What was found
AIRCRAFT RETURNED OF FLIGHT AS A CONSEQUENCE OF PRESSURIZATION WAS UNSTABLE DURING CLIMB. AT PLATFORM, THE VENTRAL STAIRWAY WAS ADJUSTED IAW MM 52-63-00. PRESSURIZATION CONTROLLERS BITE WERE PERFORMED, SYSTEM VALVES WERE REVISED, MANUAL SYSTEM OPERATION WAS PERFORMED IAW MM 21-32-03, ALL CORRECT. DURING OVERNIGHT SERVICE, THE PRESSURIZATION SYSTEM WAS CHECKED IAW MM 21-32-00, TESTED CORRECT. THE VENTRAL STAIRWAY ACTUATOR WAS REPLACED IAW MM 52-63-02, TESTED CORRECT.