In the summer of 2015,  the act of an imbecilic, self-centered, vindictive twit caused the Chicago Air Route Traffic Control Center to shut down for awhile.   The news media had all kinds of fun with that one.  Yes, there was disruption to air traffic, mostly to the airports in and around Chicago itself, but the system did what it is designed to do and things came back online in a progressive and orderly fashion.

Every ATC facility – Center, Tower, Approach and Flight Service – is required to have a contingency plan in place that is reviewed annually, not just by the facility managers but by every supervisor and air traffic controller.  Chicago ARTCC has high and low altitude sectors that abut other Center’s airspaces.  The first thing that happens when a facility becomes “ATC ZERO” is that the surrounding facilities are notified to implement the predetermined procedures.  Notices to Airmen (NOTAMs) are released by Flight Service  concerning all affected airports and airspace so pilots planning flights in those are alerted to the situation and given guidance as to how to plan flights.

In this case, Minneapolis, Kansas City and Indianapolis Centers turned on their back up frequencies, extended their radar scopes outward in the sectors bordering Chicago Center so they could “see” into the neighboring airspace and started working Chicago’s traffic.  Chicago Approach control, and all other ATC facilities that exist under the dome of Chicago Center, still had all their frequencies and radars because their systems work independently.

An Air Route Traffic Control Center (ARTCC)  is a very large building and the airspace designated as its responsibility is separated into many smaller blocks of sky.  Since the damage done at the facility was not immediately catastrophic to the building as a whole, they were able to evacuate the personnel in an orderly manner and turn over control of those chucks of atmosphere to other ATC facilities before running out the door.

What was disrupted the most was the smooth and efficient flow of aircraft into and out of the area’s major airports.  Many smaller low altitude aircraft could choose to cancel their IFR flight plans and proceed VFR to their destinations.  The aircraft traveling higher were the ones turned over to other facilities…who worked them until they had exited the airspace or landed.

Of course the first thing that happens is a time period where all aircraft on the ground and in the air that would have entered the affected airspace were either ground stopped, rerouted or just slowed down until the initial redistribution of airspace goes into effect.   Chicago is the 5th busiest Center in the country – but the airspace it controls is smaller than many of the others.  It only has two major international airports  – which are large enough that the flight delays provided the newscasters with lots of airtime.   Anyone who was keeping an eye on the situation would have seen that it only took a couple of days for the airlines to get back on track.

For really large airports, flow control normally begins well outside the airspace of the Center which supports  that airport.   Aircraft landing Chicago are lined up 10 miles in trail beginning almost 500 miles away in several well organized streams.  During the time the Center was closed, the feeder streams were diverted a little and ATC modified flight plans for high altitude aircraft to accommodate the new flow control procedures.

Historically there have been situations where power outages or disasters have caused the shut down of some towers and approach controls, but this was the first time a modern ARTCC actually went to ATC Zero.  Past experiences with older facilities are what stimulated the incorporation of back up generators and radars and today’s requirements for annual equipment and procedural reviews.  Every event requiring the closure of an air traffic facility is studied in depth by the FAA, and that the experience  engenders new ideas and requirements that enhance the safety  of all ATC facilities.