a labyrinth seal is provided for forming a seal between a first and a second component which rotate relative to each other . the seal has an abradable lining mounted to the first component , and a plurality of fins projecting from the second component . the fins are arranged in abutment with the abradable lining to form a labyrinthal path for a flow of air through the seal . the seal further has a bypass passage which extends through the abradable lining . the bypass passage allows air to flow through the seal and bypass the labyrinthal path .