The radio nebula W 50 harbours the relativistic binary system SS 433 , which is a source of the powerful wind and jets .
The origin of W 50 is wrapped in the interplay of the wind , supernova remnant and jets .
The evolution of the jets on the scales of the nebula is a Rosetta stone for its origin .

To disentangle the roles of these components , we study physical conditions of the jets propagation inside W 50 , and determine deceleration of the jets .

The morphology and parameters of the interior of W 50 are analyzed using the available observations of the eastern X-ray lobe , which traces the jet .

In order to estimate deceleration of this jet , we devised a simplistic model of the viscous interaction , via turbulence , of a jet with the ambient medium , which would fit mass entrainment from the ambient medium into the jets of the radio galaxy 3C 31 , the well studied case of continuously decelerating jets .

X-ray observations suggest that the eastern jet persists through W 50 as hollow one , and is recollimated to the opening \sim 30 ^ { \circ } .
From the thermal emission of the eastern X-ray lobe , we determine a pressure of P \sim 3 \cdot 10 ^ { -11 } erg/cm ^ { 3 } inside W 50 .
In the frame of a theory of the dynamics of radiative supernova remnants and stellar wind bubbles , this pressure in combination with other known parameters restricts W 50 ’ s origin to a supernova happened \sim 100 000 yr ago .
Also , this pressure in our entrainment model gives a deceleration of the jet by \sim 60 \% in the bounds of W 50 ’ s spherical component , of radius \sim 40 pc .
In this case , the age of the jet should be \ll 27 000 yr so as to satisfy the sphericity of W 50 .

The entrainment model comes to the viscous stress in a jet of a form \sigma = \alpha P , where the viscosity parameter \alpha is predefined by the model .