Modelling of false alarms and intermittent faults and their impact on the maintenance cost of digital avionics

It is well known that false alarms (FAs) and intermittent faults are the main causes of unconfirmed failures in modern avionics. Indeed, the rate of FAs is quite high in the aviation industry, reaching a little less than 30% of all events related to the alarms. International aviation data suggest that the rate of unconfirmed failures (No Fault Found - NFF) for avionics systems range from 20 % to 50 %. The main reason for the NFF cases associated with avionics systems is the occurrence of intermittent faults in-flight. That is why the problem of assessing the impact of false alarms and unconfirmed failures on the lifecycle cost is extremely relevant for developers and operators of avionics systems. In this study, we develop a maintenance model of avionics systems subject to FAs and intermittent faults. The model considers the trustworthiness characteristics of continuous testing of the avionics line replaceable unit (LRU) by the built-in test equipment (BITE) and random occurrence of the permanent failures and intermittent faults in-flight. Based on the proposed model, the operating cost associated with the cost of repairing the dismantled LRUs is determined. A numerical example illustrates the peculiarities of the proposed approach to assessing the impact of FAs and intermittent faults on the maintenance cost of avionics systems.