The main problem addressed in this article is the determination of an inspection interval Tmax, given the number of inspections m-1, which will result in the maximum reliability at some future point in time t=t*. The reliability model developed by Christer is used in which the notion of delay time is involved, representing the start to eventual failure of an item subject to a fault detectable upon inspection. A numerical procedure is used to solve the model for general delay time density f(h) and time to failure from new density g(y). Tmax is shown to migrate towards the left hand side of the interval [t*/m,t*/(m-1)] if the number of inspections is allowed to increase. If both densities are exponential then the optimal inspection interval is shown to be Tmax=t*/m. When costs are incorporated into the model then the problem considered becomes that of determining the optimal inspection interval and number of inspections tha will result in the maximum reliability at some future time t* at minimum cost.
