So, how does the modern autopilot of a commercial airliner work? Well, first, let's change what you call it because it is much more accurate to call it an "autoflight system" because it's often times a combination of systems that generate the desired end result. In a modern airliner almost anything that controls the movement of the airplane can be manipulated by an autoflight system....right up to the brakes once you hit the runway. What about speed and the throttles that control the engines? Autothrottles! Can they know what route to fly? Absolutely! The autoflight systems are fully integrated with the navigation systems. "Can planes land themselves", you ask? The answer is: sort of. I'll explain as we go along.
So by now, I probably haven't convinced you that the pilots are necessary. Well, let me tell you what autoflight systems haven't been developed yet: good judgement, analysis, decision making and experience systems. Autoflight systems are designed to follow certain rules and when those rules go out the window because of weather or some abnormal situation, you want to have the best pilots you can possibly have.
Let's look at a hypothetical flight from Boston, MA to Tampa, FL. The weather is predicted to be gorgeous all the way. Not a cloud in the sky. Before taxi, your pilots have your route of flight programmed into the Flight Management System (FMS) which is a little onboard computer that performs a variety of tasks. Fast forward to takeoff. You're lined up on the runway. Your pilots physically advance the throttles and pull back on the control stick or yoke and up into the air you go. As soon as the plane is climbing, they pull a lever to bring the landing gear up. Moments later, up come the flaps, slats and anything else used for takeoff. The airplane is now "clean" and climbing. No mention of the autoflight system yet. The climb continues with your pilots "hand flying" the plane....all the way up to 29,000 feet where, federal regulations dictate they must turn on the autoflight system. Why? Do they not have the skill to fly over 29,000 feet!!? Of course they do! In an effort to pack as many planes in the sky as possible, the FAA designed a way to stack planes on top of one another more closely and that requires the use of an autoflight that can hold a very precise altitude. But, get up to 41,000 feet where most modern airliners don't fly and you can again hand fly. So, on goes the autoflight system and your pilots "sit back" and "let George fly".
"George" dutifully flies the plane until you get to New York City. In that busy airspace, Air Traffic Control issues a series of climbs, turns, descents and speed changes to your pilots (vectors), each of which require the pilot to tell the autoflight systems what to do in response.
|No, autopilots don't look like this!|
OK. We get past New York and all is great with the autoflight systems flying and your pilots doing some housekeeping work, monitoring systems and maybe reviewing emergency procedures. Until you get to Georgia. There, your pilots find that some of those famous Florida thunderstorms have popped up are working their way into Tampa from the Gulf of Mexico. Remember the forecast that said clear skies? Well, have you ever seen an accurate weather forecast? I thought so.
Your pilots start to closely work the onboard weather radar and get reports from other pilots (Pilot Reports or PIREPs) and ATC to find the most appropriate route around the storms. They then start working with ATC to negotiate that route. The line of powerful storms is pretty well developed so it's going to require some careful planing to navigate around. Your descent begins and you notice it's getting pretty cloudy outside. You are now fully in the clouds and what sounds like rain starts hitting the plane. Only it's -10 degrees outside and that rain instantly freezes when it hits the plane. Your pilots turn on the ice protection systems and turn off the autoflight systems. Your pilots are now hand flying the plane. Why no more autoflight system? Because of how unpredictable ice is. Ice is one of those things that throws all the autoflight "rules" out the window because it doesn't know how the plane flies loaded with 1,000lbs of ice on its surfaces. Your pilots can figure that out pretty quickly and make the appropriate adjustments to the plane to keep you flying safely.
You continue the descent into Tampa and when the temperature goes above freezing, all the ice flies off the plane. Because of the constant turning by your pilots who are working very hard and monitoring the weather radar, you stay out of the storms and hit no turbulence. However, because of the storms passing thru, Tampa airport is now completely fogged in. Uh oh, no way to land now, right? Wrong. In steps your pilots to configure the "autoland" system. Now, this isn't a system where your pilots push a big "LAND" button, sit back and fall asleep and wake up and say "oh look, we're on the ground". First, it requires the plane and the airport to be equipped with the right systems to support an autoland approach. Your pilots even require special training and certification to be able to fly an autoland approach. Imagine that - extra training for something that everyone thinks requires less pilot skill! Autoland requires careful inputs by the pilots to get the plane to maneuver itself right onto the runway where the "autobrakes" kick in. Depending on the surface conditions and length of the runway, your pilot configures the autobrakes to stop the plane with a certain amount of force. Again - not something the plane will figure out by itself especially since pilots rely on other pilots who have landed before them to give a detailed description of the conditions on the runway.
So the next time you think there's no need for your pilots anymore, think of how comfortable you'd be with only "George" (the autoflight system) doing all the flying when you encounter thunderstorms, ice and other nasty things that mother nature can throw at your airplane. This is just one small example but I could go on for days about other situations where the autoflight systems just won't cut it and well trained pilots will.
Knowing the rigorous training programs the airlines put their pilots through, I for one will take a couple of highly trained pilots any day of the week.