It’s simple. You need a clean aircraft windshield for a clear view, especially when it comes to scanning for traffic. But, like many things in flying, there’s a right way, and a wrong way, to clean the windscreen.
Unlike car windshields, which have tough glass exteriors, your trainer airplane’s windscreen is made of acrylic, which means that it’s almost as easy to scratch the surface as it is to clean it. And a scratched windshield is both a hazard to flight and very expensive to replace.
As to cleaning fluid, surprisingly, the most popular is distilled water. Also perfectly appropriate are aero-grade acrylic cleaners. Avoid household glass cleaners—they contain ammonia, which can cloud the acrylic.
When using distilled water, dip a corner of the cloth in the water. Microfiber is slow to absorb water, so be patient. Once wet, slowly work the cloth back and forth across the windscreen using only top-to-bottom and bottom-to-top motions—never wipe in circles. You want to remove debris while minimizing the risk of scratching and ensuring that any scratch that does happen is a thin single line, not a rat’s-nest tangle. Once the surface looks good, use the dry part of the cloth and wipe off excess water to avoid spotting, using the same top-and-bottom motions.
If you use an aerospace cleaner, check the instructions. Most manufacturers recommend spraying the cleaner onto the cloth—much like the water method—rather than spraying the cleaner directly on the glass.
Of course, follow the policies of your flight school, but postflight is the most appropriate time to clean the windscreen. Bug “strikes” are the leading source of windscreen contamination, and these splats are much easier to clean when they are fresh. The longer they remain on the windshield, the harder they are to remove.
While it’s best to clean the exterior glass after every flight, the interior glass doesn’t need to be cleaned as often—only as needed to eliminate fingerprints or that weird gray “foggle-fog” that seems to attack all interior glass over time.