Re: FLY-BY-WIRE (AIRBUS vs. BOEING)

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         22 Jun 95 03:07:35 
References:   1 2 3 4
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In article <airliners.1995.829@ohare.chicago.com>,
Jean-Francois Mezei  <MEZEI_JF@Eisner.DECUS.Org> wrote:

>The 310 may have the same joystick as the 320 and 340

It does not.  The A310 (and A300) both have a conventional yoke.

>but there is a major difference: FBW. (subject of this thread).

Pedantically, yes, it is the subject of this thread because that's
what's in the subject line.  However, the *real* subject, embodied in
the discussion itself, has little to do with FBW and everything to do
with human factors and cockpit design philosophies.

>In FBW systems, the computer has much more intelligence built in

In FBW systems, electrons replace hydraulic fluid, wires replace
pipes, and generators replace hydraulic pumps.  There need not be
any computers at all, though in all implementations that come to
mind they are there.

>whereas the more "conventional" system have a basic auto-pilot that
>maintains altitude and course and then have an ILS to help position
>the plane in its landing path. Right ?

Wrong.  Many conventional systems (e.g. 757/767, A310) include a
sophisticated flight management system (FMS) which can automatically
fly the entire flight.  Even the L-1011, designed over 25 years ago,
was capable of flying itself from throttle up and brake release at
the beginning of the takeoff to roll-out after landing.

There tend to be more bells and whistles on FBW systems, partly
because its simpler to interface them to FBW controls than to
hydraulics, but FMS does not imply FBW nor vice-versa.

>If the information given to the computer is wrong, then problems occur
>(eg: crash of 320 in France where computer aborted a take-off even though the
>plan was already in air because its altimeter "value" was still at 0).

What crash is this?  The details do not even remotely match any of the
A320 crashes, nor any other Airbus crash that I'm aware of.

>In a FBW system, the pilots' commands are interpreted and "validated"
>before being acted upon.

No.  If you can get to Direct Law (by failure or shutdown of multiple
computers, or after the computers put you into truly bizarre flight
conditions as in the A330 crash), an A320 pilot's commands go directly
(hence the name) to the flight surfaces via the FBW system with no
limiting, interpreta- tion, or meddling by the computers.  The 777 has
a similar mode (the name escapes me) for dealing with total computer
failure.

>If the above is not too far off from reality, then I have the following
>questions:

The above is quite divergent from reality.  On to your questions
anyway ...

>When you have a pilot, co-pilot and computer who can "steer" the airplane, in
>the case of the "tactile feedback", how is the following handled:

...

>Can the "tactile feedback" system also feed to the computer the
>amount of force that the pilots exert?

That would be fairly trivial to implement, by a transducer to measure
the force, or by sensing the current flow to the servos moving the
controls.

>And does the computer then decide who has the most force on the
>joystick and then let that person't joystick move freely?

In the case of the 777, which has conventional control columns despite
the fact that you seem to insist on saying it has a joystick, the two
columns are mechanically connected, just like on a conventional air-
craft, so neither ever moves freely until the other pilot lets go.

>having a smart computer able to quickly adjust to a situation such as
>air pocket would fill that "critical" gap between the time the
>situation arises and the time the pilots are "fully awake".

An FMS or even an autopilot on a conventional aircraft can handle such
a situation.  In any case, at least one pilot is required to be at the
controls (and alert!) at all times.

>And when the pilot is at the controls, then the FBW system only makes
>sure that the aircrafts' structural integrity is ensured.

Even if that means flying into a forest instead of bending the plane
and subsequently landing safely.

>In the case of Boeing, it would SEEM that the pilot can do what he
>wants with just a warning on a screen if he exceeds the aircrafts'
>capabilities (what ? no tactile feedback?) :-)

The 777's system has been described here several times before.  At the
risk of boring everyone who has been paying attention, when a pilot
attempts to push the column beyond limits imposed by the system, the
system pushes back.  The pilot can still overcome this resistance (and
the limits), albeit (s)he must push considerably harder to do so.  No
warnings on screens (perhaps there are, but they are secondary) and
yes, there is tactile feedback.  That -- not FBW as you inist -- is a
keystone of this entire thread.

>In the Airbus concept, it would SEEM that the computer won't let the pilot
>exceed the aircraft's capabilities unless a special "override" button is
>engaged. Is that a correct assumption ?

No, unless you consider cutting off a nubmer of circuit breakers to
disable a bunch of computers and force the system into Direct Law to
be a reasonable "override" "button" in an emergency situation.  Again,
that's the point -- you CANNOT override the Airbus system (without a
lot of fiddling around that you won't have time for in an emergency).

>I am not a pilot, but I sure hope that pilots are trained in such a
>way that authority is based on more that just how much resistance a
>person has when try to move the joystick/steering column.

In the A330 test flight crash, Captain Nick Warner's response was
delayed by about four seconds, after which his reactions were quick
and instinctive.  That four seconds may well have been the difference
between life and death.  In such time-critical situations, substantial
amounts of training are supplanted by instinctive reactions.

>a lot of Airbus bashing is not warranted because we know so little
>about the man-computer interface in that system.

A number of contributors to this group know quite a bit about the
interface in the Airbus system, either from extensive study of it
or in at least one case from flying the beasts.  Please do not insult
them by claiming that an all-encompassing "we" are ignorant of the
facts when the ignorance is primarily yours.

>>Which is exactly what I said, if you had bothered to read what I wrote.
>>To wit:

>Sorry about that, but when traffic on this newsgroup is so sporadic, it can
>take quite a bit of time for stuff to get to end users.

How, pray tell, do turnaround delays cause deterioration of your
comprehension of an article to which you are writing a reply?!

--
Karl Swartz	|INet	kls@chicago.com
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