  A non-perturbative determination of the axial current improvement coefficient
cA is performed with two flavors of dynamical improved Wilson fermions and
plaquette gauge action. The improvement condition is formulated with
Schroedinger functional boundary conditions and enforced at constant physical
volume. Large sensitivity is obtained by using two different pseudo-scalar
states in the PCAC relation. We estimate the resulting correction to F_PS at
beta=5.2 to be around 10%.
