ERDC-CRREL is working with passive microwave radiometry in partnership with government, academia and industry to assess its potential for remotely detecting icing conditions ahead of aircraft along the flight track. Passive microwave systems are attractive because they are potentially smaller, lighter, less power-demanding, and less expensive than active technologies. However, microwave radiometry also does not provide direct ranging, works with only weak signals, and has historically been used principally for sensing to near-zenith or near-nadir. Our fundamental sensing technique is a dual wavelength system that differences the brightness temperature of space and clouds, with greater differences indicating nearer and higher liquid water content clouds. The RADiative TRANsfer model (RADTRAN), developed for assessing zenith and nadir radiometer applications, was enhanced to assess the flight track sensing concept, and a "flying" RADTRAN was additionally developed to simulate instrument responses from an inflight radiometer system flying through simulated clouds. Neural network techniques have additionally been developed to invert brightness temperatures to cloud liquid water content values. Most recently, a dual wavelength polarimeter system was built for flight testing that may discriminate large drops from cloud size drops. This paper reviews technology development to date and assesses current capability with regard to requirements.