Canadian investigators have disclosed that an ATR 42-300 which crashed shortly after take-off from Fond-du-Lac airport had not been de-iced before departure.
The turboprop came down less than 1nm from the end of runway 28 on 13 December last year.
While all 25 occupants survived the initial impact, nine were seriously injured and one passenger subsequently succumbed.
Transportation Safety Board of Canada states that the West Wind Aviation ATR had arrived at Fond-du-Lac about 45min before the accident.
It had descended through icing conditions on the approach and the inquiry says the aircraft's de-icing and anti-icing systems were engaged.
But residual ice remained on parts of the airframe after these systems were subsequently switched off.
West Wind had access to de-icing equipment at the airport including ladders, hand-held spray bottles, de-icing fluid and electric blankets.
"However, the aircraft was not de-iced before take-off," says the inquiry. "The take-off was commenced with ice contamination on the aircraft."
It crashed into a wooded region after departing Fond-du-Lac on a regional service to Stony Rapids in Saskatchewan.
Meteorological conditions for the departure airport indicated "patchy moderate rime icing" in cloud from 3,000-7,000ft. The inquiry says rime ice is rough, opaque and crystalline.
Investigators state that a "significant amount" of work has been completed regarding the inquiry, but "much remains to be done", and the probe needs to analyse the reasons for the failure to de-ice the ATR.
Transportation Safety Board of Canada adds that it will assess the adequacy of the de-icing equipment available, study the aircraft performance to determined the effect of weather, and review operational procedures.