TELDOSERIOUS,
refer to P180 AFM, Sect 2 – Limitations, Pag 2-3
VMCa AF System Operating : 100 KIAS
VMCa AF System Not Operating (propeller windmilling) : 128 KIAS
The difference is due to the fact that, with AF not operating, there is such a huge drag from the windmilling propeller that VMCa is to be increased by approx 30 KIAS, this make a lot of sense to me.
Not all the a/c shows this difference in limitations with and without AF.
Attempting a TO on the assumption that the AF system is working, if in fact it is not working, will end in a dysaster if one engine fails at a TO speed schedule which is 30 KIAS lower than the minimum reuqired.