As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLIMBING THROUGH 18000' TRI-TONE WARNING ANNUNCIATING A "CARGO FIRE LOWER" OCCURED FOR APPROX 5 SECONDS (2 CYCLES OF THE TRI-TONE). HAPPENED FOUR TIMES. INITIATED AN EMERGENCY RETURN TO AIRPORT, DECLARING AN EMERGENCY. THERE WERE NO ADDITIONAL FIRE WARNINGS WHILE ENROUTE TO AIRPORT. NO SMOKE/FUMES EXPERIENCED. LANDING UNEVENTFUL. WARNING WAS FOR THE FWD CARGO BAY. REPLACED ALL FOUR SMOKE DETECTORS IN LWR/FWD CARGO COMPARTMENT. CARGO SMOKE TEST GOOD IAW MM 26-14-01-5 REF MM 26-14-01-4