As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL FLT 759 EN ROUTE ATH TO PHL. CENTER HYDRAULIC QUANTITY WENT TO ZERO, AND SYSTEM PRESSURE AND QTY LIGHTS ILLUMINATED. EICAS MESSAGES C HYD SYS PRESS AND C HYD QTY DISPLAYED. THE LANDING GEAR WAS EXTENDED USING THE ALTERNATE GEAR EXTENSION METHOD. MAINTENANCE REPLACED THE ACMP CENTER SYSTEM PRESSURE TO CASE DRAIN FILTER LINE. ALSO, REPLACED THE CENTER SYSTEM CASE DRAIN FILTER.