Cabin Pressure Controllers Cabin pressurization is controlled during all phases of airplane operation by the cabin pressure control system. The cabin pressure control system includes two identical automatic controllers available by selecting AUTO or ALTN and a manual (MAN) pilot controlled mode. Cabin altitude is normally rate controlled by the cabin pressure controller up to a cabin altitude of 8,000 feet at the airplane maximum certified ceiling of 41,000 feet. The cabin pressure controller controls cabin pressure in the following modes: AUTO - Automatic pressurization control; the normal mode of operation. Uses a DC motor. ALTN - Automatic pressurization control; the alternate mode of operation. Uses a DC motor. MAN - Manual control of the system using a DC motor. The air data inertial reference units (ADIRUs) provides ambient static pressure, barometric corrected altitude, non corrected altitude and calibrated airspeed to both automatic controllers. The ADIRUs receive barometric corrections from the Captains and First Officers BARO reference selectors. The automatic controllers also receive throttle position from both stall management computers and signals from the air/ground sensors.