A Model for Predicting the Inventory of Navy Spares

Abstract

I _IDALog No. HO 91-37619nn nn~nnu m ni u 1n.1-lNI~ i I |II DEFINITIONSIDA publishes the following documents to report the mutts t its work. ReportsReports are the most authoritative and most carefully considered products IDA publishes. IThey normally embody results of major projects which (a) have a direct bearing on decisions affecting major programs. (b) address issues of significant concern to the Executive Branch, the Congress and/or the public, or (c) address issues that have significant economic Implications. IDA Reports are reviewed by outside panels of experts to ensure their high quality and relevance to the problems studied, and they are released by the President of IDA. Group ReportsGroup Reports record the findings and results of IDA established working groups and panels composed of senior Individuals addressing major issues which otherwise would be the subject of an IDA Report. IDA Group Reports ar reviewed by the senior individuals responsible for the project and others as selected by IDA to ensure their high quality and relevance to the problems studied, and are released by the President of IDA. PapersPapers, also authoritative and carefully considered products of IDA, address studies that are narrower in scope than those covered in Reports. IDA Papers are reviewed to ensure that they meet the high standards expected of refereed papers in professional journals or formal Agency reports. Approved for public release; distribution unlimited. ABSTRACT (Maminm 200 wards)As part of the yearly planning process, OSD analysts assess the services' budget requests for secondary items. Although good planning dictates that these requests be judged by the effects of the budgets on inventories and the readiness and sustainability of the operating forces, these links have not been developed. This study takes the first step in providing such links by developing an aggregate model for use by OSD analysts to predict the future inventories of Navy spares. Inventories are predicted from spares budgets, Fleet characteristics that determine spares usage, and historical factors derived from past data. The model was constructed by identifying the principal flows of inventory in the supply system, and relating them to the inputs using simple linear expressions. The paper validates the model using data from the 1980-88 buildup, and illustrates the model's use in forecasting. Appendices briefly describe the inventory management systems of the three military services and cost-estimating relationships for spares usage by ships and aircraft. PA&E).Its purpose is to serve as a tool for appraising budget requests for spares by the military services. The model, which takes the form of a spreadsheet consisting of 48 lines, including 16 historical factors, has been delivered to PA&E on a floppy disk.Appendices to the study cover an overview of stock funding (Appendix A), introductions to the Navy, Army, and Air Force supply systems (Appendices B-D), and a description of efforts, using regression analysis, to construct relationships...