Thousands of passengers were stranded at London Heathrow for a second day after British Airways (BA) cancelled at least 42 more flights due to an IT breakdown.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 the cancellations.It comes on the busiest day for UK air travel since 2019.

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Most of the affected flights are departing from or arriving at Heathrow.But there have also been delays to other flights, while some passengers have been unable to check in online.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, delaying flights.

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"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.

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The Independent's travel correspondent Simon Calder calculated that at least 156 flights, mainly domestic and European, have been cancelled.Aviation analytics company 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.

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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.

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Passengers also faced delays due to an IT issue in February, days after flights had been cancelled due to Storm Eunice.<img src="

alt="Lorries queue for the Port of Dover along the A20 in Kent as the getaway for half term and the bank holiday weekend begins"/>Image caption,Dover has been dogged by long tailbacks of vehicles during busy holiday

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periodsMeanwhile traffic has started building up at Dover as people embark on cross-Channel ferry trips.Ferry operator DFDS said shortly before 08:30 BST that there was a wait of around an hour at border control for travellers in cars, while coach traffic was "free-flowing".The Port of Dover tweeted that traffic is "currently processing well with no wait time for coaches, less than an hour wait for cars".

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Dover has been dogged by long tailbacks of vehicles during busy holiday periods. In the lead up to Easter some coach passengers faced 15-hour delays to board ferries to France from the Kent port.Dover's boss said this week it has done&nbsp;"everything we can"&nbsp;to prevent travel delays over the upcoming bank holiday and school half-term break.

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Elsewhere, Eurotunnel reported its cross-Channel vehicle services were busy, but trains were departing on time.On the railway, a fault with the signalling system between East Croydon and Gatwick Airport is expected to cause disruption until around 15:00.

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