In turboprops, is there a mechanism to prevent the blades running in opposite direction?
Most manufacturers realise this is a serious risk so most are 'gated' in that you have to do something to get them into this range. This is like pulling up the reverse tabs on the throttle levers on the B737 or A320 that is only possible when they are in the idle position.


ATR 42/75: Has something called Idle Gate that prevents throttles from going back too far when engaged.
Dash 8: Has gated throttles that requires pulling up a pin to get them into reverse.


There is to the best of my knowledge nothing (in general at least) to stop to the thrust from being 'reversed', or more specifically to angle to blades to what is known as the 'beta' range, if you are intent on doing it. Unlike jets where doors open for instance and the process is a little more complex, this is just rotating the blade below a certain angle.



I found the accident report [PDF] for the Manx2 flight. There were multiple things going on here rather than a single cause:


Generally bad piloting for putting them in a late go-around situation to start with.
There were errors in the engine, causing a thrust mismatch.


This meant that one engine proceeded to continue into negative thrust.



It does then not come as a complete surprise that you manage to flip the plane over from considerable unsymmetric thrust when you are close to stall speed.