When should the autopilot be turned on? If the pilot is as sharp as he should be on autopilot use, it might be turned on as soon as the airplane is off the ground. I am a cheapskate and have just an S-Tec roll-only autopilot. It can be turned on immediately after takeoff, in the heading mode, with the bug set on runway heading, and, presto, the airplane is roll stabilized from the git-go. I would say to take off with it on, but taking off or landing with it on is prohibited in the limitations. All autopilots have certification limitations that set minimum altitudes for engagement for takeoff, and on approach. Those limits are in the pilot's operation handbook supplements section.