Conditions for ice accretion (050.09.01.01)
Summarize the general conditions under which ice accretion occurs on aircraft (temperatures of outside air; temperature of the airframe; presence of supercooled water in clouds, fog, rain and drizzle; possibility of sublimation) (050.09.01.01.01).
Explain the general weather conditions under which ice accretion occurs in a venturi carburetor (050.09.01.01.02).
Explain the general weather conditions under which ice accretion occurs on airframe (050.09.01.01.03).
Explain the formation of supercooled water in clouds, rain and drizzle. (Refer to Subject 050 03 02 01) (050.09.01.01.04).
Explain qualitatively the relationship between the air temperature and the amount of supercooled water (050.09.01.01.05).
Explain qualitatively the relationship between the type of cloud and the size and number of the droplets in cumuliform and stratiform clouds (050.09.01.01.06).
Indicate in which circumstances ice can form on an aircraft on the ground: air temperature, humidity, precipitation (050.09.01.01.07).
Explain in which circumstances ice can form on an aircraft in flight: inside clouds, in precipitation, and outside clouds and precipitation (050.09.01.01.08).
Explain the influence of fuel temperature, radiative cooling of the aircraft surface and temperature of the aircraft surface (e.g. from previous flight) on ice formation (050.09.01.01.09).
Describe the different factors that influence the intensity of icing: air temperature, amount of supercooled water in a cloud or in precipitation, amount of ice crystals in the air, speed of the aircraft, shape (thickness) of the airframe parts (wings, antennas, etc.) (050.09.01.01.10).
Explain the effects of topography on icing (050.09.01.01.11).
Explain the higher concentration of water drops in stratiform orographic clouds (050.09.01.01.12).
Types of ice accretion (050.09.01.02)
Clear ice
Define ‘clear ice’ (050.09.01.02.01).
Icing that occurs slowly when large droplets of supercooled liquid droplets run back over the airframe at temperatures just below 0°C (0°C to -15°C) is called clear ice.
Describe the conditions for the formation of clear ice (050.09.01.02.02).
Explain the formation of the structure of clear ice with the release of latent heat during the freezing process (050.09.01.02.03).
Describe the aspects of clear ice: appearance, weight, solidity (050.09.01.02.04).
Due to the release of latent heat during the freezing process, the unfrozen portion of the droplet stays liquid longer. The water can flow and spread over the surface and freezes gradually from the cold surface outward. This slow, progressive freezing allows the ice to grow in compact, orderly way, without trapping much air. The result is a dense, smooth and transparent or layer of ice, which is heavy and difficult to remove.
Rime ice
Define ‘rime ice’ (050.09.01.02.05),
Ice that is formed when small (supercooled) droplets instantaneously freeze on direct impact with the airframe, is called rime ice. Supercooled liquid water droplets are in an unstable state and have the tendency to revert to its stable state – ice – when it becomes contaminated with nuclei or suffers from any physical shock like hitting the leading edges of an airframe.
Describe the conditions for the formation of rime ice (050.09.01.02.06).
In order for supercooled droplets to instantaneously freeze on direct impact, their size must be small enough and their temperature must be low enough to compensate for the latent heat released when reverting from liquid to ice.
As by rule of thumb, only 1/80st of a supercooled liquid drop freezes on impact, temperatures must be as low as -10°C to -20°C to have any substantial rime ice accumulate.
Describe the aspects of rime ice: appearance, weight, solidity (050.09.01.02.07).
As the droplets freeze on direct impact, they will trap tiny pockets of air. The air gives the ice a white look and makes it crunchy and easily broken.