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tsa737

autopilot question

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On a jet without a flight management computer, what does the autopilot control?

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The autopilot, when switched on, controls the airplane... ailerons, elevator, rudder.

 

Possibly throttle, depending on the airplane.

 

If you have an FMS, it can provide inputs to the autopilot, but the autopilot steers the airplane.

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Even with a plane with an FMC, the autopilot does not need it to control.  LNAV is Lateral Navigation, which is the flight plan entered into the FMC, however you can manually set a heading and fly without it.. like back in the "olden days" when they used INS and VOR navigation.

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It’s not so much what the autopilot controls but what controls the autopilot. The flight director (the bars or crosshairs on the primary flight display indicating the intended path) is either driven by basic commands like HDG SEL, VOR LOC, V/S, ALT or by higher level commands of an FMS. The autopilot, in turn, follows the commands of the flight director much the same way the pilot would if he were flying under manual control. The benefit of having an FMS drive the flight director is that it can take more factors into consideration and adjust multiple flight parameters continuously throughout the flight. Without the FMS, crews would need to set the proper thrust amount at takeoff, vertical speed/airspeed during climb, multiple heading changes over the length of the flight, tuning multiple VORs, and then adjust vertical speed/airspeed again during descent… the FMS can direct all these parameters using the info provided about the flight plan, plane configuration, and environmental conditions and achieve the most efficient flight path or thrust level at any given moment, from takeoff to landing. By tying together all these functions into one automated computer system, the workload on crews is greatly decreased. Whether or not that work load reduction leads to a safer flight can be (and is often) debated, but workload reduction was the primary goal of instituting computerized flight management systems.  

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Thank you Beechpapa. Very informative.

 

  !!!!!!

 

No problem. I always found the FMS to be a fascinating subject.

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Thank you. I'm very familiar with the FMS, I was just wondering if the autopilot in a DC-9 controls the flight plan, that is to say, the waypoints

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Thank you. I'm very familiar with the FMS, I was just wondering if the autopilot in a DC-9 controls the flight plan, that is to say, the waypoints

 

I believe the simple answer is: No.

 

No autopilot controls a flightplan, it follows inputs from the flight director, which in turn gets inputs from manual controls, nav radios, Gyro units, GPS units , FMS, etc depending on the avionics installed in the aircraft.

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