Active seal assembly

A seal assembly comprising:

• an annular hanger including a supporting ledge;
• an arcuate seal segment including a radially outer rail mounted on said ledge and supporting a radially inner seal;
• an arcuate carrier mounted between said hanger and said rail, and including a piston mounted in a bore, a tubular bellows having an inner end joined to said piston, and an outer end joined to said carrier around said bore;
• and
• an actuator for pressurizing said bore to deploy said piston between said hanger and said rail and retract said seal segment.