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od-bwh
Topic Author
Posts: 339
Joined: Sun Jan 13, 2002 6:25 pm

Continuous Descent Approach CDA Is Annoying!

Sat Jul 04, 2009 5:55 pm

I've been extensively flying low costs recently, and simultaneously, approach and landing became really annoying for me.

I read in an interesting article on Airliner's World that airlines (and specifically low cost airlines) are adopting CDA's in which the aircraft keeps a constant rate of descent during landing to reduce fuel consumption. The traditional approach is to fly at a certain level for a certain time, and then descending to a lower level at a fast pace. I dont know what the technical term of this approach is.

In my opinion, the CDA is annoying because pressure keeps building up in the aircrat in a way that human ears can hardly resist. I don't know if my analysis is correct. Can anyone confirm or otherwise prove the opposite?

Regards,
OD-BWH
A300, A319, A320, A321, A21N, A332, A333, A343, A346, A388, B712, B734, B736, B737, B738, B38M, B744, B752, B763, B772, B773, B788, F70, MD11, MD82, MD83, MD88, E145, E175, E190, CRJ7, CRJ2, Q400
 
wilco737
Posts: 7275
Joined: Sun Jun 20, 2004 12:21 am

RE: Continuous Descent Approach CDA Is Annoying!

Sat Jul 04, 2009 5:58 pm



Quoting OD-BWH (Thread starter):
In my opinion, the CDA is annoying because pressure keeps building up in the aircrat in a way that human ears can hardly resist. I don't know if my analysis is correct. Can anyone confirm or otherwise prove the opposite?

The descent of the airplane has not a lot to do with the descent of the cabin. So the increase of cabin pressure. It is done with a constant rate to avoid sudden changes in pressure and pain in the ear. The usual rate of climb for the cabin is about 500ft/min. This may vary a bit, just not dramatically. And NEVER above 1000ft/min as this would really hurt in your ears.

The CDA is usually flown. Try to stay at your cruising level as long as possible, then descent with idle power to the descent point of the approach and then again constantly till touchdown. But this is not always possible due to airspace restrictions or airport restrictions and regulations.

wilco737
 
DescendVia
Posts: 141
Joined: Sun Jan 18, 2009 4:26 am

RE: Continuous Descent Approach CDA Is Annoying!

Sat Jul 04, 2009 9:34 pm

Quoting OD-BWH (Thread starter):
I've been extensively flying low costs recently

That doesn't matter. All airlines are adopting this method. First it was for a safer stabilized approach on non-precision approaches that morphed into the concept for RNP approaches and now STARs.

I personally think the "descendvia" stuff is so cool, I named myself after it  

Quoting OD-BWH (Thread starter):
I dont know what the technical term of this approach is.

"Dive and Drive" for the old NPAs.

[Edited 2009-07-04 14:35:37]
 
od-bwh
Topic Author
Posts: 339
Joined: Sun Jan 13, 2002 6:25 pm

RE: Continuous Descent Approach CDA Is Annoying!

Sat Jul 04, 2009 11:05 pm



Quoting WILCO737 (Reply 1):
The descent of the airplane has not a lot to do with the descent of the cabin. So the increase of cabin pressure. It is done with a constant rate to avoid sudden changes in pressure and pain in the ear. The usual rate of climb for the cabin is about 500ft/min. This may vary a bit, just not dramatically. And NEVER above 1000ft/min as this would really hurt in your ears.

But I'm getting pain in my ears everytime I land!

Quoting WILCO737 (Reply 1):
Try to stay at your cruising level as long as possible, then descent with idle power to the descent point of the approach and then again constantly till touchdown.

I'm flying as a passenger, not a pilot.
A300, A319, A320, A321, A21N, A332, A333, A343, A346, A388, B712, B734, B736, B737, B738, B38M, B744, B752, B763, B772, B773, B788, F70, MD11, MD82, MD83, MD88, E145, E175, E190, CRJ7, CRJ2, Q400
 
Fly2HMO
Posts: 7184
Joined: Sat Jan 24, 2004 12:14 pm

RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 12:06 am

As was said, the cabin rate of climb/descent is totally independent of what the plane's actual rate of climb/descent is.

