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Recently I was flying on an Airbus A320. While cruising around 37,000 feet, I noticed half of the glass on the window had frozen. But it was a thin layer of ice.

Was it anything to be concerned about? Should I have brought it to the notice of the airline crew?

Edit: Ice formed on the inside of window with a small hole in it. I guess it was the middle layer of glass.

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    $\begingroup$ In my experience a reboot usually resolves the issue, but if there's a persistent problem it's worth checking for a patch using Windows Update. Not sure why being in an airplane would make a difference. $\endgroup$ – Reinstate Monica Feb 10 '15 at 22:17
  • $\begingroup$ @user777 ROFL My dear question is not about Microsoft windows. It's about window of Airplane! $\endgroup$ – Vijay Vankhede Feb 11 '15 at 13:12
  • $\begingroup$ @vsvankhede i.imgur.com/38BlfVp.png $\endgroup$ – Federico Feb 11 '15 at 14:14
  • $\begingroup$ @Federico Like! $\endgroup$ – Vijay Vankhede Feb 11 '15 at 17:12
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Was it anything to be concerned

No

Should I have brought it to the notice of the airline crew?

Yes, but not because it is a safety issue. Tell them so they can deal with it to give the next passenger a nicer experience.

What is happening is no different than a glass of ice water sitting on your kitchen counter. The warmer side of the glass (the outside) becomes cooler because of the cold on the inside and it transfers that coolness to the surrounding air. That surrounding air cools enough to cause the moisture it contained to condense into liquid that sticks to your glass. If the glass were cold enough, it would freeze that condensation. The window on the aircraft is that cold so the condensation freezes.

There is a mechanism under the window to keep this from happening. It is a jar of desiccant that absorbs all moisture (dries the air) in the window area so that there is no moisture to condense in the first place. Often, there is a tiny bit still.

As the desiccant absorbs moisture from the air, it retains it. So periodically, it gets saturated to the point it can't absorb anymore and the desiccant needs to be changed.

Either the desiccant in your window needed to be changed or moist air is bypassing the desiccant on its way to the inside surface of the window. Normally there is a seal between the outside window and that thin plastic window you can touch and the only way for air to get in or out of that inter-window area is through the desiccant. Your window may have a broken seal allowing moist air to bypass the desiccant.

Either way, it is a system designed only to keep the window from forming ice so the passengers can look out the window, it has no safety or structural consequences.

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    $\begingroup$ Actually, I believe that the desiccant is to prevent not ice, but corrosion. That is the reason that airliners (barring composite-construction craft such as the 787) have such low cabin humidity. $\endgroup$ – dotancohen Feb 10 '15 at 15:25
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    $\begingroup$ this answer assumes that the ice was inside the cabin and reading the question I would not be so ready to make that assumption. $\endgroup$ – Federico Feb 10 '15 at 15:26
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    $\begingroup$ @Federico I think he's assuming that the ice is on the inside of the outer window pane, not the inside of the inner window pane. That seems likely enough, though perhaps not guaranteed. $\endgroup$ – reirab Feb 10 '15 at 17:19
  • $\begingroup$ Do you have a reference for the existence of this dessicant pack? Every airliner I can remember riding in had a small hole in the thin inner window so nothing is stopping moist air from migrating into the window space. Though aircraft air is not particularly moist in-flight. $\endgroup$ – Johnny Feb 10 '15 at 22:53
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    $\begingroup$ "If the glass were cold enough, it would freeze that condensation" - practical demonstration, put a bottle of vodka in the freezer (salt-water might also work if you're not allowed vodka, the point is to keep it liquid even in the freezer). Wait a couple of hours. Pour a glass, wait a minute. Unless the air in the room is really dry you'll see ice form on the outside of the glass from condensed water, exactly as this answer describes. $\endgroup$ – Steve Jessop Feb 11 '15 at 12:52
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It is something normal, airplanes are flying at -40º outside and is very common that ice is generated.

You need to be aware that some parts of the airplane which are critical for having a safe flight are having ice protection systems to avoid generation, but ice in the windows is just avoiding you to have a nice view and enjoy the views.

Not a big deal.

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    $\begingroup$ Its even colder than that outside. Typically in cruise you are around -55C SAT for cruise. $\endgroup$ – casey Feb 10 '15 at 14:56
  • $\begingroup$ Would love to know about the ice protection systems. $\endgroup$ – Firee Feb 11 '15 at 8:58

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