Thanks for all the info, but I am still not convinced Vmca can change. If it can change by weight the definition will not include "Max all up weight" as one of the factors. Why do we do a Vmc demonstration in a twin aircraft then ? We might as well then do a Vmca demonstration. The Vmc demonstration is to show that the speed that you loose control is actually diffirent from Vmca due to the fact that the "set conditions" is now changing, is that not correct then ? That is also why Vmc is ALWAYS less than Vmca.