What was found
DURING AC C-CHECK AT ILN, MAINT DISCOVERED MAJOR SHIM P/N BA CS40R21C38F MIGRATION COMMON TO THE LEFT WING BETWEEN THE FWD O/ B DRAG FITTING ASSY PN 12N7009-11 AND FRONT SPAR ASSY PN 112N300 2-15. THE SHIM MIGRATED I/B BY APPROX 0.600 INCH AND THE THICKNE SS COULD NOT BE DETERMINED AT THIS TIME. PERFORM INSPECTIONS PER PART 2 STEP 1 OF LATEST REVISION OF ECRA 5721-01447 ON OR BEFORE 23459 TOTAL A/C CYCLES. PERFORM REPEAT I NSPTIONS THEREAFTER EVERY 1200 FLIGHT CYCLES.