What was found
GSO - FLT 1735 - THE A-HYDRAULIC SYSTEM PRESSURE DROPPED TO ZERO DURING CLIMB OUT OF GSO. CHECK LIST PROCEDURES WERE COMPLIED WITH AND THE AIRCRAFT WAS RETURNED TO GSO WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND A CHECK VALVE FAILURE OF THE A-HYDRAULIC SYSTEM MODULE. THE A-SYSTEM MODULE WAS REMOVED AND REPLACED. LEAK AND OPERATIONAL CHECKS WERE GOOD. THE HYDRUALIC WAS SERVICED IAW MM 29-11-61. (X)