A problematic FAA software update led to almost 1,000 flight delays and cancellations on Saturday in the Washington, DC area. The outage lasted from 11AM ET until about 4PM ET. It directly affected flights at Baltimore-Washington International, Ronald Reagan Washington National, and Dulles International airports, which in turn affected flights around the country.
The update was meant to enhance the En Route Automation Modernization (ERAM) computer system used by flight controllers to handle route requests and changes. Those new features have been rolled back in the meantime.
If you're having trouble grasping how big of an outage this was, watch the massive hole in air traffic open up in this time lapse created by FlightRadar24:
ERAM was built by Lockheed Martin and fully rolled out across the country this year, so it's a relatively new system. But the FAA says that it should still be considered extremely reliable, citing a 99.99 percent availability rate.