Direct Maintenance Costs Research Articles

Optimal Inspection and Maintenance Policy: Integrating a Continuous-Time Markov Chain into a Homing Problem

The state of a machine is modeled as a controlled continuous-time Markov chain. Moreover, the machine is being serviced at random times. The aim is to maximize the time until the machine must be repaired, while taking the maintenance costs into account. The dynamic programming equation satisfied by the value function is derived, enabling optimal decision-making regarding inspection rates, and special problems are solved explicitly. This approach minimizes direct maintenance costs along with potential failure expenses, establishing a robust methodology for determining inspection frequencies in reliability-centered maintenance. The results contribute to the advancement of maintenance strategies and provide explicit solutions for particular cases, offering ideas for application in reliability engineering.

Economic Aspects of Aircraft Propulsion Electrification

Aircraft propulsion electrification is currently being considered by industry and academia as one of the most promising strategies to reduce air transport emissions and increase overall efficiency levels. In the past decade, several papers were published on this subject, with the majority indicating encouraging fuel burn benefits versus conventional, fossil-fuel-based propulsion systems when future technologies, novel aircraft configurations, and synergistic propulsive-airframe integration are employed. However, a much smaller effort has been applied to the economic aspects of hybrid and fully electric propulsion, which are crucial for a successful product introduction. The present paper describes the modeling of a baseline general-aviation-type aircraft and its propulsion system retrofit with electrified architectures, exploring different electrification strategies for a fixed airframe design. Analyses are performed at the aircraft level, comparing recurring and cash operating costs for several cost and durability scenarios. While considerable CO2 reductions may be achieved in some electrification strategies, aircraft performance is significantly penalized, and important improvements in economic figures of merit are needed in order to make electrified propulsion cost-competitive. Electrified architectures tend to increase costs: turboelectric increases recurring equipment costs, while hybrid-electric increases recurring and direct maintenance costs, especially at higher degrees of energy hybridization.

Investigation into Data Mining for Analysis and Optimization of Direct Maintenance Costs in Civil Aircraft Operations

Investigation into Data Mining for Analysis and Optimization of Direct Maintenance Costs in Civil Aircraft Operations

A Study on Quantities Driving Maintenance, Repair, and Overhaul for Hybrid-Electric Aeroengines

Abstract Hybrid-electric propulsion for commercial aircraft is currently a key industry interest. Consequently, publications on its design and performance estimation are manifold. However, models addressing characteristics of maintenance, repair, and overhaul (MRO) are virtually unavailable—even though direct maintenance costs (DMC) represent a significant part of direct operating costs (DOC) in commercial aviation. Detailed analysis of hybrid-electric aircraft propulsion degradation and maintenance scenarios must integrate both methods of sizing and design as well as operational factors for conventional and electric subsystems, as operator-specific utilization strongly influences MRO. Accordingly, a holistic engine analysis model is currently being developed using the example of an Airbus A320 aircraft, taking into account flight mission, engine performance, degradation, and MRO. This paper presents an implementation of hybridization into the gas turbine thermodynamic cycle calculation for parallel hybrid-electric (PHE) engine architectures with 2 and 5 MW electric motors, and the approach necessary for resizing hybridized gas turbine components. Turbomachinery loading throughout representative short-haul missions is analyzed for conventional and hybrid-electric configurations based on the V2500 high-bypass turbofan engine, whereby unknown or uncertain boundary conditions are considered in a probabilistic sensitivity study. As a result, MRO-driving quantities such as engine performance parameters, atmospheric conditions, and ingested aerosols can be compared. The findings suggest that DMC related to the gas turbine may be considerably lowered through hybridization, as it allows for reduced peak temperatures and more uniform gas turbine operation. However, these gains are at least partially offset by additional components' DMC. For electrical machines, bearings and the stator winding insulation are life-limiting, where the latter becomes increasingly dominant for higher power densities associated with high current densities and copper losses. Thermo-mechanical stresses are considered as driving mechanisms in power electronic systems degradation. Consequently, powerful lightweight machines must be balanced against tolerable thermal and electrical loads to achieve suitable service life.

