In this paper a new problem of three stage disassembly-assembly scheduling is introduced and reviewed. This problem, which was arisen from the aviation industry characteristics, is a generalization of the two stage assembly scheduling problem. Products (helicopters) in the aviation industry return to assembler for annual overhaul repair services. In the first stage helicopters are disassembled into their components. After that, the components are sent to their dedicated machines in the second stage for repair operations concurrently. In the second stage, some of the components may require one or more spare parts. Repair operations of the components can be started when their required spare parts are available at that time. After completing all of the component operations, the assemble stage can be started.
In this problem we consider repair scheduling of components and lot sizing and scheduling of their required spare parts with the objective of minimizing sum of total completion times of the retuned products and spare parts inventory costs. In this study, an integrated formulation approach has been employed for the problem and a linear MIP was developed. A base case from aviation industry was solved and results were analyzed. The sensitivity analysis of the problem was carried out by changing key parameters of the base case. Selecting a repair strategy or changing to a new strategy is a key decision in the aviation industry. In this study, changing to a new strategy has been compared with three existing repair strategies in 120 problem instances using three types of data sets. Results showed that various strategies could be selected depend on the quality of returned products. The repairing shared items strategy has a better performance in average compared to the other strategies.