Quoting OD-BWH (Reply 3):
But I'm getting pain in my ears everytime I land!

Have you been had any sinus congestion lately, even slightly? That will cause you pain.
 
pilotpip
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Joined: Fri Sep 19, 2003 3:26 pm

RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 1:38 am

The aircraft cabin descends at a much slower rate for comfort. As a result, it will continue it's "descent" even while the aircraft is leveled off. Constant descents won't really change anything. In fact in most cases the rate will stay pretty constant all the way down unless you're going into a busy airport where they start the descent quite a ways out and have numerous step-downs.

Try clearing your ears once in a while. As you descend relieve the pressure using one of a variety of techniques instead of letting it build up to the point of discomfort.
DMI
 
Phoenix9
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RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 2:38 am



Quoting OD-BWH (Reply 3):
But I'm getting pain in my ears everytime I land!

You can trying chewing a gum while landing. Combine this with a good sinus rinse before flying....it might just do the trick  Wink
Life only makes sense when you look at it backwards.
 
FlyASAGuy2005
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RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 5:48 am



Quoting OD-BWH (Reply 3):
I'm flying as a passenger, not a pilot.

I'm sure he's simply explaining, from a pilot's perspective, how it's usually done. If you were a pilot, you wouldn't need the explanation  Wink
What gets measured gets done.
 
wilco737
Posts: 7275
Joined: Sun Jun 20, 2004 12:21 am

RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 6:49 am



Quoting OD-BWH (Reply 3):
But I'm getting pain in my ears everytime I land!

Maybe your ears are sensitive to the change in pressure.

Quoting OD-BWH (Reply 3):
I'm flying as a passenger, not a pilot.

I just tried to explain the CDA procedure...

Quoting FlyASAGuy2005 (Reply 7):
I'm sure he's simply explaining, from a pilot's perspective, how it's usually done. If you were a pilot, you wouldn't need the explanation  

Exactly. And the CDA doesn't have anything to do with the cabin pressure. The cabin rate is handled by a computer and has its limits which are never exceeded or you will hear a lot of yelling from the cabin about pain in the ears.

wilco737
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 7:04 am



Quoting WILCO737 (Reply 8):
The cabin rate is handled by a computer and has its limits which are never exceeded...

Unless you have an aircraft with a buggered dump valve which they cant seem to get sorted, which will dump cabin pressure out of schedule on the descent every once in a while! Uurgh... not used for ferrying pax about though.  Smile
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
wilco737
Posts: 7275
Joined: Sun Jun 20, 2004 12:21 am

RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 7:05 am



Quoting FredT (Reply 9):
Unless you have an aircraft with a buggered dump valve which they cant seem to get sorted, which will dump cabin pressure out of schedule on the descent every once in a while! Uurgh... not used for ferrying pax about though.  

Thank god that doesn't happen on every flight  Smile

wilco737
 
mandala499
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RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 7:37 am

Over here, we do a lot of continuous descent from cruise FL down to 2000 (even at busy airports, it's preferred whenever possible), and some people have problems with their ears when the pressurization isn't up to scratch... cabin VSI bumps and drops, etc... Slapping a CANPA or direct descent to the glideslope doesn't add much to it.

What's fun was a 737-230 (Hey! Wilco, ex LH), with a not so good outflow valve... Descents required thrust above idle... so it's redline less 5 - 10KIAS... That was a fun plane... *hehehehe* But overall, thank God it's gone.

Some planes do however go up to -750fpm cabin VSI limit... going further require the safety valve to open to prevent negative pressure, but you gotta dive for that! *grin*
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
slz396
Posts: 1883
Joined: Tue Oct 02, 2001 7:01 am

RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 2:34 pm

As Wilco and others have explained already, cabin pressure during descent is increased according to a pre-set schedule which will let the cabin descent at a comfortable and constant rate of descent, REGARDLESS the rate of descent the aircraft has...

