Acrylic Windows - Life Limits, Inspections

[Wing Land and Spars]

Just curious, for those of you who work on pressurized aircraft that use single-ply acrylic windows, are they considered on condition, or life-limited?

(On our airframe they're life-limited, and also subject to inspection for contour and condition. Usually replacement due to contour.)

[Mr @ Spotty M]

I do not know of any window on a passenger a/c (Boeing/Airbus) that is life limited, they are all on condition items.
Most pax windows get a good look at on the bigger checks when they are removed, the inspection prior to re-fit is normally when you find they are not the same shape as when you fitted them the last time.

[Wing Land and Spars]

Hm, interesting. So are Boeing/Airbus windows single-ply or multi-ply?

[boeing_eng]

The use of the term "ply" is misleading.....

All commercial aircraft I have worked on have a window assembly comprised of a outer primary pane and a thinner inner (back-up) pane which both sit in the seal.

For Boeings the windows are on-condition and are usually either replaced for poor condition (scratches etc) or misting between the panes. Usually indicates a leaking seal or deformation of the inner pane.

Hope this helps

[Wing Land and Spars]

So on the heavy iron, they're on condition, and there are two panes that are part of the pressure vessel - thanks.

But, are the individual panes multi-ply, or single-ply?

All commercial aircraft I have worked on have a window assembly comprised of a outer primary pane and a thinner inner (back-up) pane which both sit in the seal.

For comparison, on our airframe, there is only one single pane (the outer pane) that is part of the pressure vessel. And that outer pane can be either single-ply or multi-ply acrylic. (The inner pane is not part of the pressure vessel and is strictly the protection-from-pax pane. Small turboprop.)

[boeing_eng]

In all Boeings the pax windows are moulded single ply acrylic.

The only time I've heard of multi-ply windows is for use in turboprops in areas adjacent to propellors (ice damage etc)

HTH

[glhcarl]

boeing eng,

All Boeing and every other manfactures, cabin windows have an outer and inner pane, either of which must maintain full cabin pressure.

Addtionally cabin windows are made from are made of "stretched acrylic" not "moulded acraylic".

[Wing Land and Spars]

So, to summarize ...

On the big jets, there are two pressure-vessel panes for redundancy, inner and outer. They're made of single-ply stretched acrylic (and if they're curved to fit the match the fuselage, I guess they could be called moulded, too). They're on condition, but there are two of them, so if one fails, the other other one still holds the pressure.

Turboprops are different.

Thanks, all - you've been helpful.

[rcav8r]

Hi guys,

Don't mean to hijack the thread, but why are acrylic panes used instead of say, polycarbonate? I've always thought polycarb had better material properties. Is it a cost issue?

[stankou]

Hi
I'm not 100% sure, but I guess it's a question of hazardous materials in the smoke in case of fire.

[Wing Land and Spars]

Acrylic vs Polycarb - actually, that's an interesting question (another would be why bother having pax windows at all ... ).

Like you suggest, I'd guess cost is a big factor. Acrylic is strong enough to do the job, so why spend more on polycarb. I think some military jets use polycarb.

As for fire safety, I've read that the breakdown products of acrylic are merely water and carbon dioxide, so maybe that's a factor too. I haven't done the home experiment ....

As far as mechanical properties go, the real question, I think, is how do acrylic and polycarb compare in repetitive loading [I don't know], and how do they fail.