What was found
IAH - FLT 1638 - THE A-HYDRAULIC SYSTEM QUANTITY BEGAN TO DECRASE IN FLIGHT. THE LEAKAGE STOPPED WHEN THE A-SYSTEM WAS ISOLATED BY TURNING THE SYSTEM-1 FLIGHT CONTROL TO STANDBY RUDDER. THE AIRCRAFT WAS RETURNED TO IAH WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE O-RING AT THE ACCUMULATOR FITTING OF A-SYSTEM HYDRAULIC ELECTRIC PUMP LEAKING. THE O-RING WAS REPLACED. THE HYDRAULIC SYSTEM WAS SERVICED AND LEAK CHECK WAS GOOD. (X)