Reliability, Maintainability, and Supportability: Best Practices for Systems Engineers

4Reliability Modeling for Systems EngineersMaintained Systems

4.1 WHAT TO EXPECT FROM THIS CHAPTER

This chapter continues the reliability modeling exposition that was begun in Chapter 3 for nonmaintained systems. Reliability models for maintained systems are built up out of reliability models for their replaceable units. Reliability models for the replaceable units are in turn built up out of reliability models for their constituent components that are now nonmaintained. This chapter covers details of how this is done.

The key point about reliability modeling for a maintainable system is that it may experience repeated failures. That is, a maintainable system may operate, fail, be repaired, operate again, fail again, be repaired again, etc. Reliability models for this behavior focus on describing the stochastic process of operating times, failure occurrence instants, and outage times. This chapter introduces basic ideas relating to this description and some of the specific models that are in common use. It will help you become familiar with terms commonly used in reliability requirements for maintained systems, such as times between failures, failure rate, outage duration, operating times, etc. The presentation emphasizes the separate maintenance model because it accords well with the maintenance concept of replace-and-repair which is very common in the defense, telecommunication, and other industries, and state diagram reliability model for maintained system is more than adequately ...