> Tangent: what does an airplane's autopilot do? I always assumed it was basically doing lane-keeping within virtual flight-path lanes we've drawn in the sky.
It's even simpler than that: a basic autopilot can keep a set heading and altitude without constant adjustments from the pilot, and a basic autothrottle can keep a set speed without constant adjustment of the throttle from the pilot. The pilot gives them simple instructions like "heading 123" and "altitude 1234" and "speed 200" through buttons on the aircraft's panel. This allows for hands-free flying (the pilot doesn't have to hold the controls all the time when the autopilot and autothrottle are active).
More advanced autopilots can follow parts of the flight plan, like "fly to waypoint ABC then to waypoint DEF then to waypoint GHI", automatically changing their setting to the next one every time a relevant waypoint is reached, but even then the pilot still has to give it instructions regularly (for instance, when a controller tells the pilot through the radio to use a specific altitude, the pilot has to set that altitude in the autopilot). And, of course, the pilot still has to be ready to take control at a moment's notice; whenever the autopilot sees something it doesn't like, it deactivates (with a warning tone and blinking lights).
It's even simpler than that: a basic autopilot can keep a set heading and altitude without constant adjustments from the pilot, and a basic autothrottle can keep a set speed without constant adjustment of the throttle from the pilot. The pilot gives them simple instructions like "heading 123" and "altitude 1234" and "speed 200" through buttons on the aircraft's panel. This allows for hands-free flying (the pilot doesn't have to hold the controls all the time when the autopilot and autothrottle are active).
More advanced autopilots can follow parts of the flight plan, like "fly to waypoint ABC then to waypoint DEF then to waypoint GHI", automatically changing their setting to the next one every time a relevant waypoint is reached, but even then the pilot still has to give it instructions regularly (for instance, when a controller tells the pilot through the radio to use a specific altitude, the pilot has to set that altitude in the autopilot). And, of course, the pilot still has to be ready to take control at a moment's notice; whenever the autopilot sees something it doesn't like, it deactivates (with a warning tone and blinking lights).