Commercial air craft cabin pressure

[Vipers]

I have given up on googling, so using probably the best thing I should have done in the first place, PH's.

Question, commercial airlines fly up to 35,000 feet above the earth, at that altitude what is the cabin pressure maintained at, I have heard 8,000 feet.

This is because you don't want to get altitude sickness at those height. I just know someone out there knows straight away. Off home now, will check later on during the evening, thanks guys.

[illmonkey]

Cabin pressurization is the active pumping of compressed air into an aircraft cabin when flying at altitude to maintain a safe and comfortable environment for crew and passengers in the low outside atmospheric pressure.

Pressurization is essential over 3,000 metres (9,800 ft) to protect crew and passengers from the risk of hypoxia and a number of other physiological problems (see below) in the thin air above that altitude and increases passenger comfort generally. "The outflow valve is constantly being positioned to maintain cabin pressure as close to sea level as practical, without exceeding a cabin-to-outside pressure differential of 8.60 psi." At a cruising altitude of 39,000 feet (FL 390), a Boeing 767's cabin will be pressurized to an altitude of 6,900 feet.[1]



Maintaining the cabin pressure altitude to below 3,000 metres (9,800 ft) generally avoids significant hypoxia, altitude sickness, decompression sickness and barotrauma.

Edited by illmonkey on Tuesday 20th October 16:19

[Moose.]

8000ft is the generally accepted max cabin altitude for a pressurised commercial flight Fly above 10,000 for too long and you'll start getting problems with hypoxia.

I'm struggling to see why you couldn't find that via Google though. It's the first thing returned if you search for "cabin altitude"

[Vipers]

Moose. said:

8000ft is the generally accepted max cabin altitude for a pressurised commercial flight Fly above 10,000 for too long and you'll start getting problems with hypoxia.

I'm struggling to see why you couldn't find that via Google though. It's the first thing returned if you search for "cabin altitude"

Tks for all the responses, the reason I couldn't find it, is that I usually put in the wrong key search phrases, just spent the past week boning up on Torr values at altitude, and the coresponding partial pressures of oxygen. PH's have never failed me so far, tks guys.

[mrmaggit]

If you're flying and your ears give you grief, vent your spleen at the first officer, it's his responsibility.

[anonymous-user]

mrmaggit said:

If you're flying and your ears give you grief, vent your spleen at the first officer, it's his responsibility.

The first officer is responsible for the cabin altitude?

Isn't the Captain somehow involved in the aircraft's systems also?

[Simpo Two]

Another aspect is how much air they recycle - I understand it saves money but means that everybody gets a cold from the single passenger who has one.

[illmonkey]

Simpo Two said:

Another aspect is how much air they recycle - I understand it saves money but means that everybody gets a cold from the single passenger who has one.

Does this cover the fact that air used to be cleaner when people could smoke on board?

I'm not too sure behind the truth of that though...

[IforB]

el stovey said:

mrmaggit said:

If you're flying and your ears give you grief, vent your spleen at the first officer, it's his responsibility.

The first officer is responsible for the cabin altitude?

Isn't the Captain somehow involved in the aircraft's systems also?

When I'm flying, the F/O is there to sit there and shut up. The only time I want to hear them speak is when I hear the words "I'll buy these beers" or "I'll take the ugly one."

[Papoo]

Simpo Two said:

Another aspect is how much air they recycle - I understand it saves money but means that everybody gets a cold from the single passenger who has one.

It's not recycled, however. Aircraft pressurization works by the system letting in more air than it lets out. The fact it's a hot-bed for contagious illness is due to everyone's proximity to everyone else, and no wind to move germs on, just lingering air that can't get out.

It also doesn't save money. Air is free.

[phumy]

Papoo said:

Air is free.

Dont tell that to GB he will tax it if he gets to know

[Vipers]

Papoo said:

Air is free.

Except in garage forecourts.



P.S. I won't mention the Jew joke, PC brigade would have me hang, drawn and quartered at dawn.

Edited by Vipers on Wednesday 21st October 07:43

[IforB]

Papoo said:

Simpo Two said:

Another aspect is how much air they recycle - I understand it saves money but means that everybody gets a cold from the single passenger who has one.

It's not recycled, however. Aircraft pressurization works by the system letting in more air than it lets out. The fact it's a hot-bed for contagious illness is due to everyone's proximity to everyone else, and no wind to move germs on, just lingering air that can't get out.

It also doesn't save money. Air is free.

Hmm, the air certainly is recycled on most airliners. The recirc fan sure as hell does save money. Cabin air is actually bleed air from the engine (from a compressor section before it gets burnt) and so by tapping it off, you are increasing your fuel consumption.

This is a 737 pressurisation panel. It's a later Digital version and is fairly self explanatory.



Here's pic of the pneumatics panel, showing the recirc fan switches. By using recirc air, you reduce the amount of bleed air being used. About 25% of the air is recycled on a 737, so it's not exactly a "hotbed of germs" especially as the air has to go through HEPA filters aswell. (I think the 757/767 uses about 50% recycled air.)



Here's a schematic of the 737 classic aircon system.

Edited by IforB on Wednesday 21st October 10:02

Edited by IforB on Wednesday 21st October 10:03

[simonej]

IforB said:

el stovey said:

mrmaggit said:

If you're flying and your ears give you grief, vent your spleen at the first officer, it's his responsibility.

The first officer is responsible for the cabin altitude?

Isn't the Captain somehow involved in the aircraft's systems also?

When I'm flying, the F/O is there to sit there and shut up. The only time I want to hear them speak is when I hear the words "I'll buy these beers" or "I'll take the ugly one."

MCC/CRM at its best!

Edited by simonej on Wednesday 21st October 10:19

[IforB]

simonej said:

IforB said:

el stovey said:

mrmaggit said:

If you're flying and your ears give you grief, vent your spleen at the first officer, it's his responsibility.

The first officer is responsible for the cabin altitude?

Isn't the Captain somehow involved in the aircraft's systems also?

When I'm flying, the F/O is there to sit there and shut up. The only time I want to hear them speak is when I hear the words "I'll buy these beers" or "I'll take the ugly one."

MCC/CRM at its best!

Edited by simonej on Wednesday 21st October 10:19

Ahh yes CRM. The F/O is the Crew and the Resource whilst I'm the Management.

[sorrento205]

Taken from BA intranet (WRT Swine Flu):

All British Airways aircraft are equipped with High Efficiency Particulate Air (HEPA) filters. IATA advise that about 50% of the air in most modern aircraft is re-circulated. However, air is only reused after having gone through HEPA filters. Microorganisms suspended in air, including bacteria and viruses, are captured by HEPA filters applied to aircraft air circulation systems. Just like HEPA filters used in surgical operating theatres, the best HEPA cabin air filters have a microbial removal efficiency of 99.97% with bacteria and viruses.

[S3_Graham]

the G650 seems to have a nice low cabin pressure!

[JuniorD]

I've frequently been up to 11,500ft in a Cessna 172. Those flights were the few enjoyable moments in a Skyhawk.

[eccles]

I had a bet with a chap in work about this thread, I reckoned it would still be on the first page before someone started the usual air quality debate.
Bacon rolls are on him tomorrow!

[R1_NUR]

RDE said:

The reason that cabin pressure isn't maintained at sea level (in case you were wondering) is to prolong the airframe life by reducing the stress on each pressure cycle.

Well kinda!

To maintain sea level pressure at an altitude suitable for jet transport would require a huge pressure differential. That means you need a strong airframe. Strong means heavy. Heavy = bad.

I fly the 75 and 767 - at a normal cruising altitude the cabin pressure is normally around 8000'.