View Full Version : CX A340 YVR-HKG Flies 10 Hours with cracked windscreen

22nd Jun 2008, 08:44
Reported by South China Morning Post, 20 June.

Pilots thought it was safe to fly after noticing the crack 2 hours out of YVR. Diverted to SEL. Pax offloaded and put on CX777 back to HKG.

Kinda interesting, I thought. Never had a cracked windscreen - and 10 hours is something else.

gilderoy lockhart
22nd Jun 2008, 09:08
What does the MEL say? Lots of layers in a windscreen!

22nd Jun 2008, 09:24
As aircraft was airborne, MEL irrelevant...

Open questions:
What does the abnormal or emergency checklist say?
What layer, outer/middle/inner was it?
Did they change flight level?

live 2 fly 2 live

Spanner Turner
22nd Jun 2008, 09:54
From a Boeing Manual, my highlighting;

(2) Flight adequacy of the windshield shall be determined by visual
inspection of the transparent components (elements) and weather
seals and by an operation check of the electrical anti-icing system.

(3) Removal of a windshield is only required for obvious reasons such
(a) Heat inoperable for reasons internal to the windshield.
(b) Structural glass ply contains cracks, chips, or shatters.
(c) Cracking or shattering of outer glass ply. Refer Dispatch
Deviation Guide for dispatch.
(d) Cracking of vinyl ply if vision is seriously impaired.
(e) Delamination of any plies if vision is unacceptably impaired.
(f) Objectionable pressure leaks.
(g) Vision seriously obscured for any reason.
NOTE: Removal for structural reasons is not expected.
If structural deterioration does occur, the obvious
removal reasons above will have occured well before the
assembly has become structurally unsafe.

point (c) above refers you to the DDG. The Boeings I work on allow for the removal of the outer 'Glass' layer. If it's cracked or 'spider-webbed' one of us engineers gets up there and chisels off the complete layer of glass which restores the visual quality of the windscreen and then you can fly home to replace the windscreen. This glass outer layer is not structural in any way and is utilised as it's very hard and resistant to abrasion from flying at 900kph and from the windscreen wipers dragging crap to and fro across the windscreen. Imagine a plastic windscreen on your car, it would look terrible after not too long. Bare in mind that some windows also utilise glass in the primary structure (although most use plastic/vynyl) but there are generally up to 4-5 layers so a crack in one doesn't affect the strength of the complete assembly.

In addition, below is from the inspection procedure for windows;

(3) Cracks:
(a) A crack is a fissure that has a visible width or depth.
(b) Cracks can start from a scrath or a crazing mark (Fig. 601).
(c) Cracks can be single or dual (Fig. 601).
(d) Cracks in glass will usually occur 90 degrees to the surface of
the pane.
(e) Cracks in stretched acrylic plastic will occur at
a 45 degree angle to the surface of the ply and can become
in - plane cracking.
(f) The cracks in an outer vinyl ply (the ply between the middle
structural ply and the outer ply) are caused by incorrect heat
(g) The cracks in the vinyl usually occur in the window corners and
are within the edges of the release tape.
NOTE: Vinyl cracks are not a problem structurally.
NOTE: Only replace the windshield if your vision is limited.


22nd Jun 2008, 09:55
If he flew 10hours then why didnt he just carry on to hong kong? why fly 8 hours and decide to divert?

22nd Jun 2008, 11:12
Our B777 Non-Normal Checklist says:
If forward window arcing, shattered, or cracked:

SWITCH (Affected window) . . . . . . . . . . . . . . . . . . . . . .OFF
[Removes electrical power to prevent arcing.]

Do not accomplish the following checklist:

If damaged window deforms, or air leak is observed:

Plan to land at the nearest suitable airport.

If airplane altitude above 10,000 feet:

Descend to lowest safe altitude or 10,000 feet,
whichever is higher.
[Minimizes forces on the window. Outward cabin pressure
differential counters inward dynamic air load on the window.]

Sustained flight below 10,000 feet is not recommended
due to greater risk of bird strike.

Old Fella
22nd Jun 2008, 11:41
Of course the SCMP account would have to be regarded as an authoritative report, I don't think!! Why don't you ask CX what the real nature of the event was? All this speculation based on a newspaper report is a waste of effort. :ugh::ugh::ugh:

22nd Jun 2008, 11:43
Airbus (A320) drill

In case of a one ply failure, whichever one it may be, the windshield is still able to sustain the maximum differential pressure. However, because the pilot is unable to accurately determine how many plies have failed, the differential pressure must be reduced to 5 PSI by applying the following procedure :

