A model of major ejection events in Galactic superluminal sources GRO J 165
5-40 and GRS 1915-105 is proposed, in which episodes of e(-)e(+) pair creat
ion give rise to the formation of optically thick outflows accelerating pro
tons to the limiting Lorentz factor of order 2-3. Probable source of e(-)e(
+) pairs is pion production in nucleon collisions. Subsequent deceleration
of ejecta and formation of radio jets is analyzed in detail within a shock
deceleration model. The detailed data available for GRO J 1655-40 are shown
to be in good agreement with proposed scenario.