United Airlines grounded all of its flights in the US today, following a system-wide technical glitch.
The order to ground all aircraft has now been lifted.
But it is thought that around 3,500 services were affected and that the delays could now ripple out to the airline's 235 domestic and 138 international destinations.
United said in a statement: "We experienced a network connectivity issue this morning. We are working to resolve this and apologise to our customers for any inconvenience."
The US Air Traffic Control System Command Center blamed "automation issues".
Passengers are being told to expect delays and to allow extra time for their flights.
Graham Smith
