SBIR Phase I Project proposes a new passive microwave airborne sensor for in flight icing hazard detection, Microwave Radiometer for Aviation Safety. A feasibility study of a relatively inexpensive, small in size, robust, energy efficient instrument with reliable calibration, easy to use, and with minimal maintenance requirement is proposed. Extensive radiative transfer modeling will be carried out. The results of modeling will be used to optimize instrument design, parameters such as frequency of operation, individual channels polarizations, scene sampling strategy (scanning mode), antennae beamwidths, and potential use of auxiliary data will be evaluated. Phase I objective is a preliminary three dimensional model of the instrument.