What was found
DURING FUNCTIONAL CHECK FLIGHT (FCF), ON INITIAL LEVEL-OFF, WHEN POWER WAS REDUCED TO IDLE, NR 3 ENGINE N1 WAS LOWER THAN OTHER ENGINES. WHEN THROTTLES WERE ADVANCED, NR 3 ENGINE DID NOT ACCELERATE. LOW OIL PRESSURE LIGHT ILLUMINATED. INDICATED OIL PRESSURE WAS 33-35 PSI. ENGINE WAS SECURED. ENGINE WINDMILLED FOR 27 MIN WITH POSITIVE OIL PRESSURE. PERFORMED INSPECTION OF NR 3 ENGINE IAW PRATT AND WHITNEY JT3D MM 79-20-7. INSPECTED AND REPLACED MAIN OIL FILTER. NO DEFECTS WERE NOTED. OPS CHECKED GOOD ON ENGINE RUN-UP.