What was found
ORD - FLT 84 - AFTER TAKEOFF ORD-FRA, CENTER HYDRAULIC SYSTEM LOST QUANTITY FOLLOWED BY LOSS OF PRESSURE. RESERVE BRAKES/STEERING SWITCH SELECTED FOLLOWING GEAR EXTENSION WHICH MOMENTARILY RESTORED PRESSURE. ALTERNATE FLAP EXTENSION PERFORMED. AIRCRAFT RETURNED TO ORD AND LANDED WITHOUT INCIDENT. REPLACED O-RING IN NR 9 SPOILER ACTUATOR. ALSO, REPLACED AC MOTOR DRIVEN HYDRAULIC PUMPS, AIR DRIVEN HYDRAULIC PUMP, AND FILTERS AS PRECAUTIONARY MEASURE. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)