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Window Anomaly  
User currently offlineHmmmm... From Canada, joined May 1999, 2104 posts, RR: 5
Posted (8 years 4 months 4 weeks 1 day 10 hours ago) and read 5602 times:

Every airliner window has a piece, usually cylindrical in shape, about the diameter of a piece of lead in a pencil, at the bottom of the window. You can see it here in this photo. It is always on the inside between the two layers of window.

Does anybody know what purpose it serves, or is it an artifact of the manufacturing process?

http://photos.airliners.net/photos/photos/5/6/8/0937865.jpg


An optimist robs himself of the joy of being pleasantly surprised
28 replies: All unread, showing first 25:
 
User currently offlineSammyk From United States of America, joined Oct 1999, 1690 posts, RR: 0
Reply 1, posted (8 years 4 months 4 weeks 1 day 9 hours ago) and read 5574 times:
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I always thought it was a spacer but would love to know what it really is if not that.

User currently offlineN600RR From United States of America, joined Feb 2006, 171 posts, RR: 0
Reply 2, posted (8 years 4 months 4 weeks 1 day 9 hours ago) and read 5548 times:

I don't know for certain, but I always thought it had something to do with air pressure equalization between the layers of windows -- either to keep them from bowing, or to prevent them from fogging.

 alert  But more importantly, and it's hard to tell from this angle, it looks like a ramper left some safety or eye glasses on the wing...  wink 



"And the fluffy white lines that the airplane leaves behind are drifting right in front of the waning of the moon" -Cake
User currently offlineTekelberry From United States of America, joined May 2003, 1459 posts, RR: 4
Reply 3, posted (8 years 4 months 4 weeks 1 day 9 hours ago) and read 5518 times:

Quoting N600RR (Reply 2):
alert But more importantly, and it's hard to tell from this angle, it looks like a ramper left some safety or eye glasses on the wing... wink

That's part of the wing on the A320.


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Photo © Danny Fritsche - Airplanespotters


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[Edited 2006-02-25 06:33:12]

User currently offlineSpacecadet From United States of America, joined Sep 2001, 3603 posts, RR: 12
Reply 4, posted (8 years 4 months 4 weeks 1 day 6 hours ago) and read 5402 times:

I'm pretty sure that's basically a hole in one layer of the window so that the air in between can move back and forth as it heats up and cools down. You gotta remember that these planes may be sitting in 100 degree weather on the tarmac, only to hit somewhere around -50 once they're at cruise altitude. You can even feel how cold the window gets on the inside layer.

I suppose I could be wrong about that thing, but that's what I always assumed it was. Without some way for that air to breathe, the inner window would crack. (The outer layer has to be tough enough to withstand pressurization, so I'm sure it's the inner layer that would break.)



I'm tired of being a wanna-be league bowler. I wanna be a league bowler!
User currently offlineQQflyboy From United States of America, joined Oct 2003, 2264 posts, RR: 13
Reply 5, posted (8 years 4 months 4 weeks 1 day 6 hours ago) and read 5365 times:

Those "eyeglasses" on the wing are where the overwing exit ropes are attatched. Most aircraft with overwing exit windows have ropes that extend from the overhead bin or window sil to act as a hand hold during an evacuation.

And I concur the hole(s) in the window is to allow for movement of air.



The views expressed are mine alone and do not necessarily reflect my employer’s views.
User currently offlineMX757 From United States of America, joined Aug 2005, 628 posts, RR: 12
Reply 6, posted (8 years 4 months 4 weeks 1 day 5 hours ago) and read 5327 times:

Quoting N600RR (Reply 2):
I don't know for certain, but I always thought it had something to do with air pressure equalization between the layers of windows -- either to keep them from bowing, or to prevent them from fogging.

You are correct about pressure equalization, it's called a breather hole in the maintenance manual. It's located on the bottom of the middle window pane.

Fog and frosting are prevented by means of muti-pane construction with intervening cavities essentially isolated from cabin interior air conditions.

Quoting N600RR (Reply 2):
But more importantly, and it's hard to tell from this angle, it looks like a ramper left some safety or eye glasses on the wing.

Was I the only to get your joke?
Funny by the way.



Is it broke...? Yeah I'll fix it.
User currently offlineN600RR From United States of America, joined Feb 2006, 171 posts, RR: 0
Reply 7, posted (8 years 4 months 4 weeks 20 hours ago) and read 5124 times:

Quoting MX757 (Reply 6):
Was I the only to get your joke?

Apparently!  highfive 

Quoting MX757 (Reply 6):
Funny by the way.

Thanks... I know its not  rotfl  material, but I was starting to wonder. (Think I'll stick with my day job for now.)

Quoting QQflyboy (Reply 5):
Those "eyeglasses" on the wing are where the overwing exit ropes are attatched.

Even though my somewhat failed attempt at humor was lame, I appreciate the explanation.  bigthumbsup  Since I am only a mere passenger  sorry  when I fly, I actually thought it was something used for maintenance purposes.



