What was found
PHL - FLT803 - ON CLIMB-OUT FROM PHL, CREW REPORTED THE NR 1 ENGINE HYDRAULIC PUMP LOW PRESSURE LIGHT ILLUMINATED ON GEAR RETRACTION. SYSTEM "A" HYDRAULIC QUANTITY DROPPED TO LESS THAN ONE-QUARTER. FLIGHT RETURNED TO FIELD AT PHL AND LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANCE REMOVED AND REPLACED THE NR 1 ENGINE DRIVEN HYDRAULIC PUMP AND INSPECTED AND REPLACED THE NR 1 ENGINE CASE DRAIN FILTER, WHICH CHECKED OK. RESERVICED HYDRAULIC SYSTEM. OPERATIONAL CHECK AND LEAK CHECK GOOD.