Hundreds of domestic flights in Japan were cancelled or delayed on Sunday as a result of a glitch in the computer system of All Nippon Airways.
The problem hit data flowing between the airline's main reservations host computer and intermediate computers that handled downstream connections to terminals in airports, said Rob Henderson, a spokesman for ANA. The airline has the largest share of Japan's domestic air market.
Information flow between the intermediate computers and host computer was slowed by the glitch, leading to a backlog of data that eventually clogged the system. The slowdown, which meant data was coming in several times slower than normal, eventually caused 130 cancellations and delays of more than an hour for 306 flights. Around 69,300 passengers were affected, said Henderson.
The problems began to resolve themselves on Sunday afternoon and by Monday morning the airline was operating close to a normal schedule. As of 9am just one flight was cancelled and nine had been delayed.
ANA doesn't yet know the cause of the problem, he said.
However there are several possible clues. In the last two weeks, three of the six intermediate computers that sit between the host and airport check-in terminals were replaced. After the replacement a problem was suspected and the airline switched back to the old computers, but then realised it was a communications issue and not a hardware one.
ANA is just beginning the gradual phase-in of a new computer system from Unisys. The vendor's AirCore reservation and departure control solution suite will be introduced between this year and 2012, according to statements made by both companies last year. ANA has been using Unisys systems for more than 25 years, although it's not known if Sunday's problems are related to the old or new system.