A Practical Approach to Robustness Analysis with Aeronautical Applications 1. MOTIVATION In many physical situations a plant model is often provided with a qualitative or quantitative measure of associated model uncertainties. On the one hand the validity of the model is guaranteed only inside a frequency band so that nearly nothing can be said about the behavior of the real plant at high frequencies. On the other hand if the model is derived on the basis of physical equations it can be parameterized as a function of a few physical parameters which are usually not perfectly known in practice. This is e.g. the case in aeronautical systems: as an example the ae dynamic model of an airplane is derived from the flight mechanics eq tions. When synthesizing the aircraft control law it is then necessary to take into account uncertainties in the values of the stability derivatives which correspond to the physical coefficients of the aerodynamic model. Moreover this airplane model does not perfectly represent the be vior of the real aircraft. As a simple example the flight control system or the autopilot are usually synthesized just using the aerodynamic model thus without accounting for the flexible mechanicalstructure: the c responding dynamics are indeed considered as high frequency neglected 1 dynamics with respect to the dynamics of the rigid model . Preliminaries to  and LFTs Applicative Examples Computation of a Standard LFT Structure Realization of Uncertain Systems Under an LFT Form Applications Applications Computation of  Bounds Applications of the  Tools Applications Skewed  Problems in Robustness Analysis Computation of Skewed Bounds Application of the Skewed  Tools Nonstandard Applications Robustness Analysis of Flexible Structures Robustness Analysis in the Presence of Time Delays Nonlinear Analysis in the Presence of Parametric Uncertainties.