With two original sidesticks in the cockpit, also the sidestick priority logic has been implemented in our A320 Sim software.
In normal operation only one sidestick is used to give pitch and roll instructions to the flight computers and the opposite not used sidestick is kept in the neutral position. To couple both sidesticks to the flight computers, their inputs are summed together. So in the abnormal situation when both pilots are giving inputs with their respective sidesticks the summed result that is used by the flight computers is meaningless (and both inputs could even be working against each other).
In order to provide indications to the pilots in such abnormal condition, the glare shield on the Capt and on the F/O side contain a sidestick priority indicator light.
Also on the sidestick a priority takeover pushbutton is foreseen so that a pilot can takeover control and essentially cancel the sidestick input of the opposite pilot. This would indeed be needed for example when one pilot is incapacitated and would keep his sidestick outside of the neutral position.
The green CAPT and F/O lights both flash when the pilots move both sidesticks simultaneously and neither pilot has taken priority through his priority takeover pushbutton. In case when a pilot has taken priority by pressing the takeover pushbutton and the opposite pilot's sidestick is not in the neutral position, the light in front of the pilot with priority lights up. It goes out when the opposite pilot returns his stick to the neutral position.
The red arrow light comes on in front of the pilot losing authority (i.e. not having priority and having his inputs cancelled). It goes out if he has recovered authority. Whenever priority is taken, an audio voice message is indicating which side has priority.
In the following recording you see the A320Sim Glare Shields of the Capt and F/O side by side. The following sequence of actions is performed:
- Dual sidestick input by CAPT and F/O, with no priority set → flashing green lights on both sides
- Priority taken by CAPT → red arrow on right side
- Priority taken by F/O → red arrow on left side
- Priority taken by CAPT and F/O Sidestick not in neutral position → red arrow on right side, with green on left side
- Priority taken by F/O and CAPT Sidestick not in neutral position → red arrow on left side, with green on right side
Although they have been implemented, no sound is recorded so you will not hear the priority audio voice messages.