  Studies of the nature of cosmic ray particles at the highest energies are
based on the measurement of extensive air showers. Most cosmic ray properties
can therefore only be obtained from the interpretation of air shower data and
are thus depending on predictions of hadronic interaction models at ultra-high
energies. We discuss different scenarios of model extrapolations from
accelerator data to air shower energies and investigate their impact on the
corresponding air shower predictions. To explore the effect of different
extrapolations by hadronic interaction models we developed an ad hoc model.
This ad hoc model is based on the modification of the output of standard
hadronic interaction event generators within the air shower simulation process
and allows us to study the impact of changing interaction features on the air
shower development. In a systematic study we demonstrate the resulting changes
of important air shower observables and also discuss them in terms of the
predictions of the Heitler model of air shower cascades. It is found that the
results of our ad hoc modifications are, to a large extend, independent of the
choice of the underlying hadronic interaction model.