Demonstrating the Test Procedure for Preventive Maintenance of Aging Concrete Bridges

Deteriorated facility maintenance is a critical social issue in advanced countries. Its cost increases when considering the social consequences in terms of asset value and direct maintenance costs. Data from Korea’s Ministry of Land, Infrastructure, and Transport shows that there were 3454 bridges aged 30 years or over in Korea in 2017; this number will increase to 10,961 by 2027. In thirty years, maintenance costs will be incurred for more than 32,000 old bridges in Korea. These trends are also observed in the US, Japan, and Korea. Diverse studies have been conducted to predict the residual life of old bridges via bridge performance evaluation and load-carrying capacity assessments. However, criteria for evaluating bridge performance and verifying the effect of bridge maintenance are yet to be established due to two reasons. First, most studies on performance evaluation, maintenance, and rehabilitation techniques have been performed on limited specimens from building elements or through small-scale simulations that do not reflect the deterioration factors of complex materials in diverse environments. Second, the performance evaluation of bridges is difficult compared to quantitative state evaluations. As a method of predicting the future performance of aged concrete bridges, it is effective to understand the actual aged bridges through experiments, and this study intends to propose the method.

Research on Civil Aircraft Direct Maintenance Cost Analysis and Optimization Based on Data Mining

Civil aircraft maintenance cost is an important indicator to measure the maintainability and economy of civil aircraft, and it accounts for a considerable proportion of aircraft operating costs. Data mining technology can unearth potentially high-value data from massive aircraft operating data. In this paper, aiming at the problem that there are very few actual aircraft maintenance data that can be effectively used in the development stage of civil aircraft, the research on the direct maintenance cost analysis and optimization method of civil aircraft based on data mining is carried out. The theoretical basis of direct maintenance cost analysis based on data mining is studied, the factors affecting the direct maintenance cost of civil aircraft are analyzed based on data mining, and the DMC analysis method is established. On the basis of the above research, the direct maintenance cost analysis model of civil aircraft was established and optimized to achieve the goal of reducing direct maintenance costs. It is of great significance for reducing aircraft life cycle costs and improving aircraft market competitiveness.

Stochastic modelling of maintenance flexibility in Value for Money assessment of PPP road projects

Maintenance flexibility has been promoted as a value driver for long-term public–private partnerships (PPPs). However, the value and risk associated with this value driver have not been properly quantified in the Value for Money (VfM) assessment literature. To bridge the gap, a novel stochastic modelling methodology is proposed to characterize the complex interactions among the lifecycle cost (LCC), performance deterioration and maintenance strategies. Four different maintenance strategies are designed to emulate the practice in the traditional and PPP delivery methods. The LCC includes the direct maintenance cost, user cost, residual value, and payment deduction, the last three often being neglected in VfM assessments. Simulation-based optimization and dynamic programming analysis are used to determine the probability distributions of the LCC and the VfM. A hypothetical highway PPP project under an availability payment model is selected as a case study. The results show that maintenance flexibility is indeed able to reduce the LCC for the private party. However, this private efficiency, if not properly regulated, could cause a reduced asset residual value and an increased user cost, making the public party worse off. In addition, for all potential maintenance strategies, the public sector is found to retain significant lifecycle cost risk, largely in the form of user cost.

Optimisation of maintenance strategy of deteriorating bridges considering sustainability criteria

Facing the contradiction between increasing maintenance demand and limited financial, as well as smaller social and environmental impacts, the optimisation of bridge maintenance strategies should be carried out. In this paper, the assessment model of four objectives, including the safety performance, economic, social and environmental impacts, in sustainability criteria are proposed. Moreover, a systematic optimisation framework of maintenance strategy of deteriorating bridges considering sustainability criteria and a novel decision-making method are developed, based on fuzzy analytic hierarchy process (FAHP) and a decision-making algorithm based on linear programming techniques for multidimensional analysis of preference (LINMAP). The case analysis results verify the effectiveness and superiority of the previous optimisation framework, and also show that the final optimal strategy obtained by the proposed decision-making algorithm can reflect the will of experts well. Compare with the essential maintenance, the implementation of preventive maintenance is more conducive to realise the sustainable development of the deteriorating bridges. The sensitivity analysis results show that the monetary discount rate has a greater impact on the life cycle maintenance cost, which is mainly controlled by the total social cost, while the direct maintenance cost only accounts for a small part.

