737 Cabin Altitude
Roger Harrison
Can any Boeing crew tell me typical cabin differentials and resultant
cabin altitudes on:
1) 737's on domestic routes in Australia (@ say FL350), and
2) 747's on international routes.
The lighties I fly have diffs ranging from 6.5 to 8.5 psi, but I have
heard that the bigger aircraft can operate to around 13 psi diff, which
sounds a bit much - hence the question.
Thanks
Cheers - Roger
________________________________________________
To e-mail me, please remove ZZZ from my address.
ar...@erols.com
In article <34AC9C57...@t130.aone.net.au>,
You're right Roger, 13psi is a bit much. In fact, oxygen from "the
overhead compartment" would be required.
I'm not a pilot but work with an altitude (hypobaric) chamber as therapy
for asthma and allergy sufferers. Under normal conditions 8.2-9.2psi
would be the maximum allowed -- this despite the fact that you could
ascend Mt. Haleakala on the island of Maui which has an altitude of
10,000 feet. In general, the greater the distance flight, the higher the
psi. A passenger traveling with a medical condition that could be
compromised by high altitude (low pressure) ie. pregnancy, upper
respiratory infections etc. could request that the internal altitude be
set to 6000 feet or less, which the captain will do as discretion
dictates. You might want to buy an inexpensive altimeter from LL Bean or
Land's End for use on future flights. Also, major search engines will be
most helpful if you enter hypobaric chamber or altitude chamber
-------------------==== Posted via Deja News ====-----------------------
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David G. Adkins
>You're right Roger, 13psi is a bit much. In fact, oxygen from "the
>overhead compartment" would be required.
>
>I'm not a pilot but work with an altitude (hypobaric) chamber as therapy
>for asthma and allergy sufferers. Under normal conditions 8.2-9.2psi
>would be the maximum allowed -- this despite the fact that you could
>ascend Mt. Haleakala on the island of Maui which has an altitude of
>10,000 feet. In general, the greater the distance flight, the higher the
>psi. A passenger traveling with a medical condition that could be
>compromised by high altitude (low pressure) ie. pregnancy, upper
>respiratory infections etc. could request that the internal altitude be
>set to 6000 feet or less, which the captain will do as discretion
>dictates. You might want to buy an inexpensive altimeter from LL Bean or
>Land's End for use on future flights. Also, major search engines will be
>most helpful if you enter hypobaric chamber or altitude chamber
>
>-------------------==== Posted via Deja News ====-----------------------
> http://www.dejanews.com/ Search, Read, Post to Usenet
In your message, which is replying to Roger, Roger is referring to the cabin
differential pressure, that is the pressure in the cabin, in relation to the
external air pressure at the given altitude, and not the difference in air
pressure between cabin pressure and the standard sea level pressure of
14.696 psia. When an aircraft flies at around 35 000 ft for example, the
outside air pressure will be relatively low (around 3.456 psia), however the
cabin differential pressure will be relatively high (around 6.4 psid).
This differential pressure has little bearing on whether oxygen is required,
but more to do with the structural strength of the airframe.
On a Boeing 747, the normal maximum operating cabin differential pressure is
8.9 psid, if the aircraft's cabin differential pressure reaches
approximately 9.25 psid, then an overpressure relief valve will operate, to
prevent structural damage occurring to the aircraft.
A cabin differential pressure of around 9 psid, means that the cabin air is
exerting a pressure of 9 pound per square inch upon the airframe.
Oxygen masks will normally deploy when the absolute pressure inside the
cabin drops to around 8.63 psia (ie. 14 000 ft).
David G. Adkins
On a Boeing 747, the normal maximum operating cabin differential pressure is
Roger Harrison wrote in message <34AC9C57...@t130.aone.net.au>...
Martin Taylor
Hello Ar...@erols.com
While discussing "737 Cabin Altitude" Ar...@erols.com said...
> Can any Boeing crew tell me typical cabin differentials and resultant
> cabin altitudes on:
> 1) 737's on domestic routes in Australia (@ say FL350), and
> 2) 747's on international routes.
Ar> You're right Roger, 13psi is a bit much. In fact, oxygen from "the
Ar> overhead compartment" would be required.
