As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 4 ENGINE FIRE WARNING BELL SOUNDED INTERMITTENTLY. ALL FOUR ENGINES WERE TESTED. NR 4 WOULD NOT TEST. NR 4 ENGINE WAS SECURED. CSD WAS DISCONNECTED AND NR 4 FIRE BOTTLE WAS DISCHARGED. NR 4 ENGINE FIRE LOOP ELEMENT WAS FOUND TO BE DEFECTIVE. REPLACED FIRE LOOP ELEMENT IAW DC8 MM 26-10-1.