  For studying how the field lines are twisting nearby the light cylinder
surface, which provides the free motion of AGN winds through the mentioned
area, the investigation of the centrifugally driven curvature drift instability
is presented. Studying the dynamics of the relativistic MHD flow close to the
light cylinder surface, by applying a single particle approach based on the
centrifugal acceleration, the dispersion relation of the instability is derived
and analytically solved. Considering the typical values of AGN winds, it is
shown that the time scale of the curvature drift instability is much less than
the accretion process time scale, indicating that the present instability is
very efficient and might strongly influence processes in AGN plasmas.
