Mike Slay - Academia.edu (original) (raw)

Papers by Mike Slay

: The Sortie-Generation Model System provides the capability for relating aircraft spares and mai... more : The Sortie-Generation Model System provides the capability for relating aircraft spares and maintenance manpower levels to the maximal sortie-generation capability of tactical air forces over time. This volume describes the process of constructing a spares data base for input to the Sortie-Generation Model. (Author)

This study examines the application of spares optimization models to initial provisioning problem... more This study examines the application of spares optimization models to initial provisioning problems. Four case studies of Army weapon systems are included: the XM-1 tank, Patriot, Firefinder, and the Ground Laser Locator Designator (GLLD). It concludes that DoD policy be changed ...

Information and guidelines are presented pertaining to the electromagnetic compatibility (EMC) of... more Information and guidelines are presented pertaining to the electromagnetic compatibility (EMC) of ground and airborne equipments in the Aeronautical Mobile VHF Service with the proposed AEROSAT VHF avionics. Volume I provides general guidelines for AEROSAT avionics compatibility with the VHF environment and predicted interactions with aeronautical mobile VHF equipments in the United States and Canada. Volume II addresses the worldwide

: This report describes the mathematical algorithms of a prototype version of the Aircraft Sustai... more : This report describes the mathematical algorithms of a prototype version of the Aircraft Sustainability Model (ASM), a model designed to relate U.S. Air Force funding for reparable spares to aircraft sustainability measures. The ASM is a multi-echelon, multi-indenture inventory model that is unique in its portrayal of the transient effects resulting from a dynamic demand environment. Furthermore, the ASM is unique in its ability to simultaneously optimize spare requirements for multiple days of a conflict scenario. Keywords: Aircraft maintenance; Spare parts; Inventory modeling.

: Modem inventory management typically relies, when possible, on quick deliveries from suppliers,... more : Modem inventory management typically relies, when possible, on quick deliveries from suppliers, and aims to carry minimal inventory. Such practices work best in managing low-cost items with stable demand and significant market size. But supporting advanced military equipment poses unique problems: small fleet sizes and low operating tempos lead to sporadic and unstable demand pattems; components are highly specialized, have limited or uncertain sources of supply, and often procurement lead-times of years. The Aircraft Sustainability Model (ASM), developed by the Logistics Management Institute for the United States Air Force, is a mathematicai model that computes optimal spares mixes to support a wide range of possible operating scenarios. The ASM sizes spares levels based on desired weapon system readiness levels, rather than on supply-oriented measures, such as stock on shelf or percent of demands filled, The ASM has been used by the USAF to determine spares kits to support warti...

: U. S. fighter aircraft demanded surprisingly few spare parts in Desert Storm despite flying lon... more : U. S. fighter aircraft demanded surprisingly few spare parts in Desert Storm despite flying long hours. Although the sorties flown were much longer than their peacetime counterparts, demands per sortie remained about the same. This simple observation raised suspicions that parts fail on the basis of sorties flown, not hours flown, even though Air Force planning systems forecast demands on the basis of projected flying hours. This method of forecasting demands proved inadequate in 1993 when the war plans were modified to include the longer sorties that typify regional conflict scenarios. We found that demands are, for most aircraft, much more closely related to sorties flown than to flying hours. We developed a demand forecasting method that incorporates our results into the wartime spares requirements computation Called Decelerated Demand Forecasting, this method has been implemented by the Air Force for fighters and bombers, avoiding a $ 1.1 billion overstatement in the gross req...

: We model a multi-echelon (s-1,s) continuous review, resupply system in which inter-site movemen... more : We model a multi-echelon (s-1,s) continuous review, resupply system in which inter-site movement of assets within the same echelon (lateral resupplies) are permitted. Lateral resupply-the lateral movement of assets within a given supply echelon from one site to another to satisfy supply shortages - is common in large, multi-echelon supply systems. In fiscal year 1985, for example, approximately 8 percent of supply shortages affecting aircraft mission capability in the U.S. Air Force were satisfied by lateral resupply between bases. Existing methods for modeling lateral resupply are not practical for use in large-scale models such as the Air Force METRIC (Multi-Echelon Technique for Recoverable Item Control) model 1. We modify the METRIC approach, which computes total retail expected backorders by item from standard logistics input data (e.g., failure rates and wholesale and retail repair and resupply times), to include incorporation of lateral resupply in the system. Described in ...

: The Air Force's computation of replenishment spares requirements ignores the existence of s... more : The Air Force's computation of replenishment spares requirements ignores the existence of spare engines and the need for them. This overstates the contribution of engine components to aircraft availability rates and distorts the predicted availability resulting from a given investment in spares. This report documents a study of two engines, using the LMI Aircraft Availability Model, which shows that these errors can be significant. The magnitude and direction of the error depends on the balance between requirements for whole engines and the existing spares levels. In addition to quantifying the effects of engines, this report suggests specific ways in which engines can be included in the availability-based techniques now being introduced into the Air Force's computation. Keywords: Inventory modeling; Inventory systems; Multi-indenture inventory model.

: The physics of component failures is normally assumed to follow a Poisson process. However, man... more : The physics of component failures is normally assumed to follow a Poisson process. However, many studies have shown that the component demands in the U.S. Air Force supply system have a variance-to-mean ratio (VMR) much higher than 1.0, the VMR of a Poisson process. This apparent contradiction is resolved by modeling component failures as a Poisson process whose demand rate is not fixed, but rather is itself a stochastic process, wandering over time as a result of various causes such as weather, flying intensity, reliability growth, and, presumably, other unknown factors. Component and program data for the F-16 and A-10 aircraft show that demand over short time periods is Poisson. This is even more apparent when demands per flying hours are used instead of demands per day. However, when demands are aggregated over longer periods of time or more flying hours, the VMR increases. A gamma-Poisson model for future demands as a function of past observations fits the measured data. We ca...

: Based on analysis of the Air Force's F-16 program, the report examines initial estimates of... more : Based on analysis of the Air Force's F-16 program, the report examines initial estimates of two specific component characteristics: maintenance factor and unit price. The report substantiates the usefulness of an availability model in computing the best mix of recoverable spare components for a specified investment level and also demonstrates the usefulness of early operational data in revising initial estimates of component maintenance factors.