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I've watched a lot of Air Disasters episodes about crashes where pilots thought auto-pilot, auto-throttle, auto-trim were "in control" but they weren't (or vice-versa) due to some innocuous pilot action - like bumping the go around setting. See: https://en.wikipedia.org/wiki/China_Airlines_Flight_140

From a Human Factors engineering perspective, it seems that it should always be obvious who has control of the various flight controls. One simple option is to put light strips on each physical control (yoke/stick, throttle, trim) to indicate who "has control" - the pilot or the flight computer. If the throttle levers light strip is green, auto-throttle has control. If the light is off, the pilot has control of the throttle. This may seem a bit simplistic for normal aircraft operations but in times of high stress such a simple system might make a difference - preventing a crash. Lights like this would of course need to adjust to the ambient light so they're not glaring during night yet visible in bright daylight.

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  • $\begingroup$ (Re: China_Airlines_140) the copilot was manually flying the ILS when he inadvertently triggered the Go-lever, initiating a manual FD guided Go-around with auto throttle at (G/A)THR. The autopilot, which was OFF, was subsequently engaged by one of the pilots, probably the copilot who as PF, at some point reasoned that engaging the Autopilot would probably result in the safest flight path. This clashed terribly with the Captain's prevailing intent of continuing the approach which the copilot was half-heartedly carrying out. I just think these specifics shine some light on the Q at hand. $\endgroup$
    – skipper44
    Jul 28 at 20:53
  • $\begingroup$ My personal opinion is that there's sufficient Autopilot status annunciation in the jetliner cockpits of today. It is effective SOP choices (adhere to "Elements of a Stabilisd Approach") and training emphasis that'll solve the problem. Also the acceptance of 'startle factor' being a major player in these situations. $\endgroup$
    – skipper44
    Jul 28 at 21:00
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They do.

On the 737 there is a light in the button for each autopilot and next to the autothrottle switch. As well as annunciation in green text at the top-center of the Primary Flight Display (PFD).

I'll see if I can find, or take, a photo (that isn't copyrighted) to illustrate this.

The indications are there; the challenge can be getting thru the information overload so that the pilots realize what the aircraft is telling them.

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    $\begingroup$ Thanks. I've seen auto-pilot light indicators on the flight display. And the info overload you mention - lots of indicators on that display - was why I was thinking that if you put a light strip right on the yoke/stick (maybe it run around the circumference or maybe just on top), that's a more obvious indication of who's in control. Then you could look at the PFD for details. Just a thought. $\endgroup$
    – Keith Hill
    Nov 30 '20 at 22:29
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    $\begingroup$ @Keith Hill: Putting the indicators on the actual controls might cause problems for those of us who have non-transparent hands :-) And would subject them to wear &c that might cause them to fail. $\endgroup$
    – jamesqf
    Dec 1 '20 at 4:07

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