Moderators: jsumali2, richierich, ua900, PanAm_DC10, hOMSaR

 
geoffm
Topic Author
Posts: 2082
Joined: Fri Feb 27, 2004 5:58 am

Cabin Pressure

Wed Jul 21, 2004 5:09 pm

AIUI, at altitude the cabin is pressurised to about 8000ft. Now, at ground level at this altitude many people start to feel woozy, sick, and suffer from insomnia.

So wouldn't it be better to pressurise the cabin to more like 3-5000ft? I realise it takes more effort to do so, but in the interests of passenger comfort... oh I see why now!

Geoff M.
 
lmml 14/32
Posts: 2358
Joined: Tue Jan 30, 2001 2:27 am

RE: Cabin Pressure

Wed Jul 21, 2004 5:54 pm

Makes a lot of sense. I read the 7E7 will have higher cabin pressure. Which brings us to the much debated subject of the work environment of FA's, who still have to perform for long hours in an environment where most people would simply be woozy and sick.
 
ua777222
Posts: 2987
Joined: Mon Dec 22, 2003 11:23 am

RE: Cabin Pressure

Wed Jul 21, 2004 6:02 pm

An airlines cabin pressure system is pre-set to the set target alt. and will be set accordingly by the pilot. It's not like when you pass below 2000ft. and it's still pressureized at 8000ft. It's all done by computer. I hope I'm understanding your question correctly...

UA777222
"It wasn't raining when Noah built the ark."
 
miamiair
Posts: 4249
Joined: Thu Jul 15, 2004 9:42 pm

RE: Cabin Pressure

Wed Jul 21, 2004 6:24 pm

UA777:

In some airplanes, the cabin altitude is set manually, not by computers. As for lower cabin altitudes; the lower the cabin altitude, the greater stress placed on the fuselage. This will increase the fatigue on the lap joints and lead to higher operational costs due to maintenance. The frequency of inspections will have to be increased to detect any cracks before you get to the point of a catastrophic failure.
Molon Labe - Proud member of SMASH
 
MD11Engineer
Posts: 13899
Joined: Sun Oct 26, 2003 5:25 am

RE: Cabin Pressure

Wed Jul 21, 2004 6:32 pm

3-5000ft cabin altitude would mean a higher pressure differential between inside and outside, and this would mean that the cabin structure would have to be stronger and heavier.
8000ft is an altitude most people can cope with easily, so it has been chosen as a compromise.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
Sammyhostie
Posts: 467
Joined: Sun Feb 22, 2004 4:53 am

RE: Cabin Pressure

Wed Jul 21, 2004 7:07 pm

LMML,

I have to say I dont really notice the cabin pressure when im working, but i admit im absolutely knackered after a flight, even after an IBZ.

Apparently working in that altitude takes 6 times more effort than working on the ground.
Also we always joke that we are permenantly hypoxic, which is probably true, hence why we are always so giggly and hyperactive!
 
FinnWings
Posts: 633
Joined: Fri Oct 24, 2003 6:03 am

RE: Cabin Pressure

Wed Jul 21, 2004 7:18 pm

I agree with MD11Engineer, 8000ft isn't problem for normal health people and changing cabin pressure isn't wise...

If you smoke more than 3 cigarettes in a very short time or more than 1 box per day then you will have 10% CO in your blood. It means that your oxygen saturation is 90% and that equals to 10 000ft altitude!!! So basically, people who smoke most likely get more symptoms than non-smokers in long haul flights.

Situation is even worse if your hemoglobin levels are lower than normal... In that case you might lose consciousness quite easily on board. I have heard a true story of student pilot who was flying VFR flight at 9000ft in unpressurized Piper Seneca. He was a smoker and had a little bit lower hemoglobin levels and after an 1hr flight he get tired and soon lost consciousness. Luckily the flight instructor on board immediately understod what had happened and they make quickly an emergency descent.

