I’m not sure how big the difference is on auto-pilot between marinecrafts and aircrafts, so apologies for including both in the question.
It sounds like it makes the ship/plane run itself, without any need for a person to control it, but how could that be the case? These machinaries sound like they should be steered and watched at all times. It sounds dangerous to leave them on an “auto” mode.
Is there an in-depth explaination behind what auto-pilot does? What are its limits? Is it possible to go wrong in some way, and if so, does it have some kind of alarm?
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Well, first off, yes to all of your concerns. Autopilot does need to be constantly monitored. As far as an alarm if it goes wrong, that’s very airplane dependent. The plane I fly for work will trip an alarm if it gets more than 200 feet off my assigned altitude, but if for whatever reason I’m on the wrong ground track I would never know unless I’m paying attention. Autopilots work by tapping into your avionics system to pull things like altitude, attitude, and heading and then use a series of servos attached to your flight control surfaces, or just manipulate a fly by wire system, to make the surface move until those feedbacks from the avionics are what the pilot set.
On my boat, the autopilot will hold a constant compass heading. So let’s say you want to go north, you point the boat that direction and turn it on and the boat will keep going that way. If you want to turn you can press +/- 1 or 10 and the boat will turn to the new heading. It won’t avoid other boats, it won’t navigate around obstacles. It just goes straight, you need to pay attention and disable it when maneuvers are required. Does everybody pay as much attention as they should? Of course not.
I fly airliners. An autopilot in one pretty much says “I will make the plane follow the path you say at the speed you say.” Ensuring that the correct path is set and is being followed is a major part of the job. An autopilot relieves the pilot of the need to focus on hand/eye coordination, which frees up a lot of brainpower for actually planning for a safe flight.
“Autopilot” is a vague term, so it might mean something different in different types of vehicles.
Computers small enough to be useful in airplanes have probably existed since the 70s. (I’m not sure about details, I’m not an expert, but I don’t think it matters, this is ELI5.) Altitude meters and compasses are based on technology that’s hundreds of years old. You could hook a computer up to those and the plane’s guidance systems and give it commands like “if the plan drops below 10,000 feet, make it go up. If it rises above 12,000 feet, make it go down. If it varies more than 10 degrees north or south of its current direction, make it go the other way.” That’s a basic autopilot. Can it land the plane safely or deal with a complex situation like a storm? No, but it’ll keep the plane going straight long enough for the copilot to take over if the pilot had a heart attack or something like that. A modern autopilot might be able to land a plane if necessary but it’s still just an emergency backup, not the main plan.
Autopilots designed to work without a human around at all have to be very advanced and are only really used when there’s no other option, like a Mars rover.
Aviation is my playground so I’ll stick to that explanation: Your assumption is pretty much correct, that’s what it does. It can be as basic as a “wings level” function in small airplanes, which just looks at a gyroscope to make sure the wings are level and tweaks controls to correct if it isn’t, to 3-dimensional path following to prevent pilots on long flights from having to manually hold headings and altitudes and flightplans for long periods of time.
The airplane is absolutely watched at all times, there always must be a pilot in there, but they don’t have to physically sit there constantly and manually maintaining their path. Arguably the computers can handle things with far more precision than a physical pilot could, especially when you start getting into turbulence and the direction/altitude changes are random and unexpected.
The autopilot in a commercial aircraft needs an absolute minimum amount of things to work properly, and if it doesn’t have those, it will disconnect, usually with an alarm to notify the pilots (if not audible, then flashing lights and such). Aircraft are also build so very redundantly — there’s multiple airspeed/altitude sensors, multiple autopilot and flight guidance computers. I’ve been on an aircraft that had an issue with only one computer — but even then it didn’t disconnect the autopilot, it just notified the pilots ‘Hey, left computer failed’ and it automatically switched to the right computer and kept going.
It’s a pretty advanced system, and differs widely on what exactly it does and how it works between Boeing, Airbus, Embraer, etc., there’s certainly more in-depth explanations out there. At the end of the day, it’s just doing what the pilots would — comparing where they are to where they need to be and making corrections to achieve that.
I’m from a marine background.
The autopilot on a shop in its most simple form is controlling the heading. You (the Officer Of the Watch) will input the desired heading – say 045, and the autopilot will use the input from the compass to control the rudder and steer 045.
Other options include the ability to counter the effect of wind and tide – you tell it what course you want to steer and it works out what direction the head needs to point. Say you want to steer that same 045, but there’s a bit of a wind – the autopilot calculates that it needs to steer 040 to maintain a course over the ground of 045.
With the introduction of electronic charts, it’s even possible to tell the autopilot to follow a specific course. It will even automatically turn the ship onto a new heading. You can programme in specific rates of turn or maximum rudder angles or even a specific turn radius for the autopilot to follow.
The autopilot doesn’t monitor traffic or weather, so having an OOW on the bridge (as a bare minimum) is essential. Having additional personnel is desirable. The company I worked for generally had 2 lookouts (both also qualified helmsmen) and an OOW on the bridge. During the day, the Captain and Navigator would be on and off the bridge or the charthouse, and were always easy to find if you needed help or advice.
If you think of a big ship there are lots of people on the bridge who control the ship. You have the helmsman controlling the rudder, the machinist controlling the engines, left and right watchmen to look out for traffic, navigator to make sure the ship is going the right way, etc. The captain is not actually touching any of the controls but are just monitoring everything and making decisions when needed. On a smaller boat a single person might do several of these jobs at the same time but they are still jobs that needs to be done by someone.
An autopilot is a mechanism which is able to automatically do one or more of these tasks. Specifically the helmsman. The job of a helmsman is to look at a compass and adjust the rudder so the compass reads what they are ordered to. The helmsman does not even have to be on the bridge and a lot of ships actually do have the helmsman on a lower deck so they have less visibility. So it is quite easy to replace them with a mechanical or electrical device. On larger ships you can eliminate a crew member and on smaller boats you give more time for the crew to do other tasks, such as looking out for traffic and monitoring the boat.
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