MAX FL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

The maximum flight level is restricted to FL230 to obtain DELTAP 5 PSI, without resulting in an excessive cabin altitude and corresponding EXCESS CAB ALT warning.
The following procedure, allows maintaining DELTAP 5 PSI in manual cabin pressure mode.
– CAB PRESS MODE SEL . . . . . . . . . . ...... . . . . . . . .. . . . . . . . . . . MAN
– MAN V/S CTL . . . . . . . . . . . . . .. . . . . ..... . . . . . . . . . . . . . .AS RQRD
Set the cabin altitude, according to the table below :
FL 100 - CABIN 0
FL 150 - CABIN 3000
FL 200 - CABIN 6000
FL 230 - CABIN 8000

•When starting the final descent :
– CAB PRESS MODE SEL. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .AUTO

22nd Jun 2008, 11:44
"If damaged window deforms, or air leak is observed:"

And this is the decider, if it is an outer window and all else is normal just switch the window heat off, (electrical) and the air supplied window demisting on.

22nd Jun 2008, 11:48
Dont think you can switch the window heat off on an A340!! Oh and the CBs are down below!!!!

Some time ago with the same aircraft type I was involved in observing an in flight return for a cracked windscreen.......lots of arcing and smoke on the outsde as it came on the bay!!!! Not recommended.....

22nd Jun 2008, 11:53
The heat makes the windshield flexible and able to withstand bird strikes. When its un heated a birdstrike might shatter it.

22nd Jun 2008, 12:00
A330/A340 QRH Drill.

-MAX FL......................230
-MAN V/S CTL..............AS RQRD (Delta P 5 PSI or lower)

When starting final descent:

22nd Jun 2008, 12:07
F4F - as the aircraft was airborne, the mel is inapplicable, but not irrelevant. Could still contain information that would be useful.

Dream Land
22nd Jun 2008, 12:13
Well let's see, the MEL is for dispatch, you planning to dispatch with a cracked windshield?

22nd Jun 2008, 12:43
Dreamer - what Caudillo is saying is that good airmanship says you look at the MEL if time permits.:ugh: You do, don't you?

CONF iture
22nd Jun 2008, 13:53
Dont think you can switch the window heat off on an A340!! Oh and the CBs are down below!!!!
Some time ago with the same aircraft type I was involved in observing an in flight return for a cracked windscreen.......lots of arcing and smoke on the outsde as it came on the bay!!!! Not recommended.....
Actually, they are not called CB but Computer Reset Button, there is one per side, and are located on the over head panel.

Regarding the Airbus procedure, if the problem is limited to a cracked windshield, there won't be any associated ECAM Message, pilots will go straight to the Quick Reference Handbook, then they can find more information in their FCOM 3, and it doesn't hurt if they open the MEL especially if they have 10 more hours to go.

The limitation is on the differential pressure, but there is no restriction to proceed to destination ... if fuel permits !

22nd Jun 2008, 15:00
True the MEL is irrelevant once Airborne.

22nd Jun 2008, 15:21
This thread is a wind up. :zzz:

22nd Jun 2008, 16:18
That is perfectly leagle depending of what is mentioned in the MEL and ofcourse depending of the magnitude of the crack etc, that will be determined by the engineers or in some cases with photon taken and sent to manufactor of the aircraft and they could potentionally make a release to service or release for ferry flight to homebase etc all depending of the situation. But ofcourse at most cases the release to service will be without windowheating and that could be the same as ground the aircraft depending of the weathercondition during flight since no known ice condition is allowed.
And in most cases also the max allowed spd of the aircraft will be affected. This procedure have been used many times to be able to get an aircraft back to homebase for window replacement if it is difficult to perform the repair at the outstation.
But at this specific event it happened in FLT and then it depends of what conditions are related to that aircraft and how serious of a crack the commander thinks it is and decides from there and what kind of weather is expecting during FLT and at destination.



22nd Jun 2008, 16:52
The old adage used to be "Outer pane! Outta trouble!"
250 kts restriction below 10k feet.
I once took a DC 8 outer MIDDLE pane down to NBO.
Got all the way down there and found that it was
the Capt's outer that was cracked.
Nice steady flight back after a night stop and a few

22nd Jun 2008, 16:57
Wild guess, seems handled as per the QRH ;) The Diversion to SEL required due to the low Cruise Alt, and gave nearly 10 hours for CX to get a 777 to SEL to meet the pax...


22nd Jun 2008, 17:02
We're on post 20 and everyone is talking as if the pilots were left on their own. Surely CX ops/engineering at HKG were in a position to advise. Were they not asked?

22nd Jun 2008, 21:20
We got to post 11 above before someone posted a relevant QRH... :ugh:

Armchair quarterbacks R us? :suspect:

22nd Jun 2008, 23:18
Continued flight perfectly reasonable if IAW QRH and manufacturers/company policy.

And yes, some windshields are tougher than others.
L1011 for example.
Cracks develop enroute...no restrictions whatsoever.
No lower flight level.
No lower speed.
Nada. Zip. None.

