Skylane 182/RG Turbo Skylane/RG
Flight Crew Private; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 7; Flight Crew Total 144; Flight Crew Type 20
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Declared Emergency
Aircraft
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.
Reporter stated initial maintenance inspection was unsuccessful in duplicating problem; and the aircraft was released for use. A few days later; the aircraft (flown by another pilot) experienced a runaway trim; and while working on that problem maintenance experienced the same issue of the autopilot failing to disconnect.  Current theory is that reporter experienced simultaneous autopilot failure to disconnect and runaway trim; and autopilot is still being analyzed.
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.