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Pilots need to be aware, under certain icing conditions, of the limitations of ice protection on their particular aircraft. FAA certification for flight into known icing does not ensure complete safety of flight in all icing encounters regardless of skills or aircraft capability. Too many accidents where icing was a contributing factor attest to these facts. Most of the time flight crews will not encounter an extremely severe condition. However, icing conditions are so widely variable that by chance they will encounter a condition in which they are unprepared. Many years of flight research in icing by the authors have provided the opportunity to experience and measure a wide range of icing conditions in which the performance losses and flying qualities of the aircraft were determined. These results are described in this paper.

The NASA Lewis Research Center is presently conducting an aircraft icing research program, the major thrust of which, is to advance technologies that improve our ability to model the icing phenomenon and its effect on aircraft. The approach employs three interrelated elements: analysis; wind tunnel experiments; and, considerable flight testing in natural icing clouds. This paper presents a brief overview of this program with emphasis on recent accomplishments.

During the NASA/FAA Tailplane Icing Program, pilot evaluations of aircraft flying qualities were conducted with various ice shapes attached to the horizontal tailplane of the NASA Twin Otter Icing Research Aircraft. Initially, only NASA pilots conducted these evaluations, assessing the differences in longitudinal flight characteristics between the baseline or clean aircraft, and the aircraft configured with an Ice Contaminated Tailplane (ICT). Longitudinal tests included Constant Airspeed Flap Transitions, Constant Airspeed Thrust Transitions, zero-G Pushovers, Repeat Elevator Doublets, and, Simulated Approach and Go-Around tasks. Later in the program, guest pilots from government and industry were invited to fly the NASAT win Otter configured with a single full-span artificial ice shape attached to the leading edge of the horizontal tailplane.