Of course reverse on the PT-6 on the Twin Otter can be used on the ground. It could even perhaps get tweaked in the flare on a very short strip but was definitely not supposed to be used(or a bit of so-called beta) on approach. However I have read that the turbo Porter(PT-6) does use at least some beta during those straight down descents after dropping skydivers and that it is legal to do so. Maybe its an airplane specific thing. Any Porter pilots care to comment on that procedure? Any other tuboprops allowed to go below flight idle while airborne?