Rules for Planned Replacement of Aircraft and Missile Parts

An abridgment of RM-2810-PR. A study of replacement policies for aircraft and missile parts, showing how the appropriate replacement policy for any part depends on its failure characteristics and on the penalty associated with a failure in service. For planned replacement of a particular part to be worth while (i.e., replacement before failure), two necessary conditions must be satisfied. The part must display a wear-out characteristic (a failure rate that increases with time), and there must be some penalty for a failure in service (the cost of a failure in service must be greater than the cost of a planned replacement). The study discusses how an optimum planned replacement policy can be developed and presents empirical results for parts whose failure characteristics can be described by some of the better-known probability distributions of mathematical statistics. It also shows the savings that can result from following such an optimal policy instead of a replace-at-failure-only policy.