A rotor blade for a gas turbine engine, comprising an aerofoil having pressure and suction surfaces, leading and trailing edges, and an array of passages at a tip region of the aerofoil. The passages extend from the pressure surface to the suction surface of the aerofoil and are disposed so that the array creates, in operation, a planar jet of gas issuing from the suction surface. The jet is inclined outwardly from the suction surface and towards the tip, and in the direction from the leading edge to the trailing edge. The jet inhibits migration away from the suction surface of a clearance vortex formed by leakage of air over the tip of the rotor blade.