Abstract: A fan casing for an engine having a fan with fan blades that each have a centre of gravity (CoG) that lies on a fan blade CoG plane, the fan casing having a central axis and comprising a main impact region comprising carbon-fibre reinforced polymer (CFRP) blocks and glass-fibre reinforced polymer (GFRP) blocks having a constant thickness throughout the axial extent of the main impact region, wherein the total depth of the main impact region is equal to the sum of the thicknesses of the CFRP blocks and GFRP blocks, each of the GFRP blocks is positioned between two CFRP blocks, and the thickness of at least one of the GFRP blocks is different to the thickness of another of the GFRP blocks.