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

From:         Jean-Francois Mezei <MEZEI_JF@Eisner.DECUS.Org>
Organization: Digital Equipment Computer Users Society
Date:         21 Jun 95 02:56:54 
References:   1 2 3 4 5 6
Followups:    1 2 3 4 5
Next article
View raw article
  or MIME structure

The 310 may have the same joystick as the 320 and 340 but there is a major
difference: FBW. (subject of this thread). In FBW systems, the computer has
much more intelligence built in to it 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 ?

In a FBW system, the computer can make lickety split decisions if something
arises. 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).

In a FBW system, the pilots' commands are interpreted and "validated" before
being acted upon.  In a non-FBW system, if the auto-pilot is off, the commands
are just acted upon.

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

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:

Computer wants to veer left real. Pilot wants to go straight. Co-Pilot
wants to veer right.

While the pilot may at first, feel the computer pushing the joystick/whatever
to the left, he will then feel the joystick going back towards the "middle" as
the co-pilot is veering to the right. Meanwhile, how will the pilot convey that
no-movement is the thing to do while the others (computer and co-pilot) are
"playing with the joysticks " ?

Can the "tactile feedback" system also feed to the computer the amount of force
that the pilots exert ? And does the computer then decide who has the most
force on the joystick and then let that person't joystick move freely ?


I am not a pilot, but I would assume that while the auto-pilot is engaged,
pilots don't really have their hands on the joysticks/steering devices. Right ?
Pilots going asleep during very long flights has often been mentioned as a
problem where it takes a while for pilots to awaken when something does happen.
Tactile feedback would not be of much help there, but 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".

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

Now, it seems that tactile feedback is "required" in order to correctly asses
who is at the controls (pilot or co-pilot). This is based on many opinions
posted here. 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.

Personally, I would feel more at ease where a system would be on auto by
default, and if any of the two wish to go "manual", then the first one to push
the button gets a distinct audio signal that both pilots can hear. Much less
confusion than trying to figure out where the resistance is coming from in
tactile feedback.

As well, if you have feedback coming from multiple sources at the same time,
you may suffer "information overload" If you not only have to feel the
directional device to see where the plane is going but also look at the crt to
see who is steering is (other pilot or computer), then you are wasting even
more time.

While many see the lack of tactile feedback in the Airbus as a "fatal flaw", I
am not willing to dismiss the Airbus concept until I hear some REAL facts about
how it really works and what sort of computer-pilot communications exist.
Judjing from some posts and some e-mails, some people seem to beleive that
Airbus computers do a lot fo stuff and don't tell the pilot about it.

I do not wish to state that Airbus is better than Boeing. But I think that that
a lot of Airbus bashing is not warranted because we know so little about the
man-computer interface in that system. Unfortunatly, Airbus's propaganda
machine isn't as well organised as Boeing's.

Next time I fly on a 320, I'll make a point to ask to go to the cockpit and ask
the pilots a lot of questions.

>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.