In-service reliability assessment and top-down approach provides alternative reliability prediction method

The desire to develop a realistic mean-time-between-failure (MTBF), mean-time-to-failure (MTTF), or failure rate prediction method, which doesn't assume that only piece part faults cause system failures, has led to a new methodology involving in-service reliability assessment and a top-down approach. This methodology reduces uncertainty in the reliability predictions by relying primarily on line replaceable units (LRUs) field failure data history of in-service LRU designs with verified field performance that are similar in hardware and function to new LRU designs. Experience demonstrates that this new method as applied to hardware used in the commercial avionics industry reflects a high degree of accuracy on the MTBF prediction process applied to the new LRU designs. The Honeywell In-Service Reliability Assessment Program (HIRAP) method is an in-service reliability assessment process and top-down approach. HIRAP was developed for the purpose of predicting or assessing "in-use" reliability as well as a circuit design comparison measure in design trade studies. The HIRAP methodology includes an assessment of end item field experience, a top-down prediction approach, a comparison of fielded systems to new designs, and an application of algorithms to ascertain the MTBF of a new design, when there is some degree of similarity to predecessor designs in-service. The HIRAP methodology is described in this paper.