As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN TROUBLESHOOTING ISOLATION VALVE FOUND INTERCOSTAL AT STR 22L BETWEEN FRAME STATIONS 295 TO 333 CORRODED AND GROUND STUDS NOT ATTACHED DUE TO CORROSION. SHEET METAL EVALUATION REQUIRED. UPON FURTHER INVESTIGATION FOUND CORRODED INTERCOSTAL TO BE AT STRINGER 21L REPLACED STGR 21L INTERCOSTAL P/N:SH670-31822-1 BETWEEN FS295 AND FS333 IAW CRJ900 SRM 51-40-11-001-001-A01 AND 51-42-06-001-001-A01.