A production scheduling model and analysis for the maintenance repair and overhaul service providers

Maintenance, repair and overhaul (MRO) are regulated and necessary activities for the airline sector to ensure the safety and continuity of flights. Both military and commercial aircrafts must go through MRO at regulated intervals. MRO activities constitute the second largest cost component for the airline companies after the fuel. One of the important differences between MRO systems and traditional production systems is the use of rotable inventory for some expensive parts or modules. In the rotable inventory case, the arriving part for service is directly exchanged with a ready inventory. Thus, the customer airliner continues its flights with almost no break time. The MRO company overhauls the exchanged equipment and places it as ready inventory to be used for future demands. As MRO companies schedule the exchanges of rotable inventory and overhauls, considering the last date of service, they should try to bring in the aircrafts as close as possible to their regulated final dates for overhauls, since the earlier arrivals will not be preferred economically by the airline companies. The limited production capacity and inventory are the main constraints for scheduling the production. In this study, the problem is modeled with the assumptions of limited initial inventory and production capacity, multiple type rotable inventory and finite planning horizon, with the objective of minimizing the total earliness. We tested the problem thorough detailed numerical experiments. We have shown the decreasing marginal benefits for an additional unit of initial rotable inventory or additional process line and the relationship between this benefit and process time and process capacity. In addition to this, a heuristic approach is proposed to solve the problem faster and some implementations are applied on the offered heuristic for improvement. As a result of the applied implementation on the proposed heuristic, the solutions of the proposed heuristic and optimal solutions are compared with each other to determine the performance of the offered heuristic. Key Words: Production scheduling, maintenance repair and overhaul, rotable inventory, perturbation heuristic