BOAC707 From United Kingdom, joined Nov 2003, 278 posts, RR: 2 Posted (8 years 8 months 4 weeks 6 hours ago) and read 3790 times:
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?
KC135TopBoom From United States of America, joined Jan 2005, 11909 posts, RR: 52 Reply 2, posted (8 years 8 months 4 weeks 6 hours ago) and read 3754 times:
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.
KhenleyDIA From Sweden, joined Feb 2005, 425 posts, RR: 0 Reply 4, posted (8 years 8 months 4 weeks 4 hours ago) and read 3630 times:
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.
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.
Why sit at home and do nothing when you can travel the world.
320tech From Turks and Caicos Islands, joined May 2004, 489 posts, RR: 5 Reply 7, posted (8 years 8 months 4 weeks ago) and read 3437 times:
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.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
BUFJets From United States of America, joined Jan 2001, 231 posts, RR: 0 Reply 12, posted (8 years 8 months 3 weeks 5 days 17 hours ago) and read 2805 times:
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.