This Aerospace Recommended Practice recommends general criteria for the development and installation of an aircraft emergency signal system to permit any crew member (flight or cabin) to inform all other crew members that an emergency evacuation situation exists and that an evacuation has been or should be immediately started. PURPOSE The purpose of this document is to assure functionality@ usability and performance of emergency evacuation signal systems installed on transport category aircraft. NOTE: It is not the purpose of this document to specify the design method@ mechanism@ or equipment to be used in the accomplishment of the objective set forth herein.