737 MAX Flight Crew Operations Manual
Air Systems
Chapter 2
Pressurization System Description
Section 40
MN-FLT-OH-201
2.40.1
40 Pressurization System Description
Pressurization System Description
File Highlight
Introduction
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.
The system uses bleed air supplied to and distributed by the air conditioning
system. Pressurization and ventilation are controlled by modulating the outflow
valve and the overboard exhaust valve.
Pressure Relief Valves
Two pressure relief valves provide safety pressure relief by limiting the
differential pressure to a maximum of 9.1 psi. A negative relief valve prevents
external atmospheric pressure from exceeding internal cabin pressure.
Cabin Pressure Controller
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 DC motor.
• ALTN – Automatic pressurization control; the alternate mode of
operation. Uses DC motor.
• MAN – Manual control of the system using DC motor.
The air data inertial reference units (ADIRUs) provide ambient static pressure,
baro corrected altitude, non-corrected altitude and calibrated airspeed to both
automatic controllers. The ADIRUs receive barometric corrections from the
Captain’s and First Officer’s BARO reference selectors.
The automatic controllers also receive throttle position from both stall
management computers and signals from the air/ground sensors.
March 1, 2021
