General preventive maintenance model for input components of a system, which improves the reliability to "as good as new", is used to optimize the maintenance cost. The cost function of a maintenance policy is minimized under given availability constraint. An algorithm for first inspection vector of times is described and used on selected system example. A special ratio-criterion, based on the time dependent Birnbaum importance factor, was used to generate the ordered sequence of first inspection times. Problem called as "reliability assurance" is theoretically solved and answered, i.e. finding the cost of maintenance when asymptotic availability value (WRV- Worst Reliability Value) conforms to a given availability constraint (asymptotic availability value is supposed as the limiting value for time going to infinity). System representation using acyclic graph is brietly introduced. Basic system availability calculations of the paper were done by using Matlab program (analytical) for computing of the WRV value of any coherent system under maintenance. A genetic algorithm optimization technique is used and briefly described to create the algorithm (in Matlab as well) to solve the problem of finding the best maintenance policy with a given restriction.
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