As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 1 ARCDU FAILED IN FLIGHT, CAUSING NR 1 COMM PROBLEMS. RETURNED TO FIELD AND ACCOMPLISHED UNEVENTFUL LANDING. R & R NR 1 ARCDU IAW T/C 6238101. OPS CHECK GOOD. ACFT REMAINS CAT III AND PLACARD IN COCKPIT READS CAT III STATUS. ARCDU WAS REPLACED AS PRECAUTIONARY MEASURE. RETURNED TO SERVICE.