Reliability Based Life Cycle Management of Bridge Subjected to Fatigue Damage

In recent times, there has been an increase in transport infrastructure failure. This increase is due to aging infrastructure, increased number of extreme weather events caused by climate change, and increased traffic loading. Accordingly, the need for planned and unplanned maintenance interventions is rising. Associated costs do not only involve direct maintenance or reconstruction costs, but also secondary effects experienced by users of the transport network as well as the environment and society in general. Infrastructure managers require tools for accurate quantification of infrastructure resilience that will enable rational adaptation investment strategies, so as to maintain high level of safety of transport networks. Through the development of a Global Safety Framework, at the core of which is a Multi-modal Network Decision Support Tool, the SAFE-10-T project (Safety of Transport Infrastructure on the TEN-T Network) is providing integrated solutions to issues related to infrastructure safety and planning. The paper presents a reliability-based whole life cycle model developed within this project enabling strategic investment decisions that maximize safety, minimize disruption, and environmental impacts and allow for the best use of limited resources. The model is applied on a case study of a bridge in the Port of Rotterdam in the Netherlands.

Reducing Operational Costs of Offshore HVDC Energy Export Systems Through Optimized Maintenance

For the grid connection of offshore wind farms today, in many cases a high-voltage direct current (HVDC) connection to the shore is implemented. The scheduled maintenance of the offshore and onshore HVDC stations makes up a significant part of the operational costs of the connected wind farms. The main factor for the maintenance cost is the lost income from the missing energy yield (indirect maintenance costs). In this study, we show an in-depth analysis of the used components, maintenance cycles, maintenance work for the on- and offshore station, and the risks assigned in prolonging the maintenance cycle of the modular multilevel converter (MMC). In addition, we investigate the potential to shift the start date of the maintenance work, based on a forecast of the energy generation. Our findings indicate that an optimized maintenance design with respect to the maintenance behavior of an HVDC energy export system can decrease the maintenance-related energy losses (indirect maintenance costs) for an offshore wind farm to almost one half. It was also shown that direct maintenance costs for the MMC (staff costs) have small effect on the total maintenance costs. This can be explained by the fact that the additional costs for maintenance staff are two orders of magnitude lower than the revenue losses during maintenance.

An Allocation Model of Direct Maintenance Cost for Civil Aircraft Based on Entropy Weight-TOPSIS Method

An Allocation Model of Direct Maintenance Cost for Civil Aircraft Based on Entropy Weight-TOPSIS Method

Study on Unscheduled Direct Maintenance Cost of Civil Aircraft Structure

Study on Unscheduled Direct Maintenance Cost of Civil Aircraft Structure

Aircraft piston engines on-condition exploitation

PurposeCurrently, in many countries, aviation safety regulations allow piston engines exploitation above Time Between Overhaul (TBO) recommended by manufacturers. Upon fulfillment of certain requirements, which are already included in the manufacturers’ documentation, TBO extension is granted. National Aviation Authority has approved exploitation of piston engines to something like quasi on-condition maintenance, which has no technical proof behind. This leads to the conclusion that the current, simple way of the engine’s life extension is not the best solution for maintaining flight safety. Aircraft piston engines TBO extension requires changes in the current exploitation system.Design/methodology/approachThe paper provides methodology for aircraft piston engines on-condition exploitation based on engine flight parameters (from cruise and takeoff) and engine oil particles analysis. The paper describes a method of diagnostic limits for certain engine parameters and elements in the oil assignation assuming that they come under rules of normal distribution.FindingsIt has been found that piston engines installed on maximum takeoff mass <5,700 kg class aircraft are the second biggest contributor as a source of aviation events, thereby having a significant impact on aviation safety. Engine flight parameters and elements content in the oil meet Gaussian rules.Practical implicationsIntroduction of the engine on-condition exploitation into operation practices reduces the operator’s engine direct maintenance cost and increases technical knowledge of the employees and has a positive impact on flight safety.Originality/valueIt is the first scientific description in Poland, which proposes an empirically proved methodology of the aviation piston engines on-condition exploitation.

