As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A PREFLIGHT WALK AROUND CORROSION WAS OBSERVED ON THE AFT SPAR ANGLE CHANNEL OF THE VERTICAL STABILIZER. UPON FURTHER INVESTIGATION SIGNIFICANT INTERGRANULAR CORROSION WAS FOUND RESULTING IN EXFOLIATION OF THE SURFACE OT THE SPAR ANGLE. THIS RESULTED IN A MAJOR REPAIR. AIRCRAFT WAS REMOVED FROM SERVICE