Test data indicate that frost, ice or snow formations having a thickness and surface roughness similar to medium or coarse sandpaper, on the leading edge and upper surface of a wing, can reduce wing lift by as much as 30% and increase drag by 40%. Takeoff should not be attempted unless frost ice or snow contamination is not adhering to any aircraft critical surfaces. Critical surfaces of an aircraft means the wings, control surfaces, rotors, propellers, horizontal stabilizers, vertical stabilizers or any other stabilizing surface of an aircraft and, in the case of an aircraft that has rear-mounted engines, includes the upper surface of its fuselage.
In flight, there are three types of ice which pilots must contend with in
flight, Rime Ice, Clear Ice and Frost. For any ice to form the outside air
temperature (OAT) must be at or below freezing with the presence of visible
moisture. Rime ice commonly found in stratiform clouds is granular, opaque and
pebbly and adheres to the leading edges of antennas and windshields. Rime ice
forms in low temperatures with a low concentration of small super-cooled
droplets and has little tendency to spread. Clear ice commonly found in
cumuliform clouds is glassy, smooth and hard, and tends to spread back from the
area of impingement. Clear ice forms at temperatures at or just below 0°C with a
high concentration of large super-cooled droplets. It is the most serious form
of icing because it adheres firmly and is difficult to remove. Frost may form
on an aircraft in flight when descent is made from below-freezing conditions to
a layer of warm, moist air. In these circumstances, vision may be restricted as
frost forms on the windshield or canopy. Airframe icing can cause loss of lift,
loss of control, and poor visibility.
Whiteout is defined as an atmospheric optical phenomenon in which the observer appears to be engulfed in a uniformly white glow such that no shadows, horizon, nor clouds are discernible leading to a loss of depth perception and orientation. Whiteout occurs over an unbroken snow cover and beneath a uniformly overcast sky. Blowing snow may be an additional cause.