This should only be the case if you have lost your radio or have utterly incompetent air traffic control. It could also be the case if you're in class G airspac

This should only be the case if you have lost your radio or have utterly incompetent air traffic control. It could also be the case if you're in class G airspace or in some BFE remote area without a tower, but meh. As stated elsewhere, autopilot on planes is pretty much not at all what most people think of as "auto-pilot". The pilots still are doing their instrument scan, and they're still maintaining situational awareness, but they know that the plane should maintain heading, altitude, and airspeed. Source: Have private pilot's license and flew the Shadow 200 TUAV for the US Army. It is a VFR rated airframe that is flown 100% IFR, by nature of it being an ~11ft x 3.5ft x 2ft drone.