Analysis of information sources in references of the Wikipedia article "Side-stick" in English language version.
The two sidesticks are not mechanically linked as they are on older types of aircraft. This means that both sticks may be operated independently one of the other. When one sidestick is operated it sends an electrical signal to the Fly By Wire computers. When both sticks are moved simultaneously, the system adds the signals of both pilots algebraically.
To avoid both signals being added by the system, a priority P/B is provided on each stick. By pressing this button, a pilot may cancel the inputs of the other pilot. An audio signal will indicate which sidestick has priority.
A green light will come on in front of the pilot who has taken control if the other stick is not in neutral popsition, and a red light comes on in front of the pilot whose stick is deactivated.
The total is limited to the signal that would result from the maximum deflection of a single sidestick.
When a dual input situation is detected, the two green priority lights located on the cockpit front panel flash simultaneously. The visual indication is an ADVISORY of a dual input situation
In order to warn the crew in case of dual sidestick operations, Airbus has designed a package of dual input indicators and audio warning. These operate when both side sticks are deflected simultaneously by more than 2°.
After the visual indication has been triggered, a synthetic voice "DUAL INPUT" comes up every 5 sec, as long as the dual input condition persists. The synthetic voice is a WARNING of a dual input situation.
Note: This audio has the lowest priority among the synthetic voice audio alerts.
It seems surprising that Airbus has conceived a system preventing one pilot from easily assessing the actions of the colleague beside him. And yet that is how their latest generations of aircraft are designed. The reason is that, for the vast majority of the time, side-sticks are superb.
