As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT NR 421 - IAH - THE NR 1 ENGINE LOOP 'B' FIRE DETECTOR LIGHT AND MASTER CAUTION LIGHT ILLUMINATED DURING CLIMB-OUT AT 18,000 FEET. THE NR 1 ENGINE LOOP SWITCH WAS MOVED TO LOOP 'A' AND TEST WAS NORMAL. THE NR 1 ENGINE FIRE DETECTION MODULE WAS REMOVED AND REPLACED. THE NR 1 ENGINE FIRE DETECTION SYSTEM CHECKED GOOD. (M)