A method of designing a modified aerofoil shape, the method comprising the steps of: determining a plurality of resonant frequencies of a baseline aerofoil shape; determining that one of the resonant frequencies falls within a predetermined range of frequencies; providing a plurality of aerofoil sections defining the baseline aerofoil shape; and defining a modified aerofoil shape by displacing at least one of the plurality of aerofoil sections relative to its baseline position in the baseline aerofoil shape until one of the plurality of resonant frequencies previously falling within the range of frequencies is shifted outside the range of frequencies.