A method of controlling a rotor tip clearance arrangement of a gas turbine engine and a control system configured to control rotor tip clearance. Steps include measuring at least one engine parameter; determining engine power demand from the at least one engine parameter; and calculating rotor tip clearance given the determined engine power demand. The rotor tip clearance arrangement is controlled to increase or decrease the rotor tip clearance based on the difference between the calculated clearance and a predefined target clearance.