The two Pilatus accidents - Butte Montana March 2009, and Bellefronte Pennsylvania March 2005 have something in common with the Buffalo New York Bombardier -8 accident January 2009, besides icing conditions. All three aircraft were T-Tail Turboprops with high wing loading. All three appear to have stalled close to the ground and nosed in on approach. Perhaps the T-tail configuration is more susceptable to tail-stall with icing. T-tails are also susceptable to shadowing by the main wing in nose-high attitudes, or fast sink-rates
The Buffalo crash was a commercial flight and the flight recorder has now shown that the plane slowed to 150 kts, and the stick shaker activated. This meant a stall was imminent. Then, a 25 lb force was applied to the stick to RAISE the nose. This is counter to what you would do in a stall situation. The female First Officer sounded tired in her communications with ATC. Could she have been in control and confused? 25 lbs is quite a bit of force. Perhaps the resultant elevator input and attitude change at just under 150 knots stalled the tail if it was iced. The windshield deicing could not keep up and they could not see forward. Perhaps the tail leading edge deice also couldn't keep up. The flaps had just been un-deployed, so perhaps she was countering the effect of the flaps automatically, in spite of the stick shaking. Loss of the lift from flaps could have been a factor at this point. Then again, it seems the autopilot was on, so perhaps this was also a coarse attempt to disengage it.
What would the non-iced stall speed be without flaps, with gear down? Would it be just under 150 kts?
A discussion of the Buffalo accident and the NTSB findings from flight recorder is at:
Daily Herald | Evidence points to crew error in Buffalo plane crash
A very good discussion of icing and turboprops like the Dash 8 is at:
Did Regulatory Inaction Cause or Contribute to Flight 3407 Crash in Buffalo? Nolan Law Group
It still seems to me that Icing was a factor in the Butte crash with a pilot who was so very familiar with his aircraft in normal conditions (2000 hours in type, and four to five years in PC-12's. Would he push it beyond expected limits? He was said to have been a very safe and deliberate pilot. Still, 13 passengers?