What was found
EN ROUTE IAD-AMS, CREW RECEIVED EICAS MESSAGE HYD PRESS SYS C, CENTER HYDRAULIC QUANTITY INDICATED ZERO. AIRCRAFT RETURNED TO IAD. *S/D* LEFT MAIN LANDING GEAR STEERING ACTUATOR PRESSURE HOSE (P/N: AS4568G0580SS) WAS FOUND TO HAVE WORN THROUGH HOSE RESULTING IN LOSS OF CENTER HYDRAULIC SYSTEM FLUID QUANTITY. HYDRAULIC FLUID LEAKAGE RATE WAS BELOW HYDRAULIC FUSE SET POINT. CHAFING WAS AT A HOSE GUIDE LOCATED APPROX 12 INCHES AFT OF ACTUATOR. WORN HYDRAULIC HOSE WAS REPLACED AND CHAFF PROTECTION WAS INSTALLED. BOEING PROJECT IS UNDER DEVELOPMENT TO REPLACE HOSE GUIDE WITH AN IMPROVED VERSION DESIGNED TO PREVENT CHAFING PER SERVICE BULLETIN 777-32-0017.