Autopilot

In the context of aerospace engineering, an autopilot is a system used to control the trajectory of an aircraft, spacecraft, or missile without constant manual control by a human operator. Autopilots do not replace human operators, but instead, they assist them in controlling the vehicle, allowing them to focus on broader aspects of operation, such as monitoring the trajectory, weather, and systems. Autopilots are used in aircraft, satellites, and spacecraft. They can control anything from small adjustments of the wings to complete sequences of maneuvers. The complexity and capabilities of autopilot systems vary greatly, with some able to take off, fly to a destination and land, all without human intervention. Autopilots in modern complex aircraft are three-axis and generally divide a flight into taxi, take-off, ascent, level, descent, approach, and landing phases. Autopilots exist that automate all of these flight phases except the taxiing. An autopilot-controlled landing on a runway and controlling the aircraft on rollout (i.e. keeping it on the center of the runway) is known as a CAT IIIb landing or Autoland, available on many major airports' runways today, especially at airports subject to adverse weather phenomena such as fog.