5. Conclusion

The reliability-based maintenance method developed by Nowlan and Heap in 1978 was the first structured approach to defining maintenance programs in the aeronautical industry. It was the first time that a method took into account, from the outset, the consequences of failures (on safety, operational capacity and various costs) and not the contents of failure tasks. This is how they highlighted the paradox of the previously widely-used Hard Time-HT maintenance method. Through feedback, they deduced that this task was ineffective in controlling the failure rate because, in the majority of cases they identified, the probability of failure did not systematically increase over time. They were among the first to demonstrate that a maintenance policy based solely on maximum life considerations has little or no effect on the failure rate. In their report, Nowlan and Heap set out the fundamentals...