What was found
NR 1 HYD SYSTEM ACCUMULATOR O-RING (PN MS28775-212) FAILURE, CAUSING LOSS OF HYDRAULIC FLUID IN THAT SYSTEM. NR 1 SYSTEM WAS SHUT OFF AND AIRCRAFT RETURNED TO AIRPORT ON NR 2 SYSTEM WITH NO FURTHER INCIDENT. NR 1 HYDRAULIC ACCUMULATOR O-RING, (PNMS28775212). BATCH NR 64909 REPLACED, HYDRAULIC FLUID REFILLED AIRCRAFT. GROUND RUN LEAK CHECK PERFORMED, TEST FLIGHT PERFORMED. AIRCRAFT RELEASED FOR RETURN TO SERVICE.