San Francisco International Airport faced a second day of disruption on Saturday, with 264 flights cancelled and a further 310 delayed after a nationwide US ground stop exposed problems during an air traffic control system upgrade.
Passengers at the California airport were warned that the backlog could take days to clear, even though flights had resumed following Friday’s unprecedented stoppage. The Federal Aviation Administration halted departing flights across the United States after communications problems affected several air route traffic control centres.
The ground stop was lifted after roughly four hours, but airlines were left with aircraft and crews out of position. San Francisco airport officials said the resulting cancellations and delays continued to affect travellers as carriers attempted to rebuild their schedules.
US Transportation Secretary Sean Duffy said a contractor had been replacing ageing copper telecommunications lines with fibre at a remote FAA site when a router began flooding other parts of the air traffic control network with connection attempts.
The disruption affected communications between controllers and aircraft and caused interruptions to radar feeds. Officials said the decision to ground flights was taken as a safety precaution while engineers isolated the fault.
The FAA said more than 3,500 aircraft were safely brought to the ground during the incident, while more than 8,000 flight operations resumed after the stoppage was lifted. The agency said the airspace was operational on Saturday but warned passengers to expect further cancellations and delays.
Mr Duffy said officials were investigating whether the failure resulted from contractor error or a defective router. He said there was no evidence that the incident was caused by sabotage, a cyber attack or the FAA’s recently introduced artificial intelligence system.
Federal officials have also said the outage was unrelated to a separate disruption affecting Microsoft services. Airlines advised passengers to check their individual flight status before travelling, as the national backlog continued to work its way through airport operations.
