Passengers flying from Heathrow Airport are being warned to check before they travel after a problem with the runway lights.
Heathrow said the issue had been resolved by 6.05am, but that customers should still check their flight status with their airline before travelling.
The lighting issue left some London-bound passengers stranded on the tarmac in the US, although British Airways made their waits easier with snacks and drinks.
"On the ground in Atlanta due to Heathrow light failure. The bar is open and I'm not working tomorrow so not that fussed," passenger Davey Hunt wrote on Twitter.
Other passengers were less patient as they waited for updates from BA staff.
"We are on BA116 and ground staff at JFK Airport not opening the door so we can talk to someone. Pilot growing impatient as are passengers," Twitter user Shaan Khan wrote.
Nearly one in seven flights due to land at Heathrow between 6am and 8.59am were delayed, affecting 16 flights, according to aviation data firm FlightStats.
Out of 22 scheduled departures between 6am and 6.59am there was one cancellation and two flights delayed.
There was an issue with Heathrow Airport's airfield lighting during the night.