Method of order equations

Asymptotic formulation of problems needs the knowledge of relative orders of perturbations. Therefore it is worth first to formulate and solve the problem on the level of exact orders of unknown quantities. Such a problem is simpler because it lays claim to a less information. And its solution enables us to formulate a well-founded problem on the level of asymptotic equality. We present this method in general case of the boundary problem for a system of quasilinear equations and demonstrate its application to some steady and unsteady problems of aerodynamics.