ABSTRACT
The technology used for the automatic control of aeroplane autopilots varies in complexity depending on the intended functionality. The term ‘autopilot’ refers to a range of technology encompassing the simple wings leveller, through to fully automatic approach and landing. The functionality of an autopilot in its basic mode of operation is to maintain the aircraft on its desired flight path. Autopilots can also be integrated with a flight-director system; in this case the commands are presented on the flight instruments allowing the pilot to follow a desired flight path. Flight directors can be operated separately for manual control of the aircraft, or (with the autopilot engaged) allowing the pilot to monitor the autopilot's performance. The main purpose of an autopilot/flight-director system is to relieve the pilot of the physical and mental fatigue of flying the aircraft. This is particularly beneficial on long-flight legs, or in low-visibility operations. Aviation medical research and flight testing has established that an automatic system is more responsive than a human pilot. There are many types of autopilot in operational use, ranging from simple analogue systems used on general aviation aircraft through complex digital systems used on large commercial transport aircraft. This chapter establishes the basic principles based on practical examples; the schematics used are based on analogue systems, to illustrate basic principles. Combined autopilots and flight directors are referred to by various names, depending on the technology and manufacturer, e.g. automatic flight-control system, automatic flight-guidance system, digital flight-guidance system.
