The attrition experience of individual aircraft systems is found to change over the flying life of the system in such a way as to continually lower the attrition rate. This process can be represented mathematically, and the resulting model used to project future losses for the system. A study was made to evaluate the results of an earlier RAND study of peacetime aircraft attrition in light of 12 years of additional flying hour and attrition data supplied by the Air Force Inspection and Safety Center. The earlier study resulted in sufficient understanding of the attrition process to develop estimating methodologies that were adopted by the Air Force in official publications and that are still in use. The conceptual bases for the findings of the first study are discussed, and in conjunction with statistical parameters and an examination of some typical projections, the utility of the method is evaluated. 50 pp.