Guest

Most Common Causes For Cabin Pressure Changes

Mon Apr 16, 2001 4:06 am

Hello,
I was just wondering, other than ageing pressure bulkheads, what are the main causes for inflight cabin pressure changes.

Thanks alot,
Tom
 
Buff
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Joined: Fri Mar 16, 2007 1:29 pm

RE: Most Common Causes For Cabin Pressure Changes

Mon Apr 16, 2001 7:57 am

I'm assuming you are asking about pressurized aircraft.

Don't know what you mean by ageing pressure bulkheads, but pressurization changes are regulated by the outflow valve(s) which, in modern aircraft, are operated by computer driven pressurization controllers.

The reason for pressurization changes is usually a change in the aircraft operating altitude.

If you can be more specific with your inquiry, you'll get lots more detail from many others besides me!

Best Regards,

Buff

 
Guest

RE: Most Common Causes For Cabin Pressure Changes

Mon Apr 16, 2001 9:01 am

Ok, well I thought I explained it well, anyway, you know when you hear, for example : "UA A320 makes emergency landing due to drop in cabin pressure." What I mean by ageing pressure bulkheads is I thought on older aircraft, for example, 727s, 737-200s, as the pressure bulkhead ages, it is more prone to leakage. I thought that a recent incident involving a drop in cabin pressure aboard an ATA 1011 was due to a problem with the pressure bulkhead.

-Tom
 
Buff
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Joined: Fri Mar 16, 2007 1:29 pm

RE: Most Common Causes For Cabin Pressure Changes

Mon Apr 16, 2001 9:45 am

I thought that a recent incident involving a drop in cabin pressure aboard an ATA 1011 was due to a problem with the pressure bulkhead

May very well have been - I'm not familiar with that incident. Structural failures to which you refer are extremely rare.

Not so uncommon are pressurization control failures which may cause the requirement for passenger oxygen. Even so, these occurences are very rare by comparison.

Best Regards,

Buff
 
Guest

RE: Most Common Causes For Cabin Pressure Changes

Mon Apr 16, 2001 11:15 am

Duct ruptures are another cause of "failures". Outside the pressurized hull they cause cabin pressure loss. Inside the hull they give overpressure which can cause the safety valve(s) to open which then gives pressure loss until they close again at a predetermined figure causing the pressure to rise again. This can be a bit confusing for the operators as the outflow valves get confused, cabin pressure controller failures occur, cabin altitude can fluctuate, dust and very hot bleed air felt in the cabin etc. Not pretty!
Another problem that can occur is that the cabin altitude can rise during descent when power is reduced because high pressure bleeds don't open when commanded.
Hope this makes sense.
Cheers.
 
Buff
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Joined: Fri Mar 16, 2007 1:29 pm

RE: Most Common Causes For Cabin Pressure Changes

Mon Apr 16, 2001 11:35 am

Good additions Feret and very accurate. BTW, what kind of handle is that?!

Normal operations on the DH8 could be very uncomfortable during descent from hi altitude (FL250) if the descent is done too quickly. Because of the low max differential on the DH8, if the pressurization control is not set to "increased rate of descent", it is possible to "catch the cabin". What this means is that the pressurization system can go to zero differential, i.e. inside = outside pressure at an altitude significantly higher than airport elevation. This is not a malfunction, just an operating technique idiosyncracy. The aircraft is then depressurized and further descent causes the cabin pressure to increase at the same rate of the aircraft's vertical speed. If this is in excess of 500'/minute, it is very uncomfortable for all concerned, especially the passengers.

Best Regards,

Buff
 
Guest

RE: Most Common Causes For Cabin Pressure Changes

Mon Apr 16, 2001 12:53 pm

Buff,
It's an acronym for Flight Engineer (retired).  Smile

Cheers.
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: Most Common Causes For Cabin Pressure Changes

Mon Apr 16, 2001 1:34 pm

Well G'Day Mate!

