If it weren't for the guard post and security fence, most people wouldn't give 619 W. New Indian Trail Road in Aurora a second glance.
But the nondescript building belies the intense atmosphere of Chicago Center air traffic control facility.
Inside, myriad controllers hover around large screens in dim light monitoring tiny images of airplanes, noting their altitude and coordinates. They issue orders to pilots en route to O'Hare, the East Coast, West Coast and Europe, working an intricate system that millions of travelers depend on.
All that ground to a screeching halt early Friday when authorities say a Federal Aviation Administration subcontractor -- a 36-year-old Naperville man named Brian Howard -- tried to commit suicide after starting three separate fires. He cut all radar feeds and most communications lines as well and destroyed extensive hardware and processing equipment that will need to be rebuilt and reprogrammed, one official said speaking on condition of anonymity.
"I'm just astounded this would even occur," said Hanover Park Mayor Rod Craig, a retired FAA national airspace infrastructure manager who worked in Aurora. "I know the dedication of the people who work there. It's really hard to fathom what occurred ... the malice ... to think someone is that despondent, it's frightening."
As the FAA starts to put the pieces back together, it could be a rough few weeks for fliers.
The agency warned of reduced arrivals and departures in and out of Chicago through this weekend and advised travelers to check with their airlines before heading to O'Hare or Midway airports.
As of Saturday, authorities still were assessing the damage and hadn't put out a timetable for reopening.
Currently, Chicago Center traffic is being managed through high-altitude radar centers in Cleveland, Indianapolis, Kansas City, and Minneapolis, with assistance from another air traffic facility in Elgin, an FAA spokesman said.
But it's clear the loss of Chicago Center, which employs about 400 controllers handling 3 million flights a year, or 9,000 a day, is a big hit.
Part of the difficulty is the "holistic" way the technology controllers use works. "Everything interacts," Craig said.
At the O'Hare tower, controllers handle ground and air traffic within a 5-mile radius. Aircraft outside that range switch to the Elgin-based TRACON, shorthand for Terminal Radar Approach Control, which directs flights up to 40 miles from O'Hare.
At 40 miles, Chicago Center takes over, directing flights traveling through airspace in Illinois, Indiana, Iowa, Wisconsin, Michigan and Missouri.
With such a dense airspace, the facility is split into sectors, defined by geography and altitude. For example, one controller could be working an aircraft down from 32,000 feet to 24,000 feet in the northwest section, then hand it off to a colleague who guides the pilot down to 14,000 feet.
Air traffic controllers are trained in and knowledgeable about specific geographic sectors, which will make shifting workloads to other flight control centers a challenge for the FAA and could likely add to delays.
Along with the controllers are specialized National Weather Service units where meteorologists scan Doppler radar images, looking for trouble.
In the aftermath of the fire, air traffic controllers were able to rely on backup systems before handing off flights to other centers. It's a scenario they're drilled on -- ATC Zero -- when a facility's ability to function is degraded to a point it can't safely continue to operate.
Transitioning flights on such a massive scale involves some complicated choreography, but people familiar with Chicago Center said the controllers' training kicked in.
The latest challenge is for air traffic control units across the Midwest that are working overtime to assist with Chicago's workload, which involves juggling aircraft and airspace, National Air Traffic Controllers Association spokesman Doug Church said.
Hanover Park's Craig said he knows the sabotage caused "a lot of pain" to the tight-knit staff.
"I do know the character of the individuals who have the skills to restore whatever was destroyed, and they will work diligently until every component is restored," he said. "There is that much pride among those who work in that environment."