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Pressurization system/descent mode


Cheyenne Chief Pilot

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"Descent mode: The cabin full descent schedule occurs when the airplane is in descent. Cabin altitude decreases at approximately 300 to 750 ft/min, to either landing elevation, or maximum differential, whichever is highest. When the landing elevation exceeds 8,000 feet, cabin altitude will be maintained at maximum differential, until the airplane descends, then the cabin altitude will rate up to the pre-selected landing elevation."

 

So normally the cabin should not descend below landing elevation before landing mode has started - and probably not 4.000 ft below before touchdown ...    :wacko:

 

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3 hours ago, Mathijs Kok said:

(...) We got tables that are exactly as it is now implemented, (...)

 

 

The DA/AS manual introduces the table like this:

"The following table shows typical cabin altitude in relation to the aircrafts(sic!) altitude."

 

A RW CRJ document introduces the same table like this (accentuation is mine):

"The pressurization system automatically maintains cabin pressure through all phases of flight. Typical values used in the cabin/flight altitude schedule during manual mode are as follows:"

 

So the table actually serves as an indication, directed at pilots, for manual operation only.

 

Automatic mode is different from manual mode. As per the RW document (accentuation is mine):

 

"Descent mode: The cabin full descent schedule occurs when the airplane is in

descent. Cabin altitude decreases at approximately 300 to 750 ft/min, to either

landing elevation, or maximum differential, whichever is highest. When the landing

elevation exceeds 8,000 feet, cabin altitude will be maintained at maximum

differential, until the airplane descends, then the cabin altitude will rate up to the

pre-selected landing elevation.

 

Landing mode: The cabin altitude is driven below field elevation or the airplane is

unpressurized. When the cabin is below field elevation, then the cabin is rated up at

approximately 600 ft/min for 30 seconds, then the outflow valve is driven full open."

 

The table for manual operation does not take landing elevation into account, the automatic mode does, though.

 

The automatic mode in fact is pretty generic. It's almost the same (with slight variations only) for most commercial (read: pressurized) aircraft, like the B737, the A320, the Fokker 70/100, the ERJ etc. (And I !daresay! also the ATR 72-500 :P) They all drive the cabin altitude down to landing elevation during descent and, just before landing, a bit below that (150-200 ft below ldg elev). Even the German Wikipedia article covers that and also explains why:

https://de.wikipedia.org/wiki/Druckkabine#Druckverh.C3.A4ltnisse

 

Should any more questions arise, pls. do not hesitate to ask Joshua (... how he modeled pressurization in the AS A32x :P).  

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For purposes of comparison - the excellent(!) Flight1 ATR 72-500 heading towards the same destination:

 

 

 

At cruise FL a maximum pressure differential is maintained:

 

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During the descent the cabin also descends to landing elevation:

 

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Just before landing a small(!) pressure differential is achieved (cabin slightly(!) lower than the destination field - 200 ft ballpark no.):

 

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After touchdown the cabin depressurizes and reaches exactly field elevation:

 

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You're welcome!    :D

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I'd suggest 150 ft below ldg elev, rather than 200 ft. Reason is, a CRJ-200 CBT mentions 150 ft explicitly. Couldn't find a precise reference for the -700/-900, unfortunately.

 

 

 

CRJ-200 CBT, pressurization, part II (part II starts right with descent mode):

 

 

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31 minutes ago, The Dude said:

Once a tester always a tester. ;)

 

 

I paid 40+ EUR to become one of those again. Just trying to secure my investment.   :lol:

 

On a side note: Do *NOT* ask Joshua about pressurization (and *NOT* about GPWS Flaps Conf3 mode, either - got no warning during that approach! :P):

 

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Better ask Hans :rolleyes: (or Florian) :

 

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  • Deputy Sheriffs
Just now, Enter display name here ;) said:

 

I paid 40+ EUR to become one of those again. Just trying to secure my investment.   :lol:

 

 

lol

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  • 3 months later...
3 minutes ago, Mathijs Kok said:

But yet again, as far as our documents show our implementation is correct.  I'll ask Hans to look into this when he got time. 

 

 

Pls. see my post here:

 

 

 

On behalf of Aerosoft and Digital Aviation, Frank already admitted defeat (my interpretation only):

 

 

 

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  • 2 months later...
  • Developer
On 27.2.2018 at 15:55, Cheyenne Chief Pilot sagte:

So, will the TCAS RAs be next for implementation?   :D

 

It's pretty much at the top of the list now, but I need to refresh my knowledge about vectors in three-dimensional space before I start working on this.

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