Originally Posted by
rudderrudderrat
Hi IFLY_INDIGO,
Passenger comfort.
If the aircraft was depressurised before landing, you'd feel the aircraft's ROD (800ft/min) on your ears. Most passengers can cope with about -300 ft/min cabin altitude without feeling too much discomfort.
(It gives them time to equalise the pressure differential on their Eustachian tubes by yawning, swallowing etc.) If the +ve pressure differential on their ear drums builds too rapidly, the Eustachian tube will squash and equalisation is more difficult to achieve, causing greater discomfort.
+500 ft per min is easy to accommodate because the Eustachian tube is stretched open instead.
BUT why would we feel aircraft's ROD? like CPC maintains cabin altitude 200ft the landing elevation, it can also maintain landing elevation itself. I guess answer lies in the eustachian tube.
probably airbus wants to ensure that when CPC depressurises the aircraft after touchdown by opening the outflow valve fully, there would be higher pressure in the middle ear and lower pressure outside, IF AT ALL, so that eustachian tube is stretched open like you said and painful situation of tube squashed is prevented..