Normal air traffic operations are resuming gradually in the US after hours of delays, the Federal Aviation Administration (FAA) says.
It follows a problem with the system that alerts pilots to potential hazards on flight routes.
The FAA had said flights would take off again from 0900 ET (1400 GMT). It said it was continuing to look into the cause of the problem.
Flights already in the air were allowed to continue to their destinations.
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