Single and double alignment backscatterings of MeV helium ions from a silicon crystal have been simulated in a computer. Angular dependences of the backscattering yield in a (110) plane for 2 MeV helium ions along (110), (100), and (111) are calculated for regular lattice positions and various interstitial positions in single alignment. In double alignment 2.8 MeV helium ions are incident on a (100) crystal plane parallel to (110) and angular dependences of the backscattering yield for detector rotation in a (110) plane along [110], [111] and [010] are calculated. In (110) and [110] the tetrahedral (T), the hexahedral (H) and so called ytterbium atom positions (Y) show a flux peak and the split (100) and the bond-centred positions (BC) have a shallow and narrow dip. In (111) and [111] the H-and the BC-positions have a flux peak and the other positions a dip. In (100) (or [010]) the BC-, H-, Y-, S-positions (BC and H) show characteristic off axis peaks and the others a dip.