Flight disruption across Europe is set to continue, with Brussels airport in Belgium asking airlines to cancel nearly half of their flights on Monday.
Several of Europe's busiest airports have spent the past few days trying to restore normal operations, after a cyber-attack on Friday disrupted their automatic check-in and boarding software.
Disruption had eased significantly in Berlin and London Heathrow by Sunday, but delays and flight cancellations remained.
In a statement on Monday morning, software provider Collins Aerospace said it was in the final stages of completing necessary software updates.
Brussels Airport stated that the service provider is actively working on the issue but it was still unclear when the matter would be resolved.
They have asked airlines to cancel nearly 140 of their 276 scheduled outbound flights for Monday, according to the AP news agency.
Heathrow said on Sunday that efforts to resolve the issue were ongoing, and apologized to customers who had faced delayed travel.
It stressed the vast majority of flights have continued to operate and urged passengers to check their flight status before traveling to the airport.
The BBC understands that about half of the airlines flying from Heathrow were back online in some form by Sunday, including British Airways, which has been using a back-up system since Saturday.
The National Cyber Security Centre is collaborating with Collins Aerospace and affected UK airports to understand the impact of the incident, while the European Commission is monitoring the cyber-attack closely.
Cyberattacks in the aviation sector have surged by 600% over the past year, as highlighted by a report from French aerospace company Thales.
