Gyroscope

The automatic pilot, or auto-pilot, detects variations from the selected flight plan of an airplane and supplies corrective signals to the ailerons, elevator, and rudder (see Airplane). A vertical gyroscope detects changes in pitch or roll, and a directional gyroscope detects changes in heading. The altitude is sensed by a barometric sensor. The speed with which these changes occur on each axis is determined by rate gyroscopes or accelerometers. This combination of displacement (how much) and rate (how fast) provides a very precise indication of the response needed. The gyroscopes transmit electrical signals to an electronic computer that combines and amplifies them. The computer then transmits corrective signals to servomotors attached to the control surfaces of the aircraft, which move to produce the desired response (see Servomechanism). An autopilot controller attached to the computer enables the pilot manually to insert maneuvers, such as turns, climbs, and dives, that require a coordinated movement of the control surfaces. At the pilot's discretion, an assortment of navigation and radio aids can be coupled to the autopilot for automatic navigation. These include inertial navigation systems, Doppler-radar-navigation systems, and radio navigation beacons. Beams used in instrumental landing systems (ILS), installed at airport runways, can also be coupled to the autopilot. In poor visibility, the ILS used with the autopilot directs the aircraft automatically to the desired glide path and aligns it with the runway. See Air Traffic Control; Navigation.