The planar turbulent boundary layer is analyzed in the sense of the well known phenomenologic semi-empiric boundary layer theory. The analysis is based on an analogy with the rheological power laws widely used in the study of non-linear viscous flows. A simple ’’one layer method” to calculate the turbulent boundary layer is first derived and after that tested on the sphere as well as on the id. 2500 of P. Bradshow. Furthermore, an approximate procedure is proposed to evaluate the evolution of the velocity profile in a neighborhood of the separation point of the turbulent boundary layer in the case of the Prandtl turbulence model. It is assumed that the equations of the boundary layer admit two solutions around the separation point. One of them is upstream of the point and another one downstream of it. The solutions are found in two variants - triangular and parabolic -relative to the method used to approximate the Reynolds’ turbulent stress. Besides, a comparison is made with respect to the existing experimental results.