Raza A. MATHEMATICAL MAINTENANCE MODELS OF VEHICLES’ EQUIPMENT

The thesis addresses the critical scientific problem of creating appropriate maintenance models of digital avionics systems and degrading vehicles’ equipment for increasing their maintenance effectiveness. Analysis of the current state and models of digital avionics systems maintenance has been conducted. According to the analysis, the necessity to develop mathematical maintenance models of redundant digital avionics systems has been stated, considering the peculiarities of their operation, the possibility of occurrence of both permanent and intermittent failures, the possibility of organization of several maintenance levels using various equipment for failure diagnostics. Novel mathematical models have been developed to evaluate the operational reliability of continuously monitored line replaceable units and redundant avionics systems over finite and infinite time intervals, which consider the impact of both permanent and intermittent failures. Novel generalized relationships for calculation of average operating costs during warranty and post-warranty periods of redundant avionics systems have been developed for alternative maintenance options that differ by the number of maintenance levels (one, two or three), considering the impact of permanent and intermittent failures. They allow choosing the optimal maintenance option. The thesis presents the analysis of the modern trends and mathematical models of condition-based maintenance (CBM) for degrading vehicles’ equipment. The necessity for the development of CBM mathematical models for degrading vehicles’ equipment considering the probabilities of correct and incorrect decisions made when checking system suitability in the forthcoming operation interval, has been stated. Novel generalized mathematical expressions have been developed to calculate the effectiveness indicators of CBM based on suitability checks, as well as criteria for determining the optimal inspection times and replacement thresholds for systems that affect and do not affect safety. Examples have been used to show that maintenance based on suitability checks is more effective than maintenance based on operability inspections, as it ensures higher availability and lower maintenance cost with fewer inspections.