Abstract: The spreading of a fire outside of an aircraft body into the cabin through the windows is retarded by a fire retardant slide member that is movable into a window covering position guided by guide rails or the like. Both, the sliding member and the guide rails are made of fire retarding material such as thermosetting material, preferably glass fiber reinforced thermosetting materials. A thermoplastic locking element that holds the sliding cover member in a recessed position releases the cover member when the locking element melts at elevated temperatures to cover the window automatically, e.g. with the aid of gravity or with the aid of one or more biasing springs.