What was found
FLIGHT CREW REPORTED TOTAL LOSS OF PRESSURIZATION AT CRUISE ALTITUDE. INOPERATIVE IN STANDBY AND MANUAL. MAX CABIN ALTITUDE 18,500/2,000 FPM. NO RAPID DECOMPRESSION. RETURNED TO DEN AND LANDED WITHOUT INCIDENT. REPLACED AFT OUTFLOW VALVE, CABIN PRESSURE CONTROLLER, AND OVERHEAD SELECTOR PANEL. PERFORMED OPERATIONAL TEST, CHECKED NORMAL. OXYGEN GENERATORS USED AT ROWS 12 DEF, 15 ABC, 16 ABC, 16 DEF, 17 ABC, 17 DEF, 18 ABC, 18 DEF, 19 DEF, 20 ABC, AND 22 ABC. REPLACED SAME.