BTW, applies to the twin otter, not alll a/c with PT6's). Prop rpm? Depends on the a/c: twin otters we used 75-80% rpm always, unless an engine failed- then full prop.
Hang on, are you saying that the Twin Otter has high idle and low idle positions? What PT6A engines were fitted to your airplanes? And 75-80% Np always?
Takeoff and landings: Prop levers to Full increase!