  An active region filament in the upper chromosphere is studied using
spectropolarimetric data in He I 10830 A from the GREGOR telescope. A
Milne-Eddingon based inversion of the Unno-Rachkovsky equations is used to
retrieve the velocity and the magnetic field vector of the region. The plasma
velocity reaches supersonic values closer to the feet of the filament barbs and
coexist with a slow velocity component. Such supersonic velocities result from
the acceleration of the plasma as it drains from the filament spine through the
barbs. The line-of-sight magnetic fields have strengths below 200 G in the
filament spine and in the filament barbs where fast downflows are located,
their strengths range between 100 - 700 G.
