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Autopilot
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What are the procedures used regarding autopilot in an airplane? I know that some planes have autoland, but I don't think that it is enables automatically. If a p[lane were on autopilot, what would happen if everyone was incapacitated? Would the plane know to land? Would it enter a holding pattern? Would it simply continue in a straight line until it ran out of fuel?
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I don't know about commercial airliners, but on light aircraft the autopilot merely hold the plane at a steady altitude and heading- therefore it would indeed keep going in a straight line until it ran out of fuel. It would be interesting to know what would happen when you did run out of fuel- would autopilot disengage, or would it try and gold- forcing a stall!
There are some aircraft however which I'm pretty sure can land by themselves- some helicopters maybe- although I'm plucking this out of my memory.
Perhaps someone would be as kind to explain to me also how a commercial or military aircraft autopilot operates.
I typed a long answer to this question this morning - and it disappeared into the ether, causing me to say a few words the AB filter would reject! First, Ashley, yes, it would keep going in a straight line. Eventually the engine(s) would fail and the autopilot would try to maintain height (provided it didn't lose electrical power from the engine failure). The aircraft would stall, the autopilot would disconnect, and the aircraft would descend out of control and crash. That happened some years ago to a Lear jet in the US. The air conditioning was contaminated, I think.
Now, Whiskey, I am only familiar with the Boeing 757 autopilot, of the modern ones. At its heart is a computer with a database which knows the aircraft's performance, the airline's routes, and ground-based navigation aids right across the route network. The pilot will select the route and the departure runway, which allows the computer to fill in the standard published departure route. The pilot can alter any of this if necessary, and can add any height/speed constraints. He also puts in his desired cruising altitude.
After take-off Air Traffic Control will frequently vary the departure route, but eventually the pilot will be able to link to his preset routing. Up to then he has used the autopilot in its basic mode, but now he can tell it to follow the computer's demands for both route and vertical profile.
After take-off Air Traffic Control will frequently vary the departure route, but eventually the pilot will be able to link to his preset routing. Up to then he has used the autopilot in its basic mode, but now he can tell it to follow the computer's demands for both route and vertical profile.
(Continued) If everyone collapsed then, the autopilot would go on as far as it has the details entered. It would not descend, because any new height has to be set by the pilot as a way of giving the computer permission to do its thing. After the last point on the route, I think it would go on in a straight line to the end of the fuel.
Later, the pilot is able to find out and enter the landing runway, allowing the computer to build the end bit of the route. If everyone collapses then, again it would follow the route at the last height set by the pilot, and then go on into the far horizon.
Autoland is not set automatically. It is not approved on all runways anyway, and the pilot must select for the autopilot to engage and follow the ILS (Instrument Landing System), the precision aid on the ground which guides the aircraft down final approach. Once he's done that, if he collapses, the aircraft will indeed land automatically and keep itself straight. If the pilot has set auto-brakes, which he probably will have, it will stop on the runway.
The aircraft will not enter a holding pattern by itself unless the autopilot has been told to. It all depends how far along the line things are when the pilot keels over, and what he has set up.
Later, the pilot is able to find out and enter the landing runway, allowing the computer to build the end bit of the route. If everyone collapses then, again it would follow the route at the last height set by the pilot, and then go on into the far horizon.
Autoland is not set automatically. It is not approved on all runways anyway, and the pilot must select for the autopilot to engage and follow the ILS (Instrument Landing System), the precision aid on the ground which guides the aircraft down final approach. Once he's done that, if he collapses, the aircraft will indeed land automatically and keep itself straight. If the pilot has set auto-brakes, which he probably will have, it will stop on the runway.
The aircraft will not enter a holding pattern by itself unless the autopilot has been told to. It all depends how far along the line things are when the pilot keels over, and what he has set up.
Ashley, I didn't answer the last part of your question. The autopilot can be used in basic mode (steer this course, maintain this height, hold this speed, climb at this speed etc.) or it can be told to follow the computer. The computer knows the aircraft performance, it knows the airline's routes and it knows the ground-based navigation aids. The aircraft has inertial navigation - you tell it where it is to start, and it keeps track of any movement from that point - which it updates automatically by searching out two ground-based aids to give a 90-degree cut in ranges. The computer can work out the wind and its effect and calculate where to start descending to meet height and speed requirements lower down.
All this leaves the pilot sitting open-mouthed, watching in amazement! He (or she) can, of course, override the computer's suggestions and revert to basic autopilot functions, or disconnect the thing completely and fly by hand. It's a great servant, but it can never be allowed to be the master.
Autoland comes in when visibility is too bad for a visual landing, but a pilot can see enough to ensure he's landing on a runway. Three autopilot channels fly the ILS, staring suspiciously at each other to confirm that they all do the same thing. At set heights above the ground it first locks the attitude, then executes a flare (raising the nose) for landing and closes the throttles. It then keeps straight along the runway on the ILS beam.
That's how it works, but autoland is only done in bad weather or for practice. Usually the pilot likes to demonstrate and hone his skill with what he hopes will be a "greaser".
End of multi-part answer!
All this leaves the pilot sitting open-mouthed, watching in amazement! He (or she) can, of course, override the computer's suggestions and revert to basic autopilot functions, or disconnect the thing completely and fly by hand. It's a great servant, but it can never be allowed to be the master.
Autoland comes in when visibility is too bad for a visual landing, but a pilot can see enough to ensure he's landing on a runway. Three autopilot channels fly the ILS, staring suspiciously at each other to confirm that they all do the same thing. At set heights above the ground it first locks the attitude, then executes a flare (raising the nose) for landing and closes the throttles. It then keeps straight along the runway on the ILS beam.
That's how it works, but autoland is only done in bad weather or for practice. Usually the pilot likes to demonstrate and hone his skill with what he hopes will be a "greaser".
End of multi-part answer!
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