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Thread: Airline cabin air circulation

  1. #1
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    Airline cabin air circulation

    I wanted to ask about cabin air circulation. My understanding is that modern jets have compressors that take air from outside and then warm it using engine heat and then inject it into the cabin, so that the air is changed every several minutes. My question is, when did this start? Back in the eighties, when people still smoked on planes, was this already done?


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  2. #2
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    Air is bled off from the engines after the compressor stage, which warms it due to compression and then it is mixed with cabin air. That’s why it can get stuffy sitting on the ground when they aren’t running. I don’t think there has been a fundamental change since jetliners began, though they probably have better filters now.
    Last edited by Van Rijn; 2021-Jun-27 at 05:47 AM.

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  3. #3
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    Unlike other passenger jets the B787 does not use 'bleed air'. Air is drawn in before the engines, compressed and then passed through a/c units to warm it and add humidity and then fed into the cabin. From what I can see the de Havilland Comet , in service 1952, of ill repute initially, was one of the first aircraft to use bleed air. As it was the first commercial passenger jet that makes sense.

  4. #4
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    I thought that only a small proportion of the air that comes through your air vent is fresh air from outside. Most of it is recirculated cabin air, hence the concern over disease spreading on planes?

  5. #5
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    Most of the air in my house is also recirculated, only a little comes in from outside. Then again, this loon thinks the airlines are trying to kill you because the air may be as much as 50% Nitrogen!
    Edit for clarification: Disease spreading on planes IS a bit of a concern, but it's because of the concentration of people, not the air. The same applies to crowded theaters, indoor sports events, parties, etc.
    Last edited by Trebuchet; 2021-Jun-27 at 06:53 PM.
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  6. #6
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    Quote Originally Posted by Trebuchet View Post
    Most of the air in my house is also recirculated, only a little comes in from outside.
    And you haven't recycled it through HEPA filters, as is done on modern passenger aircraft. I'll travel by plane long before I'm willing to travel by train or attend a concert.

    Quote Originally Posted by Trebuchet View Post
    Then again, this loon thinks the airlines are trying to kill you because the air may be as much as 50% Nitrogen!
    Hmm. RationalWiki seems a little confused about the cause of deep vein thrombosis during long-haul flights. The correct answer is that it has nothing to do with a change in air pressure, and everything to do with people sitting on their bottoms without stirring for hours on end.

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  7. #7
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    Airline cabin air circulation

    Mentour Pilot has a video about this:

    https://m.youtube.com/watch?v=ldm3n0hEsd4
    Last edited by Extravoice; 2021-Jun-28 at 06:05 PM.
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  8. #8
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    Quote Originally Posted by grant hutchison View Post
    And you haven't recycled it through HEPA filters, as is done on modern passenger aircraft. I'll travel by plane long before I'm willing to travel by train or attend a concert.

    Hmm. RationalWiki seems a little confused about the cause of deep vein thrombosis during long-haul flights. The correct answer is that it has nothing to do with a change in air pressure, and everything to do with people sitting on their bottoms without stirring for hours on end.

    Grant Hutchison
    The air in a passenger jet cabin can be 1300ppm in CO2, which shows the air change rate can be rather slow. The average plane journey, for UK at least, is probably a lot longer than the average train journey.

    I agree that trains and concerts are probably worse for spreading viruses, but could planes be improved by setting the fresh air intake at 100%?

  9. #9
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    Quote Originally Posted by kzb View Post
    The air in a passenger jet cabin can be 1300ppm in CO2, which shows the air change rate can be rather slow.
    Planes change air slightly more frequently than trains, according to Scientific American. The Journal of the American Medical Association describes how the nature of the circulation on planes reduces risk of transmission.

    Quote Originally Posted by kzb View Post
    The average plane journey, for UK at least, is probably a lot longer than the average train journey.
    Not for my currently aspirational journeys. Your mileage may of course differ (literally).

    It depends on the train, and the plane, and the railway station, and the airport, and the mitigation in place, of course. But trains were linked, right at the start of the pandemic, with significant transmission of Covid, in contrast to air travel to the same destination.

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  10. #10
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    Quote Originally Posted by grant hutchison View Post
    And you haven't recycled it through HEPA filters, as is done on modern passenger aircraft. I'll travel by plane long before I'm willing to travel by train or attend a concert.

    Grant Hutchison
    That reminds me that I need to a) go change my overdue furnace filter right now!, and b) call the heating company and ask if there's some sort of electrostatic cleaner that can be added. My wife is concerned about smoke from the upcoming forest fire season, which has been pretty bad the past couple of years.
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