Re: Airbus A320 flight controls

From: (Jean-Marie Dany)
Date:         27 Feb 96 23:00:33 
References:   1 2 3 4 5
Followups:    1
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 I don't know if the "side stick priority logic" has been changed but I
 have found these informations from a rather old FCOM :

A320 Flight Crew Operating Manual - FLIGHT CONTROLS - CONTROLS AND
1.27.40 - P 3 - REV 16 - SEQ 002 - "For training only"

and transcribes that page of text. I referred to a later copy of
the FCOM to check. The whole manual that I referred to was at
REV 19, and the page that Francis quotes is at REV 18 in that version.

The text is identical except for two lines:-

       If a takeover push button is pressed for more than 40 seconds
       the system will latch, ...                         ^^

(changed from "30 seconds"), and:-

       However, at any time, a deactivated stick can be reactivated by
       momentarily pressing the takeover push button on either stick.
                            ^^^                     ^^^^^^^^^^^^^^^^

(changed from "... pressing its takeover pushbutton.")

The effect of the first change is obvious.

The second one is puzzling me. It would seem fairly sensible that a
crew member whose *own* stick was deactivated should be able to
reactivate it by pressing its *own* takeover pushbutton, and the
REV 16 text states this clearly. However, the REV 18 text implies
that, having deactivated FO's stick and taken control, the Captain
would reactivate FO's stick by a subsequent action on the *Captain's*
takeover pushbutton (or vice versa, reversing the roles of the two
crew members).


1. Do these changes mean that the logic has been modified, or were
   they made because the manual was originally incorrect compared
   to the existing logic?
That is correct the last guy that pushes the button is always the winner, if
ou keep it maintained more than 40 seconds you kill the other sidestick

2. Have I understood the second modified statement correctly, or
   is this another example of the practical application of the
   "fuzzy logic" for which the FCOM is famous?

In answer to C. Marin Faure's original question, I am not aware
of any change to the "left-plus-right-equals-nothing formula", nor
of any alteration to the symmetry of the sidestick logic. There
are no Operations Engineering Bulletins (OEB) relating to the
sidesticks in my copy of the FCOM.

The sticks react algebrically when they are actionned at the same time if
you don't push the priority button which is also the instinctive disconnect
of the autopilot. So the captain could push his stick to the left and the
first officer to the right nothing will happen until somebody press the
priority button. Strange !!