The malfunction did not affect information supplied to the back-up system. Overall equipment availability at the Chicago Center is 99.6 percent. Controllers already were using back-up system during maintenance procedures. Preliminary report of operational error by controller, involving a commuter aircraft and a general aviation aircraft. An investigation is under way.
Technicians attempt to reactivate primary system to ensure maximum redundancy.
A national ground stop was initiated, which holds on the ground flights with Chicago as destination. Controllers no longer need to hand write flight data information strips. Decision made to maintain operations in this mode until off-peak hours.