A bug in a Microsoft system compounded by human error was ultimately responsible for a three-hour radio breakdown that left hundreds of aircraft aloft without guidance on Tuesday, according to a report in the LA Times.
Nearly all of Southern California's airports were shut down and five incidents where aircraft broke separation guidelines were reported. In one case, a pilot had to take evasive action.
The newspaper said that a Microsoft-based replacement for an older Unix system needed to be reset every thirty days 'to prevent data overload', as a result of problems found when the system was first rolled out. However, a technician failed to perform the reset at the right time and an internal clock within the system subsequently shut it down. A back-up system also failed.
Richard Riggs, an advisor to the technicians union, said the FAA - the American aviation regulator - had been planning to fix the program for some time. "They should have done it before they fielded the system," he said.
To prevent a reoccurrence of the problem before the software glitch is fixed, Laura Brown, an FAA spokeswoman, said the agency plans to install a system that would issue a warning well before shutdown.