Here's What We Know So Far :
US Regulator Federal Aviation Administration says flight operations are gradually resuming and it expects departures to resume at airports at 9 am Eastern Time.
At least 5,400 flights are grounded and over 550 flights were cancelled in the US on Wednesday, according to online flight tracker FlightAware.
FAA lifted ground stop that halted all domestic departures until 9 am Eastern Time.
21,000 flights were scheduled to take off in the US today
FAA said that some functions of the Notice to Air Missions system are beginning to come back online.
The system alerts pilots about hazards or any changes to airport facility services and relevant procedures.
FAA is still working to fully restore the system and has no current estimated time of complete restoration.
A hotline has been activated by the flight regulator.
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