Aser,
This is basically a rehash of an old Agusta letter. These "cracks" have been on the blades for more than 4 years. Agusta put out a letter a long time ago detailing the construction used on the blades. On the fork end, there is a sacrificial layer of composite matting that protects the load carrying fibers underneath from impact damage. This layer is not in one piece, but is made up of 2 or 3 separate pieces. There is a joint between 2 of these pieces at, you guessed it, the very inboard end of the fork end near the word Blade Root on your diagram from Agusta. Agusta have always said that if you find cracking in this area you should investigate to make sure it is only in the sacrificial layer, which is NOT cause for blade rejection. You would hope that maintenance staff are actually looking at things like this on their daily inspection, after all, that is what a daily inspection is for!
I know of one 139 operator that has so far inspected over 60 tail rotor blades and have found a few with the cracking in the superficial layer, and 1 or 2 that they are sending back to Agusta for confirmation that they are Ok.
Personally, I'm still more than happy to fly in 139's from my company, just like I'm happy to fly in machines from other operators if I know their maintenance and operations are above board. There are some operators that I wouldn't fly with just now as I don't believe they're doing a very good job of maintaining their aircraft in a safe state, just like some fixed wing operators out there.
With regard to the weak tail structure, the structure is a hell of a lot stronger than any 212/412 or S76 (even with all the scab patches and CSN's applied). 2 Spars to carry the load and an enclosed box structure to handle torsion loads. It is quite a robust unit, and on the AW149 has been tested up to a max takeoff of 8000kg or more.
I'm hoping Agusta can pinpoint why this blade came apart quickly. Maintenance error/involvement, or manufacturing process errors?
I heard that Agusta had a main rotor blade fail on an early 109 (in the USA??) that killed people, which was traced back to one working not cleaning the blades surfaces properly during the bonding process (or so I was told).
Lets hope that the manufacturing process is not to blame again, otherwise we'll be looking at a major recall of tail rotor blades!!!