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Why is there a hole in airplane windows?

  1. Dec 23, 2015 #1
    The following link explains that "it serves as a bleed valve, allowing pressure between the air in the passenger cabin and the air between the outer and middle panes [an airplane window has three panes] to equilibrate", yet it mentions that it is "a failsafe designed to hold the cabin pressure in the event that the outer [pane] is fractured".

    Isn't this a contradiction? The middle pane is there to hold the cabin pressure in the event the outer pane is fractured, but the hole would cause the cabin pressure to decrease.

    http://io9.gizmodo.com/i-think-there-s-a-hole-in-your-logic-1703851837
     
  2. jcsd
  3. Dec 23, 2015 #2

    A.T.

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    One little hole could probably be compensated by the system, or closed easily.
     
  4. Dec 23, 2015 #3
    I read the text of your link. It states there are three panes, inner, middle, and outer. Only the inner has a hole. The picture in the link is not clear about the three panes?
     
  5. Dec 23, 2015 #4
    The picture only shows the outer and middle panes. The inner pane mentioned is the middle pane.
     
  6. Dec 24, 2015 #5
    Edit, read your question more carefully. The cabin air pressurization system can easily keep up with a little hole. The system must pump in enough fresh air for all the passengers so large amounts of pressurized air must in fact be constantly dumped outside.

    There are two pictures in the link. In both only two panes are shown. The pane with the hole is called the middle pane in the first picture and the pane with the hole is called the inner pane in the second picture. In any case the third pane mentioned in the text is not shown. If the are only two panes and the outer pane failed the hole the cabin pressure system I'm sure could keep up with the small air flow out the small hole. Maybe there are only two panes?
     
    Last edited: Dec 24, 2015
  7. Dec 24, 2015 #6
    There are three planes, at least for all the airplanes I've seen so far. But the inner pane is not airtight.
     
  8. Dec 24, 2015 #7

    A.T.

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    Yeah, that is just to prevent people from putting chewing gum into that hole.
     
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