Which types of fluids are approved for use on aircraft?

Type I and Type IV fluids are approved for use on aircraft primarily due to their specific properties that allow them to effectively remove ice and snow while providing anti-icing capabilities.

Type I fluid is heated and used during de-icing to melt existing ice or snow. It is typically an orange-colored, glycol-based fluid that ensures surfaces are clear before flight. However, it does not provide long-lasting protection against ice accumulation.

Type IV fluid is designed for anti-icing and is often used after Type I fluid has cleared the surfaces. It has a thicker viscosity and is typically green in color. This fluid provides a protective layer that prevents ice from forming during taxi and take-off, making it particularly useful in conditions where aircraft might be exposed to freezing temperatures and moisture.

The combination of these two types forms a comprehensive de-icing and anti-icing solution, ensuring the aircraft remains safe for operation in icy conditions. This is why the approval of both Type I and Type IV fluids is critical in aviation safety protocols.