"And the fluffy white lines that the airplane leaves behind are drifting right in front of the waning of the moon" -Cake
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 8, posted (8 years 4 months 4 weeks 17 hours ago) and read 5040 times:

Quoting MX757 (Reply 6):
You are correct about pressure equalization, it's called a breather hole in the maintenance manual. It's located on the bottom of the middle window pane.

The standard window installation is made up of a rubber seal that holds two window panes made of clear stretched acrylic. The outer pane is 0.40" thick then there is a 0.25" air gap and an inner pane 0.25" thick. The small hole at the bottom on the inner pane equalizes the pressure between the inner and outer pane. Should the outer 0.40" thick outer pane fail the 0.25" inner pane can still hold maximum cabin pressure. The two panes and the rubber seal are held in place with small clips.


User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 9, posted (8 years 4 months 4 weeks 16 hours ago) and read 4977 times:

It's a small hole to prevent moisture from building up between the inner and outer structural window.


"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineHmmmm... From Canada, joined May 1999, 2104 posts, RR: 5
Reply 10, posted (8 years 4 months 4 weeks 11 hours ago) and read 4859 times:

Thanks for the answers guys!

BTW, I had to look really hard to find a window shot that had a window in the shot! I much prefer to see the shot framed by the window. Gives a much nicer impression, like you are in the plane with the photographer.



An optimist robs himself of the joy of being pleasantly surprised
User currently onlineMir From United States of America, joined Jan 2004, 21494 posts, RR: 56
Reply 11, posted (8 years 4 months 4 weeks 9 hours ago) and read 4803 times:

Quoting N600RR (Reply 2):
But more importantly, and it's hard to tell from this angle, it looks like a ramper left some safety or eye glasses on the wing...



Quoting QQflyboy (Reply 5):
Those "eyeglasses" on the wing are where the overwing exit ropes are attatched. Most aircraft with overwing exit windows have ropes that extend from the overhead bin or window sil to act as a hand hold during an evacuation.

I heard that it was the hoist point for the wing. Maybe it's both.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 12, posted (8 years 4 months 4 weeks 9 hours ago) and read 4794 times:

Quoting EMBQA (Reply 9):
It's a small hole to prevent moisture from building up between the inner and outer structural window.

I don't want to sound like I'm disagreeing with you, but I don't know how a small hole would help. I would think that more moisture would be present on the inside of the cabin than outside during most of the useful life of an airliner, so with the hole there, it would be more likely for it to transit the space between the panes. If the opposite were true, and moisture was more likely to sporadically leak from the outside to the inside, why would it vacate the inter-pane space via the hole? There's almost always going to be higher pressure on the inside than the outside of the airliner.

I personally think the first scenario I described above is most common, since I often see ice crystals forming radially out from the hole in between the two panes. It seems likely that these are formed when warm moisture from the cabin seeps into the space between the panes via the hole and is frozen due to the cold temperature of the outer pane. Am I close?  Smile



Position and hold
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 13, posted (8 years 4 months 3 weeks 5 days 20 hours ago) and read 4572 times:

Quoting EMBQA (Reply 9):
It's a small hole to prevent moisture from building up between the inner and outer structural window



Quoting MX757 (Reply 6):
Fog and frosting are prevented by means of muti-pane construction with intervening cavities essentially isolated from cabin interior air conditions.

Uhmm yeah right..... Wink



I took this picture while flying one of AM's newest 73Ws. It also has happened to me in WN's 73Ws.

Coincidence? Big grin


User currently offlineA319XFW From , joined Dec 1969, posts, RR:
Reply 14, posted (8 years 4 months 3 weeks 5 days 19 hours ago) and read 4547 times:

Quoting 474218 (Reply 8):
The standard window installation is made up of a rubber seal that holds two window panes made of clear stretched acrylic. The outer pane is 0.40" thick then there is a 0.25" air gap and an inner pane 0.25" thick. The small hole at the bottom on the inner pane equalizes the pressure between the inner and outer pane. Should the outer 0.40" thick outer pane fail the 0.25" inner pane can still hold maximum cabin pressure. The two panes and the rubber seal are held in place with small clips.

I concur with this - that's what I remember from my Aircraft Familiarization course a few years ago  Smile


User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 15, posted (8 years 4 months 3 weeks 5 days 15 hours ago) and read 4486 times:

I always thought they drilled out the holes to reduce the weight of the plane.  Smile

User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 16, posted (8 years 4 months 3 weeks 5 days 10 hours ago) and read 4429 times:

Quoting Bobster2 (Reply 15):
I always thought they drilled out the holes to reduce the weight of the plane.

So that's how they keep the A380s weight down! Big grin



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineNonfirm From United States of America, joined Sep 2005, 434 posts, RR: 0
Reply 17, posted (8 years 4 months 3 weeks 5 days 6 hours ago) and read 4401 times:

The window need to be installed with the part number up on the outer pane and the weep hole down on the middle pane if the windows show sings of fogging there is a possible leak and the seal should inspected or replaced.The middle window pane gives the structural fail safe it can hold 1.5 times the normal pressure load.The middle pane is similar in shape to the outer pane but it does not have beveled edges.This is from the ng mm.The inner pane is non structural.

