Abstract: A first fastener component (26) is secured to an inner aircraft skin surface (6) by a mounting flange (12) and extends across a discontinuity (8) in the skin (2). A second fastener component (28) is secured to a rib (24) on the inner surface of a resilient blade (22) and extends through the discontinuity (8) into engagement with the first component (26). Inward pressure on the blade (22) urges the components (26, 28) into releasable locked engagement with each other. The components (26, 28) secure the blade (22) in a flattened use position in which it is substantially flush with and sealingly engages the outer skin surface (4). The blade (22) may be removed by inserting a tool under it and exerting a lifting force to disengage the components (26, 28). The blade (22) may be dimensioned to cover the outer ends of adjacent fasteners (14) extending through the skin (2). The blade (22) is preferably conductive to provide a continuous electrical path along the outer skin surface (4) across the discontinuity (8).