Now, obviously, IF a plane is falling from the sky like a stone, then the pre-set schedule isn't a very good one as it will build up a to large pressure difference between cabin and outside air, and so at a certain point the protection mechanism will kick in and let the cabin just follow the aircraft's rate of descent to prevent damage to the plane's fuselage.

Now, I don't know what types of aircraft you have had this on, but there are some notoriously fast descending planes out thate (e.g. the Bae146 can comfortably descent with 5,000fpm), so if the pilot would really do a full idle descent on one of these from his cruise altitude, you'll guaranteed to have the cabin not being able to follow up with any pre-set schedule and thus the outflow valves will at some point during the descent just open to equalize the pressure in the cabin with that outside, something which you'll definitely feel...
 
DescendVia
Posts: 141
Joined: Sun Jan 18, 2009 4:26 am

RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 3:50 pm



Quoting OD-BWH (Reply 3):
But I'm getting pain in my ears everytime I land!

If you know its coming, then prepare for it.
 
wilco737
Posts: 7275
Joined: Sun Jun 20, 2004 12:21 am

RE: Continuous Descent Approach CDA Is Annoying!

Sun Jul 05, 2009 7:06 pm



Quoting Slz396 (Reply 12):
Now, obviously, IF a plane is falling from the sky like a stone, then the pre-set schedule isn't a very good one as it will build up a to large pressure difference between cabin and outside air, and so at a certain point the protection mechanism will kick in and let the cabin just follow the aircraft's rate of descent to prevent damage to the plane's fuselage.

The rate of descent of the airplane must be pretty high to reach that.

Quoting Slz396 (Reply 12):
Now, I don't know what types of aircraft you have had this on, but there are some notoriously fast descending planes out thate (e.g. the Bae146 can comfortably descent with 5,000fpm), so if the pilot would really do a full idle descent on one of these from his cruise altitude, you'll guaranteed to have the cabin not being able to follow up with any pre-set schedule and thus the outflow valves will at some point during the descent just open to equalize the pressure in the cabin with that outside, something which you'll definitely feel...

it is called the negative pressure relief valve. If you descent that fast, the cabin tries to descent with the max allowable rate as well, until the max differential pressure is reached. But if the outside pressure would be higher than the inside pressure, the cabin would collaps just like a can of coke. Before that happens this valve opens and equals the pressure. THAT hurt your ears for sure. But even an idle descent from 37,000 feet to 2,000 feet didn't cause any problems for the cabin rate. We had to take a look at it, but it did a good job. And the rate of the cabin was still at a comfortable level.

wilco737
 
scrubbsywg
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RE: Continuous Descent Approach CDA Is Annoying!

Mon Jul 06, 2009 4:06 am

i always chew gum on ascent and descent and it really seems to help. The odd times i run out my ears are plugged after i land.
 
zappbrannigan
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Joined: Wed Oct 01, 2008 7:41 am

RE: Continuous Descent Approach CDA Is Annoying!

Mon Jul 06, 2009 4:30 am

Even in the unpressurised aircraft I fly, our company procedure is a continuous descent from ToD to landing, unless specific procedures or other factors require otherwise (generally an instrument approach requirement, ATC requirement, or traffic). Properly managed, this continuous descent is flown to keep vertical speed in the 400-600 fpm range (generally regarded as being fine for pax comfort).

As others have said, if you've frequently got equalisation problems in your ears/sinuses, it's something which should be looked at specifically - it's highly unlikely the problem is a high rate of descent, except for the rare times when an emergency descent is required, or something requiring abnormally high rates of descent.
 
Woosie
Posts: 104
Joined: Sun May 14, 2006 3:47 pm

RE: Continuous Descent Approach CDA Is Annoying!

Tue Jul 07, 2009 5:05 am

CDA is used to minimize fuel costs by leaving the engines in flight idle longer. It's the wave of the future, as it is part of the NexGen concept. The trick really is to manage CDA from all aircraft, but still safely allow for weather, aircraft and gnd ops events that disturb that "normal" state.

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