We experimentally investigate the effect of residual disorder on the dispersion curve of light near a band edge. A Fourier space imaging technique accurately distinguishes the propagating regime from diffusive transport and evanescent regime in planar photonic crystal. We highlight and quantify the impact of the disorder on the group velocity near a band edge. We stress that the achievement and determination of group indexes larger than 100 requires not only state of the art processing but also accurate techniques able to discriminate between propagating, evanescent and localized modes.