The influence of the presence of fatigue cracks detected in the array of operational defects of typical parts of individual units on the condition of safety of tractors has been analyzed. In the work with the help of a specialized portable vibration current flow defectoscope the presence of cracks in the details of the units of tractors with different operating periods was estimated. The defectoscopic control of more than 500 parts of various applications was carried out in 50 tractors that were in service until 17 years since the date of issue in agricultural enterprises of Ukraine. Defectoscopic inspection was carried out during the defect of the details of these tractors received for repair. Based on statistically valid data, the kinetic dependences of the probability distribution of the accumulation of operational fractures of parts of tractor units in time were constructed. The cracks analyzed in the work were detected using a high-sensitivity pulsed vibration current flaw detector, which allowed us to quantify the size of the cracks that correspond to certain operating lifetime terms. It is established that the process of accumulation of a certain type of cracks has exponential kinetics. The regularities considered in the work reflect the consequences of the statistical process of accumulation of an array of fatigue cracks in the details (knots) of tractors within the limits of the studied range of service life. Exceeding the maximum period of operation of aggregates affects the change in the probability of accidents in mechanized and transport works. It is determined that the deadline for the researched tractor types is 13-14 years.