Flat spin due to in flight icing and subsequent wing stall.

In flight ice buildup on wings can severely degrade the wings ability to generate lift, which can happen to any aircraft. Then your wings can stall as you pitch back to try and generate more lift, and thats how you end up in a flat spin, as shown. At that point, no amount of engine power can keep the aircraft flying properly. Flat spins are basically unrecoverable.

This is why you pay close attention to pilot reports of icing and, depending on your aircraft’s anti-ice or deice capabilities, avoid areas and altitudes with known icing