Extended block replacement policies with mission durations and maintenance triggering approaches

When the missions arrive, it is not feasible to shut down engineering systems for preventive maintenance policies. Otherwise, it would cause major economic losses and even unimaginable accident. Hence, it is interesting and significative to provide appropriate preventive maintenance policies with mission durations to improve the system reliability and maintainability. For the electronic systems consisting of a block or group of units whose ages are not easy observed and only failures are known, we firstly extend the block replacement policy with random arrival time of mission durations. As a required reliability is needed at the mission time and no replacement can be done during the mission durations preventively. From the points of cost and maintainability, two maintenance triggering approaches, i.e., replacement first and replacement last, are discussed in analytical ways, respectively. Furthermore, three replacement policies are compared theoretically and numerically with optimum mission durations and planned replacement time. In addition, a case illustration in maintaining the electronic systems of active phased array radar (APAR) is given when the arrival time of mission durations follows an exponential distribution and the failure time of electronic systems has a gamma distribution.