An assembly is disclosed for adjusting the radial position of one or more blade tracks radially encasing the blades of a turbine stage in a gas turbine engine. The assembly comprises a static turbine casing, a plurality of blade track carriers, an annular control ring, an actuator, and a plurality of blade tracks. The blade tracks have a radially inner surface that defines a flowpath boundary of the turbine stage. The blade tracks are carried by the blade track carriers, which are engaged with the annular control ring. Actuation of the actuator moves the control ring in an axial dimension and this movement is translated into an adjustment of the radial position of the blade track.