As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CORROSION ON INTERCOSTAL ATTACHED TO STRINGER 20RH IN STA. FS= 349.00 TO FS= 364.00 AT MAIN AVIONICS COMPARTMENT. INTERCOSTAL ATTACHED TO STRINGER 20RH IN STA. FS= 349.00 TO FS.364 STG 20RH AT MAIN AVIONICS COMPARTMENT WERE REPLACED PER CRJ900 SRM 51-42-21-001-001-A01