Abstract: A landing gear system uplock arrangement (300, 500) including: a hook (310) defining a gap (314), wherein the hook is movable between a first position, at which the hook is for retaining a movable element (299, 499) of a landing gear system in the gap, and a second position, at which the hook is for permitting movement of the element into and out from the gap; a lock (320) that is changeable between a locked state, in which the lock prevents movement of the hook from the first position to the second position, and an unlocked state, in which the lock permits movement of the hook from the first position to the second position; and a sensor arrangement (330) for sensing whether the element is present in the gap.