Several airlines at Heathrow, Gatwick and Melbourne airports experienced check-in problems.
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.
Amadeus said it had identified a « network issue » but that services were being restored.
Several airlines use the Amadeus software to manage reservations and check-in desks.
British Airways, Qantas, Southwest and Lufthansa are among its customers.
Heathrow airport said: « A small number of airlines are experiencing problems across the world and we’re working closely with them to solve the issue. »
A spokesman for Amadeus said: « During the morning, we experienced a network issue that caused disruption to some of our systems.
« Amadeus technical teams took immediate action to identify the cause of the issue and restore services as quickly as possible. That action is ongoing with services gradually being restored.
« Amadeus regrets any inconvenience caused to customers. »
