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A320 Pressurization 'peaks' cause damage to body? (packless tkof)

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A320 Pressurization 'peaks' cause damage to body? (packless tkof)

Old 12th Jun 2013, 18:05
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A320 Pressurization 'peaks' cause damage to body? (packless tkof)

Hi there. My company recently made the "PACKS OFF" takeoff as standard procedure. So now we switch on the packs after thrust reduction altitude and the Automatic Pressure Control Mode does it's work in keeping the cabin 'under pressure'. I believe Easyjet is having the same SOP.(?)

Please read my question carefully because I believe there is an unwanted high v/s of cabin altitude with this new SOP after switching on the packs. I monitored a -1000ft v/s cabin rate (going in the opposite direction) and I want to have some advise/facts. Eventually I am interested in possible long-term damage to the body if I fly for 30 years and have these high v/s of cabin rate every time I make a flight.... I placed this topic in the "tech log" because I want some factual information about the real 'peaks' of pressurization.

During normal operation (with the packs 'ON' during takeoff):
Ground: Before takeoff and 55 seconds after landing, the outflow valve opens fully to ensure there is no residual cabin pressure. At touchdown, any remaining cabin pressure, is released at a cabin vertical speed of 500 feet/minute.
Takeoff: To avoid a pressure surge at rotation, the controller prepressurizes the aircraft at a rate of 400 feet/minute until the /\P reaches 0.1 psi. At liftoff, the controller initiates the climb phase.
Climb: During climb, the cabin altitude varies according to a fixed preprogrammed law that takes into account the aircraft's actual rate of climb.
Cruise: During cruise, the controller maintains cabin altitude at level-off value or the landing field elevation, whichever is higher.
Descent: During descent, the controller maintains a cabin rate of descent, so that cabin pressure is equal to landing field pressure +0.1 PSI, shortly before landing. The maximum descent rate is 750 feet/minute.

1) What cabin rates (v/s) are accepted as 'normal'?
Airbus doesn't specify it's "fixed preprogrammed law" during the climb. So what kind of pressure-diferences may I expect? What about the "pressure-profile" on other aircraft? (yes, I know that it's actual a difference in hPa)

2) Is the Automatic Pressure Control Mode doing it's work correct when "Packs Off" tkof is used?
I am asking this because I noticed on our aircraft a very high v/s (-1000ft) of cabin rate after the first pack is switched on. It looks like it's controller isn't very well doing it's job in limiting high v/s of cabin rate. And it's the measured value on our screens; actual value may be even higher do to it's peak. To my humble opinion there is no need for high v/s of cabin rate if the aircraft is making a normal climb and air should be let out by the outflow valve........ To me it looks like the 'Automatic Pressure Control Mode' was never designed for tkofs with packs off.... (Airbus??)

3) Are there any known medical problems to the body because of (peaks of) pressurization?
What problems to the human body may occur if working in an environment where pressure is changing the whole time? Is this 'peak' that I am referring to (-1000ft v/s) any problem?

4) Has this topic been discussed before?
I couldn't find any specific topic. But maybe your airline and/or pilot association has discussed something similar before? Please provide me with any useful info you have!
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Old 12th Jun 2013, 19:24
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Why do Airbii use packs (bleeds?) off take-offs in normal operation as opposed to only when needed for performance reasons?
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Old 12th Jun 2013, 19:26
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Old 12th Jun 2013, 20:18
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A320 Pressurization 'peaks' cause damage to body? (packless tkof)

I'm guessing here but presumably packs off all the time is aimed at increasing the flex temp and hence the engine life. Perhaps there is a power by the hour maintenance contract that takes into account the flex used in the pricing structure.

Since the aircraft was not really designed to operate that way on a regular basis it's entirely possible more strain may be put on the components within the pressurisation/ air conditioning system over time, so it could end up being a false economy. By then though whoever thought up this SOP will have collected their bonus.

