E82676
500 Door Mounted Window Installation
Feb 01/95 Figure 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 56-31-0 Page 403
DOOR MOUNTED WINDOWS - INSPECTION/CHECK
1. Examine for the Following
A. Scratches, cracks and crazing of acrylic panes as described in par. 2.
B. Deterioration of seals.
C. Marks, scratches and dents in plastic reveal.
D. Loose or missing fasteners at window retaining brackets.
2. Window Replacement Criteria
A. In attempting to establish window replacement criteria for the normally expected defects as listed below it has been assumed that the optical or visibility criterion will be established by the individual operators.
B. Cracks
(1) A crack is a fissure perpendicular to the surface of the pane. No cracks are permitted in the outer and center panes since they are the primary structural and safety panes respectively. Pressurization of fuselage with one pane cracked is critical because the fail-safe feature has been eliminated in that there is now no alternate load path should the other pane crack. If the cracked pane cannot be replaced immediately the airplane must not be pressurized until such time as replacement can be effected.
C. Crazing
(1)
Crazing is defined as a series of small fissures perpendicular to the surface, but not extending all the way through the pane. There are no surface breaks visible with crazing and it is difficult to see unless the pane can be viewed from an angle so that light is reflected off the fissure surface.
CAUTION: CRAZING IN ANY CENTER PANE IS CAUSE FOR IMMEDIATE REMOVAL AND DESTRUCTION OF THE WINDOW. IF A NEW PANE CANNOT BE INSTALLED IMMEDIATELY, THE AIRPLANE MUST NOT BE PRESSURIZED UNTIL THE DEFECTIVE PANE HAS BEEN REPLACED.
(2)
Crazing, which is anticipated only in the outer pane, is usually the result of incorrect window installation, producing higher than acceptable stress levels, or the inadvertent application of one or more of the following materials: gasoline, alcohol, benzene, hexane, xylene, acetone, carbon tetrachloride, fire extinguisher fluids, lacquer thinners, and window cleaning or deicing fluids which have not been approved.
(3)
Surface crazing in the outer pane, other than at the routed edge, is permissible within the following limits:
(a)
0.060 inch maximum depth in local area not over 2 inches in diameter.
(b)
0.050 inch maximum depth over entire surface.
(4)
Determination of the exact depth of crazing is not easy, especially on an installed window, but the following method has been found to give a very close approximation. Hold a 6 inch metal scale normal to, and contacting, the surface of the pane where crazing is deepest. Viewing the reflection of the scale at about 45°, determine the apparent depth of craze. Double this apparent depth to get approximation of actual depth (Fig. 601). The apparent depth cannot be used because of the refractive qualities of the acrylic.
(5)
Routed Radius Crazing
500
Jun 20/87 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 56-31-0 Page 601
(a) Crazing in the radius of the routed edge (Fig. 602) of an outer pane is more serious than that in the overall surface. As the point of crazing moves around the radius towards the outside surface of the pane so the seriousness of the defect.
H30533
Method of Measuring Depth of Crazing 500
56-31-0 Figure 601 Jun 20/87
Page 602
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
decreases. This is due to a falling off in stress levels to the point where, at the intersection of the outside contour with the routed edge, there is very little stress.
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