I didn't fly them in Vietnam, but flew and instructed on RAAF / Aussie army ones for a reasonable while.
Obviously the kinds of failures you can practice airborne are limited and possibly not representative of what would really happen, but we would cover (as best we could) loss of T/R thrust and stuck pedals L and R in forward flight and in the hover.
There were systematic techniques to reduce a stuck pedal problem to something you could land off, either by a reducing torque method (basically a 'calibrated' throttle chop
) and run-on landing, or coming to the hover in the case of lots of left pedal and then using a combination of beep switch and rolling off the throttle in increments to slow the rotation before settling it on.
I probably still have some info written down somewhere if you're after that kind of stuff.