Why autopilot can be engaged at 400 feet?

Answer 1

There are, as governed by FAA rules, certain minimum altitudes where such deviced can be operated. basic idea is traffic control, in end terminal areas, the device would be impractical, as a hypothetical automobile auto-steering device would be wildly impractical in parking lots, which are somewhat chaotic free-fire zones. The same logic applies. an autopilot could not be practically adapted to heliciopters given constant changes in control use and flight path- in that sense akin to a Crane.