A tool for preventive aircraft maintenance scheduling

A new method was developed for preventive aircraft scheduling by the Institute for Data Analysis and Process Design in a joint project with the Swiss Air Force. It is based on a two-step approach: The first step consists of setting up an initial maintenance plan in which all calendar-based maintenance actions (CBMAs) are timed to be performed at their due date. Provisional dates for usage-based maintenance actions (UBMAs) are deter-mined by distributing the total demand for flight hours evenly over all aircraft. Each CBMA is subsequently merged with the UBMA which gives the highest reduction in service time, provided its provisional start time is within a time window around the considered CBMA. In the second step, the initial plan is optimized. The optimization is based on a heuristic algorithm which tries to shift maintenance actions so that both the number of instances where available workforce capacities are exceeded and their duration are minimized. This guarantees a reasonably even utilization of aircraft both over aircraft and over time and low mean values and standard deviations in maintenance capacity usage over time. The quality of the final maintenance plan can be judged by the degree to which constraints in maintenance capacities and the amount of both quarterly and inter-maintenance flight hours are met. The new method produces maintenance plans that are slightly better than conventional ones with respect to all these criteria but with order-of-magnitude reductions in set-up time. An additional benefit for the personnel in charge of managing flight operations is that information is available on the weekly flight hours to be assigned to each aircraft in order to follow maintenance plans