If we look at how the buffet boundary speeds converge as altitude increases we will see that the usable speed range decreases.
At the aerodynamic ceiling there is only one speed at which we can maintain straight and level flight. It follows that this single speed (Vonly?) is both the best endurance speed and the best range speed.
The quoted 1.32 Vmd (or 1.316 if you prefer) is OK at lower altitudes, but is irrelevant at very high altitudes.
Last edited by keith williams; 11th Jun 2013 at 13:02.