A fan containment system for fitment around an array of radially extending fan blades mounted on a hub in an axial gas turbine engine. The fan containment system comprises a fan case having an annular casing element for encircling an array of fan blades. An annular fan track liner is positioned substantially coaxial to the annular casing element, and one or more pockets are provided in a radially outer side of the fan track liner. One or more dampers for damping vibration of the fan track liner are positioned in each of the one or more pockets and are arranged so as to contact the annular casing element.