Statistically, the “classic” icing certification envelopes (14 CFR Part 25, Appendix C), do not cover the conditions encountered in at least 1 of every 100 icing encounters.
Icing decreases drag (CD), decreases lift (CL) and can cause loss of control.
Hot air systems may not fully evaporate all impinging water drops, resulting in runback ice.
Automatic flight control systems can mask the effects of ice accumulation.
Early detection of ice accumulation is critical to flight safety – even for airplanes with current icing protection systems.
Different airfoils have different accretion rates.
The accretion rates depend on airspeed, geometry, altitude, and angle of attack.
… such as LEWICE are usually used to calculate accretion rates (Wright, 1995).
They are also used to calculate the amount of ice accumulated in a given time interval.
Appendix C is based on data collected during 252 icing encounters by research airplanes in the 1940s (Lewis and Bergrum, 1952):
Appendix O is based on more recent data. It includes SLD, freezing drizzle, and freezing rain.