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.“
