Sultan, I agree to some extent, but I think that the other possibilities need to be investigated or excluded.
What really worries me is that this finding strongly reflects the typical manufacturer's response:
See.... I told you it was not our problem.
Until we know why the crack initiated, the manufacturer is still not off the hook. I have seen so many excuses for the older blades which grasp at straws and are then taken as "reasonable explanations".
Example 1: The paint was buffed and the high temperature caused by buffing caused the bond failure. In reality, the failure exhibited adhesion and mixed-mode failure characteristics. If the bond exhibited full strength, the failure should be by high-strength cohesion, not lower strength mixed-mode or even worse low strength adhesion failures.
Example 2: Particle abrasion causes undercutting of the adhesive layer and that leads to bond failure. Bovine excrement!!! Examination of the failure photos shows a combination of lower strength mixed-mode and weak adhesion failure. If the bond maintained full strength, then the failure would be by strong cohesion failure, not the weaker forms which result from interfacial degradation.
Example 3: Despite clear evidence of weak bond strength, the manufacturer grasped at the fact that the luggage door was not recovered and based their stance on the usual "unexplained impact caused the blade to fail". Impact will never cause adhesion failures unless the bond is already weak.
So I place as much weight on the "it is not a manufacturing problem" as I would place on Sepp Blatter's defence "I know nothing"! Who knows? Maybe the next explanation will be that these failures were due to impact with a kiwi!
What really troubles me is that four months has passed since the first cracking occurrence and several months since an in-flight break up at Queenstown NZ and yet the only interpretation of the entire problem is that it is not a manufacturing defect. In the mean time, operators, pilots and passengers wait for a plausible explanation of the cause of these failures. Doesn't ICAO require timely investigation of these events?
I think it is time for CAANZ and TAICNZ to bring in the people in areas where they may not have appropriate expertise, and I say this with no reflection on the expertise of the investigators. If they have never had appropriate training how can they know what the significant factors are in a bond-related failure? I know those capabilities exist in NZ, and I would be happy to back these people up.
The earlier -5 blades have an AD which permits use for another five years, yet in the case of DQ-IHE the IIC found that the most probable cause of the crash was due to failure of the MRB due to low bond strength. That blade had been in service for only 34 months before it failed. So how can a five year service life be justified? Worse yet, the blade had been inspected TWICE using the approved tap test and once visually within about 80 hours of failure. See
http://www.adhesionassociates.com/pa...ES%20final.pdf
If NDI can not assure bond integrity, and if there are examples of failures in a time frame well below the 5 year period of grace, then I hope someone can explain how continuing airworthiness can be managed before the lawyers have a field day in the mean time after some poor innocent people pay the price for a "She'll be right" management philosophy.
And before I get the "Robbo bashing" comments, I state again that the same analysis applies for any bonded principle structural element where the overlap length is amazingly short. See the paper.
Regards
Blakmax