Ar> I'm not a pilot but work with an altitude (hypobaric) chamber as
Ar> therapy for asthma and allergy sufferers. Under normal conditions
I've always wondered about cabin pressurisation. I thought that it
worked so that a normal atmosphere (1 bar, 100 kpa, 15 psi) was
maintained at all levels. However, when descending I always got the ear
popping, due to altitude or pressure changes.
Why would this occur if the cabin is pressurised to a constant pressure?
If the pressure varies, then why is this done? isn't the idea to
maintain a constant 1 atmosphere for the duration of the flight?
Cheers
Martin
-=- Blue Wave/QWK v2.12
---------------
Gippsland, Victoria, Australia
http://www.gips.com.au
trevfenn
Martin Taylor wrote:
> I've always wondered about cabin pressurisation. I thought that it
> worked so that a normal atmosphere (1 bar, 100 kpa, 15 psi) was
> maintained at all levels. However, when descending I always got the ear
> popping, due to altitude or pressure changes.
>
> Why would this occur if the cabin is pressurised to a constant pressure?
> If the pressure varies, then why is this done? isn't the idea to
> maintain a constant 1 atmosphere for the duration of the flight?
>
> Cheers
Even in a pressurised aircraft the cabin altitude(cabin pressure) will
change when the aircraft altitude changes, it just does so at a much
slower rate for the comfort of the passengers.
Trevor Fenn
trev...@erols.com
James Matthew Weber
On Sun, 04 Jan 1998 19:27:00 +1000, Martin Taylor
<mta...@gips.com.au> wrote:
>Hello Ar...@erols.com
>
>I've always wondered about cabin pressurisation. I thought that it
>worked so that a normal atmosphere (1 bar, 100 kpa, 15 psi) was
>maintained at all levels. However, when descending I always got the ear
>popping, due to altitude or pressure changes.
In operation, cabin altitude seems to run from about 5000 to 8000
feet, depending upon cruise altitude (I check it with a pocket
altimeter). You try not to maintain cabin pressure any higher than
you have to. This reduces the structural loads on the fuselage, it
also reduces the weight of the aircraft! typically you try for an 8psi
differential. That would maintain sea level pressure only up to about
18,000 feet however. 737's rarely get past 35,000 feet, and typical
cabin altitude for that seems to be 6600 feet.
You also don't want to max out the cabin pressure, otherwise if you
climb, your ears will get to feel the real rate of climb!
>
>Why would this occur if the cabin is pressurised to a constant pressure?
>If the pressure varies, then why is this done? isn't the idea to
>maintain a constant 1 atmosphere for the duration of the flight?
Absolutely not. If you want an interesting exercise, calculate the
difference in weight between 14.7 psi and 10psi for a 747!
Martin Taylor
Hello Trevfenn
While discussing "737 Cabin Altitude" Trevfenn said...
Tr> Even in a pressurised aircraft the cabin altitude(cabin pressure) will
Tr> change when the aircraft altitude changes, it just does so at a much
Tr> slower rate for the comfort of the passengers.
Aren't the cabins sealed against outside atmospheric pressure? If so,
then shouldn't the pressure remain static?
Whistle
The way I understand it, the pressure inside the cabin does change somewhat,
but not to that on the outside, and the inside pressure is relative to a
given height, such as around 5000 feet for example. I think commercial jets
pressurisation maybe higher than this, but I am only guessing.
This also gives you jetlag.
Regards,
Tony
PS. I think this is what happens, and I guess I will be corrected soon.
David G. Adkins
Martin Taylor wrote in message <0000...@aone.net.au>...
>Hello Trevfenn
>
>While discussing "737 Cabin Altitude" Trevfenn said...
>
>
> Tr> Even in a pressurised aircraft the cabin altitude(cabin pressure) will
> Tr> change when the aircraft altitude changes, it just does so at a much
> Tr> slower rate for the comfort of the passengers.
>
>Aren't the cabins sealed against outside atmospheric pressure? If so,
>then shouldn't the pressure remain static?