TriStar, built to a slightly higher standard.:}

22nd Jun 2008, 23:38
The heat makes the windshield flexible and able to withstand bird strikes. When its un heated a birdstrike might shatter it.
How many degress does it take to make glass flexable?

23rd Jun 2008, 01:22
The heat makes the windshield flexible and able to withstand bird strikes. When its un heated a birdstrike might shatter it.

How many degress does it take to make glass flexable?

Define flexible

23rd Jun 2008, 02:09
Just a brief comment on the use of MEL airborne:cool:

On my type/company it would be considered very prudent to consult the MEL and DDPG en-route. That is where you will find information on down grating of, P-RNAV, MNPS, RSVM, CAT II/III.
But who needs to know that anyway…:E

I.E.: What will an INOP windshield wiper do to you?… or in a similar case to above… is it any good on a window that has crap’ed out on you? :confused:
Can you or can’t you then consider it operational…?:confused:
On the B73/NG: no wiper means no CAT II/III…:(

23rd Jun 2008, 02:32
If we look back in time, to the piston/large turboprop era, we find that many aircraft had NESA installed, as pilots windshields.
This was a propriatory brand of glass/plexiglas 'sandwich', and needed to be heated to some degree, for bird protection.
The B707 used a different brand (not NESA) however, heat was still necessary.
No heat necessary, except for anti-icing.
However, do not make the mistake of leaving the heat off for takeoff, and then find out two hours into the cruise that...opps, we forgot...and switch the heat on.
The outside layer of tempered glass will crack, big time, at cold temperatures aloft.

23rd Jun 2008, 02:33
Define flexible

I don't have any idea.

Glass melts somewhere between 1400 and 1600 degrees C. So say it gets a little felxable around 1000 degrees C. At that temperature the actrylic an vinyl portions of the windshield would have melted.

The bottom line is that I don't really think windshields are heated to make the glass overlays flexable.

23rd Jun 2008, 07:24
Heating may well add some flexibility to the high-surface area interfaces at the boundaries from glass to plexi and back. Most of the change of behavior would be in the plastic layers and the bonding adhesives between plastic and glass. The overall rigidity of the glass would not be much affected, but the ability of the composite assembly to accept impact shock waves and dissipate them safely to successive layers and to the frame structure would be heightened.

Heating on the way up and down would also help relieve the inter-layer thermal stresses in the windshield panels. Fractures often result as release of the combined energy of impact plus stored internal stress.

Do not know this for certain, but it seems consistent with the behavior of the materials in the typical window sandwich.

Swedish Steve
23rd Jun 2008, 09:29
L1011 for example.
Cracks develop enroute...no restrictions whatsoever

And on the Tristar windscreen change is easy. being prepared after a reported cracked windscreen in DXB, we replaced the windscreen on the 60min transit at BAH without a delay!, and the seal is rubber so no curing time involved.
The bolts are on the outside and are all the same length, all you need is a platform to stand on, and the crew can get on with their work in the flight deck.

To change a B737 screen is about 10 hours work, then dry the sealant, and wonder what the little bracket is for you have in your pocket.

23rd Jun 2008, 10:22
if they flew happily across the pacific..why then divert at all? surely the same 'logic' would dictate they continue to hk?

23rd Jun 2008, 11:50

Maybe flying at FL230 rather than FL390 made for a slight difference in fuel endurance....?


23rd Jun 2008, 12:25
Have you ever tried to land without windscreen heat after descent from cruise? You better have a big cloth to wipe the condensation to be able to see where you are going,

23rd Jun 2008, 20:26
CONF iture
True....but they control the power to the processor in the associated computer...hence you can reboot a failed/stuck processor in a box.....The actual Circuit Breakers that control the real power to the affected system are below the flight deck......and its real power that powers the windshield heat and believe me when you see smoke and sparks coming from the top of the window its this one I would like to pull.....(along with Kylie Minogue!!).......

23rd Jun 2008, 21:35
Airbus seems to have an inordinate amount of windshield shattering. I have had two in one year on the A320 and know of 11 others in the same time period. Never experienced it on the DC-10 nor the B-727.

CONF iture
23rd Jun 2008, 23:59
It's ok with me if you're more comfortable to go and pull that CB, I remember a few years back some guys were still used to go and feed the dog once in a while airborne ...
but the "reset button....................PULL" is part of of the Airbus COCKPIT WINDSHIELD ARCING checklist.

Nevertheless I don't disagree on the KM case.

24th Jun 2008, 08:29
Springer1: Airbus seems to have an inordinate amount of windshield shattering. I have had two in one year on the A320 and know of 11 others in the same time period.

You may have been unlucky, I had none in 8 years on the type.