Severe Super-cooled Drizzle Drops

March 24, 2011

John D. Marwitz

Hosted by Tristan L’Ecuyer

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he University of Wyoming instrumented the Wyoming King Air 200 in 1976. The aircraft instrumentation documents both the atmospheric environment and the response of the aircraft to this environment. This state-of-the-art cloud physics aircraft has been operated in support of various weather modification and in-flight icing projects. These projects involved the search for super cooled liquid water. From this body of data and experience a new concept of in-flight icing was developed. The performance degradation associated with roughness and shape of ice exceeds the performance degradation associated with mass of ice by an order on magnitude.

Five in-flight icing encounters were documented where the aircraft experienced a dramatic increase in drag and was forced to descend within five minutes. These five in-flight icing environments are labeled as Severe SCDD (super cooled drizzle drops). The mean LWC, 80VD and temperature for Severe SCDD is 0.5g/m3, 80µm, and -8°C, respectively. The range of values for these parameters is narrow. A physical explanation for the relevance of these parameters is discussed.

The FAA finally issued a Notice of Proposed Rule Making for FRZL and FRZR in response to the fatal Roselawn accident on 31 Oct 1994. FAA/FAR Appendix O for certifying future aircraft for flight in FRZL and FRZR is in substantial conflict with the above results. It is not clear how this conflict will be resolved.