I put a bore scope down the leg to examine it, but the results are not definitive. Maybe a professional NDE guy could draw conclusions, but the geometry of access and lack of a 45 deg mirror to look 90 deg off camera axis made it a fruitless task for me.
Just to make sure people are aware: Performing a borescope analysis of the inside of the tube is not considered by Van's to be an acceptable method of determining whether or not the material has yielded and/or the part has been compromised. If it was a valid means, we certainly would have recommended it rather than going through the process of changing and manufacturing the new parts. I'll explain.
The primary/initially affected area is not examinable, so if you saw something inside the tube, that actually would
not be an indicator of initial-stage material yield/failure. Rather, it would indicate the part was already significantly compromised and had already progressed beyond the initial problem stage. Even a perfect-appearing tube inner surface
does not indicate whether the part is ok or not. The initial material yield/failure/subsequent crack occurs on the
outer surface/diameter of the tube, in the area on that outer tube surface that is unfortunately obscured by the adjoining parts and associated welds. In other words, the lack of a visible crack on the inside of the tube does not guarantee a healthy, unaffected part. It is possible to have a compromised part that does not yet show signs of cracking on that inner diameter surface.
In fact, on the subject airplane that was the focus of the investigation that led to this service bulletin, the material failure occurred in a way where there was
never a visible crack on the inner surface of the tube. The crack had progressed partially through the tube thickness at that location but not all the way, but
had progressed significantly circumferentially around the outer surface of the tube. The entire area of cracked material was located under the obscured area already noted above.
While a borescope analysis certainly is interesting, and can potentially show if a failure has progressed significantly and the tube is already very badly compromised, Van's must make sure we are clear on this point: Do not perform a borescope analysis of the tube as an alternate means of compliance - It simply is
not an acceptable means.
Sorry to feel the need to be blunt/direct, but in the interest of clarity and ultimately safety, we must make sure everyone knows exactly what is considered acceptable per the engineers that have very carefully examined and analyzed the parts. While a borescope might be able to tell you if the part is already badly damaged and failure is probably already imminent, you cannot examine the part to determine with any reliability whether or not it is compromised.