The bush technique of “cracking it into Beta” is not an approved method of operation in any of the Twin Otter, Dash 7 or Dash 8’s.The Dash 8 propeller is governed as far back as 2/3’s of the way between Flt Idle and DISCing, but unlike the PT6 controls, beyond that point, props are no longer governed and have what is referred to as ‘positive reverse’ in the PW100 series of engine/prop controls. At lower speeds during approach, there is insufficient airflow to drive the prop to overspeed. Reading between the lines of your (John Citizen’s) comments, is it possible that this particular pilot had used Beta without adverse effect on prior occasions, but didn’t know that the high speed characteristics of the prop were disastrous at Vmo?