for essentially the same type of ice accretion. This type of  ice is denser, harder, and sometimes more transparent than  rime ice. With larger accretions, clear ice may form “horns.”  [Figure 4-18]  Temperatures close to the freezing point, large  amounts of liquid water, high aircraft velocities, and large  droplets are conducive to the formation of clear ice. A rough, milky, opaque ice formed by the instantaneous or  very rapid freezing of super cooled droplets as they strike  the aircraft is known as rime ice.  [Figure 4-19]  The rapid  freezing results in the formation of air pockets in the ice,  giving it an opaque appearance and making it porous and  brittle. For larger accretions, rime ice may form a streamlined  extension of the wing. Low temperatures, lesser amounts of  liquid water, low velocities, and small droplets are conducive  to the formation of rime ice. Mixed ice is a combination of clear and rime ice formed on  the same surface. It is the shape and roughness of the ice  that is most important from an aerodynamic point of view. The most hazardous aspect of structural icing is its aerodynamic  effects.  [Figure 4-20]  Ice alters the shape of an airfoil, reducing  the maximum coefficient of lift and AOA at which the aircraft  stalls. Note that at very low AOAs, there may be little or no  effect of the ice on the coefficient of lift. Therefore, when  cruising at a low AOA, ice on the wing may have little effect  on the lift. However, note that the ice significantly reduces  the C$_{L-MAX}$, and the AOA at which it occurs (the stall angle)  is much lower. Thus, when slowing down and increasing the  AOA for approach, the pilot may find that ice on the wing,  which had little effect on lift in cruise now, causes stall to  Figure 4-18.  Clear ice buildup with horns. Figure 4-19.  Rime ice. Mixed Ice General Effects of Icing on Airfoils Rime Ice C L (coefficient of lift)  Angle of Attack  Clean airfoil Airfoil with ice C D (coefficient of drag)  Angle of Attack  Clean airfoil Airfoil with ice Figure 4-20.  Aerodynamic effects of icing. 4-14