Cabin Air Pressure

I just got off the phone with Southwest Customer Relations asking a
question about cabin air pressure. Two separate people informed that
cabin air pressure in flight is 14.7 psi (sea level equiv.) and that it
is 10.0 psi (about 10,000 ft equiv.) on the ground.

Obviously, this has to be backwards, right? Even so, don't regulations
require cabin air pressure to be between 5,000 and 8,000 equiv.
altitude? Wouldn't that mean one of the numbers they gave me would
have to be between 12.23 psi (5,000) and around 11.0 psi (8,000)?

The reason I ask is rather important. My friend has a heart condition
and needs pressure of 4,000 ft or less. Southwest does not allow
supplemental oxygen, and he'd rather not use it anyway. The numbers
they give out seem suspect, and I can't take chances here.
Thanks,
Josh

My understanding is that at altitude cabin pressure is about 8000
feet. On the ground it's equal to ambient, possibly a tad more but
nothing noticable. Customer relations won't know, and in a life or
death situation I would never trust Customer relations. Never. Ask a
pilot for Southwest (different airlines may have different policies).
Maybe there's one here. If not, try calling Southwest's hub
airport, and see if you can talk to a pilot.

I don't think any but a private airplane will take you at a cabin
pressure of 4000 feet or less. Your friend may be stuck with that or
ground transport.

Jose
--
Freedom. It seemed like a good idea at the time.
for Email, make the obvious change in the address.

They're definitely confused!

I suspect the "10 PSI" that they quoted was the "pressurization differential" for the airplane, the max. allowable difference
between inside and outside pressure. 14.7 as you probably know is normal sea-level atmospheric pressure.

As another poster indicated, typical "cabin altitude" for airliners is around 8000 feet. You'll definitely see above 4000
feet in a jet, and very likely in a commuter turboprop too.

I think the options are probably limited to ground transport, traveling on another airline with supplemental O2, or maybe if
it's a short trip one of the small "air taxi" carriers that usually fly low with piston-powered airplanes.

Eric Law

wrote in message oups.com...
I just got off the phone with Southwest Customer Relations asking a
question about cabin air pressure. Two separate people informed that
cabin air pressure in flight is 14.7 psi (sea level equiv.) and that it
is 10.0 psi (about 10,000 ft equiv.) on the ground.

Obviously, this has to be backwards, right? Even so, don't regulations
require cabin air pressure to be between 5,000 and 8,000 equiv.
altitude? Wouldn't that mean one of the numbers they gave me would
have to be between 12.23 psi (5,000) and around 11.0 psi (8,000)?

The reason I ask is rather important. My friend has a heart condition
and needs pressure of 4,000 ft or less. Southwest does not allow
supplemental oxygen, and he'd rather not use it anyway. The numbers
they give out seem suspect, and I can't take chances here.
Thanks,
Josh

wrote

Obviously, this has to be backwards, right? Even so, don't regulations
require cabin air pressure to be between 5,000 and 8,000 equiv.
altitude? Wouldn't that mean one of the numbers they gave me would
have to be between 12.23 psi (5,000) and around 11.0 psi (8,000)?

My experience is based on early jet transports (B-707 B-727) but
should be close for any current jet transport.

The maximum allowable cabin differential pressure was 8.6 PSI which
would permit a sea level cabin up to an airplane altitude of about
22,000'. However, if the final cruising altitude was over 22,000',
the automatic pressure controller would start the cabin "up" shortly
after lift-off. This was to ensure a moderate rate of climb for
passenger comfort...about 300-400 ft/min ROC. At a crusing altitude
of 29,000', the cabin would be at about 3,000' and at 39,000', the
cabin would be at 7,000'.]
At 29,000', the standard day atmospheric pressure is about 4.5 PSI.
Add to that the max differential of 8.6 PSI for a total of 13.1 PSI,
or an equivalent altitude of 3,000'. For 39,000', it would be 2.9
PSI plus 8.6 PSI for 11.5 PSI and an cabin altitude of about 7,500'.

Bob Moore
ATP B-707 B-727
PanAm (retired)

good luck. With a field elevation of 2 or 3K, you will often see a pressure
altitude in excess of 4K.
The point is, can you drive where you need to go without seeing a pressure
altitude of 4K?


wrote in message
.com...
I just got off the phone with Southwest Customer Relations asking a
question about cabin air pressure. Two separate people informed that
cabin air pressure in flight is 14.7 psi (sea level equiv.) and that it
is 10.0 psi (about 10,000 ft equiv.) on the ground.

