Multi-Level Inventory Systems: The Case of the Spare Aircraft Engines

摘要

Military supply systems usually exhibit a multi-level structure, i.e., stockage points at the top of the pyramid (depots) do not directly serve equipment users but their customers are themselves stockage points. The objective used in 'optimizing' depot level inventory control procedures is usually of the form: minimize the total cost of providing a specified level of service to the depot customers. The problem lies in specifying the level of service, expressed in terms of statistics such as the fraction of time in stock or the average customer waiting time that should be given to the next lower level. What is the effect, for instance, on the ultimate user and the total system cost if depots maintain a higher level of inventory, thereby providing better service to their customers. Little work has been done on the distribution of a given total inventory over different levels of stockage points in the general case. However, some specific systems, because of their special structure, lend themselves more readily to analysis. This paper presents the computational results obtained for a bi-level circular supply system for aircraft engine spares. It is shown that the overall system's performance is very sensitive to the distribution of inventory over the two levels and that maximal system performance is obtained with a surprisingly small amount of inventory at the higher level. (Author)