During the METAL campaign conducted at And¿ya Rocket Range in September--October 1991, detailed in situ measurements were performed by means of plasma probes in the TURBO rocket payload. During one of the salvoes (30 September 1991), strong plasma density fluctuations were detected above 78 km, especially on downleg. The results are shown to be in good agreement with the new instability predicted from the kinetic theory of Dimant and Sudan (1995). The new instability leads to the excitation of long wavelength plasma waves along the bisector between the drift velocity Vd and the electric field E. ¿ American Geophysical Union 1996