Several major European airports, including London’s Heathrow, Berlin, and Brussels, faced disruptions on Saturday after a cyberattack targeted Collins Aerospace, the provider of check-in and boarding systems.

The hack caused long queues, flight cancellations, and delays, though operations were largely returning to normal by Sunday.

RTX, Collins Aerospace’s parent company, described the incident as a “cyber-related disruption” affecting its MUSE software used by airlines.

Airports implemented manual workarounds, with Heathrow reporting most flights continued to operate, while Brussels still experienced significant delays, CNN has reported.

Regulators are investigating the origin of the attack, part of a wider wave of cyberattacks affecting industries from automotive to retail.