Readiness Models for Random and Scheduled Demand Systems

The control of the operational status of aerospace systems is of paramount importance to both our military and civilian aerospace programs. To establish and maintain the operational capability of an aerospace system to be ready at any demand time (random or scheduled), it is necessary to determine and evaluate its status in order to select and execute maintenance actions which will, in turn, improve the operational capability of the system. Consequently, readiness testing and replacement-repair actions are necessary, even though test severity, errors, frequency, duration and coverage as well as repair durations and uncertainties all influence the probability that the system will be ready for use when demanded. To relate the effects of these realistic factors to system readiness, a conceptual framework has been formulated which provides an apparently endless series or hierarchy of status control models. Progressively more complicated models have been developed which include the effects of imperfect maintenance, "man-in-the-loop", tolerance limit tradeoffs, and checkout equipment designs. In general, these models have been and will continue to be important for structuring the evaluation and predictive effort regarding present systems as well as for providing better standards and parametric tradeoffs for the preliminary design of new aerospace systems.