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Question about commercial airliner pressurization.
Folks,
My GF has a condition called "LAM" which is an abbreviation for a long-arsed word that describes the affected areas of the body. You can Google it for more info but suffice to say, as it progresses, it makes it harder to breathe because it reduces the ability of the lungs to transfer oxygen to the blood. For her, even a small amount of exertion can be exhausting. Anyway, she took a commercial flight to NJ a couple weeks ago - maybe a hour and a half trip. Going up she flew in a newer turboprop, the Bombardier Q400. Supposedly, the Q400 is able to closely fly the profile of a pure jet with the economy of a turboprop. On the way there, she flew a cruising altitude of 19,000 feet. On the way back, she flew in a standard Boeing 737-700 at an altitude of 27,000 feet. Now to the problem: On the way up she reported moderate respiratory distress as the aircraft was climbing to cruise altitude. This distress continued until the plane made it's initial descent to EWR. On the way back, she reported no distress of any kind in the 737-700. The question: We're trying to account for the difference in flying experiences between the aircraft. As far as pressurization is concerned, what differences, if any, are there between the T-prop and the Jet? How are they pressurized? Bleed air? Are all aircraft pressurized to a standard 8000 feet? She is a fairly frequent flier and reported feeling well and "normal" before both flights. However, she has never flown in the Q400 before. Thanks for the ideas and insight. |
If I remember correctly, I think Boeing lowered the cabin pressure to roughly 4,000 in their newer planes.
Not sure though, I'm probably wrong. |
8000' cabin altitude is the max that any commercial aircraft will ever have. The pressure differential achievable depends on the strength of the cabin ribs and skin.
All systems are the same. The cabin is fed bleed air - cooled - and then recirculated. The amount of recirculated air is dependent on the aircraft make & model. At the rear of the aircraft, is a valve that modulates to allow a certain amount of air to escape, thus providing more new bleed air to the cabin. When smoking was still allowed on board, these outflow valves would get so gummed up with nicotine, they had to be thrown out. Now they can be rebuilt if necessary. |
So when you say "max any commercial aircraft will ever have", does that mean maximum cabin pressure (lowest altitude) or maximum altitude (lowest cabin pressure)?
That is to say, 8000' is the minimum pressure and you might find aircraft with higher (<8000') pressure? I'm just trying to understand the increased comfort in one plane versus another. |
8000' is the HIGHEST cabin pressure you will encounter.
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The highest cabin pressure is at sea level...........prior to takeoff or on landing. The lowest cabin pressure is maintained at an equivalent of 8000'.........no matter how high the aircraft is actually flying. At sea level, the pressure in the cabin is 14.7 psi. The lowest pressure that any passenger will ever see is 10.9 psi. |
Yeah, it's kind of backwards sounding - higher cabin altitude, lower pressure.
So, the bottom line I'm reading is that 8000' is the highest regulated cabin pressure. You will never see anything like 4000' cabin pressure at 27k feet, etc... |
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When starting a decent from altitude, the cabin altitude must be manually started down as well. As the aircraft approaches ground level, the pressure differential becomes less. If you ever feel a slight bump in the ears on landing, this means the cabin pressure was not lowered soon enough. The idea is to have the cabin altitude arrive at ground level (not necessarily sea level) the same time as the aircraft touches down. |
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8000' is the highest regulated cabin altitude. We don't have a conclusion as to whether certain aircraft types would maintain a lower cabin altitude at 27K or higher. One suggestion was that a new 737-700 might maintain 4000'..........but, I doubt it. |
Ive found that the same plane has dramatically different pressure profiles. sometimes its very comfortable, other times they seem to just open the valve like an on off switch. I get really bad ear aches if they dont do it right so I notice. I carry on a plastic water bottle and drink it during the flight and then tighten the cap at cruise altitude. I can watch it collapse as we descend, sometimes it is gradual from the beginning of descent and sometimes it is very fast. I think one of the crew must control this, I wish it was more consistent or computer controlled. I have experience the instant depressure someone above described during landing. ouch.... so maybe your experience is related to crew and not the plane.
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"With the 787 fuselage made of composite material, it's possible to increase the humidity without corroding the airplane over time. On the 787, the manmade composite material is formed and baked into large barrels that are linked together to form the fuselage. The composite material doesn't corrode as aluminum does. As a result, the 787 cabin air system will allow 15% humidity, a more comfortable level than the current 4%. Humidity's adjustable The 787 crew will be able to program the cabin air system for optimal humidity based on the number of passengers aboard, Sinnett says. The cabin air will be compressed to resemble an altitude of 6,000 feet above sea level, instead of 8,000 feet, increasing the air pressure and oxygen inside the cabin. As a result of its lower simulated cabin altitude, the 787's air will have 8% more oxygen for absorption into the blood. In studies, only 15% of passengers breathing 787-type air reported throat irritation, vs. 30% of passengers breathing traditional cabin air. Put simply, "The lower you go, the better people feel," Sinnett says. "The impact is more pronounced the longer the flight." Boeing-sponsored studies have found volatile organic gases build up inside the tight confines of a plane, making some passengers feel ill. Sources include hand wipes, cologne and vinyl luggage. As a result, Boeing has designed the 787 with not only the HEPA filters now in widespread use, but also a second filtering system that removes as many of the bad gases as possible. |
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