It was on Tuesday afternoon in the U.S. that air traffic controllers discovered a glitch with the computer system that would require an entire reboot. The problem was discovered to be a corrupt file in the main Notice to Air Missions, or NOTAM. A corrupt file was also found in the backup system.
The NOTAM is a critical and massive safety computer system that advises pilots of issues along their route and at their destination. It was decided that the system reboot, which takes approximately 90 minutes, should be performed in the early hours of Wednesday morning before air traffic began flying on the East Coast in order to minimize disruption to flights. However, the reboot did not go according to plan and at approximately 7.30 a.m. ET the FAA issued a nationwide order to halt all domestic flight departures until the system was fully operational again.
At 8.50 a.m. ET the FAA issued a statement saying that that the ground stop had been lifted and that normal air traffic operations were resuming across the U.S. However, the knock-on effect was considerable and even by the time the ground stop was lifted, the number of delayed flights had passed 4,000. By 5.22 p.m. ET that number had risen to over 9,000 flights with over 1,300 cancellations. Having cancelled tens of thousands of flights after Christmas following a systemwide meltdown Southwest Airlines saw some 377 flights cancelled, though rival carrier American was forced to cancel nearly 400 flights.
