Originally Posted by
Speedwinner
It says that below FL200 cab alt 0. So i was assuming we slowly let the valve open during descend. The other crew member said we had to close the valve again. So can somebody explain again to me the principle of this one? Or any nice documents which explain that?
If you open the valve, the cabin altitude will eventually match your current altitude.
You must be confusing it with cabin differential pressure. That will be 0 with an open outflow valve.
Keep it simple:
If the cabin altitude must go up: toggle the man v/s ctl to UP.
If the cabin altitude must go down: toggle the man v/s ctl to DN.
If you have to get rid of any residual cabin pressure (e.g. evacuation after manual cab alt control): man v/s ctl full UP.