An analytical study on the freezing and sticking phenomena of slush on the horizontal tail surfaces of YS-11 a twin turboprop transport, in the ground taxiing and the succeeding takeoff run phase was conducted. A simple analytical model describing outflows of heat from slush to the surrounding airflow through the boundary layer, both conductive and accompanied by evaporation, was proposed. Influences upon the heat transfer rate caused by meteorological and operational conditions, were evaluated. Under an illustrative climatic condition experienced in airline operations in winter seasons in Japan, outflows of heat enough to stick the elevators were predicted.One of the large operators of YS-11s, Japan Air System Co., Ltd. (JAS) which had been worried about the related problems, took measures to enhance safety operation and introduced the type II ADS (Aircraft De-icing Solution) with two steps treatment. The operational experiences and test results, knowledges collected by pilots interviews at the introduction of the type II ADS, column force data and pilot comments under wide variety of conditions are described.