Originally Posted by
hoss183
If the valves were fully open (take off or landing) even a say 200ft change in a few seconds would cause discomfort, hence having a pressure slightly above ambient allows the system to control it and be stable & smooth.
Packs off takeoff....Packs on at thrust reduction. Ever noticed the “bump” ? I haven’t. Not saying it doesn’t. Just saying I haven’t noticed it. Maybe those with better senses than me can notice it.
From an engineering perspective, a coke can which is pressurised is much stronger than one that isn’t. This makes a bit of sense to me. Also better to know about a pressurisation problem at thrust set than climb.
just some additional thoughts.