  We propose a model explaining the origin of transient/episodic jets in
black-hole X-ray binaries, in which they are caused by transitions from a
collimated, strongly magnetized, jet to a wide, un-collimated, outflow. The
change occurs when the accretion flow leaves the magnetically-choked state due
to an increase of the accretion rate for a weakly varying magnetic flux. The
formed powerful jet then detaches from its base, and propagates as a discrete
ejection. The uncollimated outflow then produces a relativistic plasma that
fills surrounding of the black hole, contributing to the formation of a
low-density cavity. While the pressure in the cavity is in equilibrium with the
surrounding interstellar medium (ISM), its inertia is orders of magnitude lower
than that of the ISM. This implies that the plasma cannot efficiently
decelerate the ejecta, explaining most of the observations. The modest
deceleration within the cavities observed in some cases can be then due to the
presence of clouds and/or filaments, forming a wide transition zone between the
cavity and the ISM.
