A containment assembly for a turbo fan engine, has a casing arranged in use around a rotatable fan, to form a duct for the fan and a liner element disposed on an interior surface between the casing and blades of a rotatable fan. The liner element includes a body portion mounted in a recess in the casing and a wall portion arranged to form part of an inner wall of the duct. The wall portion and the body portion being attached and defining a containment cavity therebetween for containment of a detached fan blade fragment in use, wherein the wall portion has a moveable portion movable between a first configuration in which it lies substantially flush with the inner wall of the duct, and a second configuration in which it provides an opening through which a fan blade fragment can enter the containment cavity.