What was found
DURING C2 + 6 YEAR (HEAVY) CHECK IN MSP, MTC WAS ACCOMPLISHING AA 5331-01297-01C MOD WHEN THEY REPORTED CORROSION UNDER THE SCUFF PLATE, ON THE SUBJECT (PN C02313004-007 LOWER SILL, C02313004-005 ASSY.) AT SCUFF PLATE ATTACH FASTENER HOLE LOCATIONS 1 AND 9. MATERIAL WAS BLENDED BUT DUE TO IMPROPER COUNTERSINKING, THE SILL REQUIRES REPLACEMENT. COMPLIED WITH ER/A 635362-14 PRI REV 0, ER/A 635362-14 PRI REV 1 AND ER/A 635362-14 REV ORIGINAL SECTION 1. (LP# 1731111; AIRCRAFT WAS GROUNDED)