Control Laws
Ignition Override
Any time that you have digital data feeds inputting into a flight control system (yaw damper) you must have "control laws". These accommodate (and/or negate) the type of dangerous feedback loops described by OVERTALK.
It is almost unthinkable (but not unbelievable) that in an early design, such as the A300, an unforeseen anomaly may have been allowed to creep into the system. But then again, would they have been testing for an unlikely "sometime" occurrence (such as an accumulation of water in the static lines) to create a feedback loop - and only once excitated by an external influence (such as a wake encounter). But it cannot be ruled out - basically on the grounds that I doubt that Airbus would have watered the prototype's static lines and tested for it. They'd have needed to go seek out an external excitation (such as a wake encounter, stall or similar upset) whilst having a significant amount of water trapped in the lines. See my point there?
Neither can the possibility of hydraulic feedback loops be ruled out. Both possibilities are far more likely to have caused the AA587 accident than a pilot pedalling into a destructive yaw cycle. It's just that the non-aerodynamic FEDEX hangar incident points more to the actuator having broken because of a straight hydraulic anomaly.
B