Re: Airbus safety (was Re: TWAs Status)

From:         rdd@cactus.org (Robert Dorsett)
Date:         10 Dec 92 16:07:03 PST
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In article <1992Dec01.173212.27936@news.mentorg.com> philip@mentorg.com (Philip Peake) writes:
>
>It wasn't unintentional - it was a deliberately (contrived) example.
>The arguments I have heard so far seem to say that just because its always
>been done that way, it always should be - aircraft design has changed a LOT
>since the stick control was introduced - maybe this is no longer the
>correct control mechanisim ?

Transport aircraft design hasn't changed much at all in the last 30 years.  
We fine-tune various features, change the aspect ratio, develop better drag 
profiles, better powerplants, occasionally build a better, lighter system.  
Certainly improved manufacturing techniques.  But the *engineering* discipline 
is so WELL defined that if you give three manufacturers the task of developing 
three different airplanes for the same mission profile, you'll now come up 
with almost identical airplanes.   It is a discipline so evolved that we can 
come up with physical implementations which can match design performance 
objectives to within a percentage point.  

This is not the result of "wild-catting," or breaking the rules: it's the 
result of decades of working over the same problem, developing a very 
intimate understanding of this particular type of development problem.  We
should expect that the same considerations must be applied to how the 
pilots control the airplane.  The "old" model may not be the best available,
but it's well-understood, and is likely preferable to any "replacement"
we are likely to produce with current technology.


>If you are against the idea of insulating the pilot, maybe we should
>remove servo brakes and power steering from cars too ?

The pilot IS in the loop.  You can complain about that, and try to eliminate
that, if you want to.  However, since he IS in the loop, the unique feedback
requirements needed to let him do his job require a more interactive environ-
ment than either contemporary glass cockpits *or*, in this case, the A320
sidestick, provide.

Christopher Davis already addressed your point in his reply: *hydraulics*
is the equivalent of power steering, not FBW control.  However, note that 
we've been providing completely artificial feel to go along with this, for 
the past thirty years.  Yet all of a sudden, on the pretext that the "FBW"
in their airplane mandates it, Airbus, which is in the business of selling 
technology, cavalierly introduces a control device which:

	1.  Has no interconnect between the pilots.
	2.  Has no active feedback.
	3.  Utilizes artificial control laws in the normal and alternate 
            flight modes.

I suggest that the issue has NOTHING to do with technological "advantages"
human requirements: it is completely marketing-driven.  


>|> In essence, my point is that standards don't exist because of happenstance.
>|> They exist because it makes life easier for everyone.  This is particularly
>|> important when human lives are at stake.
>
>Standards are also perpetuated by vested interests,

Yeah, that powerful yoke-manufacturer lobby.  The bastards.  Just because
they won't retool to build sidesticks, they gotta ruin it for the rest of
us. :-)

Seriously, this is a tremendously conservative industry.  What isn't broken,
doesn't get fixed.  However, when a better mouse-trap is invented, it is
almost always adopted, universally.  The fact that no other manufacturer
is rushing to repeat Airbus' example suggests the arbitrariness of the
use of the sidesticks: if there were even minor operational or material
advantages in using them (and modified control laws) as interfaces to the
EFCS, you could bet your last dollar every other manufacturer would be doing 
so, not least as the result of airline demand.   We don't see that.


> even when better ideas
>ar around. 

This isn't one of them.  We aren't operating in a vacuum: NASA, as one example,
has been running a lot of research (over, and over) over the last 20 years, 
addressing precisely these issues: the Airbus implementation is arguably on
the weaker of a variety of choices available.


>If all new pilots were taught nothing but the side stick,
>how long would the old arangementy last - and if the old arangement

Why should pilots be taught nothing but a unique, *proprietary* side-stick 
design that no pilot had any experience with before four years ago, and which 
is only one of a variety of other possible designs?  

You imply that the sidestick's just a yoke wrapped up in a little handle.  It 
isn't: the issue's a lot more complex, and, within that simple interface, 
there are *many* ways to proceed.  The certification authorities, you will 
note, have not codified mandatory control qualities of this interface (and 
WON'T): thus, in a worst-case, we could have Airbus running its stick (+ 
control laws), Boeing running its own, MDC running its own, etc.


>is so wonderful, why do military fighter aircraft, where tight control
>by the pilot os ESSENTIAL use side stick controls ?

Not all do: several continue to use center-sticks.  In either case, the
issue is in large degree driven by the need to effectively control
the aircraft at high g's--but even then, it's a significantly different 
design than that used in the A320.

I would also note that in fighter aircraft, there isn't the issue of 
two-pilot "peers" having to quickly and instinctively figure out who is
flying the airplane.  On the A320, there is no interconnect between the
sidesticks: the captain can command a full-left in an emergency evasive
maneuver, the F/O full-right, and the net result will be an algebraically
added "zero."  


>The problem is the PILOTS, not the design

Here we flip to cockpit integration, not sidesticks.

The problem is a design philosophy which is unwilling to accomodate the human
element.  I also see a great deal of "stick it to the pilots" going on: a 
number of proponents of pilot-isolation don't even bother to cite alleged 
economic or safety benefits, anymore: the pilot-isolation increasingly appears
to be an engineering-driven goal in itself. 

The Airbus approach has gone too far.  Thankfully, however, it seems to be
on its way out: new designs, such as the 777, are more sophisticated,
yet have more conventional and interactive interfaces.  And the research 
community is coming squarely on the side of more interactive, appropriate 
feedback.  New designs will be more human-factors-driven, not engineering-
driven.  And, with luck, we'll see a return to the *evolutionary* application 
of high technology, rather than the *revolutionary* application of the same.

And who knows, in 20 years, when we have enough underlying experience and
research under our belts, we can try a *standardized* alternate interface.


BTW, and for the record, I *like* the idea of sidesticks: for no other reason
than to be able to see the entire instrument panel, unencumbered.  I simply
don't like this particular implementation, and have concerns about the 
human requirements any sidestick design could introduce.





>Philip


---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd