Which form of icing is considered the most hazardous and why?

The most hazardous form of icing is clear icing, primarily because it forms a thick layer on aircraft surfaces, significantly disrupting airflow and affecting aerodynamics. Clear icing, which appears as a smooth, transparent layer, can build up rapidly in conditions of high humidity and temperatures near the freezing point. This type of icing typically occurs when large supercooled water droplets freeze upon contact with the aircraft.

The severity of clear icing comes from its ability to create a heavy accumulation, which not only adds weight but can also alter critical flight surfaces like wings and control surfaces. This alteration can lead to increased drag, decreased lift, and ultimately pose a serious threat to aircraft performance and safety during flight. The rapid buildup in specific weather conditions makes it particularly dangerous, as pilots may not have adequate time to respond or take corrective measures.

While rime icing and mixed icing also pose risks, they generally do not accumulate as heavily or disrupt airflow to the same extent as clear icing, which is why clear icing is regarded as the most hazardous form. The notion of freezing rain, while it has its own dangers, does not directly pertain to the ice accumulation on aircraft surfaces in the same critical manner that clear icing does.