Travel chaos has hit thousands of Britons with many flights to and from the USA and Canada cancelled or diverted following a massive power cut.
Passengers were handed notices telling them of the cancellations
More than 2,000 travellers were stranded at New York's JFK Airport on Thursday night after British Airways cancelled seven flights.
Two BA flights from Toronto were also grounded, and one Virgin Atlantic plane en route from London to New York had to turn back three hours into the flight. Other US-bound flights were re-routed.
Up to 50 million people were left without power after the blackout on Thursday afternoon affected large parts of the North Eastern USA and Canada.
Heathrow was the worst affected airport on Friday, with BAA reporting 18 departures and 15 arrivals cancelled or delayed from North America.
The problems at Heathrow affects the schedules of British Airways, Virgin Atlantic, United Airlines, American Airlines and Air Canada, although some flights are getting through.
BA cancelled five flights to JFK, Toronto, Philadelphia and Montreal on Friday.
But passengers were advised to check in as normal, or call ahead if they know their flight has been cancelled.
BA's director for Heathrow, Mervyn Walker, said the delays should be kept in perspective: "We've cancelled five of our 45 North American flights today. But apart from those five flights our full programme is running normally."
A spokeswoman for Virgin said they were expecting delays to run through Friday, while US authorities battle to restore power.
Three inbound flights, due to depart on Thursday, were rescheduled to leave on Friday morning. One Heathrow to JFK flight has been cancelled, and three services heading to Boston, Miami and Newark have been delayed.
At Gatwick, two inbound and two outbound Air Transat and US Airways flights are heavily delayed, with three unlikely to fly until Saturday.
The North Terminal scheduled transatlantic departures and arrivals are unaffected.
Glasgow and Edinburgh airports have also suffered a few delays, and one cancellation from Toronto.
Flights to and from Manchester have been delayed by up to 16 hours, while one Toronto-bound flight due to leave on Friday morning was cancelled.
US officials have found no evidence to support fears that terrorism was responsible for the power cut.
Exhausted passengers from Virgin Atlantic flight VS017 arrived back in the UK at 0200BST on Friday, after an aborted attempt to reach New York, and were taken to a hotel overnight.
Virgin hopes to fly most of them to New York at 1530BST on Friday.
Businessman Arthur D'Arcy, 45, originally from Surrey but now living in New Jersey, said Virgin had treated passengers well.
Heathrow - 18 departures and 15 arrivals cancelled or delayed
Gatwick - South Terminal: 2 departures and 2 arrivals delayed
Glasgow - One flight cancelled, Newark flight landed late
Edinburgh - Inbound Toronto flight delayed 7.5 hours
Manchester - In and outbound flights delayed up to 16 hours, one cancellation
He said: "About three hours in the pilot came on the tannoy and said, 'I'm sure you are wondering why we are taking a left turn in the middle of the Atlantic'.
"He then told us it was a power failure in the US and because we were before the halfway point we would have to go back."
But Becky Jones, 27, from Swansea, said the situation was "ridiculous".
"All just because there was a power cut," she said. "You can't tell me that the whole of the US and Canada can't even sort out their national grid.
"We were basically sitting on the plane the whole way back worrying that there has been some terrorist attack or a plane has flown into a building."
Amateur photographer Danny Axworthy, 21, from Knutsford, Cheshire, said: "Virgin were pretty good about it all. It's not their fault. They have been as helpful as they can.
"You've got to blame the authorities in the US, but that's America for you."
BA has asked passengers to check the status of flights before heading for the airport, by calling 0870 8509850, or via their website.
Virgin Atlantic can be contacted on 01293 454101.