Moisture Between the Windshields
Have you ever seen a waterline in between the inner and outer windshield panes of a Westwind? That is a result of sealant around the outer windshield becoming hard and brittle like concrete, with a tendency to crack, allowing moisture to seep down between the inner and outer windshields. The waterline forms from the rise of water between these panels, because it is filling up faster than it can drain out. It will eventually drain out through the desiccant bottles and then into the avionics bay (oh, boy!!) near the AC inverters via an elbow-style fitting mounted in the forward pressure bulkhead.
This can cause some very expensive damage if not repaired ASAP. Water can cause the heating network electrical terminals to corrode; corrosion causes electrical resistance to increase; and as resistance increases, so does heat at the point of resistance. It can get hot enough to melt and burn the inner windshield, which is made of a very tough plastic, where the electrical terminals pass through.
If the damage to the inner windshield does not exceed one inch in diameter, it can be repaired with a fiberglass-like plug, saving the owner/operator from having to replace it. If the damage is greater than one inch in diameter, the inner windshield will have to be replaced, which happens to be quite costly and very labor intensive.
Nitrogen can be used to purge moisture from the windshield, per Maintenance Manual 56-10-01. However, I have seen many outer windshields removed in order to clean off the waterline and remove corrosion on the electrical terminals and contact plates in an attempt to save the owner/operator a bunch of money in the long run.
Maintenance Tip:
When re-installing the outer windshield, you should take extra effort to keep the sealant flexible for as long as possible. After it cures, it is a good idea to paint the sealant between the outer windshield and aluminum frame with black polyurethane paint, in order to protect it from the sun’s harmful ultraviolet rays, which harden and, eventually, crack the sealant, allowing moisture in. The sealant on the outside of the frame should also be painted and color matched with the airframe to help protect it as well.
Thursday, May 28, 2009
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ReplyDeleteWhat a great tips here. That's one of my problem and now I know the solution. Keep up the good work. You can visit here also lakewood colorado windshield repair
ReplyDeleteOne other thing you should consider before you even get to this point of water between the winshield. If you find yourself changing the desicannt in the cockpit on both sides often that is a tell tale sign that you are getting moisture in the windshield system. A careful inspection of the outer windshield sealent would be in order and check for any cracking of the sealent. Unfortunately, over time the sealent will need to be replaced due to the fact the sealent over time does harden and crack over time no matter what you do. But another area that would need to be checked would be any leak in the desicant system from moist pressurized air getting in from the cabin via the window retainer screw holes or the plumbing for the desicant system. Just some more to think about and check.
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