Some extracts from this article:
"With a double-side door design, five commandos can fast-rope from the Z-20 helicopter simultaneously... All 13 commandos can complete the fast-roping operation within half a minute.
It can be seen from the exercise that China's domestically-developed Z-20 and Z-8G helicopters have become the standard equipment of the air assault brigade. This also reflects the general trend that the Z-20 is replacing the Mi-17 series.
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The combination of Z-20 and Z-8G gave full play to their respective advantages in this exercise. The Z-20 helicopters concentrated on fast-roping operations, while the Z-8G carried out heliborne operations.
The joint operation of the Z-20 and Z-8G resulted from the tactical considerations. Being designed for multi-services from the very beginning, Z-20 helicopter does not have a tail hatch, which means that some larger equipment and vehicles cannot be transported through its cabin doors and can only be transported in the form of external mounting."