Instantaneous availability model of repairable systems with repair time omission

In view of the shortage of a single-unit Markov repairable system, assuming the lifetime and repair time are random variables with general distributions, this paper defines the available state of the single-unit non-Markov repairable system. The critical repair time is considered into two classes. One is a constant and the other is a non-negative random variable. An instantaneous availability model of the new system is built, which can describe the system performance more accurately. Some numerical examples are given to compare the instantaneous availability of the former and the later model, concluding that the later is better than the former in instantaneous availability.