Aerospace Instrument-Making Annotation << Back Aircraft Turbofan Engine Piecewise-Linear Model H&#8734; Uncertainty Evaluation Leibov R.L. This paper presents aircraft turbofan engine piecewise-linear model H∞ uncertainty ||∆||∞ evaluation method. The piecewise-linear model is a set of linear models i.e. set of normalized steady-state control and state values vectors and matrices of static and dynamic linear models for these steady-state modes. In order to improve the approximation of piecewise-linear model time responses to nonlinear model time responses additional vectors of normalized steady-state control and state values are used. These vectors are calculated using multiple linear interpolation of the initial vectors. Instead of the control variables, auxiliary variables, which are changing more slowly, are used to select current steady-state control and state values vectors. These variables are the solutions of linear differential equations with coeffi cients, which are determined by solving nonlinear programming problems for chosen steadystate modes. H∞ uncertainty evaluation is reduced to solving a set of linear programming problems for uncertainty matrix rows and Frobenius matrix norm calculation. Also is shown the transition to new normalized control and state values for which ||∆||∞ ≤ 1. The results of proposed approach application for H∞ uncertainty norm approximate evaluation are presented. Keywords: aircraft turbofan engine, piecewise-linear model, nonlinear programming, linear programming, uncertainty matrix, H∞ norm. DOI: 10.25791/aviakosmos.3.2025.1467 Pp. 25-47.