The lifting surfaces comprise a torsion box capable of bearing aerodynamic and inertial loads. The torsion box has lateral parts that are connected together by an attachment comprising a rib, having a central upper part and a central support lower part joined only by angled cross bars, forming a truss structure along the length of the central support upper part and the central support lower part. The angled cross bars are attached to the upper and the lower parts of the central support: alternatively to both sides of a plane of symmetry defined by said upper and lower parts of the central support, dividing the torsion box in the two lateral parts making a zone of access perpendicular to the length of the central supports, where said zone of access is closed with a piece provided with at least one hole for permanent access.