Efficient aircraft spare parts inventory management under demand uncertainty

In airline industries, the aircraft maintenance cost takes up about 13% of the total operating cost. It can be reduced by a good planning. Spare parts inventories exist to serve the maintenance planning. Compared with commonly used reorder point system (ROP) and forecasting methods which only consider historical data, this paper presents two non-linear programming models which predict impending demands based on installed parts failure distribution. The optimal order time and order quantity can be found by minimizing total cost. The first basic mathematical model assumes shortage period starts from mean time to failure (MTTF). An iteration method and GAMS are used to solve this model. The second improved mathematical model takes into account accurate shortage time. Due to its complexity, only GAMS is applied in solution methodology. Both models can be proved effective in cost reduction through revised numerical examples and their results. Comparisons of the two models are also discussed.     

Managing lumpy demand for aircraft spare parts

This paper deals with effective forecasting methods for typically lumpy demand for aircraft spare parts, and analyzes the behavior of forecasting techniques when dealing with lumpy demand. Twenty forecasting techniques are considered and tested and historical data from Alitalia are used to analyze and compare their performance. The results demonstrate that item lumpiness is the dominant parameter and show that demand forecasting for lumpy items is a complex problem; results from previous studies are not very accurate. The best approaches are found to be weighted moving averages, the Croston method, and exponentially weighted moving average models.     

A note on managing lumpy demand for aircraft spare parts

This Note provides comments on an earlier paper that appeared in the Journal of Air Transport Management in 2005 by Regattieri et al.     

Sources of intermittent demand for aircraft spare parts within airline operations

Owing to the sporadic nature of demand for aircraft maintenance repair parts, airline operators perceive difficulties in parts demand forecasting. In this paper we investigate the sources of demand lumpiness, as a function of flying hours, that may affect the parts demand rate. Experimental results of demand lumpiness, measured by the square coefficient of variation (CV²) and the average inter-demand interval (ADI), are examined and clarified through statistical analysis. The general linear model approach is used to explain the variation attributable to the various experimental factors and their interactions. Actual historical data for hard-time and condition-monitoring components from an airlines operator are used. This study shows that aircraft utilization rate can be a major source of lumpiness since it increases and decreases the square coefficient of variation and the average inter-demand interval respectively for the observed demand. This assumes a strictly linear relationship between demand and flying hours/landings.     

Reliability and operations: Keys to lumpy aircraft spare parts demands

This study provides unique new insights into the reasons for lumpy aircraft spare parts demands, and identifies opportunities to improve the regularity of aircraft spares demands. The study develops its unique insights into aircraft spare parts demands by considering the typical failure probability distribution (Weibull Distribution) for aircraft spare parts. The study identifies the range of Weibull model parameters that explain typical aircraft part failure rates, and uses these parameters to perform a Monte Carlo simulation of notional aircraft components in typical aircraft fleet sizes and operations. Each notional component is repeatedly used to failure and replaced, providing a simulated spare part demand rate. The data is evaluated to uncover patterns that allow a deeper understanding of how reliability and operational input factors impact the spare part demand characteristics. The study finds that the aircraft fleet size has the greatest impact on the lumpiness of aircraft spare parts demands. The study also recommends other measures that fleet managers may take to reduce the lumpiness of their spares demands.     

A two-echelon inventory allocation and distribution center location analysis

The optimization of locations for distribution centers is influenced by the demand for individual products. Lower demand products are often more effectively held in more centralized locations than higher demand products. This paper presents a model for optimizing the location of inventory for individual products in a multi-product two-echelon inventory system and the integration of those decisions into the location analysis for distribution centers. A realistic application of the analysis process is discussed.     

Fulfillment source allocation,inventory transshipment,and customer order transfer in e-tailing

We consider an inventory fulfillment-allocation and transshipment problem in an e-tailing environment. For a typical e-tailer, each customer demand is fulfilled from the closest fulfillment center if there are enough inventories. Otherwise, the e-tailer would transship stock from a nearby facility or transfer the customer order so it is fulfilled from another facility, depending on the economics of transportation. We develop a mixed-integer programming model to help e-tailers optimally fulfill customer orders while minimizing logistics costs. We propose a Benders decomposition-based approach to efficiently find optimal solutions. Our computational results demonstrate the importance of considering inventory transshipments in online deliveries.     

Cost adjustment for single item pooling models using a dynamic failure rate: A calculation for the aircraft industry

This paper presents an analytical model for cost estimation in a single-item, multi-hub (S-1,S) inventory policy-pooling model for high-value spare parts in the aviation industry. The model extends existing, static pooling models by implementing a dynamic failure rate, using a maintenance free operating period (MFOP) as a measurement technique to increase availability of aircraft components. The gained results through a dynamic failure rate show significant effects for a reduction of total costs of ownership and achieving a better operational stock planning, which is demonstrated in a numerical application.     

Cost adjustment for single item pooling models using a dynamic failure rate: A calculation for the aircraft industry

This paper presents an analytical model for cost estimation in a single-item, multi-hub (S-1,S) inventory policy-pooling model for high-value spare parts in the aviation industry. The model extends existing, static pooling models by implementing a dynamic failure rate, using a maintenance free operating period (MFOP) as a measurement technique to increase availability of aircraft components. The gained results through a dynamic failure rate show significant effects for a reduction of total costs of ownership and achieving a better operational stock planning, which is demonstrated in a numerical application.     

