As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DISCOVERED ON REMOVAL OF LEFT TAIL BOOM PANEL DURING ROUTINE MAINTENANCE. LONGERON WAS CRACKED IN THREE PLACES. SUSPECT CAUSE INDICATES LACK OF PROPER DEBURRING AT RIVET HOLES IN SEVERAL PLACES. PREPPED COMPLETELY PRIOR TO INSTALLATION.