Re: A320 and a bit on the bloody DC-10 (was: cockpit visit)

From:         Robert Dorsett <rdd@cactus.org>
Date:         29 Jun 93 09:22:52 PDT
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In article  <airliners.1993.480@ohare.Chicago.COM> spagiola@frinext.stanford.edu (Stefano Pagiola) once wrote:

>Robert Dorsett <rdd@cactus.org> writes
>> 1.  The A320 should be compared to aircraft with similar avionics
>> and operating philosophies: [747-400, 757, 767, A300-600, A310]
>
>I'm not sure what `similar' means in this context but it seems to me  
>that the A320 isn't really comparable to any of these designs.  Yes,  
>they all have `glass' cockpits and digital avionics (as do the MD-88,  
>MD-11, and Fokker 100), but none of the other designs is FBW, and  
>none attempts to give the kind of `protection from errors' that the  
>A320 attempts

I'll try to word this carefully, since there are a number of nuances at
play.  The A320 is rather aggressively compared to the first-generation-glass 
airplanes (757, A310) by *Airbus*, not me.  They're proud of the high-tech,
but use this to try to silence critics that view the airplane as a radical
departure.

In particular, the operational philosophy is a derivative of the A310.  The 
major environmental changes are the use of fully integrated flight displays 
(doing away with electromechanical instrumentation), and a full-time 
electronic flight control system (FBW).  Further adaptations to the flight 
management & guidance system (FMGS) operational philosophy have been made to 
take advantage of various features offered by the EFCS.  What results is a 
relatively simplified "management" environment (or, at least, fewer controls).

Now, *I* think that the various changes are pretty radical departures, when
considered in totality, and I doubt you can find too many experts that view
the A320 as a 1981-vintage product, but like I said, Airbus (these days, at 
least) prefers to point out the overt similarities with other, pre-existing
systems.  Electronically and physically, there are certainly similarities.


> (what Bob Dorsett called the `cocoon' approach). 

I believe the credit should go to E. Wiener and R. Curry, who, as far
as I know, first outlined this concept in detail in a 1980 document.


> The  
>A320 will be comparable to the 777, when it comes out.  I fully  
>expect the 777 to compare favorably, if only because Boeing could  
>draw on 5 years of A320 experience.   

I am not sure that's the case.  *Electronically*, the 777 is a significantly
different, more advanced airplane, and really does push new frontiers.  The 
cockpit environment itself will have more in common with the 747-400 than 
the A320, however.  

When it comes to nuts and bolts, when I talk about airplanes of the same 
vintage, I'm mainly referring to the technological goals and capabilities, 
not *necessarily* the specifics of design.  Somewhat like comparing a Russian 
and American warship ca. 1965: there will be no doubt they're of the same 
vintage, but there will also be definite differences in design approaches.


>Rephrase that a little and it won't seem so bad: Airbus believed (and  
>probably still does) that its interface approach was the future.

I can't really see that.  It's a highly proprietary, closed system.  They
do not license it, it isn't in the public domain.  The source code for all
the software is a jealously guarded secret, one which not even the author-
ities are privy to.  The various schema are the byproduct of marketing product 
definition, and changed throughout the airplanes' development.  Even keeping
an open mind, I can't really find anything in the literature which suggests 
they expect or would desire that others follow their example: only that what 
they're doing is *better* than what others have *done*.  It's a defensive
posture (rightfully so).

I WOULD agree that Airbus CERTAINLY believes that its interface approach is 
*its* future. :-)


>debate that can be undertaken a priori.  You have to try it to see.   
>I think Airbus deserves praise for attempting the transition to a new  
>way of flying.

Given the academic research, which really doesn't support the design 
decisions, I can't help but think that this is "technology for technology's 
sake," which is often counter-productive to safety.  Once again, my battle-
cry: evolution, not revolution!


>> If you are aware of the
>> problem, you can work around it; if not, you can fall victim to
>> the environment and make a mistake that kills you and your
>> passengers.
>
>As I said, I think most A320 pilots are, at this point, aware of the  
>potential pitfalls and treat them with respect.  That's why I don't  
>lose any sleep over flying on A320s.  But I hope it doesn't take a  
>periodic crash to keep people watchful.

Take the following with a grain of salt: I mention it both for the moral
and a slightly different take of the mechanics of the crash (as opposed
to how it's generally treated in the media--but it's generally supported
by the accident report, p. 35, subsection 1.17.3).  Also consider that
the man really dislikes the DC-10.

I had an interesting conversation with a maintenance type a few weeks ago.
We were discussing the DC-10.  He was kind of down on pilots, and mentioned
a DC-10 pilot who was real proud of his airplane.  They got to talking about
the O'Hare crash, when the pilot got offended and insisted that the slat-
retraction problem had been "fixed."  "How?" he was asked.  "Well, changes to 
the hydraulics system were made such that you couldn't lose your slats if 
you lost hydraulic pressure."  Fine, my friend said, but that wasn't the cause 
of the crash.  Yes, they lost one (maybe two) hydraulic systems, but the 
problem was that the slats were moved and held in place by *cables*, which 
are driven by "hydraulic motors" in the middle of the main fuselage.  In 
fact, a common actuator is used for both the left and right slats.  When 
the engine tore off, it took out the #1 system, but more importantly, it
took out the cables, so there weren't opposing forces, and the slats simply 
retracted.  

The "real" fix to the problem was that the DC-10 takeoff profile was *really* 
shallowed-out, so that appropriate airspeed margins were kept in case of a 
similar catastrophic engine failure.  But *this* pilot had a mystical faith 
in a non-existent "hardware solution."  Kind of like the expectation a lot
of us had that the MD-11 MUST have been changed significantly, SOMEHOW... 
but really wasn't. :-)

So the moral of the story, I guess, is that knowledge of the problem isn't
always indication that the problem (or the nature of its work-around) is
really understood.  I'll concede that this is kind of apples and oranges, and 
thus far, pilots have been surprisingly good at working around the problems 
posed by glass (maybe it does have a benefit--at least in most glassy 
airplanes, it keeps 'em on their toes? :-))





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