Estimating the Expected Number of Failures for Items with Minimal or Perfect Repair
The area under the failure rate curve constructed from the first times-to-failure of a set of components is often used as an estimate of the number of spare parts needed during a mission. This method of estimating spares is applicable only under certain conditions. The primary assumptions of the method are that minimal repair is performed on the components in the population and that the size of the population remains constant over time. However, in many cases, reliability engineers erroneously apply the method to estimate the number of failures of non-repairable components. This article uses an example to clarify when it is appropriate to estimate the number of failures using the area under the failure rate curve and when other methods must be employed.