boac707
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Cracked Windshield

Mon Mar 28, 2005 9:50 am

I saw a news rocker this morning about an Air Canada flight from Calgary to Toronto on March 26 that had to make an emergency landing in Winnipeg due a cracked windshield. I can't find anything in the forum, and I was wondering if anyone had more info...also, beyond a bird strike what makes a windshield crack in cruise?
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EMBQA
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RE: Cracked Windshield

Mon Mar 28, 2005 10:00 am

.....a runaway heater will do it. Also, just like any glass, it can develop stress cracks, especially if chipped.
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kc135topboom
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RE: Cracked Windshield

Mon Mar 28, 2005 10:04 am

Each window in the cockpit has it's own electric heat, to prevent fogging and icing inflight. Sometimes the heater for a window fails, or it overheats. The rapid temperature change can crack a windshield. Since these windows are very thick multiple layers of glass, where the crack is is very important. If I remember correctly, from my KC-135 days, when you see a crack, you draw a grease pencil mark on the crack, then lean over to one side or the other to determine weather the crack is on the inner or outer paine of glass. If the crack is on the inner paine, you must reduce the cabin pressures and land, If on the outer paine, you could reduce the cabin pressure and continue the mission. But, once on the ground, the aircraft is grounded the windshield is replaced, then another 24 hours to allow the sealant to cure.

But, things that can crack a window include bird strikes, rapid temperature changes, hail, and bullets.
 
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RE: Cracked Windshield

Mon Mar 28, 2005 10:17 am

A few thunder storms have cracked some windscreens and I think one even partly smashed throu one
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khenleydia
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RE: Cracked Windshield

Mon Mar 28, 2005 11:42 am

Quoting KC135TopBoom (Reply 2):
But, things that can crack a window include bird strikes, rapid temperature changes, hail, and "bullets".

You forgot sledge hammers and explosives.  scratchchin 

Back to being serious, they can crack from a number of things, but considering all the possibilities and the number of flights, it is rather rare. Of course, don't take that as a fact, I don't know the ratio of cracked windscreens / uncracked windscreens.

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kc135topboom
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RE: Cracked Windshield

Mon Mar 28, 2005 12:04 pm

It is about 1 cracked windshield for every 10,000,000 window flight hours!

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whitehatter
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RE: Cracked Windshield

Mon Mar 28, 2005 12:07 pm

Windscreens will delaminate more often than form traditional cracks. Both mean that the aircrfat needs to be landed quickly.
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320tech
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RE: Cracked Windshield

Mon Mar 28, 2005 4:24 pm

Windscreens will delaminate more often than form traditional cracks. Both mean that the aircrfat needs to be landed quickly.

Not necessarily. It depends on which layer the crack is in. It's common - relatively speaking - for the outer ply to crack. The outer ply is not structural, so other than that the pilot can't see through that windscreen, it's not a major emergency. Obviously, they'll still land as soon as they can.

If the inner structural ply cracks, that's a whole different situation. I'm not aware of it happening with the airplanes I've worked on - mostly Dash-8's and A320's.

Delamination is much more common. Depending on the degree of damage, the window might not be replaced at all. Delamination usually happens along the edges of the windscreen, and so doesn't interfere with pilot vision much.

A common cause of windscreen cracking on the Dash-8's was a water build-up in the window frame. At altitude the water would freeze, and put enough pressure on the windscreen to crack it. The problem was solved by opening a drain in the frame.
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boac707
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RE: Cracked Windshield

Tue Mar 29, 2005 8:29 am

thank you all for the info...you learn something new everyday....
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777wt
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RE: Cracked Windshield

Tue Mar 29, 2005 8:54 am

A long time ago here on A.net, there was a story of a 777 starting to descent to Milan, the window heater malfunctioned and the pilots shut it off. When they did, the glass cracked!
 
jeb94
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RE: Cracked Windshield

Tue Mar 29, 2005 9:11 am

If it was a CRJ its possible the curvature of the windshield wasn't exactly right for the aircraft. Its a known problem, especially on CRJ 700s and 900s.
 
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HAWK21M
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RE: Cracked Windshield

Tue Mar 29, 2005 8:44 pm

What was the Aircraft model.Probably Faulty Heat element/Controller.
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BUFjets
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RE: Cracked Windshield

Tue Mar 29, 2005 10:38 pm

I once had a flight cancelled due to a cracked windshield. We were leaving the first flight out of BUF on a cold February morning. They turned on the heaters (I assume window heaters) and one window cracked. It was a US flight. They flew the 737 out of BUF empty to BOS for repair.