  We study the effect of electrostatic disorder on the conductivity of a
three-dimensional antiferromagnetic insulator (a stack of quantum anomalous
Hall layers with staggered magnetization). The phase diagram contains regions
where the increase of disorder first causes the appearance of surface
conduction (via a topological phase transition), followed by the appearance of
bulk conduction (via a metal-insulator transition). The conducting surface
states are stabilized by an effective time-reversal symmetry that is broken
locally by the disorder but restored on long length scales. A simple
self-consistent Born approximation reliably locates the boundaries of this
socalled "statistical" topological phase.
