Now, the question is :
What kind of system, and how it happens :
That the flight idle pitch stops ( so +9,30° blade pitch ) are removed to allow blades to rests on ground low pitch stops ( Bęta, -0,30° ).
I know on some bigger planes like the Dash 8Q400 it's some kind of system related to pressure on landing gear, when the senser know you are firmly on ground, it allow the flight idle low pitch stops to be lifted, so the blade can go to Bęta range, or mostly " Ground Fine ".
On the PC-6 I don't know. If you think this is not really realted to the general Bęta range, I can start another thread especially about the Bęta used on PC-6 aircrafts.
Thanks for your help