Domestic flights across the U.S. were temporarily grounded on Wednesday morning, after an IT failure in a critical aviation safety system. The Federal Aviation Administration (FAA) said that the system that alerts pilots and airlines about any hazards was not functioning. The breakdown led to more than 7,800 flights being delayed and 1,200 being cancelled, the flight tracking website FlightAware showed. The disruption was due to "irregularities" in the system that alerts pilots to potential hazards on flight routes, officials said. 

The ground stop was lifted at 9am with the FAA declaring that operations were “resuming gradually across the United States”, but travelers were still left facing another chaotic day of air travel following severe disruptions over the holiday period. The White House said there was no evidence of a cyber-attack but the causes of the IT failure would be investigated in full by the Department of Transportation. International US-bound flights were continuing to take off from Europe and elsewhere.