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CX A340 YVR-HKG Flies 10 Hours with cracked windscreen
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. |
What does the MEL say? Lots of layers in a windscreen!
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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 |
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 as: (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 application. (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. :ok: |
If he flew 10hours then why didnt he just carry on to hong kong? why fly 8 hours and decide to divert?
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Our B777 Non-Normal Checklist says:
If forward window arcing, shattered, or cracked: FORWARD WINDOW HEAT SWITCH (Affected window) . . . . . . . . . . . . . . . . . . . . . .OFF [Removes electrical power to prevent arcing.] Do not accomplish the following checklist: WINDOW HEAT FWD 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. |
CX Cracked Windshield
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:
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Airbus (A320) drill
COCKPIT WINDSHIELD/WINDOW CRACKED 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 : DELTAP = 5 PSI 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 |
"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. |
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..... |
The heat makes the windshield flexible and able to withstand bird strikes. When its un heated a birdstrike might shatter it.
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A330/A340 QRH Drill.
-MAX FL......................230 -CAB PRESS MODE SEL...MAN -MAN V/S CTL..............AS RQRD (Delta P 5 PSI or lower) When starting final descent: -CAB PRESS MODE SEL...AUTO |
F4F - as the aircraft was airborne, the mel is inapplicable, but not irrelevant. Could still contain information that would be useful.
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Well let's see, the MEL is for dispatch, you planning to dispatch with a cracked windshield?
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Dreamer - what Caudillo is saying is that good airmanship says you look at the MEL if time permits.:ugh: You do, don't you?
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Originally Posted by spannersatKL
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..... 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 ! |
True the MEL is irrelevant once Airborne.
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Yawn.
This thread is a wind up. :zzz:
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dispatch with cracked window
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. Regards 1011 |
I'm cracking up!
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 Tuskers!:sad: |
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...
NoD |
A windup?
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?
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We got to post 11 above before someone posted a relevant QRH... :ugh:
Armchair quarterbacks R us? :suspect: |
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.:} |
The heat makes the windshield flexible and able to withstand bird strikes. When its un heated a birdstrike might shatter it. |
Quote:
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? |
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…:( |
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. TriStar. 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. |
Define flexible 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. |
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. |
L1011 for example. Cracks develop enroute...no restrictions whatsoever 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. |
duh
if they flew happily across the pacific..why then divert at all? surely the same 'logic' would dictate they continue to hk?
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Blunderbus
Maybe flying at FL230 rather than FL390 made for a slight difference in fuel endurance....? T'bug |
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,
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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!!)....... |
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.
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spannersatKL,
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. |
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. |
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