Personnel scheduling for aircraft line maintenance-solution methods for the tactical and operational decision level.

Labor is one of the most significant costs for companies in highly developed countries. In the last decades, many companies have relocated their production facilities to low wage countries. Since service needs to beprovided on site, service companies, however, cannot escape from the costly wage expenses. Therefore, it is very important that overstaffing and idleness are avoided by creating good personnel schedules. The personnel scheduling problem we will study in this dissertation originates froma line maintenance department of an aircraft maintenance company. A line maintenance program represents the regular short inspections of aircraft between their arrival and their departure at some specific airport. Whereas the workload that stems from the tasks that need to be done during these inspections is rather stable, the main source of uncertainty forthese inspections is the timing of the demand. Delays can originate forinstance from earlier flights, bad weather conditions, or air traffic management. In this dissertation, we propose methods which should facilitate the scheduling in practice, and offer thereby an alternative for thecurrent practice of scheduling by paper and pen. Chapter 2provides a classification of the personnel scheduling literature from 2004 onwards. The classification fields, such as applied methods, decision delineation, and uncertainty incorporation, guide the reader in his/her search for specific problem settings and the corresponding approaches of the research community. The current literature mainly addresses the staffing and/or scheduling of workers considering fixed inputs. We adviseresearchers to integrate multiple decisions into the personnel scheduling problem such as demand forecasting, machine scheduling, or considering multiple locations. The last decades, companies more and more consideremployee preferences (such as requests for specific working days or shifts, assignments to a specific location or working partner, preferred durations or start times) in order to satisfy the workforce and to allow them to flexibly manage their personal lives. There are still great opportunities in finding algorithms that efficiently cope with those preferences. Lastly, most papers appear to feature a deterministic approach, while real-world personnel scheduling problems have to deal with a variety of uncertainty sources. In situations where uncertainty has a strong effect on the personnel schedule, such as volatile demand or last-minute changes, it could prove very beneficial to incorporate this uncertainty inthe decision-making process. Instead of integrating this uncertainty, researchers could also test the robustness of their solutions, for instance by simulating the stochastic behavior of demand, or worker availabilities. In the literature, however, we hardly ever encountered this type of analysis. In Chapter 3 the different types of aircraft maintenance that appear in literature are discussed. We found the terminology consisting of many overlapping definitions very confusing. To obtain a better insight into the different types of aircraft maintenance, we provide a taxonomy that classifies all types and we discuss the literature that addresses the combination of aircraft maintenance and personnel scheduling. In the second section of this chapter we provide the details of a given personnel scheduling problem of an aircraft maintenancecompany. In this problem, personnel rosters need to be created while minimizing the labor costs that stem from the provision of a line maintenance program. This problem setting is the basis for the problems studied in Chapters 4, 5 and 6. Chapter 4 is dedicated to a three-step evaluation procedure for personnel rosters. Due to the usage of heuristics and multi-objective performance criteria, solution procedures typically generate multiple solutions, or in this case, personnel rosters. For the management, it is difficult to create a ranking among these solutions. Therefore, we present an approach in which the rosters, which arecreated based on a deterministic problem setting, are used in a stochastic environment. This results in performance criteria, such as service rate and tardiness values, that are evaluated by means of a Data Envelopment Analysis (DEA). This approach should enable that management decisions are no longer based on instinct but on objective criteria. In Chapter 5, we study two variants of the resource loading problem (RLP), in which a number of jobs with time windows need to be scheduled with monotone execution patterns. This latter characteristic ensures that a given job can only be assigned a non-decreasing (resp. non-increasing)number of workers over the periods in which the job is processed. We distinguish between RLP-selection in which no non-regular capacity isavailable and selected jobs yield a reward, and RLP-capacity in which all jobs need to be executed and non-regular capacity is minimized. The resulting integer programming (IP) formulation for real-life problem instances tends to be too hard in order to be solved in limited time with a commercial solver. Therefore, we carry out a Dantzig-Wolfe decompositionand try to solve the resulting problem with column generation. Unfortunately, these two CG methods do not give good results. The CG method thatuses execution schemes (i.e., columns which state in which period and with which intensity a job should be executed) has the advantage that it is the only solution method which is able to find results for the large instances (with 300 flights). Finally, Chapter 6 follows with the presentation of a proactive/reactive policy to deal with the maintenance job scheduling problems on the operational level which areinfluenced by uncertainty in the arrival times of the jobs. The proactive policy consists of creating a personnel roster and a baseline schedule which take into account the delay distributions of the jobs and schedules each job as late as possible. In the reactive policy, we use a rolling horizon algorithm which makes use of the most recent information withrespect to the arrival times of the jobs. The results indicate that thequality of information is highly important. Better estimations on the real release times of the jobs (i.e., the arrival delays of flight) and the earlier these are retrieved, the cheaper the reactive scheduling policy. Also the job characteristics play an important role with respect to the costs which have to be made to create feasible schedules.status: publishe

