Experience has shown that aircraft structures are generally affected by structural nonlinearities. The focus in this paper is concentrated on backlash and friction described in hysteresis loop of the classical aircraft command systems and their influence on flutter of aircraft. Based on AGARD No. 665 in paper is done nonlinear flutter velocity analysis in function of backlash and friction in the classical command system of aircraft. Unsteady aerodynamic forces are calculated based on well known Doublet- Lattice Method (DLM). Structural input data are taken from AGARD No. 665. Flutter eigenvalues are obtained by modified k-method. The flutter model of nonlinear aircraft structure is developed on base of harmonic linearization. The aim of paper is to achieve useful and relatively reliable tool for critical observations on different recommendations given in the various airworthiness regulations for nonlinear characteristics of hysteresis loops in the classical command systems of aircrafts.