(4)
Examine windows for scratches.
(a)
Scratches in the routed radius can have the same criteria applied as for crazing at the same place, except in the case of very severe scratches.
(b)
As with in-plane cracking, 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.
(c)
Again the scratches in the routed radius will be impossible to see, unless the windowpane is removed. Thus, the same general criteria as were applied for crazing and in-plane cracking are repeated here. If scratches exceeding 0.005 inch in depth, regardless of length, are found, the windowpane should be replaced. Undetected scratches approximating the foregoing are considered safe until overhaul or other reason for window removal.
(d)
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.
(e)
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.
(f)
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 Passenger Cabin Windows, Approved Repairs. Minor scratches
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0.002 inch or less (barely felt with fingernail) are not critical and do not require polishing.
Scratch Depth Max. Length One Scratch Max. Total Length
0.02 inch 1 inch 5 inches
0.01 inch 3 inches 9 inches
0.005 inch 4 inches 10 inches
(g)
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. (f) above.
(h)
The inner pane, mounted in the emergency exit hatch trim panel, is not structural. Only optical or visibility criteria apply for removal and replacement.
(5)
Examine windowpanes for chipping.
(a)
No surface chips are allowed in the center pane. Small, shell shaped, edge chips no greater than 0.06 inch in the maximum dimension are permissible. V-shaped chips shall be cause for removal of the center window.
(b)
Criteria for allowed chipping in the outer window are given in par. (3)(f).
(6)
Examine windowpanes for creep deformation.
(a)
Creep deformation is center pane damage created by window retainer against the edge of pane (Fig. 604).
(b)
Center pane creep deformation is permissible within the following limits: 1) Without discrete surface discontinuity, surface or edge is slightly displaced, but a fingernail cannot detect a discontinuity. No rework is necessary. 2) Discrete discontinuity, but no evidence of a vee notch crack. Window should be reworked (Ref Passenger Cabin Windows - Approved Repairs).
3) Discrete surface discontinuity and a vee notch crack less than 0.05 inch inward from edge of pane, window should also be reworked, or replaced, if crack is greater than 0.05 inch from edge.
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(7) Examine windowpanes for concavity.
(a) 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. 1) Extreme localized distortion and thickness variances.
a) Check for uneven surface contour and reduced optical quality. Exposure to high temperature such as photoflood lamp is cause. 2) Gentle uniform concavity.
a) 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.
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