A prototype fast RICH detector with a CsI photocathode coupled to a wire chamber filled with atmospheric pressure ethane has been studied in a 3.5 GeV/c π− beam. Using a 1 cm thick C6F14 radiator, 8.5 photoelectrons per ring were detected. Measurements were made of the CsI quantum efficiency, photoelectron position resolution, and Cherenkov ring radius resolution. UV photon feedback appears to have degraded the resolution of the detector. Techniques to improve the photon detection efficiency and reduce backgrounds are discussed.