Assessing the impact of intermittent failures on the cost of digital avionics' maintenance

Modern aviation data suggest that there are more than 400,000 no fault found (NFF) cases per year, where a false alarm is given and no fault is detected after investigation. The NFF cost was estimated to be over $2Bn per year in 2013. The existence of the NFF phenomenon has a negative impact upon avionics systems safety, availability and life cycle cost. Therefore, it is important to reduce the negative impact of NFF events. Intermittent failures are the leading causes of NFF events in avionics systems. In this study, we consider a line replaceable unit (LRU) subject to permanent and intermittent failures with an arbitrary law of failure time distribution. We assume that LRU is continuously tested and both types of failures are automatically detected by the built-in test equipment (BITE). When the LRU is rejected, the replacement is carried out. Dismantled LRUs are directed to repair facilities for re-testing, and if necessary, repairing. A mathematical model is developed to determine the LRU availability and the mean time between unscheduled removals (MTBUR). Different variants of avionics maintenance management are considered for warranty and post-warranty period. MTBUR, total expected cost (TEC), and availability of redundant systems are determined for each variant of warranty and post-warranty avionics maintenance management. Numerical examples demonstrate the efficiency of each variant of avionics maintenance management. It is shown that excellent economic efficiency has the variant of post-warranty maintenance with automatic test equipment (ATE) and intermittent fault detector (IFD).