It's undoubtedly irritating but the pressure changes are relatively small and few flyers of unpressurised aircraft, including high performance ones have suffered any ill effects, so I think it unlikely you will.
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Old 12th Jun 2013, 20:42
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@PH-Chucky
3) Are there any known medical problems to the body because of (peaks of) pressurization?
I can testify that in non pressurised airplanes any cabin vertical speed up to -3000 ft/min induces no medical problems, provided that eustachian tube and sinuses are not blocked.
If they are blocked, a valsalva manoeuvre is needed about every 1000 feet (at low levels).
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Old 13th Jun 2013, 00:37
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Suddenly subjecting the pax to a -1000ft/min cabin bump whilst they are climbing is a bit harsh in my book. Don't think it'd do any long-term damage, though. In the 146 we used to switch each pack on separately to reduce the pressure "bump". My current machine switches the packs off, then back on, automatically, so I don't even notice!

I can testify that in non pressurised airplanes any cabin vertical speed up to -3000 ft/min induces no medical problems, provided that eustachian tube and sinuses are not blocked.
If they are blocked, a valsalva manoeuvre is needed about every 1000 feet (at low levels).
-3000ft/min in an airliner is totally and utterly unacceptable in my book. You would have serious problems with pax ears on a regular basis if they were subjected to that. If you think that's quite OK, you're either not a aviator or a pax.

I throw a wobbly at the FO if we catch the cabin on final at 700ft/min!
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Old 13th Jun 2013, 00:57
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Passenger comfort is what we all strive for. Occasionally do to performance requirements we did a packs off take off. Anybody that uses packs off take offs to increase engine life at the cost of passenger comfort doesn't understand the priorities of air travel and should be fired.
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Old 13th Jun 2013, 01:04
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Pretty sweeping statement there Bubbers... Are you aware that MANY of the Airbus (and I'm sure Boeing) operators operate a pack off SOP.

Incidentally, have you ever flown an Airbus? (as the original poster asked for Airbus specific information)

For the Op. As you engineering to look at the issue - they can get far more data than you see in the flightdeck to see if there is indeed something wrong with the system or if it is just an indication error.

Last edited by airbus_driver319; 13th Jun 2013 at 01:08.
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Old 13th Jun 2013, 04:15
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Since a few years already now, we're doing packs off take-off in our company as an SOP.

It's really no big deal. I don't see or feel any abnormal cabin climb rates after take-off and when switching on the packs with 20 secs interval, there's no discomfort to pax or crew either.

It's really no big deal. Many companies do it and it does save on engine wear, maintenance (and probably fuel as well)
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Old 13th Jun 2013, 07:00
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I don't feel any problems either. It is an efficient way to operate the aircraft and 1000ft/min is something we are perfectly capable of handling in the human body, assuming nothing is blocked up.

The stress associated with worrying about this topic will probably shorten your life more
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Old 13th Jun 2013, 07:55
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It's not the pressure bump you should be concerned about

It's the extra workload switching on Packs that can ( and has multiple times ) led to premature flap retractions on Airbus Aircraft during what is a critical phase of flight, especially with an Engine out......

A major Airline used to do packs off until the number of these premature Flap retractions made them reconsider the practice. Since then no more events.....

You decide.....
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Old 13th Jun 2013, 10:26
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Thanks for all of your answers!

So apparently not a big deal? I still wonder why Airbus made a complete "fixed pre programmed law" with a logic to pressurize the cabin and to increase passenger comfort. But that the moment the packs are switched on, a huge peak of pressure is recorded (-1000ft v/s). Is there a flaw in the Airbus logic because I still find it unnecessary that such a huge pressure peak is noticeable in the aircraft after switching on the packs.....

@oceancrosser
It's all about engine wear/tear. We already 'flex' during takeoff and we set climb thrust at 1000ft AAL. And now the company has made the "packs off" takeoff as SOP because apparently it reduces the engine's EGT a couple of degrees during TKOF and sometimes results in a higher FLEX temp, resulting in fewer maintenance costs.

@EcamSurprise
Never noticed any discomfort? Please press the "PRESS" button on you ECAM control panel. I am interested in your findings.

@Capn Bloggs
Our SOP is that at 1000ft/1500ft reduce from takeoff power to climb power. Thereafter we switch on PACK 1, and wait at least 10 seconds before switching on PACK 2. The high v/s I noticed was during our 'normal procedures' by only switching on the first pack.

