A software issue has caused check-in delays at several airports worldwide, and booking problems for many airlines.
Passengers reported problems at Gatwick, Paris Charles de Gaulle and Melbourne airports among others.
Gatwick blamed a passenger management system called Amadeus Altea but said the problem had been resolved and there were no further delays.
The BBC has tried to contact Amadeus but representatives hang up when asked about the global software problem.
More to follow.