when the cabin door closes on 14.7 # pressure [assuming sea level takeoff]and the objective is to maintain pressure at say the 8,000 ft. level [10.9psi] is pressure first extracted
until that altitude is attained and then pressure maintained
through the bleed system? thanks for clearing this up, george

To answer George's question, the climb through 8000 feet only takes a few minutes, and the cabin pressure controller allows the cabin pressure to follow the decrease in outside pressure until the target pressure is reached, then maintains that pressure throughout the remainder of the flight until the descent through 8000, then allows cabin pressure to again follow ambient outside pressure to touchdown. At least that's how I understood it when banging around in back of C-141B's as a USAF flight nurse. I remember my ears popping on the way up to a particular point, and again on the way down after a particular point.

My wife are missing 2 bones in her head (parietal)and I want to Know if presure in the cabin will affect her.
I will apreciate this information.
Editors reply: We aren't qualified to answer. We suggest you ask a neurosurgeon.

George,

Aircraft are not designed to ever have a negative pressure differential (more pressure on the outside than on the inside). If the cabin altitude is set at 8,000ft before takeoff, the air inside the fuselage will gradually escape through the aircraft's outflow valves as the aircraft climbs. For example, if the aircraft is climbing at 4,000 feet per minute, the cabin altitude might only be increasing at 500 feet per minute. Once the cabin altitude reaches its set value (8000 ft in this example) the outflow valves will modulate to maintain the cabin altitude. If an 8000 ft cabin altitude can be maintained with a 5 psi differential (as would be the case if the aircraft were flying at ~25,000ft) and the aircraft climbs to a higher altitude (35,000 as an example), the aircraft will have to increase the differential pressure (~8 psi).

I would like to know the pressure inside the luggage part of a plane. Is it the same as in the passenger area?
And what about pressure inside the freight area?
This is specific information I need for transport of sensitive medical products.

I am searching for a chart or graph plotting aircraft altitude versus cabin altitude at various pressure differentials.

For example, what would be the aircraft cabin altitude flying at 15,000 feet with a differential of 2.5 psi?

The text says that the air pressure change is kept to a climb rate of 350 ft per minute whilst the aircraft climbs at thousands of ft per minute.
If this is true then the airframe will be stressed beyond its design limits.
The reason for reducing the cabin pressure is to reduce the weight of the airframe. (It would need to be stronger and therefore heavier to withstand the extra pressure)
The pressure chosen is a trade off between weight and passenger comfort, and safety for medical reasons.
The rate of change of cabin pressure is determined by the climb rate and will match it until the minimum pressure is reached. This is automatic and ensures that the airframe is not overstressed.
When descending the cabin pressure is maintained until the outside pressure equals the interior pressure and they remain equal for the rest of the descent.

Richard. (ex airframe fitter)

I have just flown and experienced a first ever problem, in many years of flying, prior to take off with the cabin pressure. I would be grateful if someone could answer what the worst case scenario would be if a commercial plane took off with the cabin presurisation computer not working? Between taxi off the stand to the far away start of the runway, pax on board started having ear pain discomfort, children crying, me personally started to feel sick and light headed. Having to keep swallowing every 10 seconds or so to clear the ears, the experienced crew member immediately knew their was a problem and rang the captain. he aborted the flight and went back to base where the engineers very swiftly replaced the controller/computer for the cabin pressure. thank goodness these tests are done prior to take off, a very worrying time.

Is the air pressure in the cabin maintained at that of sea level or is it lower than that of sea level? I have weak lungs and I suffer from altitude sickness and need oxygen in form of liquid cans or a concentrator if I have to travel somewhere which is more than 800 ft. high. Does this mean if I go on a flight I would need extra oxygen if the air pressure is not at the equivalent of sea level?

Vinny,
The cabin pressure is reduced to a value equivalent to about 8000 feet.
You would not be allowed to fly with your condition without a doctor's approval.

Answer to Frank E. Adams: Only today I see your request. I have a table that may be usefull for you. It is a table made from compiled data of several aircrafts AOM's.
As I don't know how to attach documents here, if you send me a mail, I can answer with the attached table (thadeuamello@gmail.com).

Does anyone know of any specific airlines or airplanes that pressurize their cabins at say, 7000 or 7500 feet? I tend to feel disoriented above 8000 feet, and am trying to find an airline and/or airplane that is pressurized below 8000 feet. Thank you.

