The metastabie $β$ phase in Cu-based shape memory alloys (SMA) undergoes two order-disorder transitions during quenching from high temperature. First, it undergoes a B2 ordering at the nearest neighbors and then a second one at the next nearest neighbors that has nor been clearly established. The kind of order obtained and the ordering evolution during aging at low temperature influence on the martensitic phase since it inherits the atomic order of the $β$ phase. Neutron Powder Diffraction measurements have been performed at room temperature in a fully ordered alloy (Cu-27.4 al-3.6 Ni at.%) obtained after quenching from 1173 K and aged during 2 hours at 473 K. The differences in the neutron scattering factors for Ni and Cu atoms promotes differences in reflestions depending on the kind of order (dO$_3$ or L2$_1$). Rietveld analysis allows to conclude that a L2$_1$ order at next nearest neighbors is present in the ordered phase.