  We investigate the long distance contribution via charmed hadron loops in the
processes $\eta_c$, $\chi_{c0}$ and $h_c$ decaying to baryon anti-baryon pairs,
which are supposed to be highly suppressed by the helicity selection rule as a
consequence of the perturbative QCD framework. With an effective Lagrangian
method, our estimation result indicates that such hadron loops play an
important role in these hadronic decays. It is a further test of the evading
mechanism for the helicity selection rule in charmonium baryon-antibaryon
decays.
