Repairable and Non-Repairable Systems

When maintainability and reliability characteristics are to be designed for a system, one should first identify the repairable or replaceable features in it. Thus the system is to be first defined as one of the two alternatives, viz. replaceable (non-reparable) system or repairable system. For a non-repairable system such as electric bulb, reliability is the survival probability over the items expected life or for a period during its life, while only one failure might occur, during the time of life, the instantaneous probability of the first and only failure is called the hazard rate.

Non-repairable system may be individual parts (light bulb, transistor, etc.) or a machine (e.g. a fan or a lathe or milling) or systems comprised of many subsystems or parts (e.g. Space craft). Even one component fails in a non-repairable system, the total system fails (usually) and system reliability is, thus, a function of the time to the first (part) failure.