From: ggr@koonda.acci.com.au (Greg Rose)
Subject: Re: Coffe cups in the cockpit (Re: A320 yarns)
Organization: Australian Computing and Communications Institute
Date: Thu, 23 Jul 1992 06:57:47 GMT

In article <5807.2a6d92a2@hayes.com> bcoleman@hayes.com (Bill Coleman) writes:
>In article <1992Jul21.133757.17508@bony1.bony.com>, richieb@bony1.bony.com (Richard Bielak) writes:
>How would pilots react to a system where a "ghost-like" influence keeps
>moving levers on them? For example, the pilot chooses the reduce the
>throttle levers. The flight system, detecting a possible impending
>stall condition (or something), moves them back up. The pilot, seeing that
>the computer has moved the levels back up, again pulls them down. Soon
>we have a battle of wits in which the pilot stops flying the plane 
>because he is fighting with the computer. 

Are you seriously trying to say that it is better that the engines get
spooled up without moving the levers? In this case, the pilot CAN'T
pull back on the levers because they are already at the rear end of
travel...

This also sounds a lot worse when the situation is reversed -- the
pilot commands more power and the autothrottle decides to pull it off.
If the lever is still at the front of travel, and the mountain is
looming...

Autopilots are designed specifically so that the pilot can overpower
any commands they issue, and other autothrottle systems are too. That
is, if the pilot pulls back and the autothrottle pushes forward, the
pilot *does* have the option of just pulling back and HOLDING it
there. Tough luck if the lever isn't moved.

Anecdote: I spent an entire hour in a C182RG trying to get the
landings right once, and didn't discover till back on the ground what
the problem was. I was switching the autopilot on and off with the
on-off switch! The problem is that this switch was extremely close to
the mixture and throttle knobs, and on the first circuit I managed to turn it
on again, and had to fight it all the way. Now I turn them off by
pulling out the turning knob thing, and even the circuit breaker if I
know I won't be using it. At least I could successfully fight it. To
this day I can't understand how I fought it for so long without
realising what was happenning. But I was very low time, and had never
even had an autopilot before. The instructor didn't notice it
either...
>
>As someone who designs user interface as part of his job, it isn't easy to
>say which is the better system: that which introduces indirect feedback vs
>physical feedback. The only way to descern the truth in these cases is to
>perform user testing. And even that may not single out a "best" solution.
>
>-- 
>Bill Coleman, AA4LR                ! CIS: 76067,2327    AppleLink: D1958
>Principal Software Engineer        ! Packet Radio: AA4LR @ W4QO
>Hayes Microcomputer Products, Inc. ! UUCP: uunet!hayes!bcoleman
>POB 105203 Atlanta, GA 30348 USA   ! Internet: bcoleman%hayes@uunet.uu.net
>Disclaimer: "My employer doesn't pay me to have opinions."
>Quote: "The same light shines on vineyards that makes deserts." -Steve Hackett.
>


--
Greg Rose                 Australian Computing and Communications Institute
ggr@acci.com.au                                              +61 3 282 2532
Newsgroups: rec.aviation