We report experimental evidence of topological Dirac fermion charge carriers in pure and robust -Sn films grown on InSb substrates. This evidence was acquired using standard macroscopic four-point contact resistance measurements, conducted on uncapped films with a significantly reduced bulk mobility. We analyzed and compared electrical characteristics of the constituting components of the -Sn/InSb sample, and propose a three-band drift velocity model accordingly. A surface band, with low carrier density and high mobility, is identified as the origin of the observed Shubnikov -- de Haas oscillations. The analysis of these quantum oscillations results in a non-trivial value of the phase shift , characteristic for topologically protected Dirac fermions. For the same uncapped samples we estimate the momentum relaxation time , which is significantly larger in comparison with the previous reports on grown -Sn films.