As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
**WHILE AIRCRAFT WAS OUT OF SERVICE FOR HEAVY CHECK** CORROSION LOCATED ON THE UPPER SURFACE OF INTERCOSTAL OF FLOOR ASSY BETWEEN FR90 AND AFT PRESSURE BULKHEAD. REPLACED RH INTERCOSTAL IAW SRM 51-41-02 AIRCRAFT REMAINS OUT OF SERVICE FOR HEAVY CHECK COMPLETION.