Half-term holiday plans for thousands of families have been thrown into disarray after British Airways' flight cancellations due to an IT failure reached 175.
Most of the affected flights were on short-haul routes to and from Heathrow Airport.
British Airways said the "technical issue" was resolved on Thursday night, but disruption continued into Friday because of aircraft and crew being out of position.
On Friday it was expected the most flights since December 20, 2019 would depart from UK airports, with more than 3,000 flights planned.
This is due to the combination of many families heading overseas for the half-term school holiday in England and Wales, and Monday being a bank holiday.
Aviation analytics company Cirium said 83 British Airways flights due to operate on Friday were cancelled, in addition to 92 flights on Thursday.
This means more than 20,000 passengers' journeys were axed.
It follows a day of havoc on Thursday, when about 80 flights at London's Heathrow and Gatwick airports were grounded.
The cancellations have put the half-term holiday plans of thousands of families in limbo, on what was anticipated to be the busiest day for UK air travel since before the Covid-19 pandemic.
Most of the affected flights on Friday were on short-haul routes to and from Heathrow Airport.
As well as the cancellations, many other flights have been delayed, while some passengers have reported that they have been unable to check in online.
A British Airways spokeswoman said: "While the vast majority of our flights continue to operate today, we have cancelled some of our short-haul flights from Heathrow due to the knock-on effect of a technical issue that we experienced yesterday.
"We've apologised to customers whose flights have been affected and offered them the option to rebook to an alternative flight with us or another carrier, or request a refund."
The airline has attempted to manage the disruption by concentrating cancellations on routes that have several flights a day, allowing passengers more flexibility in rebooking at alternative times.
The problems were not related to a strike by security officers at Heathrow's Terminal 5, the airport said.
British Airways has suffered several IT failures in recent years, including a significant system fault in the run-up to Christmas 2022.
Many families are heading overseas for the half-term school holiday in England and Wales.
British Airways assured customers on Thursday, saying “systems are back up and running”, but warning of potential “intermittent issues”.
The airline has promised refunds or rebookings for affected customers, and will provide meals and hotel accommodation for those forced to stay overnight.
Passengers have formed long queues at Heathrow as they try to arrange alternative flights, while many arriving at the airport have been unable to disembark planes.
Cities including Vienna, Dublin, Dusseldorf, Edinburgh, Venice, Rome, Hamburg, Aberdeen and Milan are among the destinations currently affected by the issue at Heathrow.
Long-haul cancellations include Boston, New York and Mumbai.
The British airline has been affected by other IT problems in recent years, including a major computer system failure in 2017 that stranded 75,000 passengers over a holiday weekend, causing a public relations disaster and pledges from the company that it would do better in future.
Passengers affected by delays and cancellations took to Twitter to express their frustration.
Travellers also seem to not be receiving information from British Airways on why their flights have been cancelled.
It also seems that baggage will be lost in the chaos.
Holiday traffic kicks in
The Port of Dover reported increased activity on Friday as thousands of people set off on cross-Channel ferry trips.
Ferry operator DFDS said at 8.30am there was a waiting time of about one hour at border control for car travellers, while coach traffic was “free-flowing”.
Despite the widespread disruption in air travel, many UK residents are still expected to make the most of the bank holiday weekend.
The RAC estimated that drivers in the UK would embark on 19.2 million leisure car trips between Friday and Monday. However, transport data company Inrix has said that there could be long delays on major motorways.