Difference in cabin pressure?
Nov 22, 2010 | 8:26 am
#1
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Difference in cabin pressure?
I was asking a pilot friend of mine why I suffer headaches more in Airbuses than Boeings. He said that when an Airbus descends, the cabin pressure changes in stages rather then gradually like on a Boeing. Is this true?
Nov 22, 2010 | 11:17 am
#2
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I don't notice any difference in this regard between 737-700s and A32xs and 319s. My ears do seem to get that plugged-up sensation when I'm on a 737-300.
Nov 22, 2010 | 5:38 pm
#4
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Wow, interesting. I never knew this was how it worked. I always thought that it was some kind of a continuous process with bleed valves that gradually equalize the cabin. Hard to imagine how/why there would be steps/stages as described ... hmm ... time to wiki ...
Nov 23, 2010 | 6:47 am
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Nov 23, 2010 | 7:14 am
#6
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I can't answer this for sure (I am a pilot but not type rated for any Airbus models), but I'd be extremely surprised if this is the case. The norm is for the air conditioning packs to maintain a constant pressure differential (dictated by airframe strength) between inside and outside until the inside pressure reaches the expected outside pressure at the destination airport, after which it is held constant until the engines are shut down after landing. It would be possible for there to be a pause in the re-pressurisation if the aircraft stays at one altitude for a while (e.g. if holding) but this would affect all aircraft not just Airbuses.
Nov 23, 2010 | 7:21 am
#7
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So this is what happens when you take an hour to type a reply - someone else posts a better reply first!
As GodAtum's diagram shows, there is indeed a smooth (though non-constant) pressure differential on descent, complete with a pause in re-pressurisation when the aircraft is level, so this part mostly agrees with my expectations. What's very different is that some differential is kept until landing, and then the pressure is decreased after landing. Presumably this is to ensure that the doors are forced closed by the pressure.
Anyway, to answer the original question, no this will not be cause of your headaches.
As GodAtum's diagram shows, there is indeed a smooth (though non-constant) pressure differential on descent, complete with a pause in re-pressurisation when the aircraft is level, so this part mostly agrees with my expectations. What's very different is that some differential is kept until landing, and then the pressure is decreased after landing. Presumably this is to ensure that the doors are forced closed by the pressure.
Anyway, to answer the original question, no this will not be cause of your headaches.
Nov 24, 2010 | 6:59 am
#9
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The rate of pressurization/depress is generally computer controlled, but can be manually controlled by the crew. If you ran into one that felt like it was changing in steps instead of a smooth rate- it may have be in manual mode at that time.
The air for conditioning/pressure is supplied at a mostly consistent pressure from the engines (~54psi on a CRJ-900; depending on bleed air requirements), and the cabin pressure is regulated by an outflow valve (generally in the rear pressure bulkhead).
The air for conditioning/pressure is supplied at a mostly consistent pressure from the engines (~54psi on a CRJ-900; depending on bleed air requirements), and the cabin pressure is regulated by an outflow valve (generally in the rear pressure bulkhead).