AIRBORNE OBSERVATIONS OF ICE ACCRETION AND AIRCRAFT PERFORMANCE IN ARTIFICIAL AND NATURAL SUPERCOOLED ICE CLOUDS ON DORNIER 228- AND 328 AIRCRAFT

Results from two airborne experiments investigating aircraft icing, aircraft performance and cloud microphysics associated with supercooled large drops (SLD) are presented. Dornier-Luftfahrt performed in-flight tests, where external surfaces of a DO-328 turboprop aircraft were exposed to artificially generated SLD with 180 µm mean volume diameter (MVD). High liquid water content (LWC) up to 0.65 g m -3 caused substantial ice accretion behind boot-protected regions of the wings. Visual cues associated with SLD are described. Limitations for flights in severe icing conditions and exiting procedures have been derived. DLR performed several research flights within natural icing conditions on a Do-228 aircraft equipped with cloud microphysicaland icing documentation instrumentation. Specified weather-forecasts helped to find atmospheric regions that were characterized by at least moderate icing conditions and temporarily by the occurrence of SLD. Two cases with severe icing and ice accretion rates exceeding 3 mm min -1 , temporarily associated with SLD, have been met. SLD did not dominate, but significantly contributed to LWC during icing incidents. Back-running ice has been observed in the presence of SLDs. Heavy icing was experienced in stratiform clouds with embedded convection, average LWC below 0.3 g m -3 and within a -10 to -7 o C temperature interval.