Just had the AD completed on my machine. It looks like the Derby crash was caused by a sheared clutch shaft at the aft bolthole. This was caused (according to ATSB) by a combination of paint and a non approved jointing compound between the yolk and the clutch shaft. The tourqueing of the bolts may have been done correctly but when the paint and jointing compound wore away, the whole show started to flog out. Apparently this jointing compound is used by a large section of the industry on R22's (and is or was very good). It is not however, in the Robinson R22 Maintenance Manual. The flex plate was not mentioned in the AD.