User currently offlineJush From Germany, joined Apr 2005, 1636 posts, RR: 3
Reply 18, posted (8 years 4 months 3 weeks 5 days 4 hours ago) and read 4378 times:

Quoting Tekelberry (Reply 3):
That's part of the wing on the A320.

I don't want to be nitpicking... but well the heck I will.
Easyjet does have the A319 and no A320 whatsoever.
It still is a part of the A319 as well.

Regds
jush



There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
User currently offlineA319XFW From , joined Dec 1969, posts, RR:
Reply 19, posted (8 years 4 months 3 weeks 4 days 21 hours ago) and read 4313 times:

Quoting Jush (Reply 18):
I don't want to be nitpicking... but well the heck I will.
Easyjet does have the A319 and no A320 whatsoever.
It still is a part of the A319 as well.

Not wanting to nitpick either...
It is also part of the A318 wing, too Big grin
That's because the A318, A319 and A320 wings are identical.


User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 20, posted (8 years 4 months 3 weeks 4 days 17 hours ago) and read 4261 times:

Quoting FLY2HMO (Reply 13):
Uhmm yeah right.....



Quoting Bri2k1 (Reply 12):
don't want to sound like I'm disagreeing with you, but I don't know how a small hole would help.

I just got back after my weekend and dug into the manuals. I looked at a few different aircraft on our server and and found the following information...Taken from the D&O section.

CRJ 700/900:

AMM Part 1, 56-20-00- Page 1

The inner pane is an acrylic plate that molds to the same contour as the fuselage. It has a hole drilled in the bottom half to allow warm air from the passenger compartment to heat the outer pain and prevent condensation

SF340:

AMM Part 1, 56-20-00-Page 1, B-2

The inner pain is made of acrylic and has a small hole in the bottom to allow air flow and prevent moisture build up.

[Edited 2006-02-28 22:38:43]


"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 21, posted (8 years 4 months 3 weeks 4 days 16 hours ago) and read 4238 times:

Here's an idea. Put a little piece of paper up againt the hole and see if the cabin air pressure holds it in place. If the paper falls down, then there is not a significant air flow through the hole, and that would disprove the claim that warm air is flowing out the hole.

I personally think the hole is there to put the full cabin pressure on the outer window pane, which is clearly the primary pane since it is thicker than the inner pane. As others have pointed out, the hole provides pressure equalization, not heat conduction.


User currently offline2enginesonly From Netherlands, joined Jun 2005, 91 posts, RR: 0
Reply 22, posted (8 years 4 months 3 weeks 4 days 15 hours ago) and read 4223 times:

Quoting Bobster2 (Reply 21):
Here's an idea. Put a little piece of paper up againt the hole and see if the cabin air pressure holds it in place. If the paper falls down, then there is not a significant air flow through the hole, and that would disprove the claim that warm air is flowing out the hole.

Bobster,

I can tell you right away that the paper will fall off.
When an aircraft climbs, the cabinpressure will get lower than the pressure at groundlevel ( but still higher than outside )....with the piece of paper in place on the hole, the pressure between the 2 panes should remain the same as the groundlevel and will therefore blow the piece of paper away.

The only reason for that hole is to prevent moisure being trapped between the 2 panes.....that's the reason the hole is at the bottom of the pane.
It doesn't mean that condensation won't happen ( humid air in cabin + cold windowpane = condensation on window ) but after the flight it will disappear.

I hope my explanation is satisfactory.
And all this because of a tiny hole in a window  Smile

Arjan


User currently offlineNonfirm From United States of America, joined Sep 2005, 434 posts, RR: 0
Reply 23, posted (8 years 4 months 3 weeks 4 days 15 hours ago) and read 4222 times:

Quoting Bobster2 (Reply 21):
I personally think the hole is there to put the full cabin pressure on the outer window pane, which is clearly the primary pane since it is thicker than the inner pane. As others have pointed out, the hole provides pressure equalization, not heat conduction.

From both the 737/MD-80 manual both windows are capable of carrying the full load of pressurization the hole is to help vent moisture so the windows panes do not fog up.


User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 24, posted (8 years 4 months 3 weeks 4 days 15 hours ago) and read 4216 times:

I believe it now. Who am I to disagree with an AMM excerpt? And, its true they rarely fog up to the point that it impairs visbility. Sometimes the inner pane will fog up if you breathe on it, but the outer one usually stays fog-free.

At least we're concerned about a hole in the plane! It's not like another rant about thrust reversers... duck 



Position and hold
25 Hmmmm... : Thanks for posting that photo. Nothing like that on A.net. But just to clarify, I a not talking about the bullet-shaped hole apparent in your photo. I
26 Bri2k1 : I don't think that's a hole. That's frozen moisture on the inner surface of the outer pane, which presumably entered the inner-pane gap via the hole
27 Post contains images David L : Agreed. The small cylindrical shape is the hole. That moisture pattern has formed directly opposite the hole on the next pane outboard. Where are tho
28 HAWK21M : If you see a stain around that hole.Replace the seal between the Outer & Inner Panes. regds MEL
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