Airlines are racing to schedule autumn flights after London's Heathrow Airport extended its cap on passenger numbers until the end of October.
The cap — limiting the number of passengers departing each day to 100,000, because of staff shortages — had been due to end on September 11.
Its extension could affect thousands of travellers, as it covers the October half-term holiday week for schools.
Ryanair chief executive Michael O’Leary described Heathrow — Britain's busiest airport — as “hopeless”, for the continuing disruption to services.
Mr O’Leary said Ryanair will now add 500 flights from its UK hub at Stansted Airport, in Essex, south-east England.
British Airways and Virgin Atlantic are reviewing schedules for the period but no decisions on further cancellations have been made.
Mr O’Leary said both his airline and Stansted have sufficient staff to handle the extra flights.
The Dublin-based airline said the extra flights mean it has capacity for 100,000 extra passengers.
“While hopeless Heathrow continues to cut flights and raise fares for families, Ryanair and London Stansted continue to add flights, and offer thousands of low-fare seats for the autumn midterm break,” Mr O'Leary said.
“While hopeless Heathrow continues to mismanage air travel, Ryanair and London Stansted will continue to grow and deliver for London families, the way we have through all of summer 2022.”
The Heathrow cap on passenger numbers was a reaction to a chaotic spring and summer, where thousands of passengers saw flights cancelled and travellers whose flights took off endured lengthy waits in terminals.
On Monday, Heathrow announced its extension to October 29.
Last week, the airport said the cap was working — reporting “fewer last-minute cancellations” and “shorter waits for bags”.
A Virgin Atlantic spokeswoman said: “We are disappointed that Heathrow Airport has already decided to extend the passenger capacity cap until the end of October, as additional resources come on line every week and the airport experience improves.
“Airline customers have a right to expect their bookings will be honoured and we're doing everything in our power to minimise disruption, getting our customers to where they need to be smoothly.
“We urge Heathrow to provide a comprehensive plan for returning to normal operations as soon as possible.”
Heathrow was unable to provide figures on the number of people who have already booked flights for the half-term holiday.
“Our primary concern is ensuring we give our passengers a reliable service when they travel,” said Heathrow chief commercial officer Ross Baker said.
“That's why we introduced temporary capacity limits in July which have already improved journeys during the summer getaway.
“We want to remove the cap as soon as possible, but we can only do so when we are confident that everyone operating at the airport has the resources to deliver the service our passengers deserve.”
