Characterization of Aircraft Icing Environments with Supercooled Large Drops for Application to Commercial Aircraft Certification

Observations of aircraft icing environments that included supercooled large drops (SLD) greater than 100 tun in diameter have been analyzed. The observations were collected by instrumented research aircraft from 134 flights during six field programs in three different geographic regions of North America. The research aircraft were specifically instrumented to accurately measure the microphysics characteristics of SLD conditions. In total 2444 SLD icing environments were observed at 3-km resolution. Each observation had an average liquid water content (LWC) > 0.005 g m(-3), drops > 100 mu m in diameter, ice crystal concentrations <1 L-1, and an average static temperature <= 0 degrees C. SLD conditions were observed approximately 5% of the inflight time. The SLD observations were segregated into four subsets, which included conditions with maximum drop sizes <500 mu m and >500 mu m in diameter, each with median drop volume diameters <40 mu m and >40 mu m. For each SLD subset, the observations were used to develop envelopes of maximum LWC values as a function of horizontal extent and temperature. In addition, characteristic drop size distributions were developed for each SLD subset. The maximum LWC values physically represent either the 99% or 99.9% LWC values, as determined from an extreme value analysis of the data. The analysis is sufficient for simulation of SLD environments with either numerical icing accretion models or wind-tunnel icing simulations. The SLD envelopes are similar in structure and supplemental to existing aircraft icing envelopes, the difference being that the existing envelopes did not explicitly incorporate SLD conditions.