Such network problems are not at all unusual, but they're usually confined to specific airlines and airports. Today's outage, by contrast, has seemingly affected airports and airlines on at least four different continents.

Computer problems with @Lufthansa check-in computers. Flights delayed, at least out of TXL.



Glad I checked-in on the Lufthansa app! #travel — Les Jordan (@ljrdn3) September 28, 2017

Passenger @ljrdn3, for instance, reported problems at Berlin Tegal, saying that Lufthansa flights were delayed. Another, @msmith_ky, said that "all of the computers at DCA Southwest Air terminal are down." In response, Southwest indicated that "we should be back up and running very shortly."

So far, airlines affected include at least Air France, Southwest, China Air, Qantas, Korean Air, Lufthansa and British Airways, according to CNN Money. Affected airports other than those mentioned are Incheon, Seoul, Haneda Tokyo, Frankfurt, Zurich, Heathrow, Reagan National.

"Amadeus technical teams took immediate action to identify the cause of the issue and restore services as quickly as possible," a spokesman for Amadeus said. "That action is ongoing with services gradually being restored."