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An autopilot is a system used to control the path of an aircraft, marine craft or spacecraft without requiring constant manual control by a human operator. Autopilots do not replace human operators. Instead, the autopilot assists the operator's control of the vehicle, allowing the operator to focus on broader aspects of operations (for example, monitoring the trajectory, weather and on-board systems). When present, an autopilot is often used in conjunction with an
autothrottle An autothrottle (automatic throttle, also known as autothrust, A/T) is a system that allows a pilot to control the power setting of an aircraft's engines by specifying a desired flight characteristic, rather than manually controlling the fuel flo ...
, a system for controlling the power delivered by the engines. An autopilot system is sometimes
colloquially Colloquialism (), also called colloquial language, everyday language or general parlance, is the style (sociolinguistics), linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom norm ...
referred to as ''"George"'' (e.g. ''"we'll let George fly for a while"''). The
etymology Etymology ( )The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the form of words an ...
of the nickname is unclear: some claim it is a reference to inventor George De Beeson, who patented an autopilot in the 1930s, while others claim that
Royal Air Force The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...
pilots coined the term during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
to symbolize that their aircraft technically belonged to King
George VI George VI (Albert Frederick Arthur George; 14 December 1895 – 6 February 1952) was King of the United Kingdom and the Dominions of the British Commonwealth from 11 December 1936 until Death and state funeral of George VI, his death in 1952. ...
.


First autopilots

In the early days of aviation, aircraft required the continuous attention of a pilot to fly safely. As aircraft range increased, allowing flights of many hours, the constant attention led to serious fatigue. An autopilot is designed to perform some of the pilot's tasks. The first aircraft autopilot was developed by
Sperry Corporation Sperry Corporation was a major American equipment and electronics company whose existence spanned more than seven decades of the 20th century. Sperry ceased to exist in 1986 following a prolonged hostile takeover bid engineered by Burroughs ...
in 1912. The autopilot connected a
gyroscopic A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rotat ...
heading indicator The heading indicator (HI), also known as a directional gyro (DG) or direction indicator (DI), is a flight instrument used in an aircraft to inform the pilot of the aircraft's heading. Use The primary means of establishing the heading in most ...
and
attitude indicator The attitude indicator (AI), formerly known as the gyro horizon or artificial horizon, is a flight instrument that informs the pilot of the aircraft orientation relative to Earth's horizon, and gives an immediate indication of the smallest orie ...
to hydraulically operated
elevators An elevator or lift is a cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or decks of a building, vessel, or other structure. They are ...
and
rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally aircraft, air or watercraft, water). On an aircraft the rudder is used primarily to ...
. (
Aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...
s were not connected as wing dihedral was counted upon to produce the necessary roll stability.) It permitted the aircraft to fly straight and level on a compass course without a pilot's attention, greatly reducing the pilot's workload.
Lawrence Sperry Lawrence Burst Sperry (21 December 1892, Chicago, Illinois, United States – December 13, 1923, English Channel) was an aviation pioneer who invented the autopilot and the artificial horizon. Biography He was the third son of the gyrocompa ...
, the son of famous inventor
Elmer Sperry Elmer Ambrose Sperry Sr. (October 12, 1860 – June 16, 1930) was an American inventor and entrepreneur, most famous for construction, two years after Hermann Anschütz-Kaempfe, of the gyrocompass and as founder of the Sperry Gyroscope Company. H ...
, demonstrated it in 1914 at an aviation safety contest held in
Paris Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. S ...
. Sperry demonstrated the credibility of the invention by flying the aircraft with his hands away from the controls and visible to onlookers. Elmer Sperry Jr., the son of Lawrence Sperry, and Capt Shiras continued work on the same autopilot after the war, and in 1930, they tested a more compact and reliable autopilot which kept a U.S. Army Air Corps aircraft on a true heading and altitude for three hours. In 1930, the
Royal Aircraft Establishment The Royal Aircraft Establishment (RAE) was a British research establishment, known by several different names during its history, that eventually came under the aegis of the Ministry of Defence (United Kingdom), UK Ministry of Defence (MoD), bef ...
in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
developed an autopilot called a pilots' assister that used a pneumatically-spun gyroscope to move the flight controls. The autopilot was further developed, to include, for example, improved control algorithms and hydraulic servomechanisms. Adding more instruments, such as radio-navigation aids, made it possible to fly at night and in bad weather. In 1947, a
U.S. Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Signal ...
C-53 The Douglas C-47 Skytrain or Dakota (RAF, RAAF, RCAF, RNZAF, and SAAF designation) is a military transport aircraft developed from the civilian Douglas DC-3 airliner. It was used extensively by the Allies during World War II and remained in f ...
made a transatlantic flight, including takeoff and landing, completely under the control of an autopilot.
Bill Lear William Powell Lear (June 26, 1902 – May 14, 1978) was an American inventor and businessman. He is best known for founding Learjet, a manufacturer of business jets. He also invented the battery eliminator for the B battery, and developed the ...
developed his F-5 automatic pilot and automatic approach control system, and was awarded the
Collier Trophy The Robert J. Collier Trophy is an annual aviation award administered by the U.S. National Aeronautic Association (NAA), presented to those who have made "the greatest achievement in aeronautics or astronautics in America, with respect to im ...
in 1949. In the early 1920s, the
Standard Oil Standard Oil Company, Inc., was an American oil production, transportation, refining, and marketing company that operated from 1870 to 1911. At its height, Standard Oil was the largest petroleum company in the world, and its success made its co-f ...
tanker ''J.A. Moffet'' became the first ship to use an autopilot. The Piasecki HUP-2 Retriever was the first production
helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
with an autopilot. The
lunar module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed ...
digital autopilot of the Apollo program was an early example of a fully digital autopilot system in spacecraft.


