(2)
As with delamination, the outer pane seal will help protect the radius against scratching during installation. Care in handling while the pane is out of the airplane is also of prime importance in reducing the amount of possible damage of any kind in the routed radius.
(3)
Again the scratches in the routed radius will be impossible to see, unless the window pane is removed. Thus, the same general criteria as were applied for crazing and delamination are repeated here. If scratches exceeding 0.005 inch in depth, regardless of length, are found, the window pane should be replaced. Undetected scratches approximating the foregoing are considered safe until overhaul or other reason for window removal.
(4)
Measurement of the depth of scratch can be made either approximately with the fingernail or accurately by using an optical micrometer. It can also be done by visual comparison with scratches of known depth.
(5)
The most likely place for scratches to be found is on the exterior surface of the pane which is exposed to weather and washing and the accompanying foreign bodies which inevitably get on that surface.
(6)
Scratches in exterior surface of outer pane, easily detected by visual examination, are critical if they exceed limits set out below. This surface of the pane is in tension under cabin pressurization load and severe scratches act as stress raisers. In certain cases exterior surface scratches can be hand polished or buffed out. For such procedures, refer to Door-Mounted Windows, Approved Repairs. Minor scratches 0.002 inch or less (barely felt with fingernail) are not critical and do not require polishing.
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Scratch Depth Max. Length One Scratch Max. Total Length
0.01 inch 0.50 inch 2.5 inches
0.005 inch 1.5 inches 4.0 inches
(7)
The center pane provides the fail-safe feature under cabin pressurization loads if the outer pane should fail. Therefore, scratches are critical in the center pane if they exceed the limits described in par. (6) above.
(8)
The inner pane, mounted in the cabin sidewall lining, is not structural. Only optical or visibility criteria apply for removal and replacement.
F. Chipping
(1)
No surface chips are allowed in the center pane. Small, shel1 shaped, edge chips no greater than 0.03 inch in the maximum dimension are permissible. V-shaped chips shall be cause for removal of the center window.
(2)
Criteria for allowed chipping in the outer window are given in par. D.(7).
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G. Windowpane Concavity
(1) Concavity, out of contour, windowpanes. The outer stretched acrylic pane bows inward. The middle cast acrylic panes bows outward. Concavity in its self is not a reason for window replacement, even if panes touch.
(a)
Extreme localized distortion and thickness variances.
1) Check for uneven surface contour and reduced optical quality. Exposure to high temperature such as photoflood lamp is cause.
(b)
Gentle uniform concavity.
1) Place straightedge across narrow width of outboard surface of outer pane. If gap exists between straightedge and center of pane, window is concave. Windows prone to fogging are prone to uniform concavity.
2) Windows can be returned close to their original contour by removing them from airplanes and drying them. This can be accomplished by leaving them exposed at room temperature. Drying time is depended on local humidity and how badly window is deformed.
NOTE: Windows generally do not return completely to original contour.
3) Check seals for leakage into window cavity between outer and middle pane.
4) Check window edges thoroughly for delamination per par. D.
5) Replace concave windows with leaking seals.
H. Examine Middle Pane for Warping and Deformation.
(1) Minor warping or deformation alone is not a cause for rejection unless pressure sealing is affected.
CAUTION: DO NOT PRESSURIZE AIRPLANE IF PRESSURE SEALING IS AFFECTED. PRESSURIZATION INTEGRITY OF FUSELAGE IS CRITICAL BECAUSE FAIL-SAFE FEATURE HAS BEEN ELIMINATED.
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ENTRY AND GALLEY SERVICE DOOR WINDOWS - APPROVED REPAIRS
1. General
A. Area of the entry and galley service windows most likely to get scratched is the exterior surface of the outer pane, at the fuselage skin line. The apparent depth of a scratch may be deceptive. This is due to a furrowing action which may cause a material buildup on each side of the crevice which is usually two to three times as high, from the acrylic surface, as the crevice is deep.
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