“…Assume that at time , the operator knows the event that “the system still operates at time , but exactly components have failed at that time.” Under this information, Memari et al 148 have proposed some PM policies for optimal preserving of the system. If denotes the lifetime of the system and denotes the th ordered component lifetime, then this event is equivalent to saying that and the event occurs, where Under these conditions, the residual lifetime of the system is Then, the reliability function of , denoted by , is represented as where …”