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Extreme rain and hail conditions have caused engine rundowns during commercial airplane flights. In some cases, rain and hail conditions have caused all of the engines on the airplane to rundown simultaneously. This paper presents an analysis that quantifies the rain and hail threat in terms of the probability of encountering a storm of a given intensity for a given period of time. This analysis was used to establish recommended rain and hail concentration levels for design and certification of turbine engines.

The design and certification icing envelopes for ice protection systems do not consider potentially severe icing conditions associated with supercooled large droplets (SLD). Criteria for the SLD icing conditions have not been established. Since aircraft operate in freezing rain and freezing drizzle during the winter months, it is important that we recognize the supercooled large droplet (SLD)1 environment and analyze its impact on aircraft operation and performance. Currently no database exists on freezing rain and freezing drizzle to describe the operating environment in which the aircraft may be exposed. There is a present need to have a better understanding of freezing rain and freezing drizzle conditions. Drop-size distributions (DSD) in icing clouds are analyzed. These data were obtained during the Canadian Freezing Drizzle Experiments (CFDE) I and III over the St. John’s Newfoundland regions and the Great Lakes, respectively.