While everyone knows that pilots rely on an autopilot during flight, it’s a subject that still intrigues many passengers, who wonder exactly what it does, how far it can go, and to what extent it takes charge of all or part of the flight. That’s what we’re going to explain here.

What is autopilot?

The autopilot is a software program that controls all or part of the aircraft’s controls to enable it to follow a given route, at a given speed, at a given altitude.

Depending on the system and aircraft type, the autopilot can control :

• the elevators, which control the aircraft’s altitude
• the rudder, which controls the aircraft’s trajectory
• the ailerons to control the aircraft roll
• the aircraft speed

We’ll assume that we’re talking about the autopilot of a commercial aircraft capable of controlling all this at once. On leisure aircraft, you can have systems that control only part of the controls.

It relies on a multitude of sensors and GPS, which it interrogates several times a second to correct these various factors. The autopilot is therefore not only capable of keeping an aircraft on course, but also of executing the entire flight plan.

In concrete terms, the pilot has three buttons for setting a heading, altitude and speed. He engages one, two or all three, and the autopilot does the rest.

When is the autopilot used?

Over time, the autopilot has improved considerably, becoming capable of operating more and more phases of a flight, including the most critical ones.

Initially used only for cruising, with pilots having to make regular corrections, today it can theoretically cruise from A to Z if no changes are made to the flight plan on the way. In case of very low visibility the autopilot is also used to land the aircraft and in December 2019 an Airbus A350-1000 even achieved the first fully automatic take-off but for the moment, automatic take-off is only at the experimental stage as part of the ATTOL (Autonomous Taxi, Take-Off and Landing) program.

The pilot engages the autopilot more or less quickly after takeoff. At very congested airports, they’ll keep control for longer to carry out numerous maneuvers, while in other cases they’ll activate it quite quickly. There are only two limits:

The first is that it is forbidden to engage the autopilot below 400 feet (120m).

The second is that it is mandatory to use it above 28,000 feet (8,500m), and this requires some explanation.

In the 2000s, ICAO (International Civil Aviation Organization) introduced Reduced Vertical Separation Minimum (RVSM) rules. They mean that two aircraft flying in opposite directions can be separated by just 1000 feet (300m), which is why you can often see other aircraft through the window. Technically speaking, all flights going in the same direction (say, east-west) are separated by 2,000 feet, as are those going in the opposite direction, so there’s a plane every 1,000 feet.

This is justified by the increase in the number of aircraft in flight, which justifies trying to get them to fly as close to each other as possible, without imposing distances that would increase fuel consumption for those obliged to fly at the lowest altitude, but has been made possible precisely by the improved performance of autopilots. At these speeds and altitudes, manual piloting cannot reliably maintain the correct spacing between aircraft, which is why autopilot use is mandatory.

That’s why, just a few days after entering service in 2009, an Air France A380 had to turn back 1h30 after take-off from New York because its autopilot had failed. The pilot could have flown manually to Paris, but this would have prohibited him from flying below 28,000 feet, which would have increased his fuel consumption while he hadn’t loaded the fuel needed to fly that low.

Finally, the autopilot is often engaged in phases: first altitude control, then speed, then heading.

So what does the pilot do in flight?

You mustn’t think that the pilot is twiddling his thumbs and doing nothing in flight. His role remains to oversee the smooth running of the flight, with the autopilot reducing his workload so that he can concentrate on the essentials.

So he’ll continue to make altitude and heading changes when necessary, but never by taking control of the aircraft manually: he’ll change the autopilot settings by turning a small knob, and the autopilot will apply his instructions.

Thanks to the automatic throttles, which automatically control thrust to obtain the right speed, he can concentrate almost entirely on changing heading and altitude, without worrying about speed.

What does autopilot improve?

Autopilot brings a host of benefits, some obvious, others less so.

Firstly, by reducing the pilot’s workload, it increases the level of safety: the pilot is more focused on what matters, and is fresher to intervene in the event of a problem.

Still on the subject of safety, as we’ve seen, it ensures that the spacing between aircraft in cruise mode is respected, thus avoiding collisions, as humans are less precise and reactive to act at such speeds.

It also helps to save fuel and protect the environment. By maintaining a constant altitude, for example, for every 1,000 feet below its optimum flight altitude, an aircraft consumes 1% more fuel. And since it reduces the separation between aircraft, it allows twice as many aircraft to fly simultaneously at their optimum altitude.

Still on the subject of fuel consumption, the autothrottles that automatically control thrust to achieve the right speed, better than a human could, also contribute to the aircraft’s energy efficiency.

Finally, it contributes to passenger comfort. In the event of crosswinds or turbulence, a pilot will compensate, reacting more slowly and in fits and starts, whereas the autopilot will react instantaneously with micro-adjustments.

A bit of history

Finally, you may be surprised to know that the invention of the autopilot dates back to 1912. It was first demonstrated in Paris in 1914 at an aviation safety competition. The same Lawrence Sperry is credited with founding the Mile High Club, and it’s easy to see how being freed from the constraints of piloting gave him the idea of indulging in other leisure pursuits in the air.

Hello George !

Finally, the autopilot is often referred to as “George”, but we don’t really know why. For some, it’s a reference to George De Beeson, who patented the first autopilot in the 1930s; for others, it’s a tribute from Royal Air Force pilots to their King George VI during the Second World War.

Photo : B747 autopilot by Arjan Veltman via Shutterstock