What type of ice is formed over aircraft surfaces due to freezing moisture?

The correct answer is identified as instrument ice, which occurs when moisture freezes on the sensitive surfaces of aircraft instruments, potentially impacting their function. This type of ice formation is particularly problematic because it can lead to malfunctions or misreadings in critical gauge systems that pilots rely on for safe operation.

Instrument ice forms when supercooled water droplets, which are prevalent in certain weather conditions, come into contact with the colder surfaces of the aircraft. The immediate freezing of this moisture creates ice deposits that can obscure instruments or sensors, violating the stability and accuracy required for optimal aircraft performance.

The other types listed—clear ice, mixed ice, and rime ice—have distinct characteristics and effects. Clear ice grows on surfaces smoothly and is notably heavy; mixed ice combines elements of both rime and clear ice, resulting in a complex formation; while rime ice forms from rapid freezing of supercooled droplets, creating a more opaque and brittle layer. Each type of ice has different implications for flight safety, but instrument ice specifically targets the functionality of aircraft instruments, emphasizing its critical role in aviation.