Dennis, you may find the following story of interest. Friend was flying an Enstrom doing survey work in outback Oz. Heavy vibration set in so pilot, wanting to get on the ground as rapidly as possible, basically did a power recovery auto. Having put it on the ground the passenger made a comment to the effect "look, someone's been here before us, there's a tail rotor over there". The pilot was somewhat confused as the landing had been nothing out of the ordinary, despite the vibration. Hopping out everything looked normal, save for the obvious fact that the tail rotor had been chopped off by the main rotor. No other damage was evident, however investigation found the forward main transmission mounting bolts had let go (cause of the initial vibration) and at some point during the landing with the pitch pull the gearbox rotated aft and chopped the tail off. With pitch reduced the gearbox fell back into place.