LONDON — Flights were delayed and travelers struggled to check in at airports around the world on Thursday after a software program used by several major airlines went down.

The program, known as Altea and developed by a company called Amadeus, encountered problems as a result of what Amadeus called a “network issue.” Altea helps airlines manage customer reservations, including tagging luggage and issuing boarding passes.

Amadeus software is used by 189 airlines — including major carriers like British Airways, Lufthansa, Thai Airways and Air France — and Altea in particular is designed with full-service airlines in mind.