The study investigates the transport properties of the Dirac semimetal Cd$_3$As$_2$. Despite being predicted to be a Dirac semimetal, Cd$_3$As$_2$ exhibits ultrahigh mobility ($9 \times 10^6$ cm$^2$/Vs) at 5 K, attributed to a strong suppression of backscattering in zero magnetic field. This suppression results in a transport lifetime $10^4$ times longer than the quantum lifetime. The lifting of this protection by a magnetic field leads to a large magnetoresistance. The findings suggest that an unknown mechanism strongly protects carriers moving parallel to the crystal axis against backscattering, leading to the observed high mobility. The study also discusses the implications of these findings for the Fermi surface changes induced by the magnetic field.The study investigates the transport properties of the Dirac semimetal Cd$_3$As$_2$. Despite being predicted to be a Dirac semimetal, Cd$_3$As$_2$ exhibits ultrahigh mobility ($9 \times 10^6$ cm$^2$/Vs) at 5 K, attributed to a strong suppression of backscattering in zero magnetic field. This suppression results in a transport lifetime $10^4$ times longer than the quantum lifetime. The lifting of this protection by a magnetic field leads to a large magnetoresistance. The findings suggest that an unknown mechanism strongly protects carriers moving parallel to the crystal axis against backscattering, leading to the observed high mobility. The study also discusses the implications of these findings for the Fermi surface changes induced by the magnetic field.