An approach to optimize the maintenance program for a repairable system

Scope of study. The optimization of two preventive maintenance policies for an aircraft integrated drive generator (IDG) have been considered in this work. The objective is to determine the optimal replacement intervals for the Type II and Type II{dollar}spprime{dollar} maintenance policies. The nonhomogeneous Poisson process (NHPP) with power law intensity function and the natural estimate methods are used to quantify the peril rate for the failure data. An analytical method and Monte Carlo simulation are used to determine the optimal replacement interval for the Type II and Type II{dollar}spprime{dollar} maintenance policies, respectively.; Findings and conclusions. The integrated drive generator's failure times can be represented using the nonhomogenous Poisson process with power law intensity function. The failure data must be left-truncated to remove the effects of infant mortality failures. Once the failure data is left-truncated, the NHPP parameters indicate that the IDG is a deteriorating system. The peril rate is also characterized by using the nonparametric natural estimate method. This nonparameteric approach is in agreement with the peril rate determined using left-truncated data and the NHPP.; The optimal replacement interval for the Type II maintenance policy was found using an analytical approach proposed by Barlow and Hunter. The results indicate that the optimal replacement interval for the IDG with a Type II maintenance policy is between 7,000 and 9,000 flight hours. Using this replacement interval results in a minimum maintenance cost per flight hour. There is no analytical model for the Type II{dollar}spprime{dollar} maintenance policy based on the NHPP. To circumvent this, a Monte Carlo simulation was used. The Monte Carlo simulation required seven states to represent the complete operational and maintenance cycle that the IDG experiences. The simulation results indicate that the optimal mandatory overhaul interval is 6,000 flight hours. By overhauling the IDGs that enter the repair facility that have at least 6,000 flight hours, the maintenance cost per flight hour is minimized and the mean time between failure and availability are maximized.