Probably, the model you have was not built per the FS2002 SDK (not using gmax or FSDS2) or that the model was not built to allow reflections (i.e., the alpha channel controls reflections, otherwise, transparency)

Parts need to be tagged during model construction so that flight simulator recognizes these parts as reflective, and then the texture's alpha channel is read to see the level of reflections - otherwise, the alpha channel is read as the level of transparency.