British Airways (BA) has apologized for canceling dozens of flights at London Heathrow due to IT troubles on Thursday.

The airline stated that it is working to resolve “technical issues” that are causing difficulties with online check-in and delaying flights.

According to aviation data firm Cirium, 43 flights, or about 5% of its services, have been canceled as of 17:00 BST.

Today, over 800 flights were planned to depart from the United Kingdom.

BA has seen a string of reputation-damaging IT failures in recent years, including one in December that resulted in the cancellation of dozens of long-haul flights in the week before Christmas.

The problems on Thursday impacted flights departing and arriving at Heathrow.

“No one at @british_airways can tell us when our flight will leave,” one individual affected by the delays tweeted. And it appears that if it does leave, it will do so without luggage.”

“My daughter is stuck in Heathrow after already diverting to Iceland from Canada due to a medical emergency,” commented another. She hasn’t slept in 24 hours and is unable to board a flight back to Dublin.”

BA stated that the majority of its flights had continued to operate, and that affected customers had been informed and provided choices such as a refund or rebooking on another airline or BA.

According to Rory Boland, travel editor at consumer organization Which?, any tourist whose flight was cancelled would be legally entitled to compensation or rebooking as soon as possible.

“Passengers are frequently given the runaround on this right, but it is the law, so being persistent is worthwhile,” he added.

“It appears that the technical issue in this case was caused by BA, so any flight cancellations or delays of more than three hours should also be compensated.”

The problems arise as security personnel at Heathrow Airport go on strike for three days over pay.

The Unite union represents approximately 1,400 striking workers at Terminal 5 and in campus security. The airport has stated that operations will be unaffected.

Other IT issues have plagued BA in recent years, including a significant outage in 2017 that stranded 75,000 customers during a holiday weekend.

The episode generated customer outrage, prompting the carrier to promise that it will do better in the future.

Passengers were also delayed in February due to an IT problem, only days after flights were grounded due to Storm Eunice.

Passengers said their experiences with the airline were “utterly disastrous” and “truly woeful” at the time, leading the airline to apologize.