3 replies to this topic

[trechan]

I need help trying to pressurize the cabin in this PMDG MD-11

[Joey McCormick]

Huh? It's an already pressurized aircraft...

[Peter797]

Yeh. It's already pressurized dude.

[THBatMan8]

My apologies for the bump (I need to pay more attention to this subform) but the cabin automatically pressurizes to 100 ft below field elevation when the leading edge slats are extended. This is done to prevent a surge of pressure at rotation. Once the CPCS (Cabin Pressurization Control System) enters climb mode, the airframe is pressurized at a rate proportional to the aircraft's rate of climb (the CPCS is limited to climbing/pressurizing the cabin at 750FPM) until the maximum differential pressure of 9.1PSI is meet.

In other words, the cabin isn't going to be pressurized to 9.1PSI while on the ground as there is no need. Also note I stated the CPCS descends the cabin to 100 feet below the field elevation (it's linked to the captain's flight instruments via the ARINC 429 data bus). This is because the CPCS regulates the cabin pressure by managing the amount of discharged air through the outflow valve. The system isn't capable of creating a negative differential pressure while on the ground.

Edited by Da Bat Man, 15 September 2009 - 07:06 AM.