hmm is right. Lots of 135 operators out there just got a big wrench throw in the face.
On another note, do older boots have a lot of ice bridging issues? I mean with modern boots, bridging almost never happens. But the fact that even a small amount of ice causes low speed handling issues, shouldn't be a surprise to anyone. I mean, its ice screwing with the leading edge and upper camber right? If a little bit of frost causes take off accidents/performance issues, why wouldn't this cause other handling issues? But kudos to the FAA, IMHO. If people aren't safely flying the aircraft consistently in a specific condition, then something needs to change. Spotting the root cause is good for now, but a longer term solution is needed. TKS retrofits and other de-ice, likely heated elements like Kelly Aerospace "therma wing" comes to mind.