Benefits Analysis of Prognostics &amp; Health Monitoring to Aircraft Maintenance using System Dynamics

The benefits of applying Prognostics &amp; Health Monitoring (PHM) techniques to Aircraft Maintenance are evaluated using System Dynamics (SD). It is well known that a key motivation for PHM is to increase aircraft availability by reducing unscheduled removals and downtime, ultimately reducing Direct Maintenance Costs (DMC). The benefits to aircraft maintenance are tested by modelling two maintenance philosophies using SD: the traditional approach driven by scheduled &amp; reactive maintenance; and through Condition Based Maintenance (CBM) by considering PHM functionality in maintenance practice. The study is focused on an Electromechanical Actuator (EMA) for an aircraft flight control system across a fleet of 25 aircraft over an 8 year maintenance overhaul period. The study indicated there were fewer unscheduled removals as a result of CBM in comparison to the traditional approach. Further sensitivity studies on varying degradation patterns led to instability in maintenance planning with more reactive maintenance due to more abrupt failures of the EMA. The cost effectiveness of CBM as a function of PHM efficiency is demonstrated through DMC accumulation where it was found that CBM is no longer cost-beneficial when over 85% of the EMA life has been used. Overall, the SD models presented a general level of systems understanding of the causalities that are inherent within the two maintenance policies and are a useful methodology to consider PHM benefits through analysing the impact of different policies on the system behaviour.

A railway maintenance scheduling problem with customer costs

An important aspect of infrastructure management is the scheduling of maintenance tasks, which implies the allocation of tasks to different crews or machines and the determination of an execution order. To this end, different aspects have to be considered. On the one hand, the maintenance operator is interested in reducing direct maintenance costs, e.g. travel costs. On the other hand, priorities must be considered by scheduling maintenance tasks. Often, this is done by urgency rules, an inflexible method that resolves prioritised tasks first. In this paper, another approach is discussed. Instead of urgency rules, the maintenance tasks are afflicted with penalty costs that have to be paid for every day until the task is resolved. Then, the later the execution time of such a job, the higher are the penalty costs. By minimising the sum of penalty costs and travel costs, a solution with small overall costs can be found. The resulting scheduling problem is a multi-depot vehicle routing problem with travel and customer costs. For this extension of a vehicle routing problem, different formulations as mixed-integer linear program are developed. For small instances, these formulations are compared with respect to their computation time in a solution method that uses a commercial solver.

Direct maintenance cost prediction of civil aircraft

Purpose The purpose of this paper is to analyze parameters that influence direct maintenance cost (DMC) in the civil aircraft operational phase. Reducing direct maintenance cost of civil aircrafts is one of the important ways to improve economy. DMC prediction can provide decision support for the optimization of the design parameters optimization to realize the objection in decreasing the maintenance cost, and it can also improve the aircraft competitiveness.

Life-Cycle Cost Evaluation of Conventional and Corrosion-Resistant Steel for Bridges

Steel bridges that are under severe chloride exposure due to deicing salts or marine environmental effects require frequent maintenance and repair activities to extend their service life and maintain an adequate performance level. In addition to the direct maintenance cost, these maintenance actions may lead to indirect costs associated with traffic delays and environmental effects that can significantly increase the life-cycle cost of the bridge under consideration. The use of more sustainable materials, such as maintenance-free steel, may increase the initial cost of the structure; however, the life-cycle cost, including the maintenance actions during the service life and their associated indirect effects, can be significantly reduced. This paper presents the computational approach and results of an analytical investigation to quantify the life-cycle cost of a steel bridge constructed using conventional painted carbon steel and to compare this cost to that of the same bridge constructed using maintenance-free steel. Indirect environmental, social, and economic impacts of maintenance actions are computed to quantify the sustainability metrics associated with steel bridges during their life cycle. The approach is illustrated using an existing bridge located in Pennsylvania.

