  We explore proton decay in a class of realistic supersymmetric flipped
$SU(5)$ models supplemented by a $U(1)_R$ symmetry which plays an essential
role in implementing hybrid inflation. Two distinct neutrino mass models, based
on inverse seesaw and type I seesaw, are identified, with the latter arising
from the breaking of $U(1)_R$ by nonrenormalizable superpotential terms.
Depending on the neutrino mass model an appropriate set of intermediate scale
color triplets from the Higgs superfields play a key role in proton decay
channels that include $p \rightarrow (e^{+},\mu^+)\, \pi^0$, $p \rightarrow (
e^+,\mu^{+})\, K^0 $, $p \rightarrow \overline{\nu}\, \pi^{+}$, and $p
\rightarrow \overline{\nu}\, K^+ $. We identify regions of the parameter space
that yield proton lifetime estimates which are testable at Hyper-Kamiokande and
other next generation experiments. We discuss how gauge coupling unification in
the presence of intermediate scale particles is realized, and a $Z_4$ symmetry
is utilized to show how such intermediate scales can arise in flipped $SU(5)$.
Finally, we compare our predictions for proton decay with previous work based
on $SU(5)$ and flipped $SU(5)$.
