>icing on this plane type was fixed, the error addressed.
If you read the NTSB report you'll see that the icing occurred beyond the edge of the de-icing boot, Anon. In any event, subsequent to ATR's engineering changes due to the Indiana loss of aircraft incident there was a loss of control due to icing over Norway:
"Same model of plane in doomed Brazil flight has killed nearly 500 people in series of crashes"
"ATR, the French-Italian plane manufacturer, also improved its de-icing system after the horror. But another ATR-72 stalled out in 2016 in Norway when ice built up on the plane. The pilot in that incident was able to regain control of the aircraft."
https://nypost.com/2024/08/13/world-news/same-model-of-plane-in-doomed-brazil-flight-has-been-in-other-crashes/
>not flutter around like a leaf on the way down.
The aircraft was in a flat spin.
https://pilotinstitute.com/what-is-a-flat-spin/