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= 319.70 TO FS= 349.00 AT MAIN AVIONICS COMPARTMENT. CORROSION ON INTERCOSTAL ATTACHED TO STRINGER 20RH IN STA. FS= 319.70 TO FS= 349.00 AT MAIN AVIONICS COMPARTMENT WAS EVALUATED OUT OF LIMITS PER CRJ900 SRM 53-21-23-101-001-A01 AND WAS REPLACED PER CRJ900 SRM 51-42-21-001-001-A01