As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SJO - DURING FERRY FLIGHT OUT OF C-CHECK, MASTER FIRE WARNING LIGHT CAME ON AND FIRE WARNING BELL SOUNDED AFTER APPROX 25 MINUTES OF FLIGHT. WARNING LIGHT WOULD NOT EXTINGUISH AND BELL WOULD NOT SILENCE. NO OTHER SYSTEM FIRE WARNING LIGHTS WERE ON. AIRCRAFT RETURNED TO BASE, NO EMERGENCY DECLARED. DETERMINED THE CARGO SMOKE DETECTOR CONTROL PANEL TO BE AT FAULT AND REPLACED SAME. PERFORMED SMOKE DETECTOR SYSTEM TEST IAW MM 26-20-00/26-20-13 AND NO FAULT INDICATED. (M)