MelEagerToo,
I had mixed experiences with KFC-150.
Some worked real fine for flying heading or route, keeping altitude or making initial descent.
I remember also KFC-150 that fly a heading with a 12° error or a route with constant wobbling from -5° left to +5° right and which accept descent rates of -200 ft/min but jump to -800 fpm if I make any increment to the descent rate.
I never trusted this AP enough to use it elsewhere than cruise or initial descent, usually in heading/alt mode.
To all the contributors who investigate a complex chain of events involving the autopilot and airframe icing, I don't think all of this is necessary to explain this LOC-I accident. I wouldn't be surprised if the final report states that the airplane was perfectly fine until it hit the sea.