I asked to go to [a nearby airport]. ATC asked if I wanted [a closer airport] but I didn't feel I had enough control of the aircraft to burn that much altitude. We worked our way back to [my preferred airport] based on power reductions and slow; painful turns. Every time I tried to override the autopilot to the right; we shot straight up. ATC was great; [and] I finally got [destination tower] on the radio and advised them of my situation. They attempted to walk me through all of steps I had already taken; and finally said there was no other alternative but to do a landing using only manual trim and power. We lined up a long 8-mile final approach with direct headwinds and came in with no flaps; and no real yoke control. We landed safely.

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Original NASA ASRS Text

Title: C182T Pilot reported he could not disconnect his GFC700 autopilot; causing control difficulties. Pilot declared emergency and diverted to a suitable airport; where a safe landing was made using manual trim and power for control.

Narrative: Twenty minutes into the flight; ATC told me to go to 8;000 feet. I was on autopilot - A G1000 glass cockpit with a GFC700 autopilot. I set us up for 8;000 feet and we simply blew straight through it. I evaluated and couldn't figure out why this happened; so I disengaged the autopilot to fly by hand and re-establish; but it wouldn't disengage; and I was still climbing. I attempted to disengage using the AP Disc Switch; AP button; MET; and I pulled the circuit breaker but the autopilot would not disengage. I pushed with all my might against the yoke; and my copilot had her knees buried in the yoke just to get the aircraft to stop climbing. We reduced power and I came left as I called 'mayday'. ATC asked if I wanted to declare an emergency; and I asked to go to [a nearby airport]. ATC asked if I wanted [a closer airport] but I didn't feel I had enough control of the aircraft to burn that much altitude. We worked our way back to [my preferred airport] based on power reductions and slow; painful turns. Every time I tried to override the autopilot to the right; we shot straight up. ATC was great; [and] I finally got [destination Tower] on the radio and advised them of my situation. They attempted to walk me through all of steps I had already taken; and finally said there was no other alternative but to do a landing using only manual trim and power. We lined up a long 8-mile final approach with direct headwinds and came in with no flaps; and no real yoke control. We landed safely.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.