A microwave refractometer has been developed for use in a Type L‐20 ``Beaver'' single‐engine light aircraft. A two‐channel recording system is used providing simultaneous profile and turbulence records with rms noise levels of approximately 0.05 and 0.01Nunit, respectively. Power requirement is 25 amperes at 28 volts dc, and installation requires one‐half hour for two men. No structural modification of the aircraft is required. The results of flight tests are presented.