Abstract： Weak superconducting proximity effect in the vicinity of the topological transition of a quantum anomalous Hall (QAH) system has been proposed as a venue to realize a topological superconductor (TSC) with chiral Majorana edge modes(CMEMs). Recent experiment [He, et al., Science 357, 294 (2017)] claimed to have observed such CMEMs in the form of a half-integer quantized conductance plateau in the two-terminal transport measurement of a QAHsuperconductor junction. While the presence of a superconducting proximity effect generically splits the quantum Hall transition into two phase transitions with a gapped TSC in between, in this work we propose that a nearly flat conductance plateau, similar to that expected from CMEMs, can also arise from the percolation of quantum Hall edges well before the onset of the TSC or at temperatures much above the TSC gap. Our work, therefore, suggests that in order to confirm the TSC, it is necessary to supplement the observation of the half-quantized conductance plateau with a hard superconducting gap (which is unlikely for a disordered system) from the conductance measurements or the heat transport gap. Alternatively, the half-quantized thermal conductance would also serve as a smoking-gun signature of the TSC.