What was found
JFK - FLT 57 - EN ROUTE LHR-MIA - DURING CRUISE, FIRE DETECTOR 3 FAIL ALERT ILLUMINATED FOLLOWED BY NR 3 ENGINE FIRE WARNING. ACCOMPLISHED SHUTDOWN OF NR 3 ENGINE AND DISCHARGED BOTH FIRE BOTTLES. AIRCRAFT DIVERTED TO JFK AND LANDED WITHOUT INCIDENT. REPLACED NR 3 ENGINE A AND B SYSTEM GEARBOX FIRE DETECTOR ELEMENTS. REPLACED BOTH NR 3 ENGINE FIREBOTTLES. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)