As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CRACKS FOUND IN UPPER TUBE OF CARRY THRU ASSEMBLY, PN 391-030-401-30, AT LOW POINT OF THE TWO CUT OUTS WHICH ARE MILLED IN THE TUBE TO ALLOW INSTALLATION OF WING ATTACH BOLT. THE MILLING PROCESS LEFT A SHARP EDGE THAT CREATED A STRESS RISER. THIS IS A CRITICAL FACTOR CONTRIBUTING IN HOW THESE CRACKS DEVELOP. WE HAVE SINCE DRESSED THE SHARP EDGES ON OUR OTHER CARRY THRU ASSEMBLIES TO FORM A 1/8" RADIUS POLISHED BULL NOSE PROFILE.