What was found
IN CRUISE, THE NR 3 ENGINE LOW OIL PRESSURE LIGHT BEGAN FLICKERING. NR 3 OIL PRESSURE DECREASED FROM 35 PSI TO 20 PSI. ENGINE POWER WAS REDUCED TO IDLE AND A SIGNIFICANT AIRFRAME VIBRATION DEVELOPED. NR 3 ENGINE WAS SHUT DOWN USING COM PROCEDURE. DUMPED 90,000 LBS OF FUEL AND RETURNED TO SEA. MAINTENANCE FOUND METAL IN OIL TANK, FILTER AND ON CHIP DETECTORS. AIRCRAFT WAS PREPARED FOR THREE ENGINE FERRY. PART CAUSING PROBLEM TO BE DETERMINED.