Initial Provisioning with Spare Deterioration

Initial provisioning is analyzed for the case where parts in use and spares have exponential failure distributions with different failure rates. Expressions are given for system reliability and its asymptotic expansions for small time, large time, large numbers of spares, and small spare failure rate. The incremental reliability associated with each additional spare part is analyzed. Graphs are presented that yield, for arbitrary failure rates of spares and parts in use, the minimum number of spare parts needed to achieve system reliabilities of 90, 95, and 99 per cent.