By double pressing the ap/priority button you gain priority over the other side stick. An aural 'priority left/right' is heard, red arrow to the side of the fcu pointing to which side has control over the other/green on side which has prioriy. If the button is held down for 20-30 secs you lock out the other side stick for the remainder of the flight and can only be reset on the ground. (p45 button). Only used in extream cases but was mentioned during my type rating as only using this in-case of side stick malfunction. Hope this helps........