What was found
APU FAILED IN FLIGHT. RESET, AND IT FAILED AGAIN. ATTEMPTED RUN/LEAK CHECK, APU WOULD NOT RUN. INTEROGATED ECU AND FOUND LOW OIL PRESSURE FAULT AGAIN. INSPECTED GEAR BOX MAGNETIC CHIP DETECTOR IAW AMM 49-27-04-2, FOUND METAL SHAVINGS. REINSTALLED MCD. REMOVED OIL PRESSURE FILTER HOUSING AND FILTER ELEMENT IAW AMM 49-27-03-2. FOUND METAL PARTICLES INBEDDED IN FILTER AND VERY FINE METALIC PARICLES IN BOTTOM OF FILTER HOUSING. REPLACED THE FILTER ELEMENT. APU RUNNING NORMAL IAW JRH AND AMM 49-11-00-6. NO FURTHER METAL FOUND ON GEARBOX CHIP DETECTOR AFTER SEVERAL GROUND RUNS. RETURNING APU TO SERVICE.