  We construct a semi-analytic model for MHD flows in Kerr geometry, that
incorporates energy loading via neutrino annihilation on magnetic field lines
threading the horizon. We compute the double-flow structure for a wide range of
energy injection rates, and identify the different operation regimes. At low
injection rates the outflow is powered by the spinning black hole via the
Blandford-Znajek mechanism, whereas at high injection rates it is driven by the
pressure of the plasma deposited on magnetic field lines. In the intermediate
regime both processes contribute to the outflow formation. The parameter that
quantifies the load is the ratio of the net power injected below the stagnation
radius and the maximum power that can be extracted magnetically from the black
hole.
