A fan (12) for a turbofan gas turbine engine comprises a rotor hub (36) and a plurality of radially extending fan blades (20) integral with the hub (36) to form an integrally bladed rotor. Each fan blade (20) defines a leading edge (34). A hub radius (R HU...

A reduced-diameter portion (44) with a taper portion (46), a portion whose diameter is reduced in a tapered form, is provided on an inner peripheral wall of a cylinder sleeve (20a, 20b, 20c). On the outer peripheral wall of the top end of the cylinder slee...