A gas turbine engine comprising a casing, a bonding patch (10, 22) bonded to a surface of the casing, and a liner attached to the bonding patch. The bonding patch (10, 22) comprising a bonding region (12) configured to receive an adhesive for bonding the patch (10, 22) to a surface. A plurality of de-bonding elements (16) is configured to be movable relative to the bonding region (12) in response to an energising signal.