An outer skin of an aircraft body is supported by a frame of longitudinal stringers and circumferential ribs or frame elements interconnecting the stringers. Additionally, the outer skin is strengthened by a reinforcing strip formation adhesively bonded to the inwardly facing surface of the outer skin between the ribs and stringers. The reinforcing strips are made of a material that is damage tolerant, for example high strength aluminum alloys and fiber composite materials are suitable for making the reinforcing strip formation. The reinforcing strips of the strip formation may extend in parallel to the stringers and/or the ribs and preferably form a lattice work. The reinforcing strips need not cross each other at right angles but should cross a crack propagation direction in the outer skin.