How Does Autopilot Actually Work?


Autopilot isn’t as “auto”
as you might think. There’s no robot that
sits in the pilot seat and mashes buttons while
the real pilot takes a nap. It’s just a flight-control system that allows a pilot to fly an airplane without continuous hands-on control. Basically, it lets a pilot fly
from New York to Los Angeles without white-knuckling the
controls for six straight hours. But how does it actually work? Kind of like a polar bear. A polar bear’s core temperature sits at about 98.6 degrees Fahrenheit. It is so well insulated
against the frigid Arctic cold that it often overheats. When that happens, its body reacts by releasing excess heat
through its hairless parts, like its nose, ears, and feet. The polar bear’s body temperature returns to a comfortable 98.6, and it’s free to hunt seals another day. That cycle is called a
negative feedback loop, and it’s the same way
an autopilot functions. A negative feedback loop
is a self-regulating system that reacts to feedback in a
way that maintains equilibrium. Generally, it uses a sensor to receive some sort of data or input, and the system uses that data to keep functioning in a preset way. For the polar bear, that
preset is body temperature. For an airplane, it’s lateral
and vertical movement. A modern automatic flight-control system (that’s autopilot’s full name) is made of three main parts: a flight-monitoring computer, several high-speed processors, and a series of sensors placed on different parts of the plane. The sensors collect data
from the entire plane and send them to the processors, which in turn tell the
computer what’s what. AFCSs come in three different
levels of complexity. There are single-, two-,
and three-axis autopilots, based on the number of parts they control. Single-axis controls the ailerons, which are these guys. They make the plane do this. Single-axis autopilot is also
called the “wing leveler” because it controls the roll of the plane and keeps the wings
perpendicular to the ground. Two-axis handles everything
the single-axis does, along with the elevators, located here. They move the plane like this. And three-axis juggles
those two plus the rudder. That one there is in
charge of this movement. Then the computer tells the servomechanism units what to do. Servos are the little instruments that actually move the parts. All of these pieces come together to make sure your plane stays in the air, where it belongs. But they don’t just work on their own. The success of the autopilot depends on the knowledge of
the actual human pilot. Greg Zahornacky: Autopilots
are dumb and dutiful, meaning this: that if you
program them incorrectly, they will kill you. Dumb and dutiful are the
“two Ds of automation,” according to Earl Wiener, a former US Air Force pilot
and an aviation scholar. He once described autopilot
as, “Dumb in the sense that it will readily
accept illogical input; dutiful in the sense that the computer will attempt to fly whatever is put in.” It’s crucial, and I cannot
emphasize this enough, that you know how to fly a plane before you use an autopilot. Step one is inputting a flight plan. And step one is also where things could start going wrong. To get from New York to
LA, a pilot needs a route. That route translates to a flight plan, and that flight plan gets
punched into the computer and logged into the database. If the pilot doesn’t know
what the heck they’re doing, then they can end up
programming the autopilot to fly the plane upside down or to spell out “I’m a
Bad Pilot” in the sky. If they correctly navigate step one, step two is simply
turning on the autopilot. The system executes the flight plan and takes over from there. Zahornacky: That will
stay operational until such time as they tell it or turn it off. But it is capable of flying the aircraft essentially from takeoff all the way to touchdown and including touchdown. Narrator: But you can’t
just tap it and nap it. It’s the ABCs of autopilots: Always be checking. Because autopilots can and do fail. Sometimes it’s user error
when entering the flight plan. Sometimes it’s a sensor
or servo malfunction. Either way, this is when it becomes very important that an inflatable toy isn’t flying the plane. – Why is it doing that?! Zahornacky: If it’s not
doing what I expect it to do, I’m gonna disengage the autopilot. I’m gonna go back to
hand-flying the aircraft and say, OK, this is
what I want you to do. I’m gonna rebuild it again. Narrator: The good news is autopilot will never take over a plane, à la HAL. Worst case, the pilot
turns it off and on again or pulls the circuit
breaker if that doesn’t work and reprograms it to behave itself. Worst-worst case, the pilot just has to fly the plane themselves. Zahornacky: So, I am a very
large proponent of hand-flying that airplane to keep your skills high because, you know what, you’ve gotta go through a check ride at least once a year. Narrator: A check ride is a practical test regulated by the Federal
Aviation Administration that US pilots must pass
to get their licenses. And most airlines require
yearly check rides to make sure their
pilots can actually fly. Zahornacky: ‘Cause if it’s
on autopilot all the time, how can you keep your skills sharp? Narrator: There’s a reason we still have pilots flying planes and haven’t handed the
yoke over to robots. As advanced as the technology is, an autopilot is not auto
enough to think for itself, which means it’s not smart enough to fly a plane by itself, and that’s another thing autopilots have in common with polar bears.

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54 thoughts on “How Does Autopilot Actually Work?

  1. Great but the real question is how does Auto pilot work in humans? Like when you go to Vegas get piss drunk to the point where you black out but manage to get something to eat walk back to the correct room grab a bottle water and go to bed that's the real mystery…

  2. I really have to say, this was a great video and great explanation about an aviation topic and not only some random facts wrongly matched together! As a pilot, I can say there are far too few educational, correct videos about aviation online here. Keep it up with this good work! 👍🏼

  3. You explained what an autopilot does however you did not explain HOW it works, autopilots use a little thing invented by Sir Isaac Newton which is called CALCULUS! All parameters of the autopilot are controlled via a PID controller (proportional-integral-derivative controller). Parameters such as air speed, rate of climb, and rate of decent all use calculus to control them.
    Here are a couple videos to help explain it if your interested, don't feel bad if you don't understand it at first it takes alot of schooling to cover all the material, I'm an operating engineer 4th class (stationery engineer for you older people's lol). I hope this helps!
    https://youtu.be/wkfEZmsQqiA
    https://youtu.be/sFqFrmMJ-sg

  4. You should Celsius degrees too whenever talking about temperatures… it would spare people the google conversions

  5. So most of the time the pilots are using autopilot?
    What are they doing? Drinking vodka?
    I'm never going to see pilots the same way again… 😂

  6. What exactly did you guys exPLANE in this video? I don't feel like this really helps anyone understand an autopilot at all.

  7. ok ok ok autopilot won't flip your plane upside down trust me. There's always something that prevents it so a mistake shouldn't be that bad!

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