In an airline system, there's quite a bit of equipment at each location, and much of it is specialized. There are interfaces to baggage systems and bar code readers. There are interfaces to airport systems and incoming information from air traffic control. The aircraft themselves transmit information and need flight plan uploads. There's probably more machine to machine communication than user interfaces. They may be having troubles resynchronizing everything with the backup systems in the data center.
In this case, it sounds very much like the backup servers were running the wrong version of some user interface programmed in an arcane IBM programming language from the 1970s that is built entirely around the record-oriented database typical of a machine like the AS/400.
More specifically "lipstick on a pig" =D