(2)
Apply wax directly to acrylic surface or to flannel polishing cloth and spread a thin coat evenly and thoroughly over the surface.
(3)
Remove excess wax with flannel cloth.
(4)
Polish to a high luster by light polishing with a clean flannel cloth. Polishing may be done before or after wax has dried.
(5)
Remove any streaks or fingerprints from waxed acrylic surfaces by lightly polishing with a clean flannel cloth. If appearance is still unsatisfactory, reapply wax in accordance with above procedure.
4. Damage Criteria
A. A delamination is the separation of a glass pane from the vinyl core. It is sometimes difficult to detect unless viewed at an angle with indirect light. The delaminated area is usually smooth in appearance, although visual distortion may occur along the perimeter. Delamination occurs most frequently around the edges of the windows, and in the unheated areas. Care should be taken not to confuse a delamination with the edge of the parting medium, slip panes, or soft vinyl layers which are sandwiched between the inner glass pane and the vinyl core around the periphery of each window.
NOTE: Delaminations on the glass windows do not affect the structural integrity of the window assembly.
B. Chips are flakes or layers of glass broken from the surface (Fig. 201). They usually occur on the laminated surfaces in the unheated areas and are caused by high internal window stresses. They can also occur on the exterior glass surfaces if these are struck by a sharp object. Chips have a rough or grained appearance and are readily detectable. The rough surface usually makes visibility through the area very poor. There are two types of chips: conchoidal and V-shaped. Concoidal chips are usually circular or curved in shape with many fine striations that follow the outline of the outer edge, rather similar to a clamshell. V-shaped chips have a sharp narrow V-shaped which appears to propogate toward the interior of the glass. These chips occur only rarely in tempered glass.
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C. Small bubbles within the vinyl core of a glass window are not a delamination nor are they structurally dangerous. They are formed by a gas liberated by the vinyl under overheat conditions (at approximately 230 degrees Fahrenheit) and need not be a cause of window replacement unless they excessively impair the optical qualities or they continue to grow. Their presence, however, may indicate a defective window heat control system and before heat is applied, the control system for that particular window should be checked. Refer to Chapter 30, Control Cabin Window Anti-Icing System.
CAUTION: IF BUBBLES CONTINUE TO GROW, OPEN APPLICABLE WINDOW HEAT CIRCUIT BREAKERS LOCATED ON P6 CIRCUIT BREAKER PANEL UNTIL CAUSE OF TROUBLE CAN BE REMEDIED.
D. The inner glass pane is the major structural component of each window. Since the glass is fully tempered both surfaces are under compression, and scratches or chips on either surface will cause stress concentrations, which may cause window failure if the scratches or chips are excessively deep. Conchoidal chips are permitted on these panes within the limits specified. A V-shaped chip is likely to propagate and is definite cause for window replacement.
E. Glass windows are structurally unpredictable. One that appears in good condition may fail unexpectedly, while one that has scratches, chips or delaminations may endure for along time before failure. This makes it difficult to establish rules for window replacement, and each window should be considered individually. Operational experience, however, supports the criteria, and these may be used as a guide in determining the necessity for window replacement.
F. Arcing is the visible passage of current between two points of circuit discontinuity. Arcing usually occurs at or near window bus bars, painted stripes or conductive material along the top and bottom interior of each window. Brown and/or black burned spots are evidence that arcing has occurred. Confirmed existence of arcing in the main heating system is cause for window replacement because it will often lead to cracking of the outer pane. However, if the windshield warms when heat is turned on and there is no additional arcing or decrease in the visual capacity, the windshield does not have to be replaced immediately provided all other inspection criteria are met. Also, the main heating system may be inoperative if the requirements of the Boeing 737 Flight Manual are met. On windshields with embedded wires some arcing may occur. This usually appears as an intermittent glow, but may not be visible in daylight. This arcing is caused by a break in the wire and forms a small bubble (approximately 0.03 inch in diameter) in the vinyl interlayer. These windshields may be left in normal service as long as the arcing is not too distracting to the flight crew and all other inspection criteria are met.
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