Obviously, this has to be backwards, right? Even so, don't regulations
require cabin air pressure to be between 5,000 and 8,000 equiv.
altitude? Wouldn't that mean one of the numbers they gave me would
have to be between 12.23 psi (5,000) and around 11.0 psi (8,000)?

The reason I ask is rather important. My friend has a heart condition
and needs pressure of 4,000 ft or less. Southwest does not allow
supplemental oxygen, and he'd rather not use it anyway. The numbers
they give out seem suspect, and I can't take chances here.
Thanks,
Josh

wrote:

I just got off the phone with Southwest Customer Relations asking a
question about cabin air pressure. Two separate people informed that
cabin air pressure in flight is 14.7 psi (sea level equiv.) and that it
is 10.0 psi (about 10,000 ft equiv.) on the ground.

Obviously, this has to be backwards, right? Even so, don't regulations
require cabin air pressure to be between 5,000 and 8,000 equiv.
altitude?

My understanding is that the pressure altitude in the cabin is to be
kept at 8000' or below. I've monitored the pressure altitude on quite
a few flights on various airlines and have noticed quite a bit of
variation. Some flights were kept very close to the 8000' limit
(around 7900'), while the lowest I've seen while at cruising
altitude was around 5500'.

Wouldn't that mean one of the numbers they gave me would
have to be between 12.23 psi (5,000) and around 11.0 psi (8,000)?

The reason I ask is rather important. My friend has a heart condition
and needs pressure of 4,000 ft or less. Southwest does not allow
supplemental oxygen, and he'd rather not use it anyway. The numbers
they give out seem suspect, and I can't take chances here.

Unless special arrangements are made for the flight it would almost
certainly exceed an equivalent pressure altitude of 4000'.

I just found another fun thing to do on a flight! Thanks. Hmmm...how much
would I freak out a flight attendant when I pull out my laptop with a psia
transducer and start logging data? Is the baggage compartment
unpressurized? I could compare data with a remote logger after the flight
WIFI is frowned upon.

I've monitored the pressure altitude on quite
a few flights on various airlines and have noticed quite a bit of
variation. Some flights were kept very close to the 8000' limit
(around 7900'), while the lowest I've seen while at cruising
altitude was around 5500'.

Baggage is pressurized. Animals ride back there. Baggage is usually
under the floor of the cabin on the big girls and behind the cabin for
the little girls.. The floor is not designed to be strong enough to be
part of the pressure containment vessel.
Michelle

Slip'er wrote:

I just found another fun thing to do on a flight! Thanks. Hmmm...how much
would I freak out a flight attendant when I pull out my laptop with a psia
transducer and start logging data? Is the baggage compartment
unpressurized? I could compare data with a remote logger after the flight
WIFI is frowned upon.



I've monitored the pressure altitude on quite
a few flights on various airlines and have noticed quite a bit of
variation. Some flights were kept very close to the 8000' limit
(around 7900'), while the lowest I've seen while at cruising
altitude was around 5500'.

wrote :
The reason I ask is rather important. My friend has a heart condition
and needs pressure of 4,000 ft or less.

I would never bet my life on a Southwest customer service rep :-)

I've had an altimeter watch for a around 10 yrs. and always monitor
the cabin altitude on commercial flights. At cruising altitudes above
30K ft. I've always seen a cabin altitude of between 6K ft. (newer
planes) and 8K ft. (older models). I believe the regs call out a
maximum altitude of 8K ft.

John Galban=====N4BQ (PA28-180)

wrote in news:1103218583.498295.269250
@z14g2000cwz.googlegroups.com:

The reason I ask is rather important. My friend has a heart condition
and needs pressure of 4,000 ft or less. Southwest does not allow
supplemental oxygen, and he'd rather not use it anyway. The numbers
they give out seem suspect, and I can't take chances here.

Without knowing where you are located, I would suspect that your two best
bets to meet your requirements are automobile and train.

If this is a medical flight then Angel Flight is a possibility. Although
keeping the plane below 4K would obviously be limited to the "low/flat"
parts of the country. OTOH, Angel Flight has no problem with the patient
bringing along his own small medical oxygen container.

A charter flight in a pressurized aircraft could keep the cabin pressure
higher (sea level) as long as they were flying relatively low. An
expensive possibility.

jmk