ORIGINAL: Flying freak
Also just something id like to add to the diagram that ken posted, that black line between the red/green is probably the WORST place to be if i was a betting man and had to bet which way a prop blade would go should it decided to leave the hub its gonna be somewhere n that black line 90% of the time...
Actually, the black line is fairly safe. But just forward of the black line is the most dangerous.
It's true that a broken prop will spit out to the side, but it is also pulling forward with a lot of force (Face it, it's not going to break at idle - it will do it while turning high RPM)
So the prop will be pulling forward and when the centrifugal force sends it out to the side it will go slightly forward of the 90 degree plane.
But again, the basic rule of thumb is:
With the exception of starting the engine, STAY BEHIND THE BLACK LINE!!!!