The article presents the developed mathematical model for calculating the parameters and characteristics of an indirect reaction gas turbine engine, which is implemented in asoftware environment and embedded in the general algorithm of the pro-gram "Calculation of traction-economic and mass-specific characteristics of a power plant and aircraft motion parameters". At the same time, special attention is paid to the features ofmathematical modeling of indirect reaction gas turbine engines with respect to turbojet engines. A description of a mathematical procedure for solving systems of nonlinear algebraic equations in determining the parameters and characteristics of a power plant in off-design modes of operation using a modified Newton's method is presented. The results of verification of the modified program are also shown by comparing the parameters and char-acteristics of the power plant based on the AI-24VT turboprop engine calculated with its help, with the characteristics taken from the technical description, with a detailed analysis of the qualitative and quantitative flow of throttle characteristics in accordance with the generally accepted theory of aviation engines