Elements of drilling equipment are subjected to random loads with very high amplitudes during operation. Classical methods of probabilistic calculation of gearings don't allow us to estimate the probability of their failure taking into account the real operational data obtained by telemetry when these data cannot be described by standard distribution laws. The offered technique is based on application of methods of non-parametric statistics therefore it is free from these restrictions. All its

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... tages are realized in the Mathcad mathematical processor. The article describes the technique of failure probability of gearing of drilling rig top drive system in accordance with criterion of bending endurance of teeth. Results of its realization for failure probability assessment of gearing at its operation in the heavy loading mode agree well with failure statistics. Also, the technique allows us to determine the probability of gearing failure for any load distribution laws during operation, including, when the loading mode is defined by sample.