The FAA says flights will be allowed to depart as its facilities recover and coordinate with its command centre in Virginia, according to CNN, which cites an FAA update issued roughly two hours into the nationwide ground stop.
It is the first indication of how the stop will be lifted. Until now the advisory had said only that departing traffic was to remain ground stopped until further notice.
The same update confirmed that planes were still barred from taking off, CNN reports.
Flight tracking data cited by CNN is consistent with that. Flightradar24 said in a post at 5.25pm ET (10.25pm UK time) that no flights had left Chicago O'Hare in over two hours. It put the last recorded takeoffs at JFK and Ronald Reagan Washington National at 3.35pm ET (8.35pm UK time).
That is 19 minutes before the 3.54pm ET start of the advisory's effective period, as reported earlier by Yahoo News.
CNN aviation correspondent Pete Muntean told Jake Tapper there was "no real end in sight" for delays and cancellations, which he said could continue for some time.