Shubnikov de Haas resistance oscillations of highly mobile two dimensional helical electrons propagating on a conducting surface of strained HgTe 3D topological insulator are studied in magnetic fields B tilted by angle θ from the normal to the conducting layer. Strong decrease of oscillation amplitude A is observed with the tilt: [Formula: see text], where ξ is a constant. Evolution of the oscillations with temperature T shows that the parameter [Formula: see text] contains two terms: [Formula: see text]. The temperature independent term, [Formula: see text], signals possible reduction of electron mean free path [Formula: see text] and/or enhancement of in-homogeneous broadening of the oscillations in magnetic field B. The temperature dependent term, [Formula: see text], indicates increase of the reciprocal velocity of 2D helical electrons: [Formula: see text] suggesting modification of the electron spectrum in magnetic fields. Results are found in good agreement with proposed phenomenological model.