Originally Posted by
Old Fella
PW1830. By "Outflow Valve location" I assume you meant "Outflow Valve position in relation to being between Open and Closed". If you operatd DC3's or C47's as your Pen name suggests you had no such worries. Cheers Old Fella.
Its is not valve position (open or closed) it is the valve location on the aircraft. Boeings typically have them at the back where the tail starts to taper. On rotation and flare that area typically suffers a pressure bump due to the distance change to the ground. To ensure that the pax are not inconvenienced by this sudden change in pressure a small positive pressure is programmed into the pressurization software.
This is from the 737 but it also applies to the 777:
"The cabin begins to pressurize on the ground at higher power settings. The controller modulates the outflow valve toward close, slightly pressurizing the cabin. This ground pressurization of the cabin makes the transition to pressurized flight more gradual for the passengers and crew, and also gives the system better response to ground effect pressure changes during takeoff."
