What was found
DURING CLIMB OUT OPERATION, THE MAIN DECK FIRE WARNING LIGHT ILLUMINATED. THE AIRCRAFT RETURNED TO DEPARTURE WHERE IT LANDED WITHOUT INCIDENT. POST FLIGHT INSPECTION REVEALED THAT THE LT WARNING LIGHT ILLUMINATED STEADY. VERIFIED THAT NO SMOKE OR FIRE WAS PRESENT. LIGHT EXTINGUISHED AFTER RESEATING THE NR 8 SMOKE DETECTOR. REMOVED AND REPLACED THE NR 8 SMOKE DETECTOR AS PRECAUTION REMOVED AND REPLACED THE NR2, NR 4, NR 6, NR 10, NR 12 ON THE LT SIDE AND NR 9 ON THE RT. ALL OPERATIONAL CHECKS GOOD. NO OTHER DEFECTS WERE NOTED AIRCRAFT WAS RETURNED TO SERVICE. (K)