Dear editor,rnComponents such as gyros,turbines,and bearings are vital in aircraft and spacecraft,and must run safely during their entire life cycle.However,gradual damage inevitably occurs resulting in component failure.Therefore,necessary main-tenance such as component replacement should be sched-uled.Traditional maintenance models are generally time-based,and in such models,maintenance decisions are made to minimize the expected cost rate,regardless of the actual degradation condition.Therefore,traditional models are in-appropriate for individual servicing components.Advances in sensor technologies have enabled the monitoring of criti-cal components for detecting degradation signals,which can enhance condition-based maintenance(CBM)[1].In CBM,maintenance activities are scheduled only if necessary based on the collected degradation signals.In contrast to time-based maintenance,CBM can potentially improve operating reliability and reduce economic costs.