A fan containment system for fitment around an array of radially extending fan blades mounted on a hub in an axial gas turbine engine, including: a fan case having an annular casing element for encircling an array of fan blades and an annular fan track liner lining a radially inner side of the casing element, including a first fan track liner panel positioned circumferentially adjacent a second fan track liner panel. An engagement arrangement engages the first fan track liner panel to the second, extending along at least a portion of adjacent sides of the liner panels, and is configured and the liner panels are shaped such that axial movement of the first fan track liner panel by a distance less than the length of the engagement arrangement, being measured in a direction parallel to the adjacent sides of the liner panels, disengages the first liner panel from the second.