Thousands of US flights were cancelled or delayed on Sunday as the US air-traffic control system continued to recover from a technical failure that led to a rare national ground stop.
Secretary of Transportation Sean Duffy said normal operations may not be restored until Monday.
"We have airplanes and crews that are out of position, so it takes a little bit of time," he told the BBC's US partner CBS. More than 5,000 flights were delayed and 2,000 cancelled on Sunday.
President Donald Trump urged Congress on Sunday to approve more money to modernise the air-traffic control system. The grounding of all aircraft scheduled to depart the US on Friday caused chaos at airports across the country.
More than 3,500 airplanes were in the air when the FAA announced at 15:54 EST (20:54 GMT) that flights would be grounded until further notice. Some were diverted to other airports and others flew on to their destinations.
In the aftermath, 8,500 flights were delayed and another 8,000 cancelled, according to FlightAware.
The stoppage left passengers stuck inside planes on the tarmac, unable to take off or to return to their gates. Others were stranded in airports, sleeping on the floor and desperately trying to get in touch with their airline.