Diffraction by edges and cavities play an importan! role in obtaining the global Radar Cross Section of complex targets.We discuss here how the Modal Serie-Boundary Element Method can be used to provide the far-field scattering pattern of a finite-length arbitrary edge when the incident field is a plane wave with arbitrary polarization. Combining it with the Physical Optics reflected field, the total RCS contribution of the wings and flaps in a real airplane can be easily obtained.