Modern autopilots

Not all of the passenger aircraft flying today have an autopilot system. Older and smaller
general aviation General aviation (GA) is defined by the International Civil Aviation Organization (ICAO) as all civil aviation aircraft operations with the exception of commercial air transport or aerial work, which is defined as specialized aviation services ...
aircraft especially are still hand-flown, and even small
airliner An airliner is a type of aircraft for transporting passengers and air cargo. Such aircraft are most often operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an ...
s with fewer than twenty seats may also be without an autopilot as they are used on short-duration flights with two pilots. The installation of autopilots in aircraft with more than twenty seats is generally made mandatory by international aviation regulations. There are three levels of control in autopilots for smaller aircraft. A single-axis autopilot controls an aircraft in the
roll Roll or Rolls may refer to: Movement about the longitudinal axis * Roll angle (or roll rotation), one of the 3 angular degrees of freedom of any stiff body (for example a vehicle), describing motion about the longitudinal axis ** Roll (aviation), ...
axis only; such autopilots are also known colloquially as "wing levellers," reflecting their single capability. A two-axis autopilot controls an aircraft in the pitch axis as well as roll, and may be little more than a wing leveller with limited pitch oscillation-correcting ability; or it may receive inputs from on-board radio navigation systems to provide true automatic flight guidance once the aircraft has taken off until shortly before landing; or its capabilities may lie somewhere between these two extremes. A three-axis autopilot adds control in the yaw axis and is not required in many small aircraft. Autopilots in modern complex aircraft are three-axis and generally divide a flight into
taxi A taxi, also known as a taxicab or simply a cab, is a type of vehicle for hire with a driver, used by a single passenger or small group of passengers, often for a non-shared ride. A taxicab conveys passengers between locations of their choice ...
, takeoff, climb, cruise (level flight), descent, approach, and landing phases. Autopilots that automate all of these flight phases except taxi and takeoff exist. An autopilot-controlled approach to landing on a runway and controlling the aircraft on rollout (i.e. keeping it on the centre of the runway) is known as an Autoland, where the autopilot utilizes an Instrument Landing System (ILS) Cat IIIc approach, which is used when the visibility is zero. These approaches are available at many major airports' runways today, especially at airports subject to adverse weather phenomena such as
fog Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...
. The aircraft can typically stop on their own, but will require the disengagement of the autopilot in order to exit the runway and taxi to the gate. An autopilot is often an integral component of a
Flight Management System A flight management system (FMS) is a fundamental component of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that mode ...
. Modern autopilots use
computer software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consists ...
to control the aircraft. The software reads the aircraft's current position, and then controls a
flight control system A conventional Fixed-wing aircraft, fixed-wing aircraft flight control system consists of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction ...
to guide the aircraft. In such a system, besides classic flight controls, many autopilots incorporate thrust control capabilities that can control throttles to optimize the airspeed. The autopilot in a modern large aircraft typically reads its position and the aircraft's attitude from an
inertial guidance system An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dire ...
. Inertial guidance systems accumulate errors over time. They will incorporate error reduction systems such as the carousel system that rotates once a minute so that any errors are dissipated in different directions and have an overall nulling effect. Error in gyroscopes is known as drift. This is due to physical properties within the system, be it mechanical or laser guided, that corrupt positional data. The disagreements between the two are resolved with
digital signal processing Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...
, most often a six-dimensional
Kalman filter For statistics and control theory, Kalman filtering, also known as linear quadratic estimation (LQE), is an algorithm that uses a series of measurements observed over time, including statistical noise and other inaccuracies, and produces estimat ...
. The six dimensions are usually roll, pitch, yaw,
altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
,
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
, and
longitude Longitude (, ) is a geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter l ...
. Aircraft may fly routes that have a required performance factor, therefore the amount of error or actual performance factor must be monitored in order to fly those particular routes. The longer the flight, the more error accumulates within the system. Radio aids such as DME, DME updates, and
GPS The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
may be used to correct the aircraft position.


