There was an SB that came out in 2007 (Revised in 09) regarding the modification to the strake.
http://www.eurocopter.com/techpub/do...0014ENREV1.pdf
I was told it was partially due to cracking at the base/ attachment points of the upper vertical fin to the tailboom. The reasoning in the SB is:
"
To:
- improve vertical fin's aerodynamic efficiency in order to increase yaw control margins in autorotation at airspeeds in excess of 100 Kts (MOD 073148),
- advise customers having equipped aircraft with vertical fins post-MOD 073148 that they must embody they ollowing modifications:
. MOD 073158 in order to restore yaw control margins,
. MOD 073169 in order to suppress the risk of interference between bearing
No. 5 of yaw control rod and a bolt of the load compensator,
. MOD 073205 in order to avoid end-of-travel abutment of tail servo-control during yaw control pitch adjustment.
If aircraft is equipped with AFCS, the following modifications must also be embodied:
. MOD 073170 in order to suppress the risk of interference between the rod
located downstream of the series actuator and the airframe (aircraft
equipped with AFCS only),
. MOD 073282 in order to restore minimum clearance between the new fool-
proofing device of the lever and the rod end, during flying control motion
towards low pitch (in yaw)."
We modded all of our aircraft when the SB came out and haven't had any issues since.
Hopefully the link works. It's a direct link from Eurocopter's TIPI site.