Window Crack Pane Determination
 

HI GENTLMEN

Do any of you know of a universally accecepted method to determine the cracked pane on a multiple pane window of a jet transport aircraft
to be used for the purpose of reducing cabin differential pressure when performing e.g the window failure checklist on a boeing aircraft

thank you for your inputs

In my experience a crack of any length = window replacement.

Also, if electrical arcing is observed within the window.

We do measure and monitor delamination according to limits defined by the manufacturer and/or type certificate holder. The limits depend upon type and manufacturer. In general, arcing occurs once delamination reaches the bus bars and a window should be replaced before any delamination reaches a bus bar. Thus the rate at which delamination is occurring is the limiting factor. Obviously any delamination in the direct line of vision would also be a good reason for replacement, but delamination generally occurs at the edges and progresses inwards.

We are talking about WHICH pane is broken, not whether to take off with a broken window.

If it is the inner pane, touching it will confirm this.

If it is the outer pane you may be able to tell looking at the edges or where the wipers touch.

Anyone have a better answer (to the question)?

Oh, and put your oxy mask on before dumping the cabin.

Oh, and don't dump the cabin if you don't have to. :)

Determining which pane is cracked
 

My company recently had a diversion for this reason, it turned out to be the outer pane though, the initial indication was a warning about the window heat failing (B777). :confused:

True: but its better to stop them cracking in the first place. Maintenance examine windows during hangar checks and often find windows with clear signs of arcing. Several pilots must have observed this happening - you can't miss it at night - but none reported it in the tech log...

Blacksheep- I can't believe you said that. You are infering that pilots saw arcing on their windscreens and didn't report it? Quite an accusation! Are you sure the arcing was visible, and didn't take place in a short burst during the day? You can bet your favourite spanner that any pilot that sees arcing in his plane will put it in his tech log, sure as eggs is eggs!

A loud 'CRACK' was heard ex-BOM one night.
Close examination determined that the LH forward pilots window had a significant crack, about 20 inches long.
In the L1011, no cabin pressure change is called for, nor desired.
These windows are really tough...and expensive, but last a long time.
These windows are curved, with quite good optical qualities.

Cost new...$68k.

Compare this with B707 windshields.
Cracks require a lower cabin pressure, and can develop significant deformation, which certainly gets your attention...darn quick.:uhoh:

Notso: Arcing begins with pinprick flashes around the bus bar. It isn't dramatic, but it should be noticeable and if reported in the early stages the window can be replaced before it is in danger of cracking. The maintenance schedule calls for inspection of the windows for signs of arcing and, yes, maintenance do find such signs. Often. It is a fact that most windscreen replacements are for delamination and/or evidence of arcing discovered during such maintenance checks.

Thank you all for some very informative replies to my question
also special thanks to HOWFLYTRG for his answer becuse it solves a problem for me should the need arise
crack in window's OUTER pane ..reduce cab diff...to 2psi
INNER pane.....................................5psi....etc


Again many thanks for all of you

Hello, sorry for bumping up such an old thread but I didn't want to make a new one.

In the 737 non normal checklist there's a condition called arcing. What exactly is meant by arcing?

Arcing means you will see small sparks on the heating element.

Thanks alot!

That center pane really does hold the bears share of the structural integrity of a windshield. On older aircraft (74C in my experience), the outer pane could be placed on MEL. The process was to hammer out the glass with a rubber mallet, I looked for it in the MMEL recently as the subject came up and the process is not there any more.

In many cases the outer pane is sacrificial, there to absorb bird strikes, impacts etc. Once determined as such and pressurization is normal, many Boeing check lists permit normal operation. Once on the ground there may be no relief to depart again and that is often the reason for cracked windshield diversions, manintainance and parts availability, not imminent doom!