>
>Cheers
>
>Martin
Aircraft cabin pressures vary in relation to the altitude of the aircraft,
while trying to maintain a relatively constant differential pressure. Cabin
altitudes may vary from approximately 0 to 10000 ft, depending upon the
altitude of the aircraft, in automatic mode, or the preference of the pilot,
in manual mode.
Nathan Currie
Martin Taylor wrote:
>
> Hello Trevfenn
>
> While discussing "737 Cabin Altitude" Trevfenn said...
>
> Tr> Even in a pressurised aircraft the cabin altitude(cabin pressure) will
> Tr> change when the aircraft altitude changes, it just does so at a much
> Tr> slower rate for the comfort of the passengers.
>
> Aren't the cabins sealed against outside atmospheric pressure? If so,
> then shouldn't the pressure remain static?
>
> Cheers
>
> Martin
Cabin Pressure must change as the aircraft climbs and descends. If they
Cabin was totaly sealed at Sea Level Then as the the cabin climbed the
pressure in the cabin would be greater than the outside pressure. It
would get to a height that it would structually fail - and this would be
uncomfortable for the passengers and crew. The same would happen if the
cabin was sealed at say FL380, once nearing sea level the Cabin would
implode as it would be of less pressure - again this would be
uncomfortable for the passengers.
Thus cabins are given a higher altitude than that of sea level ie approx
5000'. This makes it still comfortable for the passengers - as even
though the average person can survival in a pressure altitude of about
14000' - those will small lungs ie children, and the aged tend to suffer
from lack of oxygen. 5000' also relates to a good pressure that the
cabin can structually sustain.
Poping of the ears will thus still occur as you are 'climbing' and
'descending' inside the cabin.
Regards Nathan
Rod Lovell
David G. Adkins <adk...@wr.com.au> wrote in article
<34b1f...@nachos.wr.com.au>...
>
> Aircraft cabin pressures vary in relation to the altitude of the
aircraft,
> while trying to maintain a relatively constant differential pressure.
Two elements are required to provide cabin pressurisation. One is a
constant source of air. The other is a method of controlling the flow of
air into or out of the airplane to achieve the desired differential
pressure and resultant cabin altitude. The flow of air into the cabin is
fairly constant, and cabin outflow valve(s) normally control the flow out
and therefore the pressurisation. .
In modern aircraft, the pressurisation system is capable of maintaining sea
level cabin pressure up to an aircraft altitude of around 24,000 ft, where
max diff of around 9 psid is obtained.
However what happens then if you are in a Learjet, or the like, and still
have an aircraft rate of climb of say 2-3,000 ft/min? Answer, the cabin
climbs also at the same rate as the aircraft (2-3,000 ft/min). Not very
comfortable for the crew or pax.
Therefore, normal practice is to immediately start the cabin climbing after
take-off rather than maintaining a sea level cabin. This is done so that
the cabin will reach its preset altitude at approx the same time as the
aircraft reaches its cruise altitude.
The reverse is carried out for the descent. Normal cabin rates of
climb/descent, vary from 300 - 900 ft/min, depending again on aircraft
performance.
--
Rod Lovell
"V1....Oops!"
Peter Kerwin
Martin Taylor <mta...@gips.com.au> wrote:
> Tr> Even in a pressurised aircraft the cabin altitude(cabin pressure) will
> Tr> change when the aircraft altitude changes, it just does so at a much
> Tr> slower rate for the comfort of the passengers.
> Aren't the cabins sealed against outside atmospheric pressure? If so,
> then shouldn't the pressure remain static?
> Martin
Even if it did remain constant inside, the pressure differential between
inside and out would certainly increase with altitude. If keeping a sea
level cabin was a requirement, and bleed air type pressurisation systems
are usually more than adequate to do that, then to fly at 35,000ft a
Boeing might better be built in a submarine shipyard.
Such a heavy robust structure isn't required, however, if a compromise
is made and the cabin is allowed to go to say 7 - 9psi differential
pressure. Beside now being light enough to leave the ground with
passengers, this means the cabin altitude might be up around 8,000ft in
the flight level cruise, but the cabin climb and descents are much less
dramatic than the one that happens outside and not too many ears notice.
