  The binary chalcogenides Bi2Te3 and Bi2Se3 are the most widely studied
topological insulators. Although the quantum anomalous Hall effect has recently
been observed in magnetically doped Sb2Te3 this compound has been studied to a
much lesser extend. Here, by using energy resolved quasiparticle interference
mapping, we investigate the scattering events of pristine Sb2Te3 surfaces. We
find that, in addition to the Dirac fermions, another strongly spin polarized
surface resonance emerges at higher energies in the unoccupied electronic
states. Although the two surface states are of different origin, i.e.
topologically protected and trivial, respectively, both show strongly
directional scattering properties and absence of backscattering. Comparison
with ab-initio calculations demonstrates that this is a direct consequence of
their spin momentum locked spin texture which is found to exhibit an opposite
rotational sense for the trivial state and the Dirac state.