Hello, i've a doubt. The outflow valve is a "hole" in the fuselage that controls pressurization, and we know if there's a hole in another area of the fuselage caused by a gunshot for example, it can get bigger and despressurizes the aircraft. As the outflow is a "hole", why doesn't it get bigger and the structures aroud it don't crack? Is there a reinforcement material aroud outflow?

In response to Vinny's question/comments about cabin pressure & altitude sickness. There are a couple of different types of portable concentrators or oxygen generators out there that are FAA approved and run on 120V, 12V and have a 6-8 hour battery life dependent upon litter flow/usage. This option allows car & flight travel and the ability to be portable for several hours. Ask your doctor if this option would be a viable option with your specific diagnosis or if you are already working with an oxygen supply company ask about rental options.

This is for Steven Borkowski...
Hi, I am a flight simulation enthusiast and as a virtual pilot I find this subject extremely important to read and understand in order to know how the system functions and how to control it. Although its late I just want to answer Steven Borkowski's question about airlines pressurizing their cabins below 8,000 ft.
I came accross this link http://en.wikipedia.org/wiki/Cabin_pressurization in Wikipedia. It says that the Boeing 767 does it at 6,900 ft.
Cheers,

Sometimes when i fly on some local flights i get this very painful feeling on my forehead that spreads to the rest of my head as we land but disappears a few minutes after landing. Is it normal and what causes it? EDITORS' REPLY: We're not qualified to answer, except to advise: Call your doctor before your next flight.

If an aircraft is cruising at, say, 35000 ft. and all packs stop working, will the aircraft be able to maintain its cabin pressure? Or will the air start leaking and the pressure slowly drop?

I am concerned about flying since I have had two small heart attacks after skiing in the Rockies. Both times they happened the day after I got back from the ski trip. The first time it happened my cardiologist said it would have happened no matter where I was, but the second time he said "I guess you have a problem with the altitude."Now I'm not sure what to expect since I have not flown since both episodes. I live in Iowa so I'm used to the flatlands.I have a wedding to go to in SanDiego over a weekend and aren't sure if I should go or not.
Any ideas would be welcome.

Very well explained. Thanks

hey everyone i guess this blog is old but ill try to post my question .. im taking this flight attendant course and i got this . how much time it takes the a/c to drop from 35000 ft to 10000 ft incase of rapid decompression .. ty EDITORS' REPLY: It would depend on the aircraft model, its volume, etc.

I have flown twice a week for the past ten years without a physical incident. (1000 plus flights)
9 months ago I had a heart attack 6 hours after getting off a flight. Recent Danish studies show a cumulative effect of the differential pressure on humans. (DVT's etc.)
It is common knowledge that airline manufacturers test the fuselages of aircraft thousands of times to determine when the differential pressure will cause the windows and the cabin itself to rupture.
What data is available on how this pressurization effects humans ?

Why do airplane passengers not feel the effect of low atmospheric pressure at a high altitude?

I have emphysema and have only 60% lung capacity left. Recently I was on a long haul flight from London to Sydney and after about 12 hours into the flight I went to the toilet, I was standing almost 15 Minutes waitng in line. During this wait I felt like there was a huge weight on top of me. When I returned to my seat it took me almost 15 minutes to get my breathing back to normal. During the worst of this I felt like my head was going to burst. Technically what would have caused this? I am not asking for a medical answer but a tecnical one. Thank you.

EDITORS' REPLY: Even when the cabin is pressurized, it's not pressurized to the level you'd experience on the ground. Simply put, at the altitude at which you were flying, there were fewer oxygen molecules for you to breathe, so your diminished lung capacity was exacerbated. Standing for an extended period may have been an additional stress; for some people, standing causes a drop in blood pressure.

I have COPD and Bowlus giganticus of the lungs, or blebs. My lungs produce large balloon-like blebs on the outside of my lungs; when one bursts it can collapse my lung, as it's full of air. What would be the effect on the blebs when flying? EDITORS' REPLY: We can't advise you on medical issues; you should check with a pulmonologist before flying.

The XC-35 was not the first aircraft with a pressurized cabin. The three earliest experimental models are a modified Dayton-Wright USD-9A in 1921, the German Junkers Ju 49 in 1931 and the French Farman F.1000 in 1932.

Loved your article! I have a question if you could answer it in layman's terms. How does the change in atmospheric pressure in the airplane affect human blood pressure?