these figures are not so much different from average of all helicopters.
Engines 15%.
Human factors 54%
All mechanical 32%.
I think that engine failure is line 2 , and 2a , 2b and 2c are subsets of line 2.
See
http://www.rotor.com/portals/12/Stat...01997-2006.xls
Interesting observation , I did detail analysis of 2006
While engine failure made up 21 of 164 accidents.
It was only primary cause in 1 of 26 fatal accidents that year.
compare that to wire strikes 9 of 164 accidents
but 5 of 26 fatal accidents.