Linear and quasi-linear theories of Farley-Buneman waves predict that coherent scatter can only be observed at aspect angles of about 1¿ or less. Coherent echoes at large aspect angles, with values greater than the linear upper bound, are not very well understood theoretically. Radar observations have revealed the existence of such plasma irregularities at aspect angles as large as 10¿ and larger (Millstone Hill and European Incoherent Scatter). In this paper we suggest a possible mechanism capable to excite Farley-Buneman waves at large aspect angles, which are otherwise damped according to the known conventional models. The proposed model is based on a nonlinear mode-coupling mechanism channeling energy between waves at small aspect angles (linearly unstable) and ones at large aspect angles (linearly stable and damped). We studied the nonlinear coupling of Farley-Buneman waves with significant parallel components. We are able to show that the interaction of the three modes can be very selective but very efficient at the same time. It is also found that the finite aspect angle effects have a profound impact on the saturation levels of Farley-Buneman turbulence in the auroral region, a subject of further study indeed. ¿ 2001 American Geophysical Union