As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT, MASTER WARNING LIGHTS ILLUMINATED ALONG WITH THE LT AND RT ENGINE FIRE LIGHTS. BOTH ILLUMINATED AT THE EXACT TIME WITHOUT ANY ABNORMALITIES IN ENGINE INSTRUMENTATION. PERFORMED A VISUAL OF BOTH ENGINES WITH NO POSITIVE SIGNS OF FIRE OR SMOKE. CONTINUED TO CHECK ALL ENGINE INSTRUMENTATION FOR THE REMAINDER OF FLIGHT, WITHOUT ANY ABNORMAL INDICATIONS. ONCE AT DESTINATION AIRPORT, TROUBLESHOT SYSTEM AND FOUND THE NR 1 ENGINE LOWER AFT FIRE DETECTOR WAS PROBLEM. DETECTOR WAS REPLACED AND ACFT WAS RETURNED TO SERVICE.