What was found
DURING DESCENT, NR 3 OIL PRESSURE DROPPED TO 25 PSI WITH NR 3 OIL PRESSURE LIGHT ILLUMINATED. ENGINE SECURED, OIL QUANTITY 9 GALLONS, OIL TEMPERATURE 75 DEGREES CELSIUS AT SHUTDOWN. WIND MILLED APPROXIMATELY 12 MINUTES, OIL PRESSURE DID NOT GO BELOW 24 PSI. RAN NR 3 ENGINE AT IDLE, COULD NOT DUPLICATE. SUSPECTED ENGINE OIL PRESSURE RELIEF VALVE. UPON INSPECTION OF OIL PRESSURE RELIEF VALVE, FOUND VALVE STICKING IN VALVE HOUSING. REPLACED NR 3 OIL PRESSURE RELIEF VALVE IAW PRATT AND WHITNEY MM 72-0. RAN ENGINE AND ADJUSTED OIL PRESSURE RELIEF VALVE IAW DC-8 MM 79-20-5, OPS CHECKED GOOD. RESERVICED OIL TANK.