Concerning the minimum fuel routeing, the algorithm stated in Section 2 is very effective in the calculation of the (sub)optimum route for most environmental conditions. However, when the weather around the great circle route is extremely severe and the final isochrone bends backwards sharply near the destination, there is a possibility that the route passing through the other side of the great circle causes less fuel consumption than the calculated minimum fuel route. In such a case, to investigate the fuel consumption of that alternative route it is necessary to apply the algorithm for only the other side of the great circle route.