EMERGENCY EXIT HATCH WINDOW - INSPECTION/CHECK
Emergency Exit Hatch Window Inspection
A. General
(1)
The optical qualities of windows are of prime importance. If window condition impairs visibility, replace the window.
(2)
During inspection of windows, if damage or normal deterioration of a component of the window installation exceeds limits described, remove window and replace component (Ref R/I).
B. Examine for the following:
(1)
Scratches, cracks and crazing of acrylic panes as described in par. C.
(2)
Deterioration of seals.
(3)
Marks, scratches and dents in plastic reveal.
(4)
Loose or missing fasteners at window retaining brackets.
C. Definitions of various types of damage are as follows:
(1)
Crazing: Series of very fine fissures usually 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 reflecting from smooth surfaces of fissures when viewed at varying angles to the incident light. 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.
(2)
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 chevron or clamshell growth lines (Fig. 601).
(3)
Scratch: The removal or displacement of material from surface of a pane along a line. The ratio of depth to width is usually quite small.
(4)
Chips:
(a)
Spall (Shell Type) Chips have circular or curved periphery with may fine hairlines or ridges that follow the outline of outer edge and degenerate toward the center of deepest point of chip, similar to a clamshell.
(b)
Vee shaped chips have sharp narrow V shape and appear to propagate toward the interior of plastic.
(5)
In-plane cracking (formerly identified as delamination): A smooth surfaced fissure, or series of fissures, parallel to panel 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.
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Window Surface Crack Development - Typical 500
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Page 602 Figure 601
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
D. Equipment and Materials
(1) Optical Micrometer - Model 966A1
Edwards Aerospace Company
1841 Business Pkwy
Ontario, CA 91761
Tel (714) 923-3533
Fax (714) 923-6781
E. Examine Windowpanes
(1) Examine windowpanes for cracks or crazing.
(a) Replace cracked or crazed middle panes.
CAUTION: DO NOT PRESSURIZE AIRPLANE WITH CRACKED OR CRAZED MIDDLE PANE. PRESSURIZATION INTEGRITY OF FUSELAGE WITH ONE PANE CRACKED IS CRITICAL BECAUSE FAIL-SAFE FEATURE HAS BEEN ELIMINATED.
NOTE: Middle pane may be repaired if minimum thickness after approved repair procedure is 0.165 inch (Ref Overhaul Manual).
(b)
Replace outer pane if depth of any single crack or craze equals or exceed 0.05 inch.
(c)
Replace outer pane if cracking or crazing is deep enough that pane thickness after rework will be less than 0.260 inch. Outer pane may be repaired if minimum thickness after Approved Repair Procedure is 0.260 inch.
NOTE: Cracks can develop in outer pane from scratches and/or crazing (Fig. 601).
(d)
Exact depth of crack or craze may be measure with an optical micrometer. To obtain correct measurement, multiply acrylic plastic index of refraction (1.49) by micrometer reading.
(e)
Any accurate method for determining crack depth is acceptable (Fig. 602).
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