Walnut, is probably talking about the Bristow Flight 56C Puma that had tail rotor separation in flight. It was caused by atmospheric discharge, causing destructive failure in one of tail rotor blades at the boundary between carbon fiber and aluminium sections. Apparently difference in resistance between both materials was enough to produce a lot of heat, that destroyed the part.
There was an documentary on that, it is available on YouTube:
Part1
Part2
Part3
Part4
Part5