WINDOW NO. 3 - INSPECTION/CHECK
1. General
A. The optical qualities of any window are of prime importance. Any window whose condition impairs visibility requires replacement.
(1) Definitions of various types of damage are as follows:
(a)
Crazing: Series of very fine fissures perpendicular to surface of plastic. Due to extremely narrow width of fissures, crazing is very difficult to detect when viewed normal to surface. It can be seen by reflection from smooth surfaces of fissures when viewed at varying angles to the incident light.
(b)
Crack: A fissure which has visible width when viewed parallel to the faces of the fissure. A crack may propagate at any angle to surface of a plastic pane depending on direction of the driving force. Cracks in stretched acrylic may have a chevron or clamshell growth lines (Fig. 601). A crack will propagate from a stress riser such as a scratch or craze.
(c)
Scratch: The removal or displacement of material from the surface of a pane along a line. The ratio of depth to width is usually quite small.
(d)
Chips:
1) Spall (shell type) chips have circular or curved periphery with many fine hairlines or ridges that follow the outline of outer edge and degenerate toward the center or deepest point of chip, similar to a clamshell.
2) Vee shaped chips have sharp narrow "V" shape and appear to propagate toward the interior of plastic.
(e)
Delamination also identified as in-plane cracking: A smooth surfaced fissure, or series of fissures, parallel to pane surfaces. In-plane cracking can occur in stretched acrylic and starts at edges of pane or at deep penetrations of the surface. It is most readily detected by the reflection of light from the smooth surfaces of the fissure.
(f)
Crackling: A series of cracks in the urethane layer that propagate around the window circumference adjacent to the frame toward the center of the window. These cracks may be accompanied by a slight yellowing or blurring of vision while looking through this area of the window (Fig. 603).
2. Materials and Equipment
A. Optical Micrometer - Model 966A1
Edwards Aerospace Company
1841 Business Pkwy
Ontario, CA 91761
Telephone (714) 923-3533
Fax (714) 923-6781
500
Jun 20/93 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 56-11-21 Page 601
H26910 G42757
Window Surface Crack Development - Typical
(Outer Pane Stretched Acrylic) 500
56-11-21 Figure 601 Jun 20/84
Page 602
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
500 Limits - Acylic Edge Cracking
Jun 20/89 Figure 602 56-11-21
Page 603
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
3. Examine The No. 3 Window (Fig. 601)
A. Examine the window for cracks on the inner or outer panes.
NOTE: Cracks which occur between the bolt and the window edge are permitted.
(1)
If you see cracks on the two panes, do not pressurize the airplane until you repair or replace the window.
(2)
If you see cracks on only one of the two panes, you can pressurize the airplane before you replace the window.
B. Visually examine the outer pane opposite the vent hole in the top forward corner of the inner pane.
NOTE: Stains at this location show that the outer pane does not hold pressure. Replace the window (Ref 56-11-21/401).
C. Examine and replace the No. 3 window if you find these conditions:
(1) Scratches:
(a)
Scratches on outer stretched acrylic panes if the following limits are exceeded:
(b)
Minor scratches 0.001 or less (barely felt with fingernail) are not critical and do not require polishing.
(c)
Scratches may be polished out. For procedure refer to Approved Repairs. Polishing panes to less than the following indicated thickness is not permitted.
(d)
Scratches on inner pane are not allowed if they exceed 0.005 inch deep, 1 inch maximum length of any one scratch, or 5 inches maximum total length of all scratches.
Scratch Max Length of Max Cumulative
Depth Each Scratch Length of All
(in.) (in.) Scratches (in.)
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