L13 Blanik Mandatory Bulletin

Let's not overreact here.

It is incorrect to say that all metallic materials have a finite
fatigue life. Metal structures have been certified with an infinite
fatigue life.

I doubt anyone here is a structures engineer with experience in, or
access to DaDT tools.

If you want to get closer to the real story, There is an EXCELLENT,
plain language discussion of the design considerations and fatigue
calculations in the Blanik repair and overhaul manuals published in
the mid 70's. The Factory went to great lengths to educate the
operators, more than I have seen in ANY light aircraft manual or
publication. Sadly, many do not RTFM, put prefer to pontificate in
forums.

Corrosion is the real intractable issue with metals, and causes much
more cumulitive damage in aircraft structures than fatigue alone. I
would inspect visually the affected area, as stress corrosion cracking
in the short tranverse direction in common in high heat treat or alloy
metals, and can appear to be fatigue at first blush.

Aerodyne