Aircraft Escape Strategy from Supercooled Cloud Layers

Abstract

Vertical profiles of liquid water in supercooled frontal stratiform clouds have been studied in order to estimate the potential rate of ice accretion at different levels within the cloud and to develop recommendations for escape strategies to avoid severe in-flight icing. The vertical soundings of the supercooled liquid clouds were obtained using the National Research Council of Canada Convair-580 equipped by Environment Canada for cloud microphysical measurements. The data were collected during five flight campaigns (CFDE 1, CFDE 3, AIRS 1, AIRS 1.5 and AIRS 2). In total 584 vertical LWC profiles were analyzed. A statistical summary has been prepared from the profiles of the potential thickness of accreted ice, liquid water content, temperature, and cloud depths. The maximum potential accreted thickness of ice does not exceed 2cm for a transit with a 3 degree glide slope thoughout the cloud depth. Based on the statistics, in order to avoid severe icing once significant icing is encountered, it is suggested that a climb or descent should be initiated. The aircraft should not stay at the same altitude within the cloud layer. I. Introduction T is difficult for pilots to decide to climb, descend, or stay at the same level when encountering in-flight icing, especially in icing events associated with drizzle. During these periods the airplane may have to traverse one or several supercooled cloud layers and as a result experience in-flight icing. To estimate the potential consequences of in-flight icing, liquid water content (LWC) profiles in supercooled cloud layers associated with frontal systems were analyzed. The vertical distribution of liquid water and temperature inside supercooled clouds is important for estimation of icing severity during any traverse of such layers. The statistical characteristics of supercooled stratiform frontal clouds collected during five aircraft field campaigns are presented here. Effort was focused on an analysis of the statistics of cloud depths, vertical distribution of liquid water and temperature inside clouds, and the potential thickness of accreted ice. The results provide an overview of conditions that pilots may encounter in mid and high latitude winter clouds. Based on these results suggestions have been made to minimize in-flight icing and avoid severe icing during climb and descent.