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Plane Answers: When do pilots use the autopilot?
My question concerns the autopilot. During the course of a flight how often is it used? Are there times where it can not be used because of heavy turbulence and other weather phenomenon?
Great question, Justin.
First, I should describe the autopilot system in a jet. It's essentially a device that a pilot will program to climb, descend or hold an altitude while following a specified route of flight. The system also includes autothrottles, which maintain the speed of the airplane in cruise and adjust the power automatically for climbs and descents.
The autopilot in an airliner is really analogous to the cruise control feature in your car. Just as you wouldn't use your cruise control when leaving your driveway, we never use the autopilot for takeoff. In fact, there's a limitation on the 757 and 767 that doesn't allow the autopilot to be used below 1000 feet, after takeoff. Above that and it's the flying pilot's option if they'd like to use it.
I usually prefer to 'hand-fly' the airplane to about 18,000 feet before turning on the autopilot. We generally don't hand-fly after leveling as it becomes rather tedious after a while. And one sudden push of the yoke would cause the passengers to float toward the ceiling. Some airlines charge for this weightless experience, but our passengers tend to prefer a straight and level ride.
Some pilots will bring the autopilot on right after takeoff, and again, that's their option. When I first started flying commercially, we tooled around in a commuter airplane that didn't have an autopilot, so I sometimes crave a little stick and rudder time.
But there are times when the other pilot is busy making the PA or talking on the radio and you need to take a closer look at the weather radar up ahead or you're trying to decide what the best cruise altitude will be. In these cases, the moment you start getting busy, it's a good idea to get the autopilot on to reduce the workload for you and the non-flying pilot.
Some airplanes (I'm looking at you, 737-800) have a tendency to hunt or oscillate during climbs and especially descents. The airplane will go from 500 feet per minute down to 2500 feet per minute and back again before eventually stabilizing. This makes for a rather uncomfortable ride in the back and it's probably why many 737 pilots prefer to hand-fly most of the climbs and descents.
The autopilot can handle a significant amount of turbulence. There's no requirement to turn it off during the bumps, but if you feel it's not doing an effective job at holding an altitude or airspeed, then you're encouraged to 'click it off' using a thumb activated button on the control yoke and fly the airplane yourself.
There are times when the weather is below a certain level of visibility where airplanes must be flown using the autopilot. If the visibility is less than 1800 feet (550 meters) and the airport has the capability, we will still be able to land using the autopilot. In fact, the 757, 767 and the 777 can be flown down to a visibility of 300 feet (75 meters) with touchdown occurring without actually seeing the runway.
When we print out the current weather and it reports a low enough visibility to require an autoland you can just about read the disappointment on the flying pilot's face. Hand-flying the landing is the icing on the cake for pilots, and to fly all the way across the country only to be denied a landing takes some of the fun out of coming to work.
These autolandings (known as Cat III approaches in pilot-speak) also require more setup to fly, and a significant amount of monitoring to be sure the airplane is tracking correctly. We don't have to fly them very often--I think I only had two autolandings last year.
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