Buff
 
Guest

RE: Most Common Causes For Cabin Pressure Changes

Mon Apr 16, 2001 5:34 pm

Gidday mate! BTW, I learnt to speak Canadian by flying (and drinking) with some of those ex Ward Air piss-pots who are over this way.  Nuts
Cheers.
 
Guest

RE: Most Common Causes For Cabin Pressure Changes

Wed Apr 18, 2001 6:12 am

Let's not forget " flagellation!!
 
prebennorholm
Posts: 6409
Joined: Tue Mar 21, 2000 6:25 am

RE: Most Common Causes For Cabin Pressure Changes

Wed Apr 18, 2001 6:52 am

Main causes for inflight cabin pressure changes...
Well, for me the ONLY reason is easy: Flying on a Tu-134  Pissed

Twenty years ago during one of the many strikes at SAS I was on an Interflug (East German) Tu-134. It seemed to me that the plane was going steady and level at 27,000 ft (so the captain said - "siebenundtwanzig tausend Füsse"), but the cabin pressure was fluctuating up and down so I had pain in my ears for the next three weeks.

I have only had three flights on Tu-134, my first, last and only flight. Ten wild horses will not be able to pull me on board a 134 again.

Going home I changed my ticket to a Yugoslavian DC-9. Before that flight I noticed that the captain emptied a pint of beer in the transit hall bar and walked directly on the plane. And he didn't walk too steady. But man what a pleasant flight compared to Interflug. I guess that the captain took a nap in his seat and put the co-pilot to work. Isn't that what we have co-pilots for?

Yeah, that's how it was. Fortunately the good, old days have changed to the better.

Best regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs
 
JohnM
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RE: Most Common Causes For Cabin Pressure Changes

Wed Apr 18, 2001 12:20 pm

We sometimes have leaking door seals around pax doors and cargo doors. Also leaking ducts that were mentioned earlier. Rather than a decompression, I think a more common writeup is " Aircraft can't maintain cabin pressure" type of thing. When an aircraft comes back with rags sticking out of cracks in doors into the airstream, that is a giveaway. The crew will hear the leaks and stuff rags into the leak area while flying!
 
242
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Joined: Tue Oct 24, 2000 1:10 pm

RE: Most Common Causes For Cabin Pressure Changes

Wed Apr 18, 2001 3:06 pm

Another vote for door seals. Usually it's the most used passenger/crew door (the one that gets opened and closed every flight, has the jetway run into it etc..). Service doors as well, have catering trucks bump the seals all the time. Cargo door seals see untold levels of abuse, and I've seen several blown out before.
 
L-188
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Joined: Wed Jul 07, 1999 11:27 am

RE: Most Common Causes For Cabin Pressure Changes

Wed Apr 18, 2001 10:28 pm

I'll have to vote for the door seals also....

honorable mention to either a bleed air vavle or an outflow valve getting dirty and sticking.

Other then that on the pressurization system there is this dial that you turn........
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
Guest

RE: Most Common Causes For Cabin Pressure Changes

Wed Apr 18, 2001 10:53 pm

Let's not forget the loss of all engines!!
 
prebennorholm
Posts: 6409
Joined: Tue Mar 21, 2000 6:25 am

RE: Most Common Causes For Cabin Pressure Changes

Thu Apr 19, 2001 2:37 am

Max Power wrote: Let's not forget the loss of all engines!!

Huh, Max Power, did you realize how inappropriate your user name was for this post?  Big thumbs up
Always keep your number of landings equal to your number of take-offs
 
Guest

Prebennorholm

Thu Apr 19, 2001 2:55 am

Sorry, however I was not aware that I had to check with you before selecting a name.
 
prebennorholm
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Joined: Tue Mar 21, 2000 6:25 am

RE: Max Power

Thu Apr 19, 2001 4:55 am

Oh, I like your user name.
But please check with me before you post once more about "loss of all engines" - it gives me nightmares!
Always keep your number of landings equal to your number of take-offs
 
Guest

Prebennorholm

Thu Apr 19, 2001 5:53 am

Ok,you got a "deal". Cheers.

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