  To investigate uncertainties in air shower simulations caused by the small-x
regime, a model including leading-twist hard pQCD plus soft processes was
built, which are separated by an energy dependent transverse momentum cut-off.
We provide a fit of the cut-off to the total pp cross section for different
PDFs using the eikonal formalism and show that for modern PDF sets there is
only a small uncertainty in the mini-jet cross section, and hence in the
final-state multiplicity and the number of produced muons.
