Pressurisation
Joined: Aug 1999
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From: England
BOAC / Glueball
Of course it does. If you do a dirty dive the aircraft altitude can overtake the cabin altitude, at which point the inward relief valves will open and the cabin altitude will experience whatever rate of descent the aircraft is doing.
pb
The Rate of Descent of the cabin is FIXED by the manufacturers at a figure - 500fpm is typical. A rapid descent does NOT increase this
pb
Per Ardua ad Astraeus
Joined: Mar 2000
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From: UK
Cpt PB - you did not read our posts properly, did you? I and GB said a rapid descent does not change the manufacturer's FIXED maximum rate. Try my para 1 again, especially the bit after 'What THEN happens is....' ?
Joined: Mar 2005
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From: Uh... Where was I?
BOAC
I understood GlueBall, only I disagree with him.
I know there are many different cabin pressure controlling systems for airplanes.
However, if it is required that airplanes reach field pressure before landing, the time to descend from crusing level to the airfield is the same as the time to increase the cabin pressure from its cruising value to airfield's.
So we have a time (descent time) and a pressure change requirement. These determine the average cabin rate of descent. Rapid descend, faster average rate. Slow descend, slower average rate.
As Captain Pitbull clarifies, if the cabin rate is fixed by the system and you dive like an Stuka, you will either reach the cabin (and from then on the cabin and airplane's rate are equal) or land with differential pressure greater than zero. I think that after touch down, the outflow valve will open in most airplanes, so in the latter case the cabin would unpressurize very quickly after landing.
The result would be in any case a faster average cabin rate of descent.
I do Valsalva very often and always block the other ear, otherwise can be harmful. I prefer doing it very slowly, too.
I understood GlueBall, only I disagree with him.
I know there are many different cabin pressure controlling systems for airplanes.
However, if it is required that airplanes reach field pressure before landing, the time to descend from crusing level to the airfield is the same as the time to increase the cabin pressure from its cruising value to airfield's.
So we have a time (descent time) and a pressure change requirement. These determine the average cabin rate of descent. Rapid descend, faster average rate. Slow descend, slower average rate.
As Captain Pitbull clarifies, if the cabin rate is fixed by the system and you dive like an Stuka, you will either reach the cabin (and from then on the cabin and airplane's rate are equal) or land with differential pressure greater than zero. I think that after touch down, the outflow valve will open in most airplanes, so in the latter case the cabin would unpressurize very quickly after landing.
The result would be in any case a faster average cabin rate of descent.
I do Valsalva very often and always block the other ear, otherwise can be harmful. I prefer doing it very slowly, too.
Joined: Aug 1999
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From: England
BOAC,
You're correct, I didn't read the rest of your post. My apologies.
I don't think it makes any difference though; it is still factually inaccurate to state that the maximum rate is FIXED. It isn't.
pb
You're correct, I didn't read the rest of your post. My apologies.
I don't think it makes any difference though; it is still factually inaccurate to state that the maximum rate is FIXED. It isn't.
pb
Per Ardua ad Astraeus
Joined: Mar 2000
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From: UK
No probs! I think we will have to agree to disagree there. Perhaps if I said 'normal programmed max rate'.............? I don't know of any a/c where if you start a screaming descent at 10,000 ft per minute the cabin instantly follows you down (screamingly
) at a high rate. Maybe I'm out of touch.
) at a high rate. Maybe I'm out of touch.
Joined: Oct 2005
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From: USA
I don't know of any a/c where if you start a screaming descent at 10,000 ft per minute the cabin instantly follows you down (screamingly) at a high rate. Maybe I'm out of touch.
Leakdown tests today are mostly performed on the ground, but certain older aircraft still use airborne leakdown tests at a specified altitude. With cabin pressure set to a known value, bleeds are shut off and the rate of cabin change timed. Even with the bleeds off, there's no instant dump. If there is, and if the pressure vessel is leaking so sufficiently as to allow the cabin to change rapidly (eg follow the aircraft rate of climb or descent), then there are serious problems with the sealing of the pressure vessel.
Per Ardua ad Astraeus
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From: UK
SNS - my posts are about controlled cabin rates of descent, not 'leak rates'. I would have thought that any a/c that allowed a programmed high rate of cabin descent would cause significant complaints from our salary payers. The cabin crew would need earplugs to block out the screaming.
Joined: Aug 1999
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From: England
<nod> fair enough 
btw... to all concerned...
The valsalva can really mess you up. I'd been using for years. I eventually had a load of ENT trouble. When I went to see 'the man' and described my history he tutted a lot. Basically forcing pressurised air around those tubes and cavities is not recommended. Since I had festering puss emerging from my tear ducts I was forced to concede he might have a point!
pb
btw... to all concerned...
The valsalva can really mess you up. I'd been using for years. I eventually had a load of ENT trouble. When I went to see 'the man' and described my history he tutted a lot. Basically forcing pressurised air around those tubes and cavities is not recommended. Since I had festering puss emerging from my tear ducts I was forced to concede he might have a point!
pb
Per Ardua ad Astraeus
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From: UK
Cpt PB - so glad I had finished my lunch
Micro - nasal spray, solid inhaler stick, don't fly with a head cold or sore throat if you are 'sensitive', learn to 'exercise' the openings of the Eustachion tubes in your throat (practice 'ear wiggling' until you hear the eardrums click - when you don't have a cold). None of them 'foolproof'. Check the med forum here for more on the topic. I fully endorse the warning CPB issues - frequent VS can force infection/germs into the tubes which are there purely to allow pressure equalisation. I have just finished 45 years of professional aviation having 'small' eustachion tubes (according to an RAF ENT specialist). There have been times when life has been difficult.
The primary secret is to keep the openings 'open', since like any 'soft' opening they tend to close up under positive external pressure.
The very worst is sinus blockage which is what I assume the OP's husband had on the second flight. VS does not normally help with this. The pain can be excruciating and can cause you to pass out. Repetitive cycles of 'ear problems' (and almost certainly dodgy sinus 'openings' at the same time) can cause scarring of the damaged sinus drain tissues and then they can definitely block. All good fun, yes (and VERY interesting when on your own with 10 minutes of fuel remaining....)?
Micro - nasal spray, solid inhaler stick, don't fly with a head cold or sore throat if you are 'sensitive', learn to 'exercise' the openings of the Eustachion tubes in your throat (practice 'ear wiggling' until you hear the eardrums click - when you don't have a cold). None of them 'foolproof'. Check the med forum here for more on the topic. I fully endorse the warning CPB issues - frequent VS can force infection/germs into the tubes which are there purely to allow pressure equalisation. I have just finished 45 years of professional aviation having 'small' eustachion tubes (according to an RAF ENT specialist). There have been times when life has been difficult.
The primary secret is to keep the openings 'open', since like any 'soft' opening they tend to close up under positive external pressure.
The very worst is sinus blockage which is what I assume the OP's husband had on the second flight. VS does not normally help with this. The pain can be excruciating and can cause you to pass out. Repetitive cycles of 'ear problems' (and almost certainly dodgy sinus 'openings' at the same time) can cause scarring of the damaged sinus drain tissues and then they can definitely block. All good fun, yes (and VERY interesting when on your own with 10 minutes of fuel remaining....)?
Last edited by BOAC; 14th August 2009 at 15:31.
Joined: Oct 2005
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From: USA
SNS - my posts are about controlled cabin rates of descent, not 'leak rates'.
My point is that not the cabin won't follow the aircraft down in a high rate, even with the bleeds off...it's going to lag. With a pressure controller doing the work, it's going to be a much slower rate of change.
