There has been a second day of disruption for travellers at Heathrow after British Airways cancelled at least 42 more short-haul flights following Thursday's IT problems.
BA said cancellations are still happening due to the "knock-on effect of a technical issue" resulting in staff being in the wrong location.
Around 16,000 passengers have been affected by flights being cancelled.
It comes on the busiest day for UK air travel since 2019.
Most of the cancellations are for European and domestic flights, but there have also been delays to other services, while some passengers have been unable to check in online.
Meanwhile traffic has started building up in Dover as delays are expected on roads and ports over the bank holiday and school half-term break.
On Thursday, BA apologised for cancelling dozens of flights at Heathrow. The airline said it was related to "technical problems" causing difficulties with online check-in.
"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," BA said in a statement on Friday.
Those affected have been offered the option to rebook an alternative flight or request a refund, BA added.
The Independent's travel correspondent Simon Calder calculated that at least 156 flights, mainly domestic and European, have been cancelled.
According to data firm Cirium, 83 BA flights, or around 8% of its planned Friday services, were cancelled as of 08:00 BST. Cirium said that BA cancelled 92 flights on Thursday, out of 860 that were scheduled.
A spokesperson for BA told the BBC that only a very small number of departures from Heathrow were actually affected.
Cirium said Friday was expected to see the most departures from UK airports since before the Covid pandemic, with more than 3,000 flights planned.
This is partly down to families heading on holiday for the half-term break.
Gavin Lanoe, 43, from Guernsey, was stuck at Heathrow on Thursday afternoon.
"We were told to go to the flight cancellations desk to get assistance but there were thousands of people there and a few staff, most of the desks were empty," he told BBC News.
Eventually he said BA staff told them they could not rebook as their systems were still down and instructed passengers to leave, pay for their own hotels and claim back up to £200.
Mr Lanoe then booked a ticket on another airline from Gatwick. He said BA told him they would send his luggage to Gatwick but this morning he discovered his bag was still at Heathrow.
"They've had enough IT failures now and they should be more practiced at dealing with them but they are not," he said.
The issues started as security guards at Heathrow Airport belonging to the Unite union began a three-day strike over pay. The airport has said operations will not be affected.
BA has been hit by other IT problems in recent years including a major breakdown in 2017 that stranded 75,000 passengers over a holiday weekend.
The incident sparked a customer backlash with pledges from the carrier that it would do better in future.
Passengers also faced delays due to an IT issue in February, days after flights had been cancelled due to Storm Eunice.
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