A covering structural element is adapted to close an elongate gap provided on an aerodynamic surface of an aircraft. Such an element has a strip-shaped body made of metal material, including a fixing portion, adapted to be fixed along one of the longitudinal borders of the elongate gap; a sliding portion adapted to urge in a sliding manner on the other of the longitudinal borders of the strip-shaped gap; and a connection portion, connecting the sliding portion to the fixing portion, the thickness of which is so sized as to allow, in use, a controlled elastic bending of the structural covering element. The covering structural element has a profile so sized as to be tapered at the transition from the fixing portion to the connection portion and from the sliding portion to the connection portion, the covering structural element having a smooth surface on the side intended to face away from the elongate gap.