Mag failure Bell 47-G2
I had one Mag on a Bell 47-G2 fail in flight during my PPL training. We didn't notice until I pulled power during my final approach flair. Ugly landing, and my instructor gave me the evil eye because I was pretty far into training to have such an bad final. I complained that I didn't have any power, but it was hot and the first assumption was that I was late on the throttle (no govenor, just slight corolation on the G2).
After getting chastised when I finally put the a/c down on a taxiway he said something along the lines of "alright lets do THAT again", he took the controls, and attempted to lift off. Hot day, and he could barely get the thing off the ground (redline on MP). That's when we did a mag check and decided to call in the mechanic.
Interesting failure that I would never have been able to train for, but it could have been a big problem if I'd needed to go around near the ground. Certainly made me more aware hot temps, and steep approaches.