Which type of structural icing is considered the most dangerous?

Clear icing is considered the most dangerous type of structural icing due to its specific characteristics and the risks it poses to aircraft performance. This type of icing forms when supercooled water droplets encounter a surface that is below freezing temperature and freeze on impact, creating a transparent layer of ice. This clear ice can accumulate rapidly and tends to adhere strongly to the aircraft's surfaces, leading to significant aerodynamic drag and weight increase.

The smooth and clear nature of this icing can create a deceptive appearance, making it difficult for pilots to detect until it has built up significantly. Additionally, clear ice can severely disrupt airflow over wings and control surfaces, leading to dangerous conditions such as stall or loss of control. These factors contribute to why it is often seen as the most hazardous type of icing that pilots need to be particularly vigilant about.

In contrast, other icing types, such as rime ice, generally have a rougher texture and can be less dangerous due to their easier removal when encountering warmer conditions. Mixed ice has characteristics of both clear and rime, making it variable and thus somewhat less predictable than clear ice. Thin icing, while still a concern, doesn't generally pose the same level of significant threat as clear ice.