Annual maintenance budget estimation for a plant system

Purpose – The purpose of this paper is to propose a methodology to evaluate the annual maintenance budget (AMB) for a plant system as a percentage of its asset replacement value (ARV). Design/methodology/approach – Variables influencing the budget for the plant system are identified and modeled in terms of a plant maintenance Budget digraph. The nodes in the digraph represent the function of budget influencing variables and edges represent the degree of influence among these. The plant maintenance budget function is derived from the equivalent matrix of the plant maintenance budget digraph and is used to evaluate the AMB for the plant system as a percentage of its ARV. The presented model is illustrated with an example. Findings – The proposed methodology enables the maintenance managers and practicing engineers to evaluate the AMB for maintenance tasks based on plant specific variables that can vary from one plant to another, without resorting to general rules-of-thumb method of budgeting or to expert judgment. Research limitations/implications – The methodology suggested does not claim to cover all aspects of budgeting and is confined to direct maintenance costs. Practical implications – A fair estimation of AMB for a plant system gives an appropriate direction to maintenance actions and ensures that the assets will be kept in healthy and reliable state. This is desirable because it will ensure that maintenance resources are appropriately benchmarked and the resources are utilized judiciously. This ensures maintenance effectiveness. Originality/value – The paper presents a structural approach to budgeting for maintenance tasks. This approach is valuable for plant managers, with ease in implementation.

Applying an Improved CBR Model to Predict the Civil Aircraft Direct Maintenance Cost in the Design Stage

Accurate prediction of civil aircraft maintenance cost in the design phase of a civil aircraft manufacture project plays a key role in success of the airplane sale and market share. Accordingly, many researchers or organizations have proposed various methodologies for predicting the cost in the design phase with limited information. This study was aimed at improving the prediction performance of a cost prediction model based on the Case-based Reasoning (CBR) technique, which has recently become widely used. Toward this end, an improved CBR model that uses the K-means technique in the retrieving phase of the CBR technique was developed. The proposed K-means-based revised CBR model is expected to be useful in estimating the civil aircraft maintenance cost in the initial phase of a project.

EMBRAER Perspective on the Challenges for the Introduction of Scheduled SHM (S-SHM) Applications into Commercial Aviation Maintenance Programs

This paper presents an overview of the challenges an original equipment manufacturer (OEM) such EMBRAER may face to introduce scheduled structural health monitoring (S-SHM) applications in the maintenance programs of its commercial aviation aircraft models. S-SHM solutions have the potential to reduce aircraft operators direct maintenance costs and fleet downtime while keeping aircraft airworthiness at a minimum maintenance downtime and costs. As part of new approach in terms of scheduled maintenance practices, the replacement or complementation of traditional structural inspections tasks by new maintenance procedures taking credit of SHM technologies must be done in ways that meet the expectations and requirements of Regulatory Authorities, OEMs and airlines maintenance and engineering departments related to topics such as: safety, continued airworthiness, cost/benefits ratio, S-SHM systems built-in redundancies and reliability to support higher fleet availability, as well as necessary mechanics qualification. Besides the efforts for validation, verification, qualification and certification of such systems to deliver the expected effectiveness levels to verify structural integrity and withstanding the operational conditions to which it will be exposed, an OEM intended to offer their customers with the benefits of S-SHM solutions will be required initially to revise its policy and procedures handbooks (PPH) to adopt the new S-SHM Air Transport Associations Maintenance Steering Group 3 (MSG-3) Methodology guidelines. This will alter in different ways the current Maintenance Review Board processes conducted by each OEM to develop and revise the minimum scheduled maintenance program for a given commercial aircraft type certificate. The contents of the Maintenance Review Board Reports (MRB) will need to be revised in order to clearly indicate the scope and frequencies of each approved S-SHM task, and how they will replace, complement and/or be an alternative means of compliance of the more traditional maintenance tasks types such as general and detailed visual inspections (GVI and DET, respectively). Additionally, the Airplane Maintenance Manuals (AMM) will need to be revised to include specific S-SHM procedures on how to perform the intended inspection, how to proceed when degradation is detected in the monitored structures and how to repair such systems in case of failures.