isitcheerie,
You can tell your ATR buddy retracting the flaps at 400' agl is utter rubbish. Do not confuse the minimum acceleration altitude with flap retraction.
400' may be used as the lowest acceleration altitude, and in case of engine failure (no obstacles indeed) you would maintain until flap retraction speed.
In daily ops,most operators choose an acceleration between 800' to 1500' based on a number of factors, which is the altitude at which the airplane starts to accelerate, while keeping a positive climb. Only after reaching the White/Red Bug can (should) the flap retraction start.
However I do not know the UT specific SOP's. But if the aircraft was not de-iced, retracting flaps that early with a contaminated wing (and seemingly a high AOA on 2nd segment climb) can have only one outcome: the one that happened.
Sad story, thoughts for the families.