  We propose to realize a two-dimensional chiral topological superconducting
(TSC) state from the quantum anomalous Hall plateau transition in a magnetic
topological insulator thin film through the proximity effect to a conventional
$s$-wave superconductor. This state has a full pairing gap in the bulk and a
single chiral Majorana mode at the edge. The optimal condition for realizing
such chiral TSC is to have inequivalent superconducting pairing amplitudes on
top and bottom surfaces of the doped magnetic topological insulator. We further
propose several transport experiments to detect the chiral TSC. One unique
signature is that the conductance will be quantized into a half-integer plateau
at the coercive field in this hybrid system. In particular, with the point
contact formed by a superconducting junction, the conductance oscillates
between $e^2/2h$ and $e^2/h$ with the frequency determined by the voltage
across the junction. We close by discussing the feasibility of these
experimental proposals.
