Was the wing clean on the ground before takeoff?
Did anybody get up on a ladder or platform to check the tail?
The operator, West Wind Aviation, had some de-icing equipment in the terminal building (see photos) at the airport. The de-icing equipment that was available to WestWind Aviation in Fond-du-Lac consisted of two ladders, a hand-held spray bottle with electric blanket and wand, and a container of de-icing fluid. However, the aircraft was not de-iced before takeoff, and the takeoff was commenced with ice contamination on the aircraft.
Canada TSB Investigation of Fond du Lac crash