We report a fast tailward flow event on July 19, 1994, observed in the deep tail by the GEOTAIL spacecraft then located at 133 RE from the Earth. This event was associated with an isolated substorm and GEOTAIL continuously remained inside the plasma sheet during the 2.5 hours period following the substorm onset. Thus, this event provides the opportunity to analyze the substorm dynamics in deep-tail plasma sheet. Using magnetic field (MGF), electric field (EFD), plasma (LEP) and energetic particle (EPIC) data, we show that the fast tailward flow associated with the substorm expansion exhibited clear features: (i) the flow was quasi-stationary during its 2.5 hours long duration; (ii) its structure across the plasma sheet thickness showed two layers associated with two clearly distinct flow regimes. In the central plasma sheet, the plasma speed was roughly constant and uniform. Its value was close to the lobe Alfven velocity. The separation between the two layers precisely took place where the plasma parameter beta was close to one. ¿ 2000 American Geophysical Union