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The paper studies the reliability of passively redundant subsystems of aircraft, taking into account tolerances for a decrease in their output parameters in case of sudden component failures. The influence of the reliability values of elements, tolerances of two levels and the redundancy ratio on the reliability of passively redundant subsystems as a whole have been investigated; the examples of such subsystems have been given. There have been presented the results of analysis of the aircraft subsystems features with allowance for tolerances. First of all, these include the availability of technical specifications and realized tolerances determined by the reservation structure; implementing each tolerance with different values of the multiplicities of redundancy; using the main tolerance grid by multiple backup methods; presence of critical probabilities narrowing the reliability range of the elements, where this type of reservation is beneficial from the range 0–1 to the range of the supercritical area (pkr–1). The influence of the element reliability values, tolerances of two levels and the redundancy ratio on the failure-free operation of passively redundant subsystems in general and in supercritical areas has been investigated. It is shown that the minimum redundancy multiplicities in the interests of increasing the reliability of the considered subsystems of aircraft are advantageous to use only with large tolerances and low probabilities of failure-free operation of their elements. Under close tolerances and any reliability values of elements, as well as with large tolerances (more than 25%), high reliability values of this class of aircraft subsystems can be achieved only with large redundancy multiplicities. It has been inferred that there are extreme reliability differences of a passively redundant subsystem and its element, which allows to set the task of developing highly reliable passively redundant subsystems of aircraft taking into account tolerances from relatively unreliable elements.

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Objectives. The relevance of this article lies in the fact that the problem of increasing the reliability of subsystems of aviation and rocket and space technology in case of sudden independent refusals determines one of the important areas of scientific research. The work is aimed at identifying and analyzing specific features that must be considered when researching and developing passively redundant subsystems, taking into account tolerances in case of sudden independent failures.Method. During the study, calculations were carried out using the methods of probability, search. The necessity of taking into account assigned and implemented tolerances, multiple and non-multiple reservation, discrete scales of realizable tolerances with different levels of significance, critical probabilities, determining the probability ranges of elements, where redundancy is profitable and unprofitable, is shown.Result. The possibility of implementing any tolerance for different values of a number of increasing individual multiplicities is revealed, which allows for a given tolerance to pose the task of finding the optimal multiplicity and its corresponding optimal backup structure in the interests of ensuring maximum reliability of the redundant subsystems. Analysis of the presented dependencies for the implemented tolerances of the first and second levels shows that for each tolerance level there are equilibrium values ???????????? at which the critical values of p_kr practically do not change depending on the multiplicities ????????.Conclusion. A different nature of the change in the critical probabilities ???????????? was found depending on the multiplicities for different values of the tolerances to be realized. So, with tolerances of the first level, larger than 25%, with increasing multiplicity, p_kr increases and smaller than 25% decreases with increasing multiplicity. The similar nature of the change in the p_kr values has a 28.6% tolerance for the implemented second-level tolerances.

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