Like I said, 8000ft isn't problem for health people, but if you have some diseases or use frequent medicines then you might get some symptoms.

Best Regards,
FinnWings
 
geoffm
Topic Author
Posts: 2082
Joined: Fri Feb 27, 2004 5:58 am

RE: Cabin Pressure

Wed Jul 21, 2004 8:35 pm

UA777222, no I don't mean that as soon as the doors are shut, the pressure drops to 8000ft! I thought that would be obvious, but obviously not... pressure inside should always be greater than outside.

More pressure on the airframe makes sense, however bear in mind the higher you go, the higher the pressure differential anyway. But I'm not sure that increasing the internal pressure by a couple of thousand feet would exceed the limits, ie not sure it would require the airframe to be heavier and stronger.

Geoff M.
 
miamiair
Posts: 4249
Joined: Thu Jul 15, 2004 9:42 pm

RE: Cabin Pressure

Wed Jul 21, 2004 9:10 pm

There is one case where pressurize kills...

http://www.ntsb.gov/genpdf/GenPDF.asp?id=MIA01FA029&rpt=fa

An American Airlines A300 departed MIA enroute to Port Au Prince, Haiti, and was losing pressurization. To make a long story (see the link above for a complete NTSB report), the airplane landed pressurized. None of the doors would open to evacuate the airplane, but the purser kept trying with the L1 door until the door exploded outward, taking him with it. The purser died from the result of the fall.

FYI
Molon Labe - Proud member of SMASH
 
Sammyhostie
Posts: 467
Joined: Sun Feb 22, 2004 4:53 am

RE: Cabin Pressure

Wed Jul 21, 2004 10:30 pm

There is a proccedure for that.

On the airbus in the window of the door there are two indicators, one red, one white.

When the red flashes, this means the cabin is still pressurised, the engines are shut down, and the doors are disarmed.
We are always taught never to attempt to open the door if this is indicated, as it would eventually lead to the door being popped out/in, as happened with this AA crew.
 
desertjets
Posts: 7693
Joined: Fri Feb 18, 2000 3:12 pm

RE: Cabin Pressure

Wed Jul 21, 2004 10:37 pm

Most commercial airliners are designed to maintain an 8000' cabin altitude. For the flight levels that most airliners fly at this is a good comprimise for both passenger comfort and the need for a relatively light pressure vessel. I believe the Gulfstream V was designed to maintain a 6000' cabin altitude as is the 7e7.

If you do a little poking around on the web, you can probably find the cabin pressure differentials that most commercial and business aircraft use... for some reason 8:1 sticks out in my mind.
Stop drop and roll will not save you in hell. --- seen on a church marque in rural Virginia
 
spacecadet
Posts: 3582
Joined: Thu Sep 20, 2001 3:36 am

RE: Cabin Pressure

Thu Jul 22, 2004 12:54 am

More pressure on the airframe makes sense, however bear in mind the higher you go, the higher the pressure differential anyway.

Well, this is why the pressure in the cabin is variable...

I don't know where people are getting the idea that the pressure is always maintained at 8,000 feet. The pressure in almost any modern jet can be set to whatever the pilot wants to set it at, or it can be pre-programmed by computer and left on "auto". (Obviously if a pilot sets it manually, it's not up to him what to set it at but based on company policy.) It is possible for an airplane to be pressurized to 5,000 feet pressure up to an altitude of 30,000 feet, for example, then decreasing the pressure little by little as altitude increases, up to a maximum pressurized altitude of 8,000 feet.

It all just depends on company policy and maintenance schedules. I would guess most airlines probably try to get by on the cheap and pressurize their planes as little as they can get away with... but it doesn't have to be this way, and it's probably not a universal truth anyway (more profitable airlines might use higher pressure in their cabins, for example, and just eat the extra maintenance costs).
I'm tired of being a wanna-be league bowler. I wanna be a league bowler!

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos