Bingo, exactly what I was thinking as I was scrolling down, and...voila, secondary lighting in. Looks much better.I'm guessing that faint black fuzz in the first image was the AO that messed up but the white fringe persisted through to the second render. It kinda looks like a sharpen filter gone berserk and its having a jarring effect.
The scene could definitely use some secondary bounce light underneath there as the propeller blade are disappearing into the shadows. You could turn on FG or you can do it manually. For starters, I'm thinking lighten and soften the shadows and add a large, extremely weak area light facing upwards just below the ground plane and using light linking to not have the light affect it. That way it looks as if light is bouncing up from the ground and going from there.