Window Repair Basics: A clear view of window maintenance requirements

Window Repair Basics A clear view of window maintenance requirements July 1999 Aircraft windows are typically a low maintenance item, as long as they remain clear and scratch-free. There's little that needs to be done to keep them airworthy...

"As a mechanic, you need to look at the windows, not through them," he stresses. "To inspect properly, we recommend at least a 500 candle power light and shine it at the window at every direction; up, down, sideways, forward, upside-down, etc., to try to get any cracks or damage to reflect back at you."

Ultrasonic equipment is also a necessary part of the inspection of any window. You should ultrasound the window before making any repairs to verify that there is enough material to make the repair. Then, inspect after any repairs to make sure the windows are above minimum thickness.

One word of caution related to ultrasonics, however. The density of the material used in the window will affect the reading you get on the ultrasonic equipment. So, you have to know what you're doing and make sure that your equipment is calibrated according to data from the manufacturer.

According to Cupery, "You have to compensate for the type of material you're working on to interpret what actual thickness you have. There are standards available to check your equipment and you have to use the correct standards or you can get bad readings. So, you not only need an ultrasound machine, you need to have data and the correct standard for the material you're working on. If you don't, you may be .030 below minimums and think that you are within limits. Or, you may unnecessarily reject an entire set of windows because you think windows are beyond limits, when they are actually still serviceable.

Types of damage
Probably the most common reason for removing windows from service is crazing. Crazing is "micro-cracking" that occurs at or just beneath the surface of the acrylic. Typically, crazing can be seen but not felt. Stress, UV degradation, airborne volcanic acids, or chemical damage may cause it. Crazing, if not addressed, can not only lead to window failure; it can also lead to cloudiness or deterioration of clarity. Suffice it to say that it is not just a cosmetic problem.

And, it should not only be a concern on outer window panels. According to Cupery, "Although many recognize crazing of outer panels as being dangerous, they don't take crazing or damage of the inner panel passenger windows seriously. Yet, we have seen time and time again where the outer panel failed and the inner panel prevented total failure of the window. Although the inner panel may not seem significant to many, it is critical that it be well-maintained as it is a crucial backup in the event of an outer panel failure."

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