Optimizing inventory decisions in a multi-stage multi-customer supply chain

Most supply chain models focus on two-stage chains in which vendors supply material to one customer. In this paper, we formulate a three-stage supply chain model where a firm can supply many customers. We deal with three inventory coordination mechanisms between chain members and solve a cost minimization model for each. We show that some of the coordination mechanisms can result in a significantly lower total cost than matching production and delivery along the chain. We provide some insights into when the added complexity of the second and third coordination mechanisms lead to significant cost reductions.     

Integration of inventory and transportation decisions in a logistics system

This paper addresses some of the challenges faced by a company which is responsible for delivering coal to its four subsidiaries situated along a river, through river hired or self-owned vessels. We propose to adopt a vendor managed inventory concept that involves establishment of a central warehouse at the port, and apply the Markov Decision Process (MDP) to formulate both ordering and delivery problems, considering different transportation modes, costs, and inventory issues. An efficient algorithm is developed for solving the MDP models. Our computational tests show that the proposed strategy can significantly reduce the overall system costs while maintaining smooth Just-in-Time supplies of coal to the subsidiaries.     

ABC成本法在企业物流成刊核算中的运用

针对物流企业传统成本核算方法中，存在的忽视企业内部与物流有关成本费用问题，提出利用ABC成本法进行企业物流成本核算。ABC成本法是以作业为基础的成本计算，为此在作业分析的基础上，对ABC成本法用于物流成本核算的步骤进行了论述，并介绍了企业成本核算的应用。     

ABC成本法在企业物流成本核算中的运用

针对物流企业传统成本核算方法中,存在的忽视企业内部与物流有关成本费用问题,提出利用ABC成本法进行企业物流成本核算。ABC成本法是以作业为基础的成本计算,为此在作业分析的基础上,对ABC成本法用于物流成本核算的步骤进行了论述,并介绍了企业成本核算的应用。     

从成本核算角度探讨我国物流成本管理策略

借鉴美国物流成本核算方法,分析我国物流成本的现状.针对我国物流成本未分列记账、核算标准不明确、物流总成本过高等问题,提出物流成本实行单独核算、统一企业间物流核一算标准、采取措施降低运输成本、存货成本及物流管理成本、运用物流信息技术等建议,以提高物流效率和服务水平,不断减少物流费用支出.     

Combined fleet deployment and inventory management in roll-on/roll-off shipping

In maritime transportation of automobiles, roll-on/roll-off (ro–ro) shipping companies operate liner shipping services across major trade routes. Large ro–ro shipping companies are well placed to offer end-to-end integrated logistics services to auto manufacturers engaged in international trade of vehicles. Therefore, we present a new mixed integer programming model for fleet deployment including inventory management at the ports along each trade route. Due to the complexity of the problem, a rolling horizon heuristic (RHH) is proposed. The RHH solves the problem by iteratively solving sub-problems with shorter planning horizon. Computational results based on real instances are presented.     

Channel coordination under consignment and vendor-managed inventory in a distribution system

This paper deals with the problem of coordinating a vertically separated distribution system under vendor-managed inventory and consignment arrangements. We formulate the profit-maximization problem and carry out equilibrium analysis under cooperative and non-cooperative settings. In addition, a revenue-sharing scheme joint with a side-payment is proposed, which leads to Pareto improvements among channel participants. Our analysis reveals that the non-cooperative decentralization tends to price higher and stock less, which leads to a lower channel-wide profit. The consistent bias can be rectified by the dominant, cooperative wholesaler or by using the proposed two-part revenue-sharing mechanism.     

基于作业成本法的物流企业成本控制模式研究

一、我国物流企业成本控制现状及存在的问题在我国,物流服务业正处于快速成长时期,物流业务创新速度加快,物流管理模式不断变化,这种行业发展模式     

Incorporating location,routing and inventory decisions in supply chain network design

This paper for the first time presents a novel model to simultaneously optimize location, allocation, capacity, inventory, and routing decisions in a stochastic supply chain system. Each customer’s demand is uncertain and follows a normal distribution, and each distribution center maintains a certain amount of safety stock. To solve the model, first we present an exact solution method by casting the problem as a mixed integer convex program, and then we establish a heuristic method based on a hybridization of Tabu Search and Simulated Annealing. The results show that the proposed heuristic is considerably efficient and effective for a broad range of problem sizes.     

Optimizing inventory decisions in a multi-stage multi-customer supply chain: A note

In this paper, we propose an n-stage-multi-customer supply chain inventory model where there is a company that can supply products to several customers. We formulate the model for the simplest inventory coordination mechanism which is referred to as the same cycle time for all companies in the supply chain. We conclude that it is possible to use an algebraic approach to optimize the supply chain model without the use of differential calculus.     

防护性控制在成本控制中的应用

成本控制是会计控制中的重要内容,防护性控制是在成本控制中建立若干项规章制度和约束条件,以避免或减少成本形成过程中的偏差。为此对防护性控制的程序及影响防护性控制的主要因素进行阐述,并结合具体的实例说明防护性控制理论的具体运用方法。