A redundant structure typically consists of primary component and standby component taking over the function of the primary component when the primary component fails. In this research, we consider a redundant structure in which a standby component can take over the function of more than one primary component when primary components fail. And we assume that the system has multi-state according to the states of components while all components have two states. This system is called as the multi-state redundant system with a multi-functional standby component. This type of redundant structure is frequently adapted by the system such as an aircraft in which the weight is an important design factor. In this paper, we propose new reliability model for this multi-state redundant system with a multi-functional standby component in order for evaluating the reliability of the system. Under the assumption that all components have constant failure rate, we evaluate the reliability of the system by applying Markov analysis method. And we investigate the effect of the multi-functional standby component by comparing reliabilities of the parallel system with multi-functional standby component and a simple parallel system and a parallel system with redundant structure. As a result of the comparison, the effect of a multi-functional standby component is large when failure rates of the components is small or operating time of the system is short.
And we analyze reliability applying to system of practical interest of multi-state redundant system with multi-functional standby component extending this model, hydraulic pump system of UH-60 helicopter which has 7 components. The system consists of seven components : 2 main pumps, 1 standby pump, 2 primary servos, and 2 tail rotor servos. The standby pump can take over when one more than pumps or No.1 tail rotor servo fails. Therefore the standby pump is a multi-functional standby component. The components have 2 states : working and failed. The system has four states : good, deteriorated, dangerous, and failed. We assume the system and components are unrepairable. We estimate failure distributions and rates using collected failure time data in the field. And we classify multi-state of the system according to emergency procedure of UH-60A student handout. We obtain the reliabilities of multi-state system using Visual Basic program because the differential equations is extremely complicated and tedious to solve.