US aviation authorities expect flight schedules across America to be fully back to normal by the end of Sunday, a timeline that should bring an end to the knock-on delays and cancellations affecting Heathrow passengers travelling to the United States since Friday night.
FAA Administrator Bryan Bedford told a press conference on Saturday that "the worst is behind us, but we still have a fair amount of recovery ahead of us." He said airlines expect "full schedule integrity by the close of business on Sunday," though Saturday itself would still see further delays and cancellations, with an estimated 4,000 to 5,000 of the 41,000 flights scheduled across the US likely to be cancelled.
The disruption began on Friday when the FAA ordered a nationwide ground stop lasting around four hours after a telecommunications and radar fault hit air traffic control systems. US Transportation Secretary Sean Duffy said the problem occurred during routine maintenance by FAA contractor L3Harris, replacing old copper cables with fibre-optic lines, when a router overloaded other devices with data requests. Officials say there is no evidence of a cyberattack.
Almost 10,000 flights were cancelled across the US on Friday alone, according to tracking site Flightradar24, in what became the most disruptive ground stop since the September 11 attacks in 2001.
At Heathrow, the impact has been concentrated on transatlantic routes with American Airlines, United Airlines, British Airways and Delta. Cancellations on US-bound departures climbed from 29 to 31 by Saturday morning, with around 20 further departures delayed. By Saturday afternoon the picture had started to improve, with only a handful of US carrier flights, including American Airlines services to Charlotte, Dallas and Los Angeles, still showing as cancelled.
The UK Civil Aviation Authority has not withdrawn its warning to passengers. "While US flights have resumed, there may be some follow-on disruption as airlines work to re-book affected passengers and get all services back to normal," said Tim Johnson, the CAA's consumer director, in a statement on its website. He advised anyone travelling between the UK and the US to check with their airline for the latest information before heading to the airport.
The FAA's Bedford cited information from US airlines in giving the Sunday recovery timeline, rather than a fixed technical fix, meaning the pace of improvement at Heathrow over the next 24 to 36 hours will depend on how quickly American carriers can reposition aircraft and crews left out of place by Friday's stoppage.
What this means for your journey: if you are flying to or from the US via Heathrow this weekend, check your flight status directly with your airline before leaving home, build in extra time for rebooking queues, and avoid arriving at the terminal earlier than necessary. For getting to the airport itself amid the ongoing disruption, see our guides to Heathrow /parking/ and /public-transport/ options.