Airlines and airports have warned of delays on Wednesday after a UK air traffic control glitch.
The technical problem, which caused major disruption, was resolved by 5:10pm, the UK's air traffic control service said.
However, airports and airlines were working through a backlog of flights.
Earlier, thousands of planes across the UK were grounded at airports including Heathrow, Stanstead, Manchester and Edinburgh due to the issue.
The air traffic systems, which are run by NATS, were down for about 20 minutes.
