What was found
AIRCRAFT PERFORMED AN EMERGENCY DESCENT DUE TO PRESSURIZATION SYSTEM FAILURE. MAINTENANCE PERSONNEL PERFORMED BITE TO CABIN PRESSURE CONTROLLERS IAW AMM 21-31-00, DETECTING CABIN PRESSURIZATION SYSTEM INOPERATIVE. THE PRESSURE CONTROLLERS WERE REPLACED IAW AMM 21-31-01-000-801 AND AMM 21-31-01-400-801 AND MANUAL MODE TEST AND SYS GROUND TEST WERE PERFORMED IAW AMM 21-31-00-710-801 AND 21-31-00-700-802, CONTINUING THE FAILURE. DURING THE REVISION, THE HIGH STAGE VALVE WAS DETECTED THAT DOES NOT CLOSE PROPERLY. THE HIGH STAGE VALVE WAS REPLACED IAW AMM 36-11-06-000-801 AND 36-11-06-400-801. A CABIN DEPRESSURIZATION CONDITION INSPECTION WAS PERFORMED IAW AMM TASK 05-51-81, NO DAMAGES WERE FOUND, ALL TESTED CORRECT.