What was found
DURING 100HR AIRFRAME INSPECTION REMOVED AFT TAIL ROTOR GEARBOX COWL TO INSPECT VERTICAL STABILIZER. DURING INSPECTION FOUND 1 RIVET HEAD POPPED OFF OF FORWARD MOUNT ON UPPER VERTICAL FIN WITH NO OTHER EVIDENCE OF WORKING RIVETS OR DAMAGE. REMOVED VERTICAL TO INSPECT FURTHER AND FOUND MOUNT MOVING UNDER SEALANT, 5 SHEARED RIVETS AT FORWARD MOUNT TO VERTICAL FIN ATTACHMENT POINT. ALSO, FOUND 4 OTHER AREAS CRACKED ON THE LOWER SIDE OF UPPER VERTICAL FIN AFTER LOWER PLATE WAS DRILLED OFF TO INSPECT FOR FURTHER DAMAGE.