C120 aft spar tip crack fix

[drdave47]

A recent inspection found this aft spar tip crack underside (left side) of spar at wing attach point approximately 3/8 - 1/4 in in length.

Photo attached:

IMG_7166 (2).PNG (233.64 KiB) Viewed 1304 times

Dye penetrant placed after paint scratched off showing crack from left to right lengthwise of spar.
Wonder if this occurred due to over torque of wing attach bolt?
Would an acceptable fix be to drill stop?

[drdave47]

Added couple of photos for more clarity
dye penetration shows where paint edges have been stained = actual crack is small dark line horizontal to spar
One photo shows better as to how small it is next to wing root

[8224]

I can’t understand how or why a crack would occur in that particular location. From a structural standpoint there is little or no stress there. I am an A&P with IA and about 45 years experience. If I were doing the Annual I would stop drill and then watch it very closely for a couple of years, from the pictures the crack appears to be an old one. For what it’s worth, I use to have a piece of paper that said I was a Civil Engineer. Built and designed bridges, not airplanes.
Steve Hawley

[6643]

I can’t understand how or why a crack would occur in that particular location.

My guess is it happened when removing or installing the wing. I agree, stop drill and monitor sounds appropriate, but I'm not an engineer...

[drdave47]

Thank you! I was hoping some folks much wiser than me would come up with a recommendation that we could do.

[6643]

The more I think about it the more I think someone lowered the wing tip too far while the fitting was still in the spar. There's not much stress in that small area where the crack is, and there's that big solid bearing block in there to distribute the load and keep the spar in the right shape.