Variability in the Demands for Aircraft Spare Parts: Its Magnitude and ImplicationsMathematical models of the logistics system are used to determine spares requirements, and they play an important role in evaluating logistics policies. The kernel of many, if not most, of these models is the modeling of the failure process and the resulting series of random demands on supply and maintenance. This report describes the assumptions of these models and quantifies ways in which the behavior of the data differs from the assumptions of the models. The differences are pervasive and important. In addition, an examination of the number of parts in the repair pipeline over time reveals even more variability than does the number of demands over time. These observations have two important consequences: (1) excessive demand variability substantially reduces the confidence we can put in our requirements and capability assessment models, and (2) highly variable repair pipelines with means larger than assumed by requirements models have a damaging effect on aircraft availability and wartime readiness. Depot policies, decisions, and goals should be aimed at reducing the number of parts in these pipelines and increasing aircraft availability and wartime readiness. |
Common terms and phrases
1000 flying hours 19 PARTS DATA 9 10 Variance actuator AFB Holloman AFB Air Force aircraft availability assessment and requirement assumed assumptions Base Luke AFB CALENDAR YEAR QUARTER capability assessment models compound Poisson compound Poisson distribution compound Poisson process compounding density computed Converter Programmer COSO Cost Base LRUS Cost of LRU Cumulative VTMRs demand process demand rate demands per 1000 demands per quarter Depot LRUs depot pipeline expected Depot expected Fig expected observed Depot Gamma distribution heat exchangers high VTMRs Holloman AFB 80-2 LRU Pipeline Luke AFB Holloman maintenance mean ratio Fig MICAP NEGATIVE BINOMIAL DISTRIBUTION Number Base LRUS observed Base observed expected Cost observed VTMR Palm's Theorem Peculiar and Common pipeline contents Poisson arrival process Poisson process Poisson random variable predict QUARTER Base Luke repair pipeline repair process requirements models result sample Serviceability of Components Serviceable LRUS tion unserviceable Variance to mean variance-to-mean ratio VTMR larger wartime WRSK
References to this book
Implications for Model Validation of Multiresolution ..., Issue 1750 J. H. Bigelow,Paul K. Davis No preview available - 2003 |
Aging Aircraft: USAF Workload and Material Consumption Life ..., Issue 1641 Raymond Pyles No preview available - 2003 |