  We perform a numerical investigation of Anderson metal-insulator transition
(MIT) in a twodimensional system of chiral symmetry class AIII by combining
finite-size scaling, transport, density of states, and multifractality studies.
The results are in agreement with the sigma-model renormalization-group theory,
where MIT is driven by proliferation of vortices. We determine the phase
diagram and find an apparent non-universality of several parameters on the
critical line of MIT, which is consistent with the analytically predicted slow
renormalization towards the ultimate fixed point of the MIT. The
localization-length exponent $\nu$ is estimated as $\nu = 1.55 \pm 0.10$.
