Method and apparatus for maintaining rotor assembly tip clearances

A method of operating a gas turbine engine (10) and a clearance control system (88) for a gas turbine engine (10) is provided. The gas turbine engine (10) includes at least one engine casing (94) and at least one rotor assembly (54). The method includes directing airflow through a supply pipe (90) and into a heat exchanger (96), lowering the temperature of the airflow in the heat exchanger (96), and directing the cooled airflow into the engine casing (94) to cool the casing. The gas turbine engine (10) further comprises a high pressure aft cavity (84) and a high pressure turbine disk (60), said method further includes directing the cooled airflow to the high pressure aft cavity (84) and cooling an aft surface of the high pressure turbine disk (60).