Further ruminations on predicting icing severity

Icing severity is the effect of ice accreted during flight on the ability of that aircraft to fly. Thus, it is a function of the environment, the process of ice accreting onto the aircraft, and the aircraft's response to changes in airfoil shape and texture. Various regulations demand that icing forecasts include an estimation of the expected severity condition. In a very broad sense this has been done – the Aviation Weather Center provides AIRMETs defining moderate or greater conditions over specific areas, and the automated, supplementary Current and Forecast Icing Products include severity.

Obviously, a small single-engine airplane does not respond to an icing environment the same way a multi-engine jet does; there are disparities in capabilities of the aircraft that are not well-captured by the general severity descriptions these products provide. The ideal is an aircraft-specific severity index. This requires information for all three components of the problem: detailed size distributions of supercooled water drops (and perhaps ice crystals); full knowledge of the accretion physics and characteristics of the complete aircraft under all flight configurations; and an understanding of the response of that aircraft to the accreted ice. The current level of development , on the part of all three aspects, is a long way from that required to solve this problem. The problem and approaches to solutions will be discussed briefly.