  We show that Dirac fermion systems in two dimensions generally exhibit
disorder-induced nodal arc replacing the nodal point and tilted Dirac cone,
provided that the two components of the Dirac fermion correspond to two
distinct orbitals unrelated by symmetry. This result is explicitly demonstrated
using renormalization group analysis in a disordered Dirac model that we
introduce, where the disorder potential acts differently on the two orbitals.
As we show by numerical simulations and self-consistent Born approximation
calculation, this drives the system into a new strongly disordered phase.
