Operating Characteristics of Opportunistic Replacement and Inspection Policies

This paper calculates some of the operating characteristics of opportunistic replacement and inspection policies. An operating characteristic of a particular policy is a function defined on the stochastic process induced when the policy is implemented. An opportunistic replacement policy makes the replacement of a single uninspected part conditional on the state (good or failed) of one or more continuously inspected (monitored) parts. An opportunistic inspection policy makes the inspection of a non-monitored part conditional on the state (good or failed) of a monitored part. Some of the operating characteristics of these policies examined in this paper are: the expected rate of opportunistic (joint) replacement of the uninspected part and one of the monitored parts; the expected rate of planned replacement of the uninspected part; the probability of at least m failures of a monitored part in the interval [0, t]; the expected rate of opportunistic inspection--inspection of the non-monitored part which is triggered by a failure of the monitored part; and the expected rate of planned inspection of the non-monitored part. These operating characteristics are precisely the information needed to establish a suitable supply policy. They should also be helpful to the maintenance manager in his efforts to predict the relative frequencies of the various maintenance actions. As an example the opportunistic replacement policy is applied to the rocket engines of a hypothetical ballistic missile. Several operating characteristics are then computed and the sensitivity of these operating characteristics to changes in the rocket engine failure rate is exhibited. This illustrative analysis indicates that both the expected rate of opportunistic (joint) replacement of the rocket engines and re-entry vehicle and the expected rate of replacement of the rocket engines due to mandatory replacement are highly sensitive to changes in the rocket engine failure rate. On the other hand, the expected rate of opportunistic (joint) replacement of the rocket engines and the guidance and control system is relatively unaffected by changes in the engine failure rate.