A method of lining a turbofan casing (30) with an array (32) of liner modules (34), including the steps of: providing a liner module (34); and providing a coupling element (48) on the casing for interlocking engagement with the liner module to maintain the liner module in position relative to the casing; and interlockingly engaging the liner module (34) and coupling element (48) by progressive movement of the liner module relative to the coupling element.