There has been a second day of disruption for travelers at Heathrow after British Airways (BA) cancelled at least 42 more short-haul flights following Thursday's I.T. problems.

BBC News reports that 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 U.K. 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 May 25, BA apologized for cancelling dozens of flights at Heathrow. "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 May 26.