Following a “technical issue” with UK air traffic control systems, thousands of airline passengers have experienced protracted delays and cancellations.
After National Air Traffic Services restricted the amount of planes landing, people are stuck in the UK and abroad.
Airports and airlines issued a warning that there were still “significant delays” even though the problem was resolved within hours.
One traveller told BBC News that she expected her midday flight to depart after midnight.
Some knock-on disruptions have been forewarned to endure for days.
Heathrow stated late on Monday night that itineraries were still seriously interrupted and advised anyone flying on Tuesday to get in touch with their airline before leaving for the airport.
Despite stating that it intended to run on a regular schedule on Tuesday, Gatwick Airport encouraged travellers to contact their airline in advance to confirm the status of their trip.
Flights within UK airspace are still vulnerable to delays and cancellation, according to London Luton Airport, which also advised travellers to check with their airline for the status of their trip.
On Monday just after noon, Nats acknowledged the error before announcing at 15:15 BST that it had found and fixed the problem.
“Flights will take some time to return to normal,” it stated.
On Monday, there were delays and cancellations at several UK airports and carriers, including British Airways, Virgin Atlantic, and TUI.
It said passengers for flights on Tuesday should travel to the airport as normal unless otherwise advised.
Aviation analyst Sally Gethin said the disruption in the aftermath of the technical fault will last for days.
“Airlines will have a major headache now, looking after customers and getting the planes back to some normal schedule again,” she told BBC News.
“I think we are going to see sizable disruption in the coming hours and tomorrow, and I think for some people there could be a knock-on effect into later this week.”