A cyberattack against Collins Aerospace, a check-in and boarding systems provider owned by RTX, disrupted check-in and boarding systems at several major European airports over the weekend.

Brussels, Berlin Brandenburg, and London’s Heathrow were the hardest hit in the cyberattack that began late Friday, with passengers facing long queues, cancellations, and delays.

By early Sunday, disruptions had largely eased, though some delays continued, airport officials said. 

Brussels Airport said 45 of 257 scheduled departing flights on Sunday were canceled. “There are delays between 30 and 90 minutes,” a spokesperson for the airport told Reuters, adding that it was not yet clear how much longer the disruptions would continue.

Berlin Brandenburg Airport said on Sunday that some issues persisted but a manual workaround was in place.

“Occasionally, there are longer waiting times at check-in, boarding, baggage handling and baggage reclaim. Delays to departing flights today are in line with a normal operating day,” the airport said.

Heathrow said Sunday that efforts were ongoing to recover from the check-in system outage. It added that “the vast majority of flights have continued to operate.”

An analysis by aviation data provider Cirium said delays at Heathrow were “low,” Berlin experienced “moderate” delays, and Brussels faced “significant” delays.

Collins Aerospace described the incident as a “cyber-related disruption” but offered no further details. The company said it is working to restore its system’s full functionality. 

The incident follows other major European cyber breaches, including attacks on Jaguar Land Rover and Marks & Spencer.