The CT-7's and PW-100's both have a free power turbine. Additionally, in both engines, coming over the gates into beta or reverse disables the propeller overspeed protection. The preliminary report states that according to the FDR on the Dash, the props went to 160%, which implies the overspeed protection was not operating.
Even with the Dash's good descent performance, 13000 at 24 miles is way high. I am not familiar with the terrain in PNG, but discounting terrain issues, a standard descent ratio is about 3:1, making the correct altitude at 24 NM 7200 ft.