What was found
THE NR 2 ENGINE A FIRE LOOP DETECTOR LIGHT BEGAN TO FLICKER WHILE IN CRUISE FLIGHT FROM LGW TO EWR. WHEN THE NR 2 ENGINE THRUST WAS REDUCED THE FLICKERING STOPPED. WHEN THRUST WAS ADDED THE FLICKERING RESUMED. THE NR 2 ENGINE WAS OPERATED WITH PARTIAL THRUST, FUEL WAS DUMPED, AND THE AIRCRAFT WAS RETURNED TO LGW WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND BROKEN CLAMPS AND LOOPS A AND B WERE CHAFING. THE NR 2 ENGINE LOWER CORE DETECTOR ASSEMBLY WAS REMOVED AND REPLACED. THE NR 2 ENGINE FIRE DETECTION SYSTEM CHECKED GOOD.