you are making some mistakes gents.
first- there are no pitch locks on a pt6a .
second - going to beta ( lifting over the gate) disconnects the governor . this is -beyond flying against a wall when being airborne - one of the big reasons beta inflight is prohibited at any aircraft and the porter is no exeption of it.
third- pulling back to flight idle with props forward on a pt6 results in torque dropping to zero and the wind driving the prop . some call is "prop disc braking" and some falsly call it beta range .
on this engine no NTS is needed like on singleshafts. pulling back an pt6a to idle with props forward gives an enormous braking effect with the steep approach capability. the higher the speed the higher the effect.
thats not only for the porter tha case . pulling back both engines to full idle stop at lets say a cheyenne and pushing the props simultany full forward will result she will drop like a rock , but its not done for passenger comfort and a stabilzed descend. the porter is just used this way in jump missions.
when it comes to land a pt6 driven airplane , lets again say a cheyenne : be at vref in 50 ft over the threshold and pull back to full idle ( up to the gate , not over the gate) and you will need a cane to remove the aircraft- she will stop in the air and fell out of the sky.
even when at slower speeds the prop disc brake effect decreases its even here very significant and you have to be careful.
don,t misunderstood beta range (lever over the gate, governor off , power lever controls prop pitch ) with prop disc braking effect ( power idle , governor on , wind drives the prop )
hope this helps !
cheers