Temporary restrictions on how many planes can land or take off at Heathrow have been lifted, after a day of delays and cancellations at the airport.
The UK's air traffic services provider NATS said "staff absence and strong winds" had led to limits being imposed.
Heathrow warned of "minor" changes to schedules but declined to say how many journeys would be affected.
It could not confirm if there would be further delays this evening and said passengers should check with airlines.
Earlier, British Airways confirmed that it had made "some adjustments to our short-haul schedule".
There are normally about 175 short-haul BA flights that land at Heathrow every day.
Travellers took to X, previously Twitter, to vent their frustration, with some concerned that they would miss connecting flights to other destinations. Some were reportedly facing hours of delays.
NATS has been criticised in recent months for disruption at UK airports. In late August, thousands of flights were cancelled or disrupted when the UK's air traffic control systems suffered a technical failure.
Just over a fortnight later, flights at Gatwick were cancelled, delayed or diverted at short notice because of a shortage of air traffic controllers.
On Sunday, NATS said there was "short notice staff absence in the tower", as well as strong winds.
A spokesperson said: "We are working hard to minimise disruption, working closely with Heathrow airport and airlines. Passengers should check the status of their flight with their airline.
"Restrictions of this sort are only ever applied to ensure safety and we apologise for any inconvenience caused."
BA said that it had "contacted affected customers to apologise and offer them rebooking options or a full refund".
A spokesperson for Heathrow, said: "We want to reassure passengers that our colleagues are working in close collaboration with our airline and air traffic control partners to get them safely on their journeys as quickly as possible.
"We encourage passengers to check with their airline for the latest information."