To ensure optimal performance of rain repellant fluid, when should it be used?

• A. Periodically in light rain
• B. Periodically in heavy rain
• C. Only once before flight
• D. During maintenance cycles

Answer: (B)

Rain repellant fluid works by forming a hydrophobic layer on the windshield that helps water bead and shed more easily. That layer isn’t permanent; it wears away with time, exposure to wind and cleaning, and especially with wiper action. Because its effectiveness diminishes, you maintain good visibility by refreshing the coating periodically when heavy rain is present, when the water load on the windshield is greatest. Applying only once before flight can leave the coating degraded later in the flight, and doing it only during maintenance cycles doesn’t align with real-time weather needs. In light rain the benefit is less critical, but in heavy rain the improved visibility from a refreshed coating is most valuable, which is why periodic application during heavy rain is the best practice.