nikeson13
Topic Author
Posts: 97
Joined: Mon Dec 05, 2011 5:35 am

AC761 Broken Window

Mon Apr 08, 2013 4:04 am

Back in 2011, I was flying YUL - SFO on June 10 and halfway through the flight over Minnesota, we drop and then level out and the pilots tell us that the windshield cracked in the cockpit. We then diverted slowly and safely to YWG.

How often do windows crack due to pressure/faults or a mix of both? Can it ever become dangerous?

Thanks!
nikeson13
Nikolas
 
Horstroad
Posts: 362
Joined: Thu Apr 08, 2010 8:19 pm

RE: AC761 Broken Window

Mon Apr 08, 2013 4:44 am

windshields are fail safe designed. they consist of several layers. even if the outer ones failed due to FOD or wrong bolt torque/sequence or whatever, the remaining layers will hold the window together safely usually with no pressure loss.

it does happen, but not that often. when it happens you want to get to the ground. though it's completely safe with one layer cracked you don't want to risk the other layer being damaged. see British Airways Flight 5390 to know what happens if the windshield fails totally

[Edited 2013-04-07 21:46:33]
 
oly720man
Posts: 5755
Joined: Fri May 21, 2004 7:13 am

RE: AC761 Broken Window

Mon Apr 08, 2013 9:57 pm

The windows are most often going to fracture because of impact (birds/hail) or the window heating system causing problems. Pressure in itself won't cause problems. They don't break as such because they are multi-layered.

As far as the heating goes, the outside temperature can be below -60C and the windshield outer temperature can be raised to around 50C. Because of the nature of glass it can suffer thermal shocks and fracture if heated too quickly so the temperature control is important.

To see what a fractured front windscreen looks like


View Large View Medium
Click here for bigger photo!

Photo © Christian Frei



Read the remarks and comments below.

Report of another incident & details of the construction of the windows

http://www.fomento.gob.es/NR/rdonlyr...8D9A7/8170/2002_021_IN_english.PDF
wheat and dairy can screw up your brain
 
User avatar
tb727
Posts: 1767
Joined: Thu Jun 30, 2005 1:40 pm

RE: AC761 Broken Window

Wed Apr 10, 2013 3:54 am

Quoting nikeson13 (Thread starter):
How often do windows crack due to pressure/faults or a mix of both? Can it ever become dangerous?

I had one crack last month, the second in about a year. It's safe but I can tell you one thing for sure, my seatbelt is cinched down a little tighter until we land.
Too lazy to work, too scared to steal!
 
Tristarsteve
Posts: 3365
Joined: Tue Nov 22, 2005 11:04 pm

RE: AC761 Broken Window

Wed Apr 10, 2013 8:04 am

Quoting oly720man (Reply 2):
To see what a fractured front windscreen looks like

Depending on the window construction, some airliners can even operate safely with a cracked window.
On the B767, I had an aircraft arrive with a crazed window similar to the picture. The pilots greeted me by asking which hotel we used nowadays, and I got out the MEL and raised an ADD for the return flight. There were some checks to do, but the cracked glass stayed in.
On the Tristar, we used to completely remove the cracked outer layer, and then the aircraft continued in service.
This is not possible on many aircraft.
 
FighterPilot
Posts: 1306
Joined: Sat Jun 25, 2005 2:27 am

RE: AC761 Broken Window

Wed Apr 10, 2013 3:34 pm

Quoting tb727 (Reply 3):

The seatbelt probably wasn't the only thing clinched when the window originally cracked.

Cal   
*Insert Sound Of GE90 Spooling Up Here*
 
User avatar
tb727
Posts: 1767
Joined: Thu Jun 30, 2005 1:40 pm

RE: AC761 Broken Window

Wed Apr 10, 2013 7:18 pm

Quoting FighterPilot (Reply 5):
The seatbelt probably wasn't the only thing clinched when the window originally cracked.

Haha, yeah pretty much. It's always been on the opposite side from me and I still lean away. The time before this last one happened at night and the window heat was malfunctioning causing sparks and little lightning bolt looking arcs on the layer between the glass, it will get your attention. I've heard of a layer shattering all at once and it apparently makes a loud bang but I haven't had that happen.

Per our MEL we can go with the outer pane cracked unless it is in the line of site of the pilot for flying, which it was in the most recent case, so it was no go for me. It continued cracking little by little for a couple hours after we landed until we had a bunch of cracks all over the window instead of the original one.
Too lazy to work, too scared to steal!
 
Dufo
Posts: 796
Joined: Tue May 18, 1999 2:41 am

RE: AC761 Broken Window

Sat Apr 13, 2013 9:07 pm

Saab340 MMEL says:



We replaced some windows due to delamination and I experienced one cracked outer layer due to heater failure. Nothing dramatic.
I seriously think I just creamed my pants without any influence from any outside variables.
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: AC761 Broken Window

Wed Apr 17, 2013 8:35 am

Normally its a malfunctioning WHCU [Window heat contro, unit] or a damaged heating element in the windshield.
I may not win often, but I damn well never lose!!! ;)

Who is online

Users browsing this forum: Google [Bot], Starlionblue, zee73 and 8 guests