Yogi :
Slight technical correction. Unloading the rotor disk can lead to mast bumping if not immediately corrected or if a bit vigorous. Bumping is a consequence of unloading, not ( to my mind ) a strictly separate phenomenon.
There are recent accident reports, and if you speak to any R22 instructor I'm sure they'll quite happily explain in much more detail.
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For the last bloody time, it's "The En Ar Fairy" . . .