Many planes have already flown far away, and their locations can be seen on the monitors.
...
A monitor reported, "Boss, the signals of planes 1 to 10 are still there."
Another reported, "The signals of planes 11 to 20 are still there too."
"The signals of planes 31 to 40 are also present."
...
"The signals of planes 91 to 100 are still there!"
They report every one and a half hours.
As long as the signals are still present, it means the planes haven't entered the island's air defense domain. Once they near the island and are identified as unknown objects, they will be shot down, losing signal.
Signals remaining is actually bad news.
Ruan Tianling wants some of the signals from these planes to disappear—
"Boss, the signal of plane 57 has disappeared!" a monitor suddenly said.
Ruan Tianling immediately asked, "Are the signals of the nearby planes 56 and 58 still there?"
"They are still there."
