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Take GFC700 for example, when autopilot (or flight director) engaged, the lateral mode falls into

  • ROL, HDG, GPS, VOR, VAPP, LOC, BC, ...

and the vertical model has to fall into

  • PIT, ALT, FLC, VS, VPATH, GS, GP, ...

When disengaged (or temporarily by CWS), a pilot has to hand-fly both axes.

I am wondering if this is universal across all autopilot systems. Is there any autopilot that I may engage one axis and hand-flying the other. e.g. The autopilot only holds altitude and I may roll the yoke without any counter pressure. Are there regulations or purely from technical consideration?

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    $\begingroup$ The autopilot (Genesys System 50) in my C-177 can altitude hold while allowing the pilot to control the roll axis. Each axis can be engaged independent of each other. $\endgroup$ – Ron Beyer Apr 21 '16 at 13:12
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Some autopilots found on advanced aircraft can be engaged on selected axis only, for example Boeing 737, 747-200 & MD-11. There are three autopilot indicators on the Boeing autopilots: auto throttle, roll and pitch. Each can be in a different mode.

Here a Boeing 737's autopilot roll mode is set to Heading Select (HDG SEL) while the Pitch is flown manually (CWS P):

enter image description here

The pilot can pull or push the yoke, and the autopilot will roll the aircraft automatically. If the pilot steer the yoke left or right, the roll mode will change to CWS R.

In this image below, the pilot is manually Rolling the aircraft (CWS R), but the autopilot pitch mode is set to Vertical Speed mode. enter image description here

Later models, such as the Boeing 777, does not have this feature - both pitch and roll modes must be engaged together.

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  • $\begingroup$ @MikeSowsun not really. All Boeing 737 models can. 747-100, 747-200, 767-200 can (not sure about 757). 747-400 & 777 cannot. $\endgroup$ – kevin Apr 21 '16 at 18:17
  • $\begingroup$ You are correct. I forgot about Control Wheel Steering and I completely forgot that you can separate roll and pitch if the aircraft has CWS. From my experience, I seem to recall some 767-200's had it but no one ever used it. None of the 767-300's and 777's have CWS. $\endgroup$ – Mike Sowsun Apr 21 '16 at 18:28
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On some autopilots it is clearly possible to disconnect each axis separately as evidenced by the accident of Aeroflot flight 593. On others, including the ones used on later Airbus models (A320+; the accident was A310), it is not.

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