Abstract: A method for periodically restoring the blade tip to annular seal clearance in a gas turbine engine (10) includes incrementing (42a, 42b) the flow of external cooling air responsive only to an accumulated engine use parameter (58).

Abstract: Active clearance control is effectuated by heating the bore of the high pressure compressor spool so as to expand the compressor disc and labyrinth seals to minimize the gap between the blades and its peripheral seal and labyrinth seal. The high stages of the high spool compressor are selectively bled to achieve the desired gap control over the engine's operating envelope. The bled air is fed into the bore by conducting the air externally of the engine's case and admitting it through hollow stator vanes of the low pressure spool and tubes communicating with a cavity at the bearing supporting the high pressure compressor shaft at a juncture in line with the inlet of the high pressure compressor spool.