Abstract: A secure corset is applied in particular to the immobilization in the maximum opening position of an aircraft landing gear cage hatch. The corset has two half-shells that are able to enclose the piston of the actuator having an axis coincident with the common longitudinal axis of the half-shells once they are closed around the piston. Locking pins are able to hold the half-shells around the actuator. The corset also has a casing secured to at least one of the half-shells and equipped with a hooking unit that is able to be coupled to a fixed point on the structure. A structure for varying the distance between the casing and the hooking unit are able to move the hooking unit away from or towards the corset along the common longitudinal axis of the half-shells.