@bubbers44
Passenger comfort is not all I care about. What about safety and costs? Do you always use low braking to increase passenger comfort and challenge an overrun? Or is your company flying on this NASA jetfuel that doesn't ignites in a crash but makes a ticket 5x more expensive...? There is always tension between safety, costs and comfort. But in hot-weather situations I will keep the packs on to keep the temperature controlled. And on a contaminated runway covered with de/anti-icing fluid I tend to switch the packs off to prevent contamination of cabin air.

@The African Dude
Thanks for your remark about stress. It's just that I am very curious about this high cabin pressure peak that can be eliminated by keeping the PACKS ON during takeoff.

@nitpicker330
Interesting observation about the workload.
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Old 13th Jun 2013, 10:46
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Yes pushing two buttons one after the other "shouldn't" cause too much problem BUT the facts of the matter are that the PF and PM were distracted enough turning on Packs after T/O directly casing premature Flap retractions.............

Mainly on the A340 at heavy weights I might add.

The ergonomics of the IAS display on the PFD also didn't help with the S speed "off the scale" above.

Either way, since changing the proceedure there has been a huge reduction in these events.....

Read it how you will.

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Old 13th Jun 2013, 10:58
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@Capn Bloggs,
I agree that -3000 ft/min is a bit extreme. That was about an unpressurised airplane descent.

I was just responding to PH-Chucky's medical concerns : Even at -3000 ft/min there is no bowel implosion or lung crushing to be expected. The only issues I know of are with ears and sinuses.

IMHO, if the pressurisation system recovers about 1000 ft pressure differential at a rate of -1000 ft/min, the risk of ear pain is limited.
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Old 13th Jun 2013, 11:08
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Ok, fair enough, although I do value a low stress level health-wise

Have you confirmed this 'pressure' peak with the PSI reading? If it's just a cabin rate is -1000fpm for a few moments, it may be simply that the outflow valve is lagging behind slightly when the air from the packs starts to flow in as you switch them on.
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Old 13th Jun 2013, 11:10
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bubbers44
Ever since fuel cost started hurting measures that save fuel and other costs keep the Airlines afloat.Low cost carriers are doing OK while full service Airlines are strugling. Pilots are not resorting to packs off take off on their own. It is becoming Airline policy. It is business. Even the best pilots swim or sink with the company. When your company changes to packs off are you going to stop flying?
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Old 13th Jun 2013, 11:51
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@Agaricus bisporus
I understand the "pressure peak" is not a big deal, certainly not when compared to Extra300 skippers who experience much higher cabin v/s or skippers who fly unpressurized aircraft. But you are saying this all is pretty 'minor' in physiological terms. Do you know if there are any studies with some results/statements about certain pressure drops/peaks in relation to the human body?

Since I am involved with health issues (cabin air, radiation) within my company whereby I represent the employees side of these topics, I would really appreciate some official info (facts). I appreciate opinions, but it doesn't brings me further in representing the employees side of these topics.

Even I might have the opinion that these "pressurization peaks" are not a big deal. But I want to have this opinion being supported by official info. At the end, factual information is what counts for me and my colleagues. And if there is not enough factual information available, I am willing to dig deeper until I get satisfactory information.
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Old 13th Jun 2013, 22:51
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Eventually I am interested in possible long-term damage to the body if I fly for 30 years and have these high v/s of cabin rate every time I make a flight...
Try asking any of the office workers using any of the unpressurised lifts.
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Old 14th Jun 2013, 06:29
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Pressure changes in a commercial aircraft are trivial compared with those experienced by a SCUBA diver. Water being 800 times more dense than air.
SCUBA instructors and dive guides have now spent decades exposing themselves to this several times a day with no physiological harm so long as recommended procedures are kept to.
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Old 17th Jun 2013, 18:32
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PH-Chucky, think of it this way: If you jump into a pool down to 1 meter, you just increased your pressure by 10% in less than a second. That's about 3000' of air pressure change in less than a second, or >180 000' feet per minute.

So anyone worried that a 1000' pressure change in 60 seconds could be a problem should certainly be careful getting into the bath. I'd suggest slowly lowering yourself into the bathtub over 2 minutes minimum, preferably 3.

Can't be too careful.
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