What does the last number in the icing group format signify?

The last number in the icing group format is critical as it indicates the thickness of the icing layer. This information is essential for pilots and aviation personnel because knowing the thickness allows them to assess the potential impact of icing on aircraft performance and safety. Different thickness levels can lead to varying degrees of ice accumulation, which affects aircraft aerodynamics, weight, and engine performance. Thus, having this specific data helps in making informed decisions about flight planning and the necessary precautions to take when encountering icing conditions. Understanding the thickness is particularly vital for operational safety, as significant ice buildup can impede flight performance and increase the risk of accidents.