Development of an aircraft maintenance schedule optimisation method focused on the minimisation of workload fluctuations

Abstract

In aircraft maintenance, the initial maintenance schedule of an aircraft is highly dependent on the maintenance planning document. This document, set up by manufacturers, regulators and operators, contains all the requirements for the initial maintenance schedule of a specific aircraft. It serves as a reference for the development of an optimised maintenance schedule by the operator. The initial workload distributions obtained by using the task data in this document, show a high and irregular fluctuation along the operational life of the aircraft. After the application of common task packaging methods, the operator can improve the initial maintenance schedule, but workload fluctuations often persist after these measures. This fluctuation is considered to be unfavourable because of several reasons; maintenance resources are used inefficiently, workforce scheduling operations on fleet level can become very complex and maintenance delays are more likely to occur as a consequence.
In this research, a generic optimisation method is developed focused on the minimisation of the workload fluctuation resulting from the initial maintenance schedule of the aircraft. This method uses a single task reallocation process that systematically eliminates workload excesses by locally reducing task intervals. A software application was built for a fast, a more dynamic and a more customized reallocation process, using several variable inputs.
This application has shown to be very effective in eliminating the workload fluctuation along the lifecycle of an aircraft. As an indication, from the data of the maintenance planning document of an A330, the average fluctuation of the workload among the C-checks over a lifecycle of 15 years, was reduced by more than 79%. Theoretically, this minimisation of the fluctuation could lead to a workforce size reduction of 41% for the C-checks only. These figures are even higher for the A-checks of the aircraft over the same period.
Together with the simplification of the workforce scheduling activities and a more efficient usage of maintenance resources with constant workloads, these advantages are thought to outweigh the negative effects associated with the task interval reductions in the reallocation process, especially when an entire fleet of aircrafts is considered.
Through the implementation of process improvements and additional features, the efficiency and the generic capacity of this application can be further improved with the objective to rapidly generate optimal maintenance schedules that are adaptable to different operational scenarios or constraints.