As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MAIN AVIONICS BAY STR 21L BACK-UP SILL CORRODED BETWEEN FS 333.00 AND FS 349.00. C-CHECK RO 10/9/2020. REMOVED AND REPLACED MAIN AVIONICS BAY STR 21L BACK-UP SILL BETWEEN FS 333.00 AND FS 349.00, REF BOMBARDIER DWG AND CRJ 900 SRM. COMPLIED WITH.