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Severe Super-cooled Drizzle Drops

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March 24, 2011
John D. Marwitz
Hosted by Tristan L’Ecuyer

Abstract

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.