Re: Airbus safety

From:         Robert Dorsett <rdd@rascal.ics.utexas.edu>
Date:         13 Dec 92 12:14:14 PST
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In article <airliners.1992.148@ohare.Chicago.COM> philip@rainbow.mentorg.com 
(Philip Peake) writes:

> |> >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 are avoiding the question - read it again, the operative word is "if".
> I really don't think that a side-stick qualifies as "*proprietary*" does it ?

Not if one views it merely as a "substitute" interface.  The A320 sidestick
is not a "parallel" substitute: it's a replacement design concept. 
Besides the ergonomics, which raise their own issues, and which, as you note,
would be duplicated by just about any manufacturer attempting to develop its 
own, it's what it DOES that determines its uniqueness.

For instance, some pilots seem to like a specific feature: pull straight 
back on the stick to activate the TOGA mode.  A few pilots *prefer* this to 
the regular stick-throttle combination one would instinctively use in such 
modes, despite the fact that if you did this on a "real" airplane, you'd
soon stall it.

So, should Boeing adopt this paradigm, if it goes to a sidestick design?  This 
is one of MANY unique characteristics that solely characterize *Airbus'* 
sidestick.  There are no official standards; no "sidestick specification" is
in the public record.  The software is jealously guarded.  If Boeing decides 
to duplicate the stick concept, should it do so by examining operating manuals 
and hope it catches most of the idiosyncrasies?  Or should it run away with 
the *idea*, and improve on it, offering its own version?  

In many ways, what I fear is what happens with "consumer software."  Take a 
word processor, for instance: a simple idea, with *many* variations.  Different
companies have different ways of looking at the same problem: indeed, none of
them may be a "best" solution.  I don't think this comparison is off base: 
Airbus has REPEATEDLY and PUBLICLY stated that its technology is its selling 
point: to distinguish itself from Boeing, it MUST continue to do its own 
thing.  

The problem is that software is so much more easily changed than hardware, 
that we could very well start an avionics equivalent of "creeping featurism."
Changing the way a stick behaves can be done in just one firmware update: no 
need to develop new tooling, production techniques, train assemblers and
maintenance engineers, offer the retrofit during the next C check, etc.  
Just the internal development process, which one can assume is faster and 
cheaper than for hardware.  But, by virtue of this ease, it's also more 
*unstable* than hardware-based solutions.

Evidence to support this position?  The A320 has about 4M of code.  The A330/
A340, 10M.  It's happening as we speak...  

Do any Honeywell people reading know how big the 777 EFCS is going to be?


> Changing the subject slightly, the world's safest aircraft (Concorde) uses
> technology which was new, and for a time unacceptable to various licensing
> authorities - it didn't have a MECHANICAL link between the stick and the 
> control
> surfaces - only hydraulic. There was *much* concern over this, and lots of
> reaction from the pilots and safety mob - they almost won, and the Concorde 
> almost had to be produced with a mechanical linkage, which no FULL CREW would 
> be able to budge one mm if they all tried together - in fact, the linkages 
> would probably have failed, before it would have been possible to move a 
> control surface, when moving at full speed.

I think you're overstating the situation considerably.  Like they'd build
an unflyable mock-up?   :-)

In the late 1950's and 1960's, there was considerable controversy over 
hydraulics, much of it justified: there was a low confidence level among 
pilots with conventional hydraulic systems.  O-ring seals tended to break 
down, and the systems were rather "leaky"; many a flight had at least a 
partial failure.  Pilots fully realized the benefits of hydraulics, and,
starting after the 707, accepted the desirability of flying by hydraulics.
However, what a lot of pilots wanted was a hybrid system, fly-by-cable, 
COMBINED with hydraulic boost.  So, for instance, the 727 was developed with 
full-time hydraulic flight controls, but also a cable-driven "back-up" mode, 
which used control tabs to aerodynamically move the surfaces.  When hydraul-
ics were completely lost, controls became heavy, but the airplane had a 
"get it on the ground" capability.  The 727 was the last such airliner to
have this capability.


Much of the controversy surrounding the BIG airliners, such as the 747, but
even the 737, was that the manufacturers wanted to take away these tabs.
This debate was an important part of an industry-wide *process*, which helped 
induce the manufacturers to develop more reliable systems: a 747 with the 
hydraulics reliability of, say, a 707, would not have been acceptable.  This 
technological advance, combined with the *necessity* of using it in the 
specified mission profiles, helped silence objections.

So Concorde certainly wasn't the first to go all-hydraulic, and the debate
didn't start there.

I can't comment on Concorde-ish control forces, but on even the 747, the
"raw" forces in cruise, while high, don't require superhuman effort: the
figures I've seen ranged from 50 lbs to 150 lbs.  This would be unacceptable
for normal operations, but is hardly the equivalent of trying to lift a 
ton of cement with one's little finger.


> As I said, it has proved to be the worlds' safest aircraft.

Sure, 14 airplanes, piloted by superbly qualified and trained aircrews, 
with immaculate and detailed maintenance.  Flying what, TWO flights a day (no,
not two per plane, two FLIGHTs, in the fleet) on 2 or so very well-defined 
routes, to major international airports?

Concorde's an interesting experiment, but let's face it: its contribution is
merely that it can be done, not that it can be done economically, or, even,
safely, in the same types of conditions other airplanes are flown in.  It is,
however, an engineering achievement that France and England can be proud of,
and I hope British Airways and Air France continue turning their Concorde
profits, if, for nothing else, the living history the airplane represents.


> I don't seem to have noticed any raving about the TGV, the latest versions of
> which achieve speeds comparable to that of aircraft, and use a side-stick ...

You will no doubt be DELIGHTED to note that I know nothing about trains.  
Nor do I particularly care to learn. :-)  My interest here is airliners, not
mass transportation.  I'd suggest we compare standards within the genre.




--
Robert Dorsett
Internet: rdd@rascal.ics.utexas.edu
UUCP: ...cs.utexas.edu!rascal.ics.utexas.edu!rdd