As for the sealed container - no seal is perfect and there's also a
deliberate leak via the outflow valve(s) which meters the cabin
differential pressure. After several hours and 3 meals with 350 smelly
co-passengers sharing the same long tube, you'd appreciate this feature.
Pete
(f...@DELETEcamtech.net.au)
Adelaide, South Australia
James Matthew Weber
On Wed, 07 Jan 1998 21:06:32 GMT, f...@DELETEcamtech.net.au (Peter
Kerwin) wrote:
>Martin Taylor <mta...@gips.com.au> wrote:
>
>As for the sealed container - no seal is perfect and there's also a
>deliberate leak via the outflow valve(s) which meters the cabin
>differential pressure. After several hours and 3 meals with 350 smelly
>co-passengers sharing the same long tube, you'd appreciate this feature.
>
Actually I think deliberate leak is a bit of an understatement. I
believe the cabin pressurization system actually does a complete
change of air in the cabin every few minutes in operation.
Graeme Hogan
Martin Taylor <mta...@gips.com.au> writes: > Hello Trevfenn
> Aren't the cabins sealed against outside atmospheric pressure? If so,
> then shouldn't the pressure remain static?
Air seeps out around rivets, aerial mounting hardware, door seals, etc, etc..
if they pump it up like a tyre, the structural loads would be immense.
They draw a compromise between happy airframe, and happy pax.
Peter Kerwin
mwe...@t140.aone.net.au (James Matthew Weber) wrote:
> >As for the sealed container - no seal is perfect and there's also a
> >deliberate leak via the outflow valve(s) which meters the cabin
> >differential pressure. After several hours and 3 meals with 350 smelly
> >co-passengers sharing the same long tube, you'd appreciate this feature.
> Actually I think deliberate leak is a bit of an understatement. I
> believe the cabin pressurization system actually does a complete
> change of air in the cabin every few minutes in operation.
If only it did especially on a hot day near the dunny. The outflow valve
specs and marketing brochures might suggest a quick refreshing change,
but my nose often tells me some air hangs about for quite a while
longer.
Martin Taylor
Hello Whistle
While discussing "737 Cabin Altitude" Whistle said...
Wh> This also gives you jetlag.
Being a fellow shiftworker, and having done some study into shiftwork
for a recent course, the "jetlag" effect is more of a consequence of
changing sleep patterns than anything else. Our internal body clocks
expect us to sleep after a certain period of being awake, and external
influences, such as sunlight (to reduce caratonin effect) help us wake
up. Flying across numerous time zones get this all out of kilter. I am
not sure why, but I'm more buggered after I get to the US than I am when
I return home. I think it has a lot to do with it being easier to align
my sleeping patterns with flying in to Oz during the night (arriving
early morning), than it is flying into the US and landing at 10 pm at
night.
What I do find is that the cabin air conditioning systems, especially on
747s, to be extremely noisy and the air very dry. It is also a top way
of getting people sick (Michelle got something while on the aircraft
coming back to Oz on Monday, and as a result, Sheryl got sick too).
When I flew once, there was still smoking on international flights. I
was stuck in the smoking section. I nearly died. Talk about passive
smoking. I have to wonder how much of the air within the cabin is
recirculated.
Cheers
Marty
Whistle
I told them shiftwork was bad for you, but did they believe me???? NO!
>Being a fellow shiftworker, and having done some study into shiftwork
>for a recent course, the "jetlag" effect is more of a consequence of
>changing sleep patterns than anything else. Our internal body clocks
>expect us to sleep after a certain period of being awake, and external
>influences, such as sunlight (to reduce caratonin effect) help us wake
>up. Flying across numerous time zones get this all out of kilter. I am
>not sure why, but I'm more buggered after I get to the US than I am when
>I return home. I think it has a lot to do with it being easier to align
>my sleeping patterns with flying in to Oz during the night (arriving
>early morning), than it is flying into the US and landing at 10 pm at
>night.
Noisey all right, you would think they could build a better system.
Drinking water is a good idea when flying, and certainly not alcohol, as
this has the opposite effect.
