As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT, MAIN DECK CARGO SMOKE DETECTOR ZONE 4 WARNING LIGHT WITH CARGO FIRE LIGHT CAME ON. COM PROCEDURE COMPLIED WITH. NO VISUAL SIGN OF SMOKE OR OTHER SUBSTANCES. MAINTENANCE REPLACED 4A SMOKE DETECTOR. OPERATIONAL CHECKED GOOD AND AIRCRAFT WAS RETURNED TO SERVICE.