June 02, 2003
Ice crystal formation in airplane windows
While flying from London to Chicago yesterday afternoon, I tried taking some photos of scenery we flew past along the way. The below photo is of Greenland and the B777 wing, 37 000 feet above the ground:
However, the picture was "spotted" with white dots (and seeing that Greenland was hiding behind clouds and haze, this spurred my curiousity more...): there was formation of ice crystals on the inside of the window:
I've seen this phenomenon several times before, of course, but I've never paid much attention to whether the ice crystals were forming outside or inside of the window. As the plane headed more south toward Chicago and we started our descent, the ice melted and the drops were visibly on the inside of the window (the fact that they didn't blow off was of course also a hint ;-)
I suspect the crystals form because of condensation between the layers of the multi-layered windows, and seeing that the outside temperature was below -50°C, one would suspect that inside the first layer of glass there would be at least a few degrees minus... Googling, I don't find much information about this phenomenon (write a comment below if you know more), but ice crystal formation outside the plane, on the wings and surfaces, is certainly a known risk of winter flying...
The moisture gets inside of the cabin while on the ground and freezes at altitude. The reason that you see it on the windows is because as the cabin is pressurized the moisture tries to escape through any very small gaps in the seals around windows and doors. But, as the cabin pressurizes all of the tiny leaks in the airframe begin to seal up and it becomes trapped. As you reach a cruising altitude, the vapor condenses into a liquid and continues to cool until it reaches 32 degrees. Then you have the small ice crystals on the inner face of the outer pane of the window.
Frosting of windows is just the visible part of a greater problem in a pressurized airplane, (fortunatly, not a safety of flight problem, just a maintenace concern) The inner pane is not a structural part, it is there just so passengers cannot mark or scratch the outer pane, which is structrial, but your right, it is because of condensation on a cold window. In the Beech King Air that I fly, windows and the screws that attach the trim collect so much condensation that on descent, water acually drips down and wets my pants. Usually, a desecant is sandwiched in the window to soak up moisture.
I don't know Physics that much and I have no idea why you saw the ice crystals. When I was flying to NY, I took a couple of nice pics of Greenland. Fortunately, there wasn't a single cloud in the sky, and no ice crystals either...
why is there a tiny hole in the bottom of the airplane window pane?
i am also wondering why are there tiny holes in the bottom of the airplane window pane? Can someone answer?
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