Which type of ice is the hardest to remove from the wings?

Clear ice is the hardest type of ice to remove from the wings. This type of ice forms when supercooled liquid water droplets freeze upon contact with the aircraft's surface, creating a dense and smooth layer of ice. As a result, clear ice adheres strongly to the wing surfaces, making it more challenging to remove compared to other types of ice. The smooth nature of clear ice also can disrupt the airflow over the wings, leading to a significant reduction in lift and an increase in drag, which can severely impact aircraft performance.

In contrast, hoar frost typically forms under specific conditions and is often not as difficult to remove since it is less dense and has a more granular texture. Rime ice, while it can also pose challenges, usually forms in colder environments and may be easier to remove due to its more brittle structure. Liquid ice, though not a common term in aviation, generally refers to the presence of water on the surface, which does not present the same removal challenges as frozen ice. Thus, clear ice's strong adhesion and solid structure make it the most challenging type to handle during pre-flight preparations.