Final answer:
The flashing green CAPT and F/O SIDESTICK PRIORITY lights on an Airbus aircraft indicate that one pilot has taken priority control after dual inputs on the sidesticks were detected.
Step-by-step explanation:
When the flashing green CAPT and F/O SIDESTICK PRIORITY lights are illuminated, it indicates that one of the pilots on an Airbus aircraft has taken priority control over the other.
This situation occurs in the event that dual inputs on the sidesticks are detected, which could potentially cause confusion or conflicting commands to the aircraft's control surfaces. In such a case, either the Captain ('CAPT') or the First Officer ('F/O') can press their sidestick priority button to take full control, and this action triggers the illumination of the flashing green light.