Control Wheel Steering

An option midway between fully automated flight and manual flying is Control Wheel Steering (CWS). Although it is becoming less used as a stand-alone option in modern airliners, CWS is still a function on many aircraft today. Generally, an autopilot that is CWS equipped has three positions: off, CWS, and CMD. In CMD (Command) mode the autopilot has full control of the aircraft, and receives its input from either the heading/altitude setting, radio and navaids, or the FMS (Flight Management System). In CWS mode, the pilot controls the autopilot through inputs on the yoke or the stick. These inputs are translated to a specific heading and attitude, which the autopilot will then hold until instructed to do otherwise. This provides stability in pitch and roll. Some aircraft employ a form of CWS even in manual mode, such as the MD-11 which uses a constant CWS in roll. In many ways, a modern Airbus fly-by-wire aircraft in Normal Law is always in CWS mode. The major difference is that in this system the limitations of the aircraft are guarded by the
flight computer A flight computer is a form of circular slide rule used in aviation and one of a very few analog computers in widespread use in the 21st century. Sometimes it is called by the make or model name like E6B, CR, CRP-5 or in German, as the ''Dreieckrec ...
, and the pilot cannot steer the aircraft past these limits.


Computer system details

The hardware of an autopilot varies between implementations, but is generally designed with redundancy and reliability as foremost considerations. For example, the Rockwell Collins AFDS-770 Autopilot Flight Director System used on the
Boeing 777 The Boeing 777, commonly referred to as the Triple Seven, is an American long-range wide-body airliner developed and manufactured by Boeing Commercial Airplanes. It is the world's largest twinjet. The 777 was designed to bridge the gap bet ...
uses triplicated FCP-2002 microprocessors which have been formally verified and are fabricated in a radiation-resistant process. Software and hardware in an autopilot are tightly controlled, and extensive test procedures are put in place. Some autopilots also use design diversity. In this safety feature, critical software processes will not only run on separate computers and possibly even using different architectures, but each computer will run software created by different engineering teams, often being programmed in different programming languages. It is generally considered unlikely that different engineering teams will make the same mistakes. As the software becomes more expensive and complex, design diversity is becoming less common because fewer engineering companies can afford it. The flight control computers on the
Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
used this design: there were five computers, four of which redundantly ran identical software, and a fifth backup running software that was developed independently. The software on the fifth system provided only the basic functions needed to fly the Shuttle, further reducing any possible commonality with the software running on the four primary systems.


Stability augmentation systems

A stability augmentation system (SAS) is another type of automatic flight control system; however, instead of maintaining the aircraft required altitude or flight path, the SAS will move the aircraft control surfaces to damp unacceptable motions. SAS automatically stabilizes the aircraft in one or more axes. The most common type of SAS is the
yaw damper A yaw damper (sometimes referred to as a stability augmentation system) is a system used to reduce (or damp) the undesirable tendencies of an aircraft to oscillate in a repetitive rolling and yawing motion, a phenomenon known as the Dutch roll. ...
which is used to reduce the
Dutch roll Dutch roll is a type of aircraft motion consisting of an out-of-phase combination of "tail-wagging" (yaw) and rocking from side to side (roll). This yaw-roll coupling is one of the basic flight dynamic modes (others include phugoid, short per ...
tendency of swept-wing aircraft. Some yaw dampers are part of the autopilot system while others are stand-alone systems.
Yaw damper A yaw damper (sometimes referred to as a stability augmentation system) is a system used to reduce (or damp) the undesirable tendencies of an aircraft to oscillate in a repetitive rolling and yawing motion, a phenomenon known as the Dutch roll. ...
s use a sensor to detect how fast the aircraft is rotating (either a gyroscope or a pair of accelerometers), a computer/amplifier and an actuator. The sensor detects when the aircraft begins the yawing part of Dutch roll. A computer processes the signal from the sensor to determine the rudder deflection required to damp the motion. The computer tells the actuator to move the rudder in the opposite direction to the motion since the rudder has to oppose the motion to reduce it. The Dutch roll is damped and the aircraft becomes stable about the yaw axis. Because Dutch roll is an instability that is inherent in all swept-wing aircraft, most swept-wing aircraft need some sort of yaw damper. There are two types of yaw damper: the series yaw damper and the parallel yaw damper. The actuator of a parallel yaw damper will move the rudder independently of the pilot's rudder pedals while the actuator of a series yaw damper is clutched to the rudder control quadrant and will result in pedal movement when the rudder moves. Some aircraft have stability augmentation systems that will stabilize the aircraft in more than a single axis. The
Boeing B-52 The Boeing B-52 Stratofortress is an American long-range, subsonic aircraft, subsonic, jet-powered strategic bomber. The B-52 was designed and built by Boeing, which has continued to provide support and upgrades. It has been operated by the ...
, for example, requires both pitch and yaw SAS in order to provide a stable bombing platform. Many helicopters have pitch, roll and yaw SAS systems. Pitch and roll SAS systems operate much the same way as the yaw damper described above; however, instead of damping Dutch roll, they will damp pitch and roll oscillations to improve the overall stability of the aircraft.


