Hi Anthony:
On the new Series 400 Twin Otters, there are two autofeather switches, one on each of the outboard ends of the instrument panel. One of the reasons we put them there was to eliminate exactly the risk of confusion that you identified in your post.
The two switches work in a similar manner to the switches at the top and bottom of a set of stairs - it doesn't matter whether you push the left or right switch, whenever one of the two is pushed, it changes the state of the autofeather system (to ON or OFF as the case may be), and the autofeather system status is indicated by the illuminated nomenclature within the switches and on the CAS message screen.
The picture below shows the left side autofeather switch, the right side is a mirror image.
Michael
Autofeather Switch - Series 400 Twin Otter
