I was checking the blade tracking on my Raptor 30 Helicopter and looked away for just a second.  It was on the ground but a gust of air picked just that time to force it's way under the rotor and start tilting it over.

I corrected it and it started going the other way.  My uncle now has a nice deep little trench in it and I got to replace my first set of blades on the raptor.  :)  Moral of the story is keep your eye on the ball.