In this talk, we will first introduce the Il’in-Allen-Southwell (IAS) scheme, which is a robust finite difference scheme for treating scalar singularly perturbed convection-diffusion equations. The convergence of the IAS scheme is uniformly in the perturbation parameter in the discrete maximum norm. However, to our knowledge, it has never been achieved before in the literature to successfully construct an effective IAS scheme for strongly coupled systems of singularly perturbed convection-diffusion equations. Using the MHD duct flow as a model problem, we will then explain the difficulties that arise and give some ideas to capture the essence of the problem.