  We show that as in the flipped SU(5) models, doublet-triplet splitting is
realized by the missing partner mechanism in the flipped SO(10) models. The
gauge group $SO(10)_F\times U(1)_{V'_F}$ includes $SU(2)_E$ gauge symmetry,
that plays an important role in solving supersymmetric flavor problem by
introducing non-abelian horizontal gauge symmetry and anomalous $U(1)_A$ gauge
symmetry. The gauge group can be broken into the standard model gauge group by
VEVs of only spinor fields, such models may be easier than $E_6$ models to be
derived from the superstring theory.
