Which type of icing is the maximum permissible according to the operational limits?

Light rime icing is considered the maximum permissible type of icing according to operational limits. This classification of icing occurs when supercooled water droplets freeze upon contact with a surface, forming small, opaque ice formations. The ice is generally soft and can usually be removed by de-icing systems or procedures, making it more manageable for aircraft operations compared to heavier types of icing.

The reason light rime icing is permissible is based on its relatively low accumulation rate and the fact that it does not significantly impact aircraft performance when appropriate precautions are taken. Pilots and operators can continue safe flight operations even when encountering light rime icing, as it is less likely to disrupt control or altitude than heavier icing types.

In contrast, heavy rime icing, clear ice, and mixed icing present greater risks and operational challenges. These types are more dangerous due to their thickness and the difficulty of removal, leading to more severe aerodynamic degradation, changes in aircraft weight and balance, and potential for ice-related incidents. Therefore, maintaining operations in conditions that include light rime icing is within safety margins, while the other options exceed those safe operational limits.