Autopilot for ILS landings

Instrument-aided landings are defined in categories by the
International Civil Aviation Organization The International Civil Aviation Organization (ICAO, ) is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation, and fosters the planning and development of international sc ...
, or ICAO. These are dependent upon the required visibility level and the degree to which the landing can be conducted automatically without input by the pilot. CAT I – This category permits pilots to land with a
decision height In aviation, an instrument approach or instrument approach procedure (IAP) is a series of predetermined maneuvers for the orderly transfer of an aircraft operating under instrument flight rules from the beginning of the initial approach to a landi ...
of and a forward visibility or Runway Visual Range (RVR) of . Autopilots are not required. CAT II – This category permits pilots to land with a decision height between and and a RVR of . Autopilots have a fail passive requirement. CAT IIIa -This category permits pilots to land with a decision height as low as and a RVR of . It needs a fail-passive autopilot. There must be only a 10−6 probability of landing outside the prescribed area. CAT IIIb – As IIIa but with the addition of automatic roll out after touchdown incorporated with the pilot taking control some distance along the runway. This category permits pilots to land with a decision height less than 50 feet or no decision height and a forward visibility of in Europe (76 metres, compare this to aircraft size, some of which are now over long) or in the United States. For a landing-without-decision aid, a fail-operational autopilot is needed. For this category some form of runway guidance system is needed: at least fail-passive but it needs to be fail-operational for landing without decision height or for RVR below . CAT IIIc – As IIIb but without decision height or visibility minimums, also known as "zero-zero". Not yet implemented as it would require the pilots to taxi in zero-zero visibility. An aircraft that is capable of landing in a CAT IIIb that is equipped with
autobrake An autobrake is a type of automatic wheel-based hydraulic brake system for advanced airplanes. The autobrake is normally enabled during takeoff and landing procedures, when the aircraft's longitudinal deceleration system can be handled by the autom ...
would be able to fully stop on the runway but would have no ability to taxi. Fail-passive autopilot: in case of failure, the aircraft stays in a controllable position and the pilot can take control of it to go around or finish landing. It is usually a dual-channel system. Fail-operational autopilot: in case of a failure below alert height, the approach, flare and landing can still be completed automatically. It is usually a triple-channel system or dual-dual system.


Radio-controlled models

In
radio-controlled model A radio-controlled model (or RC model) is a Physical model, model that is steering, steerable with the use of radio control. All types of model vehicles have had RC systems installed in them, including radio-controlled car, ground vehicles, radio ...
ling, and especially RC
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
and
helicopters A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
, an autopilot is usually a set of extra hardware and software that deals with pre-programming the model's flight.


See also

*
Acronyms and abbreviations in avionics Below are abbreviations used in aviation, avionics, aerospace and aeronautics. A B C D E F G H I J K L M N N numbers (turbines) O P Q R S T U V V speeds W X Y Z See also * List of avia ...
*
Gyrocompass A gyrocompass is a type of non-magnetic compass which is based on a fast-spinning disc and the rotation of the Earth (or another planetary body if used elsewhere in the universe) to find geographical direction automatically. The use of a gyroc ...
*
Self-driving car A self-driving car, also known as an autonomous car, driver-less car, or robotic car (robo-car), is a car that is capable of traveling without human input.Xie, S.; Hu, J.; Bhowmick, P.; Ding, Z.; Arvin, F.,Distributed Motion Planning for S ...


References


External links


"How Fast Can You Fly Safely", June 1933, Popular Mechanics
page 858 photo of Sperry ''Automatic Pilot'' and drawing of its basic functions in flight when set {{Authority control Avionics Aircraft instruments Uncrewed vehicles American inventions 1912 introductions