Storm time Pc 5 wave events observed simultaneously by the GOES 2 and GOES 3 satellites in the afternoon sector during the 1-year interval March 1979 to February 1980 are surveyed to learn the wave propagation. Essentially, all storm time Pc 5 waves (~93%) are found to propagate westward azimuthally with a velocity of 5 to 10 km/s and a wavelength of 1000 km to 9000 km. (Only two to 30 events had eastward propagation with a velocity of about 150 km/s). We conclude that westward propagating waves are excited by ion drift instabilities associated with the ion ring current and that the eastward propagating waves are excited by surface waves on the magnetopause through Kelvin-Helmholtz instability.