  The Navier-Stokes equations, are understood as the result of the low-order
expansion in powers of dimensionless rate of strain $\eta_{ij}=\tau_{0}S_{ij}$,
where $\tau_{0}$ is the microscopic relaxation time of a close-to-
thermodynamic equilibrium fluid. In strongly sheared non-equilibrium fluids
where $|\eta_{ij}|\geq 1$, the hydrodynamic description breaks down.
  According to Bogolubov's conjecture, strongly non-equlibrium systems are
characterized by an hierarchy of relaxation times corresponding to various
stages of the relaxation process. A "hydro-kinetic" equation with the
relaxation time involving both molecular and hydrodynamic components proposed
in this paper, reflects qualitative aspects of Bogolubov's hierarchy. It is
shown that, applied to wall flows, this equation leads to qualitatively correct
results in an extremely wide range of parameter $\eta$-variation. Among other
features, it predicts the onset of slip velocity at the wall as an instability
of the corresponding hydrodynamic approximation.
