Airports in Berlin, London and Brussels faced continued delays on Sunday after a cyberattack on a key airline check-in system forced staff to process passengers manually.

The outage stems from a cyber incident at Collins Aerospace that knocked out its MUSE software late Friday. The platform underpins check-in, boarding and baggage systems for airlines worldwide. With kiosks and bag-drop machines offline, airports have been forced to rely on manual processing, slowing passenger flows.

Berlin Brandenburg Airport reported continuing delays, while Heathrow said “the vast majority of flights” are operating but advised travelers to check status before leaving for the airport. It advised passengers not to arrive earlier than three hours for long-haul flights or two hours for short-haul services.

Brussels Airport took the toughest measures, asking carriers to cancel half of scheduled departures to ease pressure on staff. The airport apologized, citing the “cyber issue” at its external provider.

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So far, cancellations have remained limited compared with Europe’s total daily air traffic, but the incident highlights the strain on airlines and airports when critical technology suppliers are disrupted, with recovery expected to remain uneven until Collins restores full service.

This year has seen a sharp increase in cyber threats against infrastructure and aviation. A June report by Thales SA, a French defense company, showed a 600 percent year-on-year increase in ransomware attacks in the aviation sector, with dozens of incidents affecting airlines, airports, navigation systems and services.