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CRJ200 Cabin Pressure Panel

This week I started a trip in COS and flew in the California system with an airplane cabin pressure controller that was MEL’ed. Looking in the maintenance log prior to leaving COS, cabin pressure controller (CPC) #1 was removed, replaced and ops checked as good, however…upon landing in SFO, the cabin pressure descended to -500 feet at a rate of -1200 feet per minute (fpm).

We looked at the ECS page and noticed that the cabin pressure controller was on #2.

During normal operations, the airplane would depressurize upon landing, (i.e., both outflow valves would open completely and dump any pressurization), then after three minutes automatically switch to the other controller. In this case it had been longer than three minutes and we were on CPC #2 which meant that we were flying on CPC #1…the “fixed” one.

As we pulled into the gate, the airplane switched its pressurizing trend and began pressurizing the cabin to an altitude of +500 at a rate of +1200 fpm and the pressure differential was 0.4. Normally, on the ground it should be 0.1. Ears were aching throughout the plane. We waited another minute or so to see if the cabin would settle down and equalize the pressure but it didn’t so we opened the main cabin door.

Again, uncomfortableness as the airplane now depressurized. Whoosh!

After talking to Maintenance in SFO, we did one more flight to see if the other cabin pressure controller was bad. It turns out that CPC #1 was mostly good. We did get a slight “pressure bump” after landing but not nearly as extreme as when we were on CPC #2. We couldn’t really explain it, so to avoid any further “pressure bumps” we started doing the following procedure.

After deferring CPC #2 which was obviously broken, the MEL calls for switching the CPC to the good CPC before each flight. So after landing and before the three minutes were up, we cycled the CPC back to CPC #1 and switched off both air conditioning packs. This insured that we were on the “good” CPC and it kept new air from entering the cabin and pressurizing it if there were still any problems.

Everyone was happy! Could we have done things differently? Probably. But when you are in the middle of it, the solution isn’t always obvious and you do what you can.

All this made me start wondering what the difference between the Cabin Pressure Acquisition Module (CPAM) and the Cabin Pressure Controller (CPC) were.

If you look on the ECS page, you will see that they are both listed there, so what was the difference?

CPAM

CRJ200 - Environment Control System Page

The CPAM monitors the information from the CPC, communicates with the DCU, and and displays cabin altitude (CALT), cabin rate of climb or descent (RATE), and differential pressure (delta P) on the EICAS.

If any of the following conditions are met, the airplane takes some sort of action to notify the crew:

• 8,500’ cabin altitude – CABIN ALT caution message
• 10,000’ cabin altitude -  CABIN ALT warning message and an aural alert “CABIN PRESSURE”
• 14,000’ ± 500’ – AUTO deployment of oxygen masks
• 10,000’ MSL (usually in descent) – if the SEAT BELT sign and/or NO SMOKING switches are selected to AUTO, the NO SMOKING or FASTEN SEAT BELT signs are automatically illuminated

Now, if you lose the CPAM, the standby controller will assume the CPAM duties but you lose “auto deployment” of oxygen masks and auto illumination of the NO SMOKING and FASTEN SEAT BELT signs.

What about the Cabin Pressurization Controllers?

The CPC can be manually selected on the Cabin Pressure panel. Remember, this is usually an automatic function changing controllers after 3 minutes of weight-on-wheels but you can change it as well. By pressing the PRESS CONT switchlight, you can cycle from CPC #1 to MANUAL to CPC #2 to MANUAL and back to CPC #1.

If something goes wrong with both controllers, the switchlight has a FAULT light that will illuminate and if you use manual pressurization, the MAN light is illuminated.

• FAULT (yellow) - is illuminated when both CPC’s fail
• MAN (white) – is illuminated when operating in MANUAL pressurization mode.

Automatic Mode Switching the the Pressure Controllers

The CPC also has some automatic modes which eliminate pilot intervention.

The automatic pressurization modes of operation follow:

• GROUND – Outflow valves commanded FULLY OPEN
• PRE-PRESSURIZATION – Outflow valves close to pressurize the cabin to -150’ on takeoff
• T/O ABORT – TL retarded – Returns to field elevation at 500 fpm then fully opens
• FLIGHT ABORT – The logic criterion for flight abort is: 1) Descent of 1000’ within 10 minutes of take-off and/or 2) Aircraft did not reach flight elevation 6000’ above take-off field before descent
• CLIMB – Typically limited to 500 fpm but will vary slightly with rate of climb and landing elevation
• CRUISE – Assigned cruise altitude – when reached – descent mode armed
• DESCENT – Typically 300 fpm until 150’ below landing field elevation but may vary if high descent rate
• LANDING – WOW – Cabin climbs at 500 fpm to field elevation then outflow valves fully open
• TOUCH-AND-GO – LANDING MODE to PRE-PRESSURIZTION MODE

Conclusion

So there you have it, CPAM does one thing and the CPC does another. They work together to make sure the cabin pressurization works in the most efficient manner without pilot intervention and maintains a safe cabin pressurization during the flight. If you notice a change in pressure, select the ECS page and see what is happening.

If you were interested in this discussion, please let me know, or if you would like me to discuss anything else specifically about the CRJ200, let me know.

As always, be safe…

Jeffrey

P.S. Don’t forget to get your CRJ200 Cockpit display here. Remember, when learning about the CRJ200, it is imperative that you have the cockpit layout available. This will assist you in learning to systems and the layout of the airplane. Order yours today at Training Crue Graphics. They have best layouts in the industry.

Another link you might be interested in: Bombardier CRJ Home Page

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