LONDON (AP) — British Airways cancelled dozens of flights Friday, blaming computer problems for disrupting plans for thousands of passengers at the start of a busy holiday weekend — a rocky kickoff to the summer travel season in Europe.

The technical glitches and strikes by airport staff across Europe are stirring concerns about a repeat of last summer’s post-pandemic air travel chaos that unleashed delays, cancellations and mountains of lost luggage from London to Sweden to Amsterdam.

Most of the 42 affected flights in London were on short-haul routes to and from Heathrow, Europe’s busiest airport. Computer issues on Thursday caused planes and crew to be out of position Friday, which was expected to be the busiest day for UK air travel since before the coronavirus pandemic.

Other flights were delayed, with some passengers unable to check in online. Travel is expected to be especially busy over the next few days as a three-day weekend coincides with the start of a weeklong holiday for most schools in Britain.

“We’re aware of a technical issue, which we have been working hard to fix,” British Airways said on its website.

The industry is gearing up for a busy summer season and hoping to avoid a repeat of the disorder last year, when airports and airlines struggled to keep up with demand that came roaring back after pandemic restrictions eased.

“While some disruptions can be expected, there is a clear expectation that the ramping-up issues faced at some key hub airports in 2022 will have been resolved,” the International Air Transport Association, or IATA, said this month.

“To meet strong demand, airlines are planning schedules based on the capacity that airports, border control, ground handlers, and air navigation service providers have declared. Over the next months, all industry players now need to deliver,” the airline industry group said.

IATA warned that strikes, including by airport staff such as air traffic controllers, are “cause for concern,” particularly in places like France. Labour action by French workers battling the government over pension reforms has resulted in as many as 30 per cent of flights cancelled at Paris’ second busiest airport, Orly, on some days.

In Britain, Heathrow security guards launched a three-day strike Thursday over pay after walking off their jobs over busy periods earlier this year, including Easter.

The strikes have been an issue, but “mitigation measures that have been implemented has meant that in the vast majority of cases, people have been able to travel from the UK. as expected, and we expect the same to be the case over the summer months,” said Julia Lo Bue-Said, CEO of Advantage Travel Partnership, which represents about 350 UK travel agents.

“The industry is made of many moving parts and navigating some of the issues outside of our control at exceptionally busy periods does put increased pressure on the entire ecosystem,” she said.