Pressurization

Question 1

What are the main components of the pressurization system?

Answer 1

electrical outflow valve located under the floor on the aft pressure bulkhead, ground
valve for avionics compartment cooling when the aircraft is on the ground,
two safety valves, two cabin pressure controllers, and a CABIN PRESS control panel

Question 2

How is cabin pressurization maintained?

Answer 2

By controlling the amount of
cabin air that is discharged through the outflow valve

Question 3

What are the two modes of operation for the pressurization system?

Answer 3

Automatic and manual

Question 4

The outflow valve is controlled by an actuator and one of three …

Answer 4

electrical motors.
Two of the motors are controlled by each of the cabin pressure controllers.
The third electrical motor is controlled by the manual pressurization system.

Question 5

CPC 1 Active

Answer 5

In the automatic mode, each motor is controlled by its associated Cabin Pressure Controller, or CPC.
Only one CPC is active at a time; the other CPC acts as a backup.
Therefore, if CPC 1 is the active CPC, it will operate the outflow valve through its associated DC motor

Question 6

CPC 2

Answer 6

When CPC 2 is the active controller, the outflow valve is electrically controlled by the DC motor associated with CPC 2.
The active CPC is identified on the EICAS page

Question 7

What happens in the ground mode of the automatic pressurization
system?

Answer 7

the CPCs switch between active and standby 3 minutes after
landing. This will make sure they cycle

Question 8

What is the purpose of the safety valves in the pressurization system?

Answer 8

protect the aircraft against negative cabin pressure or cabin over pressurization. They are spring loaded closed and operate pneumatically.

The safety valves will open above 8.6 psi or below -0.5 psi to relieve the
pressure differential.

Question 9

Ventilation air from the Cathode Ray Tubes (CRTs) and the avionics bay is vented overboard when the aircraft is on the ground and the passenger or service door is open.
Air is discharged overboard through a ground valve.
This ground valve also ensures that the aircraft is depressurized

Question 10

The Automatic pressurization mode has several sub-modes.
These modes include the:

Answer 10

• ground mode,
• pre-pressurization mode,
• takeoff abort mode,
• flight abort mode,
• climb mode,
• cruise mode,
• descent mode,
• and landing mode

Question 11

In the ground mode,

Answer 11

the outflow valve and the ground valve are driven fully open so that the aircraft will be depressurized.
The ground mode is active when the aircraft is on the ground with AC power supplied to the system.
Upon landing, the system switches to ground mode sixty seconds after weight-on-wheels.

Question 12

The ground valve closes automatically when

Answer 12

the passenger and the service doors are closed.

Question 13

The pre-pressurization mode is initiated when

Answer 13

both thrust levers are advanced to TOGA on the ground.
The outflow valve will close and pressurize the cabin to approximately 150 feet below the field elevation.
This helps to minimize pressure bumps on takeoff.
During a no bleed takeoff, both valves will be fully closed.

Question 14

If an aborted takeoff occurs, the pressurization system will enter the

Answer 14

takeoff abort mode.
The outflow valve will modulate to return the cabin altitude to field elevation at approximately 500 feet per minute.
After 20 seconds, the outflow valve will be fully open.
The system will then revert to ground mode.

Question 15

For the first ten minutes after takeoff, provided the aircraft altitude does not exceed 6,000 feet and the aircraft starts a descent of at least 1,000 fpm, the system will revert

Answer 15

to flight abort mode.
The system will assume the aircraft is returning to the departure airport and will automatically return to 150 feet below the field elevation.
The preset landing field elevation will be ignored

Question 16

In the climb mode, the active CPC will use the pressurization schedule to control the cabin altitude.

Answer 16

During a climb, the rate of climb is derived from the theoretical cabin altitude schedule.
In addition, the cabin rate of change is proportional to the aircraft vertical speed.
During the climb, the cabin rate of change is limited to between 500 and 800 fpm, depending on aircraft weight.
A typical climb rate is between 300 to 500 fpm

Question 17

In cruise, the automatic mode uses the pre-set pressurization schedule to

Answer 17

calculate the appropriate cabin altitude.
Once the cruise mode has been entered, the pressurization system will automatically arm the descent mode.

Question 18

During descent(-500fpm for more than 1 minute), the system will attempt to maintain a cabin descent rate that is related to the aircraft’s actual rate of descent.

