A bug in a software update to Japan's air traffic control computer system grounded all flights across the country on Saturday morning.
The computer, which handles the distribution of flight information to airports, failed at 7:00am local time, resulting in the immediate halting of all departures from Japanese airports.
An official said the fault was thought to have been caused by a bug in new software that had been loaded onto the machine at 1:00am the same morning. The software handles exchange of data between the control centre's FDP (Flight Data Processing) computer and a similar computer, the FADP (Flight Service and Air Movement Identification System Data Processing), at the Defence Ministry.
The software worked for the first six hours,only to fail at exactly 7:00am, coinciding with the running of a program that collects data on the previous day's air traffic. The ministry is looking into the possibility that an incompatibility between the two programs caused the problem.
One half of the machine, which has total redundancy to guard against hardware failure, began operating at 7:40am.with the second half of the machine coming back online at 10:58am. However, delays continued all day because of a backlog in the system.
Limited air services resumed at around 7:30am with controllers using manual methods and communicating by telephone.
The failure caused the cancellation of 192 flights and the delay of 1,342 flights.
Officials said the new software had been tested on a backup system for two weeks and no problems were observed. However, the official could not confirm whether data exchange with the new Defence Ministry system or the daily data gathering software was part of the test.