US airspace began returning to normal on Saturday after a nationwide flight ground stop caused thousands of cancellations and left travellers stranded at airports across the country.
Transportation Secretary Sean Duffy said the system was “back at full operations”, while warning that delays and further cancellations would continue as airlines moved aircraft and crews into position.
“Planes are pushing back, taxiing, and taking off, and it is safe to fly,” Mr Duffy said. He thanked pilots, airline staff, air traffic controllers and passengers for their patience during the disruption.
More than 5,000 flights were cancelled on Saturday and about 5,300 were delayed, according to flight-tracking data. A further 9,159 flights were cancelled and 7,190 delayed on Friday.
What caused the US flight ground stop?
The Federal Aviation Administration (FAA) imposed the ground stop at 3.36pm Eastern Time on Friday, when about 3,500 aircraft were already in the air. All of those planes landed safely before the restriction was lifted at around 8.20pm.
It was the first nationwide ground stop since January 2023, when a key FAA computer system malfunctioned. The previous national stoppage had followed the September 11, 2001 attacks.
Officials said the disruption was linked to ageing air traffic control infrastructure and legacy technology. Mr Duffy said a preliminary investigation indicated that a contractor was replacing a router at a remote FAA site while switching old copper wiring to fibre.
The router began flooding other routers, overwhelming the system with repeated attempts to log on. The instability spread to 17 facilities after lasting for about 45 minutes, according to FAA Administrator Bryan Bedford.
Mr Bedford said the maintenance work was routine and that the agency had been transferring the system from copper wiring to fibre for years, with about 70% of the work completed.
The FAA is still investigating whether human error was involved or whether a faulty router had been installed. Mr Duffy said the system had failed to “meet the moment”.
Officials said there was no evidence of a cyber attack. Mr Bedford also said there was “zero evidence” of anything nefarious or anything related to artificial intelligence.
Senior government sources said the issue was isolated to specific Cisco 600 series routers manufactured between 2001 and 2006. Technology and defence company L3Harris, which was involved in modernising the communications infrastructure, said it was supporting the FAA investigation and took the disruption seriously.
Airlines warn of continuing delays
Mr Bedford said about 12,000 flights scheduled for Friday could not be completed because of the stoppage. Around 3,000 were private flights, with the remainder commercial services.
He estimated that between 4,000 and 5,000 of the 41,000 flights scheduled for Saturday could also be cancelled, but said airlines should be fully back on schedule by the end of Sunday.
Delays remained possible at major airports including those serving Boston, Atlanta, Miami, Pittsburgh, New York, Los Angeles and Baltimore.
Delta said it was offering flexible rebooking options and warned passengers to expect delays and schedule changes while it repositioned aircraft and flight crews. American Airlines said the effects of the disruption would continue to cause additional cancellations and delays.
Southwest introduced a waiver allowing customers to cancel or rebook flights without penalty. Mr Duffy advised travellers to check with their airline before setting out for the airport.
Calls for more air traffic control funding
Mr Duffy said the FAA was modernising its ageing infrastructure with $12.5 billion approved by Congress, but argued that the funding was insufficient. The Trump administration increased its request for air traffic control funding to $30 billion late on Friday.
Democratic representatives Rick Larsen and Andre Carson said FAA and Transportation Department officials would brief congressional committees on Monday about the request. They said the administration had used only $1 billion of the approved $12.5 billion and would be asked to explain why further funding was needed.
Mr Larsen and Mr Carson said the stoppage had left passengers and aviation workers seeking answers, and pledged to hold the administration accountable to help prevent a repeat of the disruption.
