Low-lying Padang is seen as vulnerable to a tsunami and its residents have been trained to flee to higher ground along designated routes when an alert is sounded.

Another pilot on the ground at the heliport saw the plane approaching and tried to radio an alert to the helicopter above. But the warning was either not heard, or failed to get through in time.

For nearly 13 years, Yao and Liu spent hours in an Internet cafe next to the training ground playing "Red Alert" and "Counterstrike."