Autopilot: What is it?

    Modern commercial aircraft almost always have some form of autopilot onboard. Up-to-date systems are usually computer-controlled and highly sophisticated. Still, the underlying processes involved have changed little in more than a century. So, how do these systems work?

    A technology that’s changed little in over a century

    In 1933, famous eyepatch-wearing aviator Wiley Post touched down at Floyd Bennett Field in New York, completing the first around the world solo flight in seven days, 18 hours, and 49 minutes. His journey had begun in his Lockheed Vega Winnie Mae on July 15th that year, flying nonstop to Berlin in Germany. He continued to the Soviet Union, making stops along the way, before hopping across to Alaska, Canada, and finally back to where he started in New York.

    Wiley Post

    Post’s second famous flight, having completed an around the world operation with navigator Harold Gatty onboard to help keep him on course and alert. So how did he manage to achieve a similar flight with no extra pair of the hands-on board? The answer was autopilot, which kept him flying in the right direction while he rested.

    Post’s autopilot was not the first time pilots had used autopilot. Indeed, US aviator Lawrence Sperry created the first successful autopilot back in 1912. Today, autopilot is a standard feature on most commercial aircraft. Remarkably, it has changed very little in the past 100 years.

    Lawrence Sperry (right)

    How does autopilot work?

    While autopilots can be present on everything from ships to cars, naturally, we’ll be focusing on aeroplane autopilot technology. The autopilot can be more accurately described as the automatic flight control system (AFCS) in an aviation sense. Originally designed to provide relief to pilots during the long and often tedious cruise stages of flight, modern AFCS systems can carry out some pretty advanced manoeuvres.

    the controls of an aircraft

    Depending on the system, the autopilot will control the elevators, the rudder, the ailerons, or even all three. Basic ‘single axis’ autopilots maintain one piece of equipment, usually the ailerons, to keep the aircraft on an even keel. More advanced two- or three-axis autopilots have access to more of the controls.

    Modern autopilots use a computer with a high-speed processor to control the aircraft. Still, the underlying technology is very much as Sperry designed it in 1912. Using a gyroscope and altitude indicator remains the fundamental basis for modern autopilot, although now they are more accurate.

    every flight you have been on has been commandeered by autopilot at some point of the flight

    Other aircraft systems involved in autopilot function include compasses, airspeed indicators, and accelerometers and receiving GPS signals to indicate the plane’s position. Armed with all this information, the autopilot cannot just keep a straight and level path but execute an entire flight plan.

    Taking all the data from these various inputs, the autopilot ensures that the aircraft retains the correct pitch, speed, heading, and altitude. Slight adjustments are performed by sending signals to servomechanism units, which use either motors or hydraulics to alter the aircraft’s control surfaces.

    autopilots are a staple of everyday flights

    The crucial element of this activity is that it creates a feedback loop. The pilot sets the control surfaces and engages the autopilot. Based on the data gathered by the autopilot, it makes some adjustments, which changes the data set, and then the process starts again.

    How much does the autopilot actually fly?

    Autopilots are becoming increasingly intelligent and are capable of performing complex manoeuvres. Although they are primarily used only in the cruise stage of flight, they are perfectly capable of landing the plane. Indeed, in situations where visibility is abysmal, autoland can be used to bring the plane down. This is only possible at some airports with particular technologies installed and is used very rarely, with pilots landing manually 99% of the time.

    Recently, Airbus successfully demonstrated the use of the autopilot in a take-off situation also. One of its A350-1000s took off by itself from Toulouse in December 2019, proving possible. The Autonomous Taxi, Take-Off, and Landing (ATOL) demonstrator project is part of the plane manufacturer’s UpNext program, looking at future technologies for aircraft. However, right now, this is just a demonstration, and all take-offs are performed manually.

    aircraft being pushed back

    Autopilot can be compared somewhat to cruise control on a car. It helps maintain a constant speed on the motorway. Still, it wouldn’t help leave the garage or try to park in a space. Although autopilot is an excellent resource for giving pilots a bit of a break, they are still responsible for the inputs and control of the plane.

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