I accidentally managed to break the engine of the Gazelle but not sure how...

I've spent hours here testing the limits of the Gazelle, so that I'll know what not to do when flying it for real in multiplayer(My 1st chopper ever).

I accidentally caused an engine failure by going above 200km/h, lower collective, pitch up hard for a rapid stop, then when it's about to stop, raise the collective close to full power. If I do that a couple of times, the engine will eventually stop.

I'm not sure what causes the engine failure though, did I overstress it or something? And how should I avoid it?