An empirical study on human resource planning in Belgian production companies

This paper investigates human resource planning in Belgian production companies. First, a literature study is developed to serve as a basis for the results of the empirical research. The literature study is mainly based on papers in the field of operations research that provide interesting insights such as the research-application gap, which is the lack of implementation of models provided by literature. The most important part of this paper is the empirical research. The empirical research is mainly based on an online developed questionnaire on personnel planning, which is completed by 123 Belgian production companies. The goal of the survey is to investigate the planning tools that are used. Aspects that influence the complexity of the planning problem and the influence of company size on the use of the specific planning tools are examined. Furthermore, the future objectives and investment plans of Belgian production companies concerning human resource planning are also surveyed. Finally, some general remarks on the Belgian labor market are mentioned briefly.nrpages: 26status: publishe

A model enhancement heuristic for building robust aircraft maintenance personnel rosters with stochastic constraints

This paper presents a heuristic approach to optimize staffing and scheduling at an aircraft maintenance company. The goal is to build robust aircraft maintenance personnel rosters that can achieve a certain service level while minimizing the total labour costs. Robust personnel rosters are rosters that can handle delays associated with stochastic flight arrival times. To deal with this stochasticity, a model enhancement algorithm is proposed that iteratively adjusts a mixed integer linear programming (MILP) model to a stochastic environment based on simulation results. We illustrate the performance of the algorithm with a computational experiment based on real life data of a large aircraft maintenance company located at Brussels Airport in Belgium. The obtained results are compared to deterministic optimization and straightforward optimization. Experiments demonstrate that our model can ensure a certain desired service level with an acceptable increase in labour costs when stochasticity is introduced in the aircraft arrival times.nrpages: 29status: publishe

Workforce planning incorporating skills: state of the art

This paper presents a review and classification of the literature regarding workforce planning problems incorporating skills. In many cases, technical research regarding workforce planning focuses very hard on the mathematical model and neglects the real life implications of the simplifications that were needed for the model to perform well. On the other hand, many managerial studies give an extensive description of the human implications of certain management decisions in particular cases, but fail to provide useful mathematical models to solve workforce planning problems. This review will guide the operations researcher in his search to find useful papers and information regarding workforce planning problems incorporating skills. We not only discuss the differences and similarities between different papers, but we also give an overview of the managerial insights. The objective is to present a combination of technical and managerial knowledge to encourage the production of more realistic and useful solution techniques.publisher: Elsevier articletitle: Workforce planning incorporating skills: State of the art journaltitle: European Journal of Operational Research articlelink: http://dx.doi.org/10.1016/j.ejor.2014.10.038 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved.status: publishe

A two-stage mixed integer programming approach for optimizing the skill mix and training schedules for aircraft maintenance

This paper presents a two-stage mixed integer programming approach for optimizing the skill mix and training schedule at the aircraft maintenance company Sabena Technics. Of course, when all workers are trained for all skills, cheaper workforce schedules are possible. However, the training that is required to acquire all those skills can become very expensive. In the first stage of our two-staged approach, we therefore make a trade-off between the training costs and the resulting cheaper workforce schedule. As we assume that workers are unavailable to work during their training, the obtained result is only applicable in practice if the required training can be performed without endangering the current maintenance operations. In the second stage, we therefore want to find an optimal and feasible training schedule in order to obtain the desired skill mix with minimal costs. We illustrate our models with a computational experiment based on real-life data of Sabena Technics.nrpages: 32status: publishe

A model enhancement heuristic for building robust aircraft maintenance personnel rosters with stochastic constraints

This paper presents a heuristic approach to optimize staffing and scheduling at an aircraft maintenance company. The goal is to build robust aircraft maintenance personnel rosters that can achieve a certain service level while minimizing the total labour costs. Robust personnel rosters are rosters that can handle delays associated with stochastic flight arrival times. To deal with this stochasticity, a model enhancement algorithm is proposed that iteratively adjusts a mixed integer linear programming (MILP) model to a stochastic environment based on simulation results. We illustrate the performance of the algorithm with a computational experiment based on real life data of a large aircraft maintenance company located at Brussels Airport in Belgium. The obtained results are compared to deterministic optimization and straightforward optimization. Experiments demonstrate that our model can ensure a certain desired service level with an acceptable increase in labour costs when stochasticity is introduced in the aircraft arrival times.publisher: Elsevier articletitle: A model enhancement heuristic for building robust aircraft maintenance personnel rosters with stochastic constraints journaltitle: European Journal of Operational Research articlelink: http://dx.doi.org/10.1016/j.ejor.2015.05.008 content_type: article copyright: Copyright © 2015 Elsevier B.V. and Association of European Operational Research Societies (EURO) within the International Federation of Operational Research Societies (IFORS). All rights reserved.status: publishe

Workforce planning incorporating skills: state of the art

This paper presents a review and classification of the literature regarding workforce planning problems incorporating skills. In many cases, technical research regarding workforce planning focuses very hard on the mathematical model and neglects the real life implications of the simplifications that were needed for the model to perform well. On the other hand, many managerial studies give an extensive description of the human implications of certain management decisions in particular cases, but fail to provide useful mathematical models to solve workforce planning problems. This review will guide the operations researcher in his search to find useful papers and information regarding workforce planning problems incorporating skills. We not only discuss the differences and similarities between different papers, but we also give an overview of the managerial insights. The objective is to present a combination of technical and managerial knowledge to encourage the production of more realistic and useful solution techniques.nrpages: 38status: publishe

Integrated staffing and scheduling for an aircraft line maintenance problem

This paper studies the problem of constructing the workforce schedules of an aircraft maintenance company. The problem involves both a staffing and a scheduling decision. We propose an enumerative algorithm with bounding in which each node of the enumeration tree represents a mixed integer linear problem (MILP). We reformulate the MILP such that it becomes tractable for commercial MILP solvers. Extensive computational tests on 40 instances that are derived from a real-life setting indicate that the algorithm is capable of finding close-to-optimal solutions

Integrated staffing and scheduling for an aircraft line maintenance problem

This paper studies the problem of constructing the workforce schedules of an aircraft maintenance company. The problem involves both a staffing and a scheduling decision. We propose an enumerative algorithm with bounding in which each node of the enumeration tree represents a mixed integer linear problem (MILP). We reformulate the MILP such that it becomes tractable for commercial MILP solvers. Extensive computational tests on 40 instances that are derived from a real-life setting indicate that the algorithm is capable of finding close-to-optimal solutions. © 2012 Elsevier Ltd.publisher: Elsevier articletitle: Integrated staffing and scheduling for an aircraft line maintenance problem journaltitle: Computers & Operations Research articlelink: http://dx.doi.org/10.1016/j.cor.2012.11.011 content_type: article copyright: Copyright © 2012 Elsevier Ltd. All rights reserved.status: publishe

A three-stage approach for aircraft line maintenance personnel rostering using MIP, discrete event simulation and DEA

nrpages: 22status: publishe