The Cessna 400 is equipped with a Garmin G1000 Glass cockpit which is normally a dream to fly. If you have pressed the autopilot disconnect switch on the control stick to begin flying the plane manually and the autopilot won't disengage, don't panic. Remember your training. You have practiced emergency procedures with your certified flight instructor; you should be prepared to handle this emergency. According to the Cessna 400's operating manual, when the autopilot does not disengage, move the pitch trim switch. If the autopilot still fails to disengage, turn off the overhead autopilot trim systems switch. If the autopilot still does not disengage, immediately pull the circuit breaker to the "Off" position.
If the autopilot still won't disengage, you need to contact air traffic control. Communicating with the tower is secondary. It is more important to try and resolve the problem if you can and fly the plane. Contact air traffic control when safe to do so. Switch to the emergency radio frequency of 121.50 megahertz; if you are unable to do so, remain on the frequency you currently are on and state, "Mayday" three times then, "This is Cessna..." followed by your aircraft identifier number, excluding the first letter N. Inform the tower that your autopilot will not disengage. The controller will guide you and provide you with several instructions. If you can, without compromising safety, set your transponder to the emergency code of 7700.
If the autopilot still will not disengage, you will have to prepare for a forced emergency landing. Ensure that you and your passengers have your seat belts and shoulder harnesses fastened and secure. Make sure that there are no loose objects in the aircraft. Move the wing flaps to the takeoff position. Position your throttle so that your knots indicated air speed (KIAS) is 105 knots. Select a place to land, preferably the closest airport. Otherwise, look for any area where you can safely land. Fly over the intended landing spot, look for any obstructions and determine the direction of the wind. Ascend to 1,000 feet above ground level. When you reach a safe altitude and air speed, retract your flaps. Fly in a normal landing pattern. Land into the wind. Turn off the avionics master switch. When you reach final approach, put the flaps in the landing position. Maintain an air speed of 80 KIAS. Right before touchdown, turn the left and right master switches off. Land as slowly as you can, with a nose-up attitude. Immediately pull the mixture to the idle cutoff position. Turn the ignition switch off. Firmly place your feet on the brakes and brake hard.