What was found
NOTED LOOSE/DAMAGED RIVETS ATTACHING LT WING CENTER SECTION UPPER LEADING EDGE SKIN PANEL. UPON REMOVAL FOR SKIN PANEL REPLACEMENT, NOTED PANEL ATTACHED IN SEVERAL PLACES WITH MS20426AD TYPE RIVETS WHERE NAS1097 RIVETS ATTACHED ORIGINALLY. SKIN RIVET ATTACH HOLES WORN/ELONGATED. ALSO NOTED MINOR CRACKING IN WS 46.50, WS 56.00, WS 65.50, AND WS 75.50 WEBS IN UPPER FLANGES AT INTERSECTION WITH PN 101120017115 UPPER STRINGER. SUSPECT CAUSED BY COMBINATION OF NORMAL FATIGUE STRESS IN PROP BLAST AREA COMBINED WITH WORN/OVER COUNTERSUNK ATTACH FASTENER HOLES. PROP OUT OF BALANCE CONDITION MAY AGGRAVATE SITUATION.