Answer 18

The pressurization system calculates a remaining flight time value based on the aircraft speed.
Typically, the cabin descends at a rate of 300 fpm.
The cabin will descend per the calculated schedule until the cabin altitude reaches 150 feet below the selected landing elevation.

Question 19

The landing mode becomes active when

Answer 19

weight-on-wheels is achieved and one of the thrust levers is retarded to idle.
The cabin is directed to climb at 600 fpm, until it is completely depressurized.
At that point, both the outflow valve and the ground valve will be fully open

Question 20

Pressurization in manual mode

Answer 20

In this mode, the outflow valve is directly controlled by flight crew inputs.
In the manual mode, the cabin altitude is manually controlled with the MAN ALT lever, and the MAN RATE knob.
The manual mode of operation uses the third DC motor to operate the outflow valve

Question 21

Opening outflow valve in manual mode

Answer 21

Moving the MAN ALT lever to the UP position will cause the outflow valve to open up, allowing the cabin to climb at the rate selected on the MAN RATE knob

Question 22

Closing outflow valve in manual mode

Answer 22

Placing the MAN ALT switch in the DN position will cause the outflow valve to close, allowing the cabin to descend at the selected rate

Question 23

HOLD outflow valve in manual mode

Answer 23

When the manual altitude switch is in the HLD position, the outflow valve will modulate to maintain the present cabin altitude.

Question 24

How does the emergency depressurization system work?

Answer 24

Regardless of
the mode of operation, the cabin can be rapidly depressurized if needed
by pressing the EMER DEPRESS switch light. The emergency
depressurization system overrides both the automatic and manual modes
of operation. The EMER DEPRESS switch light causes the third DC motor
to drive the outflow valve to the full open position. when the emergency
depressurization system is operated, the cabin pressure controller will limit
the cabin altitude to a maximum of the 14,500 feet, plus or minus 500 feet

Question 25

CPAM

Answer 25

The Cabin Pressurization Acquisition Module, or CPAM is the interface that provides information to the Data Concentrator Units, or DCUs. The DCUs, in turn, display that information on the EICAS status page and ECS synoptic page. Cabin altitude, cabin rate, and differential pressure are all measured and displayed by CPAM

Question 26

A microprocessor in the CABIN PRESS Panel contains an

Answer 26

altitude sensor. The measurements from this sensor are compensated for temperature.

Question 27

The microprocessor provides information to the DCUs that is displayed on the EICAS status page and the ECS synoptic page. This information includes

Answer 27

cabin altitude, cabin rate, and differential pressure. In addition, the microprocessor controls the display of the position of the ground valve, the safety valve, and the outflow valve.

Question 28

If the microprocessor senses that the cabin altitude exceeds 8,500 feet, If the cabin altitude exceeds 10,000 feet, PRESSURE aural warning.

Answer 28

the DCUs will generate a CABIN ALT caution message. the DCUs will generate a CABIN ALT warning message and a CABIN In addition, the DIFF PRESS warning message and the CABIN PRESSURE aural warning are based on inputs from the microprocessor

Question 29

What happens if both CPCs fail?

Answer 29

the FAULT light on the PRESS CONT switch light will illuminate, and the DCUs will generate a caution message. The pressurization system will need to be manually operated per the QRH

Question 30

What is the function of the Cabin Pressurization Acquisition Module (CPAM)?

Answer 30

Provides information to the Data Concentrator Units (DCUs) which display the information on the EICAS status page and ECS synoptic page

Question 31

10.What triggers the NO SMOKING-FASTEN SEAT BELT signs in AUTO mode?

Answer 31

If the microprocessor senses a cabin altitude greater than 8500 feet

Question 32

20.What happens if the cabin altitude exceeds 8,500 feet?

Answer 32

the DCUs will generate a CABIN ALT amber caution message. If the altitude exceeds 10,000 feet, the DCUs will generate a CABIN ALT red warning message and a CABIN PRESURE aural warning will sound.

Question 33

What happens if both CPCs fail?

Answer 33

the FAULT light on the PRESS CONT switch light will illuminate, and the DCUs will generate a caution message. The pressurization system will need to be manually operated per the QRH

Question 34

WHy is this an issue If the CRJ-900 has to ditch in the water, it's tail will sink lower than the nose due to the added rear weight. How is this counteracted

Answer 34

* This is an issue, because water can flood into the pressure hull via the outflow valve Flotation valve