This paper deals with accessories as parts of a whole and the contribution that each part makes to the success or failure of that whole. The view is taken by a major airline as a typical user and is intended to be from a vantage point which will permit observation of a broad and complete picture. The scope of dealing with a multitude of accessories as individual units is portrayed through the use of typical operating statistics. These show the number of “happenings” that are normally encountered on a sizable fleet of aircraft during maintenance, both scheduled and unscheduled.The importance of a system-oriented effort, well integrated between the many organizations and companies involved in the design, development, test, and eventual use of each item is stressed. An approach to achieving understandings and objectives is recommended, the focal point of which is a general specification for gas turbine engine propulsion systems.