What was found
FOUND OIL CANNING IN LT WING OF HIGH TIME WHEN LIFTING AFT END OF TIP TANK. WING WAS INSPECTED AND ONLY DEFECT WAS LWR FLANGE ON 4 OF INTERSPAR RIBS WERE CRACKED, STRINGER PASS-THROUGH. CRACK WAS .5-.75 INCHES LONG, EXTENDED PAST FIRST RIVET. AFTER REPAIRING, OIL CANNING WAS STILL EVIDENT. OIL CANNING SKIN IS NOT RESULT OF RIB CRACKS BUT CRACKS ARE DIRECT RESULT OF OIL CANNING SKIN. IF LEFT UNDETECTED COULD LEAD TO STRUCTURAL FAILURE OF RIB. OIL CANNING WHEN GENTLE LIFTING FORCE IS PLACED ON AFT END OF TIP TANK (CAUSE OF DAMAGE) AND POSSIBLY SOME LOOSE OR SMOKING RIVETS ON RIB LINE (RESULT OF THE DAMAGE) IF RIVETS ARE LOOSE OR SMOKING BE SURE TO INSPECT INNER STRUCTURE BEFORE PUTTING BLIND FASTENER IN.