IMPORTANT NOTE: This is often mistaken, but is also specific to individual aircraft types also. Rain repellent is used in conjunction with windscreen wipers, but only ever in moderate or heavy rain. Wipers alone are not as effective as they need to be in heavy rain at high airspeeds, even if the window has a hydrophobic coating. Some aircraft types mention that wipers cannot be used after inadvertently spraying rain repellent fluid onto a dry window. This is because the smearing would reduce visibility significantly.

Windshield wipers are the most common rain protection feature. Windscreen wipers are operated separately for each pilot on each window with the switches located on the overhead panel. They are safe to use on a wet windscreen without any other features.

A rain repellent system permits application of the chemical repellent by a switch or push button in the cockpit. The proper amount of repellent is applied regardless of how long the switch is held. This system should only be used in very wet conditions. If applied on dry windows, the undiluted repellent restricts window visibility. It may be used in conjunction with the windshield wipers as, on its own, it is not always enough to clear all the water from the windshield (this can be type specific though).

• The important thing is to not apply rain repellent onto a dry windshield (it would create stains and obscure the view). Rain repellent liquid should be applied on a wet windshield (in moderate/heavy rain), and if it is inadvertently applied to a dry windshield, do NOT use the wipers to clear it, they will make the stain worse.

Pneumatic Moisture Clearance is not as complicated as it sounds. It is a jet of fast, hot air that is piped directly over the windscreen to clear any water that would usually stick to the surface. It is particularly good at clearing windscreens with a hydrophobic coating, but is not good in conjunction with windscreen wipers as they ruin the airflow and the air could damage the wipers.