The Federal Aviation Administration (FAA) is expected to reopen the air-traffic control centre near Chicago by next week that was set on fire by a contract worker last month.
The incident occurred on 26 September and led to the cancellation of approximately 5,000 flights from the O'Hare and Midway airports in the following week. Contract worker Brian Howard of Naperville had cut radio and data communications cables and set other equipment on fire as he was angry over plans to transfer him to Hawaii.
The centre in Aurora handles flights above 18,000ft in the air spanning five states and has controllers in centres like Minneapolis, Indianapolis and Cleveland.
Following the incident, hundreds of members of the National Air Traffic Controllers Association at two dozen facilities around Chicago helped in managing and handling the flights.
Officials informed staff that to prepare for the handover of air traffic control back to the center, technical teams from FAA were completing testing of equipment and systems and were also conducting flight checks using planes that are not in commercial service to verify that the system is working perfectly.
However, despite the disruption, FAA said on Saturday that O'Hare airport was handling 97% of its average traffic and most flights in the country for most of last week. Midway was handling 95% of its average traffic.
In a statement, FAA said: "The FAA has successfully tested and restored all of the critical systems and equipment at the Chicago En Route Center in Aurora, IL and is moving forward with the planned transition to full operations at the facility tonight.
"Overnight, the FAA will gradually transition flight plan information, communications and airspace back to Chicago Center. The FAA is working closely with domestic and international airlines to make sure they have all the necessary information to ensure a smooth transition."