Cs0.8Fe1.6Se2 becomes superconducting below 27K despite the presence of antiferromagnetism with a large moment of about 3.3 Bohr magnetons and an unusually high ordering temperature of about 560K. It has been proposed that different Fe vacancy ordering is associated with the superconducting and antiferromagnetic phases, and that these phases are spatially separated. We have already obtained measurements of two spatially separated superlattice phases using synchrotron x-rays, however one of these phases is currently unsolved due to the presence of lambda/2 intensity at the same position as the superlattice reflections. We propose to study the superstructures using time-of-flight neutrons on SXD, allowing us to properly distinguish the superlattice intensity and therefore solve the structure of this new and potentially important phase.