What was found
DURING DESCENT, LOW OIL PRESSURE WARNING LIGHT ILLUMINATED FOR THE NR 4 ENGINE WITH AN OIL PRESSURE INDICATION OF 33 PSI WITH ENGINE POWER AT IDLE. PERFORMED PRECAUTIONARY SHUT-DOWN OF THE NR 4 ENGINE. REPLACED MAIN OIL FILTER FOR THE NR 4 ENGINE IAW DC8 MM, CHAPTER 79. REPLACED OIL PRESSURE RELIEF VALVE FOR THE NR 4 ENGINE IAW PWA JT3D MM, CHAPTER 72. CHECKED OIL PRESSURE INDICATION IAW DC8 MM, CHAPTER 79 AND OPS CHECK WAS GOOD.