Resource-constrained project scheduling with multiple states: Bi-objective optimization model and case study of aircraft maintenance

Abstract

This paper introduces a new resource-constrained project scheduling problem in which the project has multiple possible states and whether an activity can be performed at a certain time depends on the state at that time. We are motivated by aircraft maintenance projects where activities need to be performed in particular aircraft states, such as power on/off and jack on/off. We formulate a bi-objective optimization model for this problem, which determines the schedule of activities and the selection of states over the planning horizon, subject to resource constraints, precedence relationship, and state restrictions. The model concerns both the minimization of the project duration and the minimization of the number of state changes over time. A heuristic algorithm, which utilizes genetic algorithm techniques, is developed to obtain Pareto efficient solutions of the model. Its effectiveness is demonstrated through a comparison with CPLEX and an adaptation of NSGA-II. Furthermore, we conduct a case study about aircraft maintenance C-check projects in a major airline. The case study demonstrates that our optimization-based approach is applicable and beneficial to the project scheduling practice with the consideration of states.