The FCOM states that there are two automatic pressurization modes and that they should be switched each flight.  Does the auto mode do this for the pilot, or should we run a flight in auto and then the next flight with the switch in the alt position?

Hi Mike

 

With the Pressure Mode selector in AUTO cabin pressure in the 737-800 uses two identical automatic controllers, each controller is alternatively sequenced as the primary controller for each new flight without moving the Pressurisation Mode Selector, there is no indication of this in the flight deck. The other controller is immediately available as a backup.

 

If during flight there is an issue with the automatic controller or any problem which causes an amber AUTO FAIL the pressurisation system automatically transfers to the other auto controller (ALTN mode)

 

Moving the pressurisation mode selector to the ALTN position (as instructed by the QRH) simply extinguishes the AUTO FAIL light. The ALTN light in this situation stays illuminated to indicate single channel operation through the remaining automatic controller.

 

If you moved the switch without any issues regarding the pressurisation system you would just simply use the other automatic controller!

 

Hope this helped.

 

Samuel Breese.

Ditto Sam, also see normal procedures checklist FCOMv1 pg NP21.17; set pressurization mode to AUTO. That pretty much covers it.

Hi Mike

 

With the Pressure Mode selector in AUTO cabin pressure in the 737-800 uses two identical automatic controllers, each controller is alternatively sequenced as the primary controller for each new flight without moving the Pressurisation Mode Selector, there is no indication of this in the flight deck. The other controller is immediately available as a backup.

 

If during flight there is an issue with the automatic controller or any problem which causes an amber AUTO FAIL the pressurisation system automatically transfers to the other auto controller (ALTN mode)

 

Moving the pressurisation mode selector to the ALTN position (as instructed by the QRH) simply extinguishes the AUTO FAIL light. The ALTN light in this situation stays illuminated to indicate single channel operation through the remaining automatic controller.

 

If you moved the switch without any issues regarding the pressurisation system you would just simply use the other automatic controller!

 

Hope this helped.

 

Samuel Breese.

That clears it up thanks alot.