  We investigate nonequilibrium properties of the single impurity Anderson
model by means of the functional renormalization group (fRG) within Keldysh
formalism. We present how the level broadening Gamma/2 can be used as flow
parameter for the fRG. This choice preserves important aspects of the Fermi
liquid behaviour that the model exhibits in case of particle-hole symmetry. An
approximation scheme for the Keldysh fRG is developed which accounts for the
frequency dependence of the two-particle vertex in a way similar but not
equivalent to a recently published approximation to the equilibrium Matsubara
fRG. Our method turns out to be a flexible tool for the study of weak to
intermediate on-site interactions U <= 3 Gamma. In equilibrium we find
excellent agreement with NRG results for the linear conductance at finite gate
voltage, magnetic field, and temperature. In nonequilibrium, our results for
the current agree well with TD-DMRG. For the nonlinear conductance as function
of the bias voltage, we propose reliable results at finite magnetic field and
finite temperature. Furthermore, we demonstrate the exponentially small scale
of the Kondo temperature to appear in the second order derivative of the
self-energy. We show that the approximation is, however, not able to reproduce
the scaling of the effective mass at large interactions.