>What I do find is that the cabin air conditioning systems, especially on
>747s, to be extremely noisy and the air very dry. It is also a top way
>of getting people sick (Michelle got something while on the aircraft
>coming back to Oz on Monday, and as a result, Sheryl got sick too).
Am I glkad smoking has gone, I have had the same problem. This sounds like
a great civil suite???
>When I flew once, there was still smoking on international flights. I
>was stuck in the smoking section. I nearly died. Talk about passive
>smoking. I have to wonder how much of the air within the cabin is
>recirculated.
Have you seen this problem. I went to the US in November last, and we got
the seats next to the emergency exit, which is great, plenty of leg room.
Always bug the staff at the gate for these seats, we did and got them.
Anyway, people walking around came up to these doors, sat on the sign that
said "DONT SIT HERE" and them hung onto the emergency door handle.
At 40000 feet, if we hit turbulence, they fall over, grab the emergency door
handle and open the bastard, Im gunna be one pissed off passenger, not to
mention the first bloke out of the plane (suck that first class).
Regards,
Tony
Andrew Jack
Peter Kerwin wrote in message <34b4c4d1.1669884@news>...
>mwe...@t140.aone.net.au (James Matthew Weber) wrote:
<snip>
>> change of air in the cabin every few minutes in operation.
>
>If only it did especially on a hot day near the dunny. The outflow valve
>specs and marketing brochures might suggest a quick refreshing change,
>but my nose often tells me some air hangs about for quite a while
>longer.
I used to fly around PNG a lot on the F28s. On my first trip, I was in the
*last* row (two seats on left, dunny on right). In the aisle seat, I was
the closest to the dunny. There was some turbulence (tropics), so people in
the aisle has to hang on. I spent four miserable hours having my olfactory
senses assaulted not only by the dunny, but more pungently by the underarm
BO of the unwashed PNG masses queuing to use it. I'll take the middle of
the smoking section any day. After that trip I always made sure I got row 1
in the F28s....
Jock
"Whistle" <whi...@iname.com> wrote:
<snip>
>Have you seen this problem. I went to the US in November last, and we got
>the seats next to the emergency exit, which is great, plenty of leg room.
>Always bug the staff at the gate for these seats, we did and got them.
>Anyway, people walking around came up to these doors, sat on the sign that
>said "DONT SIT HERE" and them hung onto the emergency door handle.
>
>At 40000 feet, if we hit turbulence, they fall over, grab the emergency door
>handle and open the bastard, Im gunna be one pissed off passenger, not to
>mention the first bloke out of the plane (suck that first class).
>
>Regards,
>
>Tony
Lucky for us, Mr Boeing designed the 747 entry doors to be *plug*
type. This means they have to open inwards before swinging
outwards.
With the aircraft cruising at 40000 ft, the cabin differential
pressure will be around 8.5 psi (cabin altitude 7500ft).
Now I'm no expert mathematician but you can imagine the size of
the entry door....work out it's area in square inches....mutiply
that number by 8.5 (pounds per square inch) and you will get how
many pounds of force you need to exert to pull the door inwards.
Lots :)
But of course the handle will unlock the door and wake up the
people up the front.
Cheers.
--
Jock
t...@tig.com.au
Darren Crick
Whistle....
> At 40000 feet, if we hit turbulence, they fall over, grab the emergency door
> handle and open the bastard, Im gunna be one pissed off passenger, not to
> mention the first bloke out of the plane (suck that first class).
You always did like being the first at anything... but not this time, eh?
Darren
trevfenn
Whistle wrote:
> Always bug the staff at the gate for these seats, we did and got them.
> Anyway, people walking around came up to these doors, sat on the sign that
> said "DONT SIT HERE" and them hung onto the emergency door handle.
>
> At 40000 feet, if we hit turbulence, they fall over, grab the emergency door
> handle and open the bastard, Im gunna be one pissed off passenger, not to
> mention the first bloke out of the plane (suck that first class).
>
Now that you have written that sit down and work out how much pressure
is holding that door shut. A 747 door has a lot of square inches, all
with 8.5 psi of pressure on it. I don't think you could open that door
if you tried :)
Trevor Fenn
trev...@erols.com