As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE IN HEAVY MAINTENANCE PERFORMING INSPECTIONS IT WAS NOTED THAT AT BS 620 STRINGER 23R, INTERCOSTAL CRACKED. REMOVED CRACKED INTERCOSTAL FABRICATED NEW INTERCOSTAL, HEAT TREATED TO T6. INSTALLED INTERCOSTAL, NO OTHER DEFECTS WERE NOTED. ACFT WAS RETURNED TO SERVICE.