As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING C-CHECK INSPECTION, A RIVET HEAD WAS FOUND SEVERED FROM ITS SHAFT. THE RIVET LOCATION IS AT FRAME 47, STA X16128, AT THE LEFT HAND SIDE OF THE VERTICAL STABILIZER BASE. THERE IS NO INDICATION AS TO WHAT CAUSED THE RIVET HEAD TO BECOME SEVERED. THE HOLE DOES NOT SHOW EVIDENCE OF ANY DAMAGE. SUBMITTER RECOMMENDED REPLACING RIVET AND CONTINUE MONITORING WITH ESTABLISHED C-CHECKS.