A fan blade containment assembly (38) for a turbofan gas turbine engine (10) comprises a cylindrical, or frustoconical, casing (40) arranged to surround an arrangement of fan blades (26). At least one hollow tubular member (66) is arranged radially within and secured to the casing (40) and the at least one hollow tubular member (66) contains a filler material (68). The at least one hollow tubular member (66) extends circumferentially. The hollow tubular member (66) is helical and the axial spacing between the adjacent turns of the tubular member (66) varies and the density of the filler material (68) varies in order to match the severity of the impact expected at each axial location along the casing 40 of the fan blade containment assembly (38).