The method of multiple scales is used to obtain a set of consistent equations governing the linear stability of slightly non-parallel, incompressible, steady flows. The numerical procedure for obtaining the solution of the non-parallel problem is outlined. The complete solution contains the solution of the Orr-Sommerfeld problem as the first approximation, the distortion of the Orr-Sommerfeld eigenfunctions, and the local perturbation and streamwise variation in the wave-number and spatial growth rate when the frequency of the disturbance and the Reynolds number of the primary flow are fixed.
