The convergence behavior of turbo APPM (TAPPM) decoding is analyzed by using a three-dimensional extrinsic information transfer (EXIT) chart and the decoding trajectory. The signal-to-noise ratio (SNR) threshold, below which iterative decoding fails to converge, is predicted by using the 3-D EXIT chart analysis. Bit error rate performances of TAPPM schemes validate the EXIT-chart-based SNR threshold predictions. Outer constituent codes of TAPPM are chosen to show the lowest